- POWER SUPPLY (SWITCHING)
- NETZ EINGANG BS422 MAINS INPUT ET309378996
- ANSTEUERUNG BS423 SMPS UNIT AT 349354067 WITH S417T
- CHROMA I A BS202 AT 349354052
- CHROMA IIA BS302
- SYNCHRONISIERUNG BS531 AT 349354014 WITH TBA950
- VERTIKAL ENDSTUFE BS453 AT 349354096 WITH TDA1170
- SEC. SPANNUNGSERZEUGUNG BS426 AT349354095
- IR EMPFANGER 5000 BS48 AT 349370969 WITH TFK U318M
TDA1170 vertical deflection FRAME DEFLECTION INTEGRATED CIRCUIT
GENERAL DESCRIPTION f The TDA1170 and TDA1270 are monolithic integrated
circuits designed for use in TV vertical deflection systems. They are manufactured using
the Fairchild Planar* process.
Both devices are supplied in the 12-pin plastic power package with the heat sink fins bent
for insertion into the printed circuit board.
The TDA1170 is designed primarily for large and small screen black and white TV
receivers and industrial TV monitors. The TDA1270 is designed primarily for driving
complementary vertical deflection output stages in color TV receivers and industrial
monitors.
APPLICATION INFORMATION (TDA1170)
The vertical oscillator is directly synchronized by the sync pulses (positive or negative); therefore its free
running frequency must be lower than the sync frequency. The use of current feedback causes the yoke
current to be independent of yoke resistance variations due to thermal effects, Therefore no thermistor is
required in series with the yoke. The flyback generator applies a voltage, about twice the supply voltage, to
the yoke. This produces a short flyback time together with a high useful power to dissipated power
ratio.
TELEFUNKEN CHASSIS 714 Drive circuit for an infrared remote control transmitter:
An infrared remote control transmitter includes at least one infrared light-emitting diode poled with respect to a point of reference potential so as to be conductive in response to voltages having the opposite polarity of a DC supply voltage and to be nonconductive in response to voltages having the same polarity as the DC supply voltage. A push-pull amplifier is responsive to a pulse signal encoded to represent a remote control message to selectively couple the DC supply voltage or the reference potential to a capacitor coupled in series between the push-pull amplifier and the light-emitting diode. The capacitor is charged and discharged and an alternating drive voltage for the light-emitting diode having portions with polarities both the same as and opposite to the polarity of the DC supply voltage is generated. The push-pull amplifier is arranged so that when a component failure occurs, the portions of the alternating drive voltage having the polarity opposite to the polarity of the DC supply voltage are at least inhibited to prevent the continuous (i.e., DC) emission of infrared radiation.
1. In an infrared remote control transmitter for controlling a television system, apparatus comprising: a reference circuit point for receiving a reference potential;
a supply circuit point for receiving a DC supply voltage;
a battery connected with a predetermined polarity connected between said supply and reference circuit points;
at least one light-emitting diode for emitting infrared radiation when rendered conductive, said light emitting diode having a cathode and an anode, one of said cathode and anode being connected to said reference circuit point, said light-emitting diode being poled with respect to said reference circuit point so as to be conductive in response to the application of a voltage to the other one of said cathode and anode having the opposite polarity to said battery with respect to said reference circuit point and non-conductive in response to the application of a voltage to said other one of said cathode and anode having the same polarity as said battery with respect to said reference circuit point;
a source cir
a drive circuit point;
a capacitor directly connected between said drive circuit point and said other one of said cathode and anode;
a diode directly connected between said other one of said cathode and anode and said reference circuit point and poled in the opposite sense to said light-emitting diode with respect to said reference circuit point;
push-pull amplifier means for developing a drive voltage at said drive point including first and second bipolar transistors of opposite conduction types, each of said transistors having a collector-emitter path and a base electrode for controlling the conduction of said collector-emitter path, said collector-emitter path of said first transistor being directly connected between said supply circuit point and said drive circuit point, said collector-emitter path of said second transistor being connected between said drive circuit point and said reference point; and
input means coupled between said source circuit point and said bases of said first and second transistors for rendering said collector-emitter path of said first transistor conductive and said collector-emitter path of said second transistor non-conductive in response to a first portion of said pulses of said input signal and for rendering said collector-emitter path of said second transistor conductive and said collector-emitter path of said first transistor non-conductive in response to a second portion of said pulses of said input signal.
2. The apparatus recited in claim 1 wherein:
three light-emitting diodes poled in the same direction are connected in series between said capacitor means and said reference circuit point.
3. The apparatus recited in claim 1 wherein:
a second capacitor is directly connected between said drive point and said other one of said cathode and anode in parallel with said first mentioned capacitor directly connected between said drive point and said other one of said cathode and anode.
4. The apparatus recited in claim 1 wherein:
said input means includes a first capacitor connected between said source circuit point and said base of said first transistor; first means connected between said supply circuit point and said base of said first transistor for discharging said first capacitor; a second capacitor connected between said source circuit point and said base of said second transistor; and second means connected between said base of said second transistor and said reference circuit point for discharging said second capacitor.
5. The apparatus recited in claim 4 wherein:
said first means includes a further diode poled to be conductive when said collector-emitter path of said first transistor is non-conductive and non-conductive when said collector-emitter path of said first transistor is conductive; and
said second means includes a still further diode poled to be conductive when said collector-emitter path of said second transistor is non-conductive and non-conductive when said collector-emitter path of said second transistor is conductive.
6. In an infrared remote control transmitter for controlling a television system, apparatus comprising:
a reference circuit point for receiving a reference potential;
a supply circuit point for receiving a DC supply voltage;
a battery connected with a predetermined polarity connected between said supply and reference circuit points;
three light-emitting diodes which emit infrared radiation when rendered conductive directly connected in series between a voltage application circuit point and said reference circuit point, all of said light-emitting diodes being poled with respect to said reference circuit point so as to be conductive in response to the application of a voltage to said voltage application circuit point having the opposite polarity to said battery with respect to said reference circuit point and non-conductive in response to the application of a voltage to said voltage application circuit point having the same polarity as said battery with respect to said reference circuit point;
a source circuit point for receiving an input signal having pulses encoded to represent information for controlling a predetermined function of said television receiver;
a drive circuit point;
a first capacitor directly connected between said drive circuit point and said voltage application circuit point;
a second capacitor directly connected between said drive circuit point and said voltage application circuit point;
a diode directly connected between said voltage application circuit point and said reference circuit point and poled in the opposite sense to said light-emitting diode with respect to said reference circuit point;
input means coupled between said source circuit point and said bases of said first and second transistors for rendering said collector-emitter path of said first transistor conductive and said collector-emitter path of said second transistor non-conductive in response to a first portion of said pulses of said input signal and for rendering said collector-emitter path of said second transistor conductive and said collector-emitter path of said first transistor non-conductive in response to a second portion of said pulses of said input signal.
Description:
BACKGROUND OF THE PRESENT INVENTION
The present invention relates to drive circuits for infrared remote control transmitters.
Infrared remote control systems for television receivers and the like are known. The chief advantage of infrared remote control systems in comparison to ultrasonic remote control systems is that they are less susceptible to erroneously-generated interference signals. Unfortunately, the human eye may be harmed under conditions of prolonged, continuous and direct exposure to infrared radiation.
In order to reduce the possibility of harm to the eyes of users, infrared remote control systems utilize special pulse codes which minimize the duration of infrared radiation during the transmission of remote controlled messages. However, since in conventional drive circuits for infrared remote control transmitters the infrared light source, e.g., a light-emitting diode or diodes, is typically included in a direct current path from a supply voltage, infrared radiation may be continuously emitted should there be a component failure in the remote control transmitter. Therefore, there is a requirement for drive circuits for use in infrared remote control transmitters in which component failures do not result in the continuous emission of infrared radiation. The present invention concerns such a "fail-safe" drive circuit.
SUMMARY OF THE PRESENT INVENTION
In a remote control transmitter, at least one infrared light-emitting diode is coupled to a point of reference potential and poled so as to be substantially nonconductive in response to voltages having the same polarity as a DC supply voltage for the transmitter and substantially conductive in response to voltages having the polarity opposite to the polarity of the DC supply voltage. Driver means responsive to an input signal is coupled between the source of the DC supply voltage and the light-emitting diode. The driver means normally generates an alternating drive voltage for the light-emitting diode having portions with polarities both the same as and opposite to the polarity of the DC supply voltage. The driver means is arranged so that the portions of the drive signal having the polarity opposite to that of the DC supply voltage are at least inhibited when a component failure occurs.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE of the drawing shows, partially in block diagram form and partially in schematic diagram form, an infrared remote control system constructed in accordance with the present invention as it may be employed in a television receiver arrangement.
DETAILED DESCRIPTION OF THE DRAWING
A tele
vision receiver 1 includes an antenna 3, a tuner 5, an IF signal processing unit 7, a picture signal processing unit 9, a sound signal processing unit 11, a picture tube 13 and a speaker 15 arranged in a conventional fashion to produce visual and audio responses. A power supply 17 is selectively energized to generate DC supply voltages for the portions of the receiver so far described from the AC line voltage in response to an ON/OFF control signal generated by a remote control receiver 19. Receiver 1 also includes a standby power supply 20 which continuously couples a DC supply voltage to remote control receiver 19 so that it is ready to accept messages from a remote control transmitter 21.
Remote control receiver 19 includes a photosensitive diode 23. The conduction of photo diode 23 is controlled in response to encoded optical signals having frequencies in the infrared range generated by remote control transmitter 21. A detector 25 senses the changes in the conduction of diode 23 and generates electrical signals corresponding to the encoded optical signals. The electrical signals are decoded by a decoder 27 to generate the ON/OFF control signal for tuning receiver 1 on and off, a CHANNEL SELECTION control signal for controlling the frequency to which a tuner 5 is tuned, and a VOLUME control signal for controlling the sound level of receiver 1.
Remote control transmitter 21 includes a keyboard 29 including push buttons (not shown) by which a user may control the various receiver functions enumerated above. When a push button is depressed a corresponding electrical signal is generated by keyboard 29. A pulse encoder 31 is responsive to these electrical signals to generate respective coded pulse signals. The coded pulse signals are processed by a driver 33 to cause infrared light-emitting diodes 35, 37 and 39 to generate corresponding optical signals in the infrared frequency range.
Various codes for infrared remote control systems and encoders and decoders for these codes are known. For example, encoder 31 and decoder 27 may comprise S2600 and S2601 integrated circuits manufactured by American Microsystems, Inc. of Santa Clara, Calif.
The exact nature of the codes is not directly germane to the present invention. However, it is desirable for the reasons of safety discussed earlier that the code formats are arranged so that the duration of infrared radiation during a transmission is minimized. Since the pulses of the pulse signals generated by pulse encoder 31 correspond to the intervals of infrared radiation, this may be accomplished by causing the electrical pulse signals generated by encoder 31 to have a relatively low duty cycle, e.g., less than 20 percent. In addition, for safety reasons, it is desirable that light-emitting diodes 35, 37 and 39 be physically separated on transmitter 21 from one another by a distance selected so that the power of the infrared radiation they generate is distributed rather than concentrated in a relatively small area.
While these safety precautions to some extent minimize the danger to users, they do not account for component failures which may cause the continuous, i.e., DC, emission of infrared radiation. Unfortunately, the human eye may be injured when directly exposed to continuous infrared radiation for prolonged periods. While such situations are extremely rare, since they would involve not only a component failure but the misuse of the transmitter, they may occur under extraordinary circumstances. For example, a curious child may point an infrared transmitter with a failed component directly into his eye.
Drive circuit 33 is arranged to prevent the continuous emission of infrared radiation under any foreseeable component failure mode. Driver 33 includes a push-pull amplifier 41 comprising a PNP transistor 43 and an NPN transistor 45 having their collector-emitter junctions coupled in series between a battery 47 and signal ground. Battery 47 is the source of DC supply voltage for transmitter 21. The output of pulse encoder 31 is coupled to the bases of transistors 43 and 45 through capacitors 49 and 51, respectively. Diodes 53 and 55 are coupled in shunt with the base-emitter junctions of transistors 43 and 45, respectively. The junction of the collectors of transistors 43 and 45 is coupled through parallel connected capacitors 57 and 58 to the cathode of light-emitting diode 35. Light-emitting diodes 35, 37 and 39 are connected in series with the same polarity between capacitors 57 and 58 and signal ground. The polarity of light-emitting diodes 35, 37 and 39 is selected so that they are rendered nonconductive in response to the application of voltages to the cathode of light-emitting diode 35 having the same polarity (i.e., positive) with respect to signal ground as the DC supply voltage provided by battery 47 and only rendered conductive in response to the application of voltages having the opposite polarity (i.e., negative) with respect to signal ground to the DC supply voltage. A diode 59 is connected in shunt with series connected light-emitting diodes 35, 37 and 39 and poled in the opposite direction.
In operation, pulse encoder 31 generates a pulse signal encoded as described above. The pulse signal includes positive-going pulses. In response to the leading edges of the positive-going pulses, transistor 45 is rendered conductive. In response to the trailing edges of the positive-going pulses, transistor 43 is rendered conductive. Diodes 53 and 55 serve as discharge paths for capacitors 49 and 51 during the intervals when transistors 43 and 45, respectively, are nonconductive. Diodes 53 and 55 also clamp the voltage at the bases of transistors 43 and 45 close to the battery voltage and the voltage at signal ground, respectively, in order to protect the base-emitter junctions of transistors 43 and 45 from reverse breakdown failure voltages. Desirably, capacitors 49 and 51 have relatively small values so that capacitors 49 and 51 are charged and discharged in response to each pulse. As a result, transistors 43 and 45 are alternately rendered conductive and nonconductive in response to each pulse of the pulse signal.
When transistor 43 is conductive (and transistor 45 is nonconductive) capacitors 57 and 58 are charged from battery 47. When transistor 45 is conductive (and transistor 43 is nonconductive) capacitors 57 and 58 are discharged to signal ground. As a result, an alternating drive voltage, i.e., one having polarity excursions above and below the potential at signal ground, are generated at the cathode of light-emitting diode 35. Light-emitting diodes are conductive in response to the negative portions of the drive voltage and are nonconductive in response to the positive portions of the drive voltage. Diodes 35, 37 and 39 only emit infrared radiation when they are conductive. Therefore, infrared radiation is only emitted by transmitter 21 when the drive voltage has a polarity (i.e., negative opposite to the polarity of the DC supply voltage.
Desirably, the capacitance of the combination of capacitors 57 and 58 is relatively large, e.g., 1 microfarad, so that sufficient drive current is provided to light-emitting diodes 35, 37 and 39 to cause them to emit infrared radiation. For the same reason, two capacitors rather than one are used, since the effective series resistance associated with the parallel combination is smaller than the series resistance of a single capacitor.
In the event that there is a component failure within drive circuit 33, drive voltage developed at the cathode of light-emitting diode 35 will be reduced and, in most cases, substantially inhibited. Under these conditions, since the amplitude of the negative portions of the drive signal will at least have a lower than normal amplitude, the infrared radiation will have a lower than normal energy.
Briefly, any failure of a component within driver 33 causing the component to open or short, substantially prevents the development of an alternating drive signal at the cathode of light-emitting diode 35. Since diodes 35, 37 and 39 are rendered conductive only in response to negative-going voltages, no infrared radiation is generated. Any component failure between the extremes of an open or short causes a reduction in the amplitude of the alternating drive signal. By way of example, consider the following failure modes. If either transistor 43 or 45 fails, e.g., by shorting from collector to emitter, capacitors 57 and 58 will be either permanently charged or discharged, thereby preventing the development of an alternating drive signal. If one of capacitors 57 and 58 shorts, only positive-going voltages are developed at the cathode of light-emitting diode 35. If the collector to emitter junction of transistor 43 and one of capacitors 57 and 58 short, a DC signal is coupled to the cathode of light-emitting diode 35, thereby rendering diode 59 conductive and preventing light-emitting diodes 35, 37 and 39 from being rendered conductive. If diode 59 opens, capacitors 57 and 58 will not be charged thereby preventing the development of an alternating voltage at the cathode of diode 35. If diode 59 fails so as to lose its unidirectional conductive characteristics, i.e., in essence becomes a passive element, an alternating drive signal will be developed but it will have a lower than normal amplitude. Furthermore, failures in pulse encoder 31 causing generation of a DC signal rather than a pulse signal will also cause the loss of an alternating drive signal.
Driver circuit 33 may be modified in some respects without causing the loss of its "fail-safe" nature. For example, any or all of diodes 53, 55 and 59 may be replaced with resistors. While this modification causes a reduction in efficiency of the normal operation of drive circuit 33, it does not alter its "fail-safe" nature. These and other modifications are intended to be within the scope of the present invention as set forth in the following claims.
TELEFUNKEN CHASSIS 714 Switching Power supply voltage stabilizer:
A power supply voltage stabiliz
er comprising a transformer, of which the primary winding is connected to a switching means for controlling power supply to the primary winding. An oscillator circuit is associated with the switching means in order to control on/off operation of the switching means. An abnormal overvoltage and/or overcurrent detection circuit is provided for terminating the oscillation operation of the oscillator circuit when impending overvoltage and/or overcurrent is detected.
1. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said oscillator circuit including an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
2. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxilliary winding;
said oscillator circuit comprising an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
3. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switchi
ng means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detec
tion means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxiliary winding;
said overvoltage detection circuit including a latching means for continuously developing said control signal.
4. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means;
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxiliary winding;
said overvoltage detection circui
t further includes,
a reference voltage generation means for developing a reference voltage proportional to a voltage applied from said power source; and
comparing means for comparing said voltage developed through said auxiliary winding with said reference voltage in order to develop said control signal when said voltage developed through said auxiliary winding exceeds said reference voltage.
5. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said abnormal condition detection means including an overcurrent detection circuit connected to said primary winding for developing said control signal when an overcurrent flows through said primary winding;
wherein said oscillator circuit includes an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
6. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said abnormal condition detection means including an overcurrent detection circuit connected to said primary winding for developing said control signal when an overcurrent flows through said primary winding;
said overcurrent detection circuit including a latching means for continuously developing said control signal;
said oscillator circuit including an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
7. The power supply voltage stabilizer of claim 1, 2, 5, or 6, wherein said variable impedance means comprise a photo transistor, and wherein a light emitting diode is connected to said secondary winding for emitting a light of which amount is proportional to a voltage developed through said secondary winding, said light emitted from said light emitting diode being applied to said photo transistor. 8. The power supply voltage stabilizer of claim 7, wherein said light emitting diode and said photo transistor are incorporated in a single photo coupler. 9. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxilliary winding;
said overvoltage detection circuit including a latching means for continuously developing said control signal;
said oscillator circuit including an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
10. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means;
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed th
rough said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxiliary winding;
said overvoltage detection circuit including,
a reference voltage generation means for developing a reference voltage proportional to a voltage applied from said power source; and
comparing means for comparing said voltage developed through said auxiliary winding with said reference voltage in order to develop said control signal when said voltage developed through said auxiliary winding exceeds said reference voltage;
said oscillator circuit including an astable multivibrator, and a variable impedance means for varying an oscillation frequency of said astable multivibrator.
11. A power supply voltage stabilizer comprising:
transformer means including a primary winding connected to a power source, a secondary winding for producing an output voltage, and an auxiliary winding for developing a voltage proportional to said output voltage produced by said secondary winding;
switching means connected to said primary winding for controlling the power supply from said power source to said primary winding;
oscillator circuit means for controlling the on/off operation of said switching means;
overvoltage detection circuit means connected to said auxiliary winding for developing a control signal to terminate the oscillation operation of said oscillator circuit means when an overvoltage condition is detected, said overvoltage detection circuit means including,
means for developing a reference potential, and
comparing means responsive to said voltage developed at said auxiliary winding and to said reference potential for comparing said reference potential with said voltage developed at said auxiliary winding and for generating said control signal to terminate the oscillation operation of said oscillator circuit means when said voltage developed at said auxiliary winding exceeds said reference potential.
12. A power supply voltage stabilizer comprising:
transformer means including a primary winding connected to a power source and having a voltage supplied thereto, a secondary winding for producing an output voltage, and an auxiliary winding for developing a voltage proportional to said output voltage produced by said secondary winding;
switching means connected to said primary winding for controlling the power supply from said power source to said primary winding;
oscillator circuit means for controlling the on/off operation of said switching means;
overcurrent detection circuit means connected to said primary winding for developing a control signal to terminate the oscillation operation of said oscillator circuit means when an overcurrent condition is detected, said overcurrent detection circuit means including,
means for monitoring said voltage supplied to said primary winding of said transformer means,
means for measuring the amount of current passing through said primary winding of said transformer means by translating said amount of current into a corresponding amount of voltage potential,
switching means responsive to said corresponding amount of voltage potential for switching to a first switched condition when the corresponding voltage potential exceeds a predetermined voltage potential and for switching to a second switched condition when said voltage potential does not exceed said predetermined voltage potential, and
comparing means responsive to said voltage supplied to said primary winding and connected to an output of said switching means for generating said control signal to terminate oscillation operation of said oscillator circuit means when said switching means switches to said first switched condition in response to the exceeding of said predetermined voltage potential by said corresponding voltage potential.
13. A power supply voltage stabilizer in accordance with claim 11 or 12 wherein said comparing means comprises a double base diode.
The present invention relates to drive circuits for infrared remote control transmitters.
Infrared remote control systems for television receivers and the like are known. The chief advantage of infrared remote control systems in comparison to ultrasonic remote control systems is that they are less susceptible to erroneously-generated interference signals. Unfortunately, the human eye may be harmed under conditions of prolonged, continuous and direct exposure to infrared radiation.
In order to reduce the possibility of harm to the eyes of users, infrared remote control systems utilize special pulse codes which minimize the duration of infrared radiation during the transmission of remote controlled messages. However, since in conventional drive circuits for infrared remote control transmitters the infrared light source, e.g., a light-emitting diode or diodes, is typically included in a direct current path from a supply voltage, infrared radiation may be continuously emitted should there be a component failure in the remote control transmitter. Therefore, there is a requirement for drive circuits for use in infrared remote control transmitters in which component failures do not result in the continuous emission of infrared radiation. The present invention concerns such a "fail-safe" drive circuit.
SUMMARY OF THE PRESENT INVENTION
In a remote control transmitter, at least one infrared light-emitting diode is coupled to a point of reference potential and poled so as to be substantially nonconductive in response to voltages having the same polarity as a DC supply voltage for the transmitter and substantially conductive in response to voltages having the polarity opposite to the polarity of the DC supply voltage. Driver means responsive to an input signal is coupled between the source of the DC supply voltage and the light-emitting diode. The driver means normally generates an alternating drive voltage for the light-emitting diode having portions with polarities both the same as and opposite to the polarity of the DC supply voltage. The driver means is arranged so that the portions of the drive signal having the polarity opposite to that of the DC supply voltage are at least inhibited when a component failure occurs.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE of the drawing shows, partially in block diagram form and partially in schematic diagram form, an infrared remote control system constructed in accordance with the present invention as it may be employed in a television receiver arrangement.
DETAILED DESCRIPTION OF THE DRAWING
A tele
vision receiver 1 includes an antenna 3, a tuner 5, an IF signal processing unit 7, a picture signal processing unit 9, a sound signal processing unit 11, a picture tube 13 and a speaker 15 arranged in a conventional fashion to produce visual and audio responses. A power supply 17 is selectively energized to generate DC supply voltages for the portions of the receiver so far described from the AC line voltage in response to an ON/OFF control signal generated by a remote control receiver 19. Receiver 1 also includes a standby power supply 20 which continuously couples a DC supply voltage to remote control receiver 19 so that it is ready to accept messages from a remote control transmitter 21. Remote control receiver 19 includes a photosensitive diode 23. The conduction of photo diode 23 is controlled in response to encoded optical signals having frequencies in the infrared range generated by remote control transmitter 21. A detector 25 senses the changes in the conduction of diode 23 and generates electrical signals corresponding to the encoded optical signals. The electrical signals are decoded by a decoder 27 to generate the ON/OFF control signal for tuning receiver 1 on and off, a CHANNEL SELECTION control signal for controlling the frequency to which a tuner 5 is tuned, and a VOLUME control signal for controlling the sound level of receiver 1.
Remote control transmitter 21 includes a keyboard 29 including push buttons (not shown) by which a user may control the various receiver functions enumerated above. When a push button is depressed a corresponding electrical signal is generated by keyboard 29. A pulse encoder 31 is responsive to these electrical signals to generate respective coded pulse signals. The coded pulse signals are processed by a driver 33 to cause infrared light-emitting diodes 35, 37 and 39 to generate corresponding optical signals in the infrared frequency range.
Various codes for infrared remote control systems and encoders and decoders for these codes are known. For example, encoder 31 and decoder 27 may comprise S2600 and S2601 integrated circuits manufactured by American Microsystems, Inc. of Santa Clara, Calif.
The exact nature of the codes is not directly germane to the present invention. However, it is desirable for the reasons of safety discussed earlier that the code formats are arranged so that the duration of infrared radiation during a transmission is minimized. Since the pulses of the pulse signals generated by pulse encoder 31 correspond to the intervals of infrared radiation, this may be accomplished by causing the electrical pulse signals generated by encoder 31 to have a relatively low duty cycle, e.g., less than 20 percent. In addition, for safety reasons, it is desirable that light-emitting diodes 35, 37 and 39 be physically separated on transmitter 21 from one another by a distance selected so that the power of the infrared radiation they generate is distributed rather than concentrated in a relatively small area.
While these safety precautions to some extent minimize the danger to users, they do not account for component failures which may cause the continuous, i.e., DC, emission of infrared radiation. Unfortunately, the human eye may be injured when directly exposed to continuous infrared radiation for prolonged periods. While such situations are extremely rare, since they would involve not only a component failure but the misuse of the transmitter, they may occur under extraordinary circumstances. For example, a curious child may point an infrared transmitter with a failed component directly into his eye.
Drive circuit 33 is arranged to prevent the continuous emission of infrared radiation under any foreseeable component failure mode. Driver 33 includes a push-pull amplifier 41 comprising a PNP transistor 43 and an NPN transistor 45 having their collector-emitter junctions coupled in series between a battery 47 and signal ground. Battery 47 is the source of DC supply voltage for transmitter 21. The output of pulse encoder 31 is coupled to the bases of transistors 43 and 45 through capacitors 49 and 51, respectively. Diodes 53 and 55 are coupled in shunt with the base-emitter junctions of transistors 43 and 45, respectively. The junction of the collectors of transistors 43 and 45 is coupled through parallel connected capacitors 57 and 58 to the cathode of light-emitting diode 35. Light-emitting diodes 35, 37 and 39 are connected in series with the same polarity between capacitors 57 and 58 and signal ground. The polarity of light-emitting diodes 35, 37 and 39 is selected so that they are rendered nonconductive in response to the application of voltages to the cathode of light-emitting diode 35 having the same polarity (i.e., positive) with respect to signal ground as the DC supply voltage provided by battery 47 and only rendered conductive in response to the application of voltages having the opposite polarity (i.e., negative) with respect to signal ground to the DC supply voltage. A diode 59 is connected in shunt with series connected light-emitting diodes 35, 37 and 39 and poled in the opposite direction.
In operation, pulse encoder 31 generates a pulse signal encoded as described above. The pulse signal includes positive-going pulses. In response to the leading edges of the positive-going pulses, transistor 45 is rendered conductive. In response to the trailing edges of the positive-going pulses, transistor 43 is rendered conductive. Diodes 53 and 55 serve as discharge paths for capacitors 49 and 51 during the intervals when transistors 43 and 45, respectively, are nonconductive. Diodes 53 and 55 also clamp the voltage at the bases of transistors 43 and 45 close to the battery voltage and the voltage at signal ground, respectively, in order to protect the base-emitter junctions of transistors 43 and 45 from reverse breakdown failure voltages. Desirably, capacitors 49 and 51 have relatively small values so that capacitors 49 and 51 are charged and discharged in response to each pulse. As a result, transistors 43 and 45 are alternately rendered conductive and nonconductive in response to each pulse of the pulse signal.
When transistor 43 is conductive (and transistor 45 is nonconductive) capacitors 57 and 58 are charged from battery 47. When transistor 45 is conductive (and transistor 43 is nonconductive) capacitors 57 and 58 are discharged to signal ground. As a result, an alternating drive voltage, i.e., one having polarity excursions above and below the potential at signal ground, are generated at the cathode of light-emitting diode 35. Light-emitting diodes are conductive in response to the negative portions of the drive voltage and are nonconductive in response to the positive portions of the drive voltage. Diodes 35, 37 and 39 only emit infrared radiation when they are conductive. Therefore, infrared radiation is only emitted by transmitter 21 when the drive voltage has a polarity (i.e., negative opposite to the polarity of the DC supply voltage.
Desirably, the capacitance of the combination of capacitors 57 and 58 is relatively large, e.g., 1 microfarad, so that sufficient drive current is provided to light-emitting diodes 35, 37 and 39 to cause them to emit infrared radiation. For the same reason, two capacitors rather than one are used, since the effective series resistance associated with the parallel combination is smaller than the series resistance of a single capacitor.
In the event that there is a component failure within drive circuit 33, drive voltage developed at the cathode of light-emitting diode 35 will be reduced and, in most cases, substantially inhibited. Under these conditions, since the amplitude of the negative portions of the drive signal will at least have a lower than normal amplitude, the infrared radiation will have a lower than normal energy.
Briefly, any failure of a component within driver 33 causing the component to open or short, substantially prevents the development of an alternating drive signal at the cathode of light-emitting diode 35. Since diodes 35, 37 and 39 are rendered conductive only in response to negative-going voltages, no infrared radiation is generated. Any component failure between the extremes of an open or short causes a reduction in the amplitude of the alternating drive signal. By way of example, consider the following failure modes. If either transistor 43 or 45 fails, e.g., by shorting from collector to emitter, capacitors 57 and 58 will be either permanently charged or discharged, thereby preventing the development of an alternating drive signal. If one of capacitors 57 and 58 shorts, only
positive-going voltages are developed at the cathode of light-emitting diode 35. If the collector to emitter junction of transistor 43 and one of capacitors 57 and 58 short, a DC signal is coupled to the cathode of light-emitting diode 35, thereby rendering diode 59 conductive and preventing light-emitting diodes 35, 37 and 39 from being rendered conductive. If diode 59 opens, capacitors 57 and 58 will not be charged thereby preventing the development of an alternating voltage at the cathode of diode 35. If diode 59 fails so as to lose its unidirectional conductive characteristics, i.e., in essence becomes a passive element, an alternating drive signal will be developed but it will have a lower than normal amplitude. Furthermore, failures in pulse encoder 31 causing generation of a DC signal rather than a pulse signal will also cause the loss of an alternating drive signal. Driver circuit 33 may be modified in some respects without causing the loss of its "fail-safe" nature. For example, any or all of diodes 53, 55 and 59 may be replaced with resistors. While this modification causes a reduction in efficiency of the normal operation of drive circuit 33, it does not alter its "fail-safe" nature. These and other modifications are intended to be within the scope of the present invention as set forth in the following claims.
TELEFUNKEN CHASSIS 714 Switching Power supply voltage stabilizer:
A power supply voltage stabiliz
er comprising a transformer, of which the primary winding is connected to a switching means for controlling power supply to the primary winding. An oscillator circuit is associated with the switching means in order to control on/off operation of the switching means. An abnormal overvoltage and/or overcurrent detection circuit is provided for terminating the oscillation operation of the oscillator circuit when impending overvoltage and/or overcurrent is detected. 1. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said oscillator circuit including an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxilliary winding;
said oscillator circuit comprising an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
3. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switchi
ng means connected to said primary winding for controlling power supply to said primary winding; an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detec
said overvoltage detection circuit including a latching means for continuously developing said control signal.
4. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means;
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxiliary winding;
said overvoltage detection circui
t further includes, a reference voltage generation means for developing a reference voltage proportional to a voltage applied from said power source; and
comparing means for comparing said voltage developed through said auxiliary winding with said reference voltage in order to develop said control signal when said voltage developed through said auxiliary winding exceeds said reference voltage.
5. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said abnormal condition detection means including an overcurrent detection circuit connected to said primary winding for developing said control signal when an overcurrent flows through said primary winding;
wherein said oscillator circuit includes an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
6. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said abnormal condition detection means including an overcurrent detection circuit connected to said primary winding for developing said control signal when an overcurrent flows through said primary winding;
said overcurrent detection circuit including a latching means for continuously developing said control signal;
said oscillator circuit including an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
7. The power supply voltage stabilizer of claim 1, 2, 5, or 6, wherein said variable impedance means comprise a photo transistor, and wherein a light emitting diode is connected to said secondary wind
ing for emitting a light of which amount is proportional to a voltage developed through said secondary winding, said light emitted from said light emitting diode being applied to said photo transistor. 8. The power supply voltage stabilizer of claim 7, wherein said light emitting diode and said photo transistor are incorporated in a single photo coupler. 9. A power supply voltage stabilizer comprising: a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means; and
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed through said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit;
said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxilliary winding;
said overvoltage detection circuit including a latching means for continuously developing said control signal;
said oscillator circuit including an astable multivibrator, and variable impedance means for varying an oscillation frequency of said astable multivibrator.
10. A power supply voltage stabilizer comprising:
a transformer including a primary winding connected to a power source and a secondary winding for output purposes;
switching means connected to said primary winding for controlling power supply to said primary winding;
an oscillator circuit for controlling on/off operation of said switching means;
abnormal condition detection means for developing a control signal for terminating oscillation operation of said oscillator circuit when an abnormal condition is detected;
said transformer further including an auxiliary winding for developing a voltage proportional to that developed th
rough said secondary winding, said voltage developed through said auxiliary winding being applied to said oscillator circuit for driving said oscillator circuit; said abnormal condition detection means including an overvoltage detection circuit connected to said auxiliary winding for developing said control signal when an overvoltage is developed through said auxiliary winding;
said overvoltage detection circuit including,
a reference voltage generation means for developing a reference voltage proportional to a voltage applied from said power source; and
comparing means for comparing said voltage developed through said auxiliary winding with said reference voltage in order to develop said control signal when said voltage developed through said auxiliary winding exceeds said reference voltage;
said oscillator circuit including an astable multivibrator, and a variable impedance means for varying an oscillation frequency of said astable multivibrator.
11. A power supply voltage stabilizer comprising:
transformer means including a primary winding connected to a power source, a secondary winding for producing an output voltage, and an auxiliary winding for developing a voltage proportional to said output voltage produced by said secondary winding;
switching means connected to said primary winding for controlling the power supply from said power source to said primary winding;
oscillator circuit means for controlling the on/off operation of said switching means;
overvoltage detection circuit means connected to said auxiliary winding for developing a control signal to terminate the oscillation operation of said oscillator circuit means when an overvoltage condition is detected, said overvoltage detection circuit means including,
means for developing a reference potential, and
12. A power supply voltage stabilizer comprising:
transformer means including a primary winding connected to a power source and having a voltage supplied thereto, a secondary winding for producing an output voltage, and an auxiliary winding for developing a voltage proportional to said output voltage produced by said secondary winding;
switching means connected to said primary winding for controlling the power supply from said power source to said primary winding;
oscillator circuit means for controlling the on/off operation of said switching means;
overcurrent detection circuit means connected to said primary winding for developing a control signal to terminate the oscillation operation of said oscillator circuit means when an overcurrent condition is detected, said overcurrent detection circuit means including,
means for monitoring said voltage supplied to said primary winding of said transformer means,
means for measuring the amount of current passing through said primary winding of said transformer means by translating said amount of current into a corresponding amount of voltage potential,
switching means responsive to said corresponding amount of voltage potential for switching to a first switched condition when the corresponding voltage potential exceeds a predetermined voltage potential and for switching to a second switched condition when said voltage potential does not exceed said predetermined voltage potential, and
comparing means responsive to said voltage supplied to said primary winding and connected to an output of said switching means for generating said control signal to terminate oscillation operation of said oscillator circuit means when said switching means switches to said first switched condition in response to the exceeding of said predetermined voltage potential by said corresponding voltage potential.
13. A power supply voltage stabilizer in accordance with claim 11 or 12 wherein said comparing means comprises a double base diode.
Description:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a power supply voltage stabilizer and, more particularly, to a power supply voltage stabilizer employing a switching system for controlling power supply to a transformer included in the power supply voltage stabilizer.
In the conventional power supply voltage stabilizer employing a switching system for controlling power supply to a transformer included in the power supply voltage stabilizer, there is a possibility that an abnormal overvoltage will be developed from an output terminal thereof and/or an abnormal overcurrent may flow through the primary winding of the transformer.
Accordingly, an object of the present invention is to provide a protection means for protecting the power supply voltage stabilizer from an abnormal overvoltage and/or overcurrent.
Another object of the present invention is to provide a detection means for detecting an impending overvoltage and/or overcurrent occurring within the power supply voltage stabilizer.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The
power supply voltage stabilizer of the present invention mainly comprises a transformer including a primary winding connected to a commercial power source through a rectifying circuit, a secondary winding for output purposes, and an auxiliary winding. A driver circuit including a switching means is connected to the primary winding for controlling the power supply to the primary winding. An oscillator circuit is associated with the switching means to control ON/OFF operation of the switching means, thereby controlling the power supply to the primary winding.
To achieve the above objects, pursuant to an embodiment of the present invention, an overvoltage detection circuit is connected to the auxiliary winding. The overvoltage detection circuit functions to compare a voltage created in the auxiliary winding with the rectified power supply voltage, and develop a control signal, when an impending overvoltage is detected, for terminating operation of the oscillator circuit, thereby precluding power supply to the primary winding.
In another embodiment of the present invention, an overcurrent detection circuit is provided for detecting an impending overcurrent flowing through the primary winding to develop a control signal for terminating operation of the oscillator circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention and wherein:
FIG. 1 is a circuit diagram of a basic construction of a power supply voltage stabilizer of the present invention;
FIG. 2 is a block diagram of an embodiment of a power supply voltage stabilizer of the present invention, which includes an oscillator circuit and an over voltage detection circuit;
FIG. 3 is a circuit diagram of an embodiment of the overvoltage detection circuit included in the power supply voltage stabilizer of FIG. 2;
FIG. 4 is a circuit diagram of an embodiment of the oscillator circuit included in the power supply voltage stabilizer of FIG. 2;
FIG. 5 is a waveform chart for explaining operation of the oscillator circuit of FIG. 4;
FIG. 6 is a block diagram of another embodiment of a power supply voltage stabilizer of the present invention, which includes an oscillator circuit and an overcurrent detection circuit; and
FIG. 7 is a circuit diagram of an embodiment of the overcurrent detection circuit included in the power supply voltage stabilizer of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
R
eferring now in detail to the drawings, and to facilitate a more complete understanding of the present invention, a basic construction of a power supply voltage stabilizer of the present invention will be first described with reference to FIG. 1.
The power supply voltage stabillizer mainly comprises a transformer T including a primary winding N 1 connected to a commercial power source V, a secondary winding N 2 connected to an output terminal V 0 , and an auxiliary winding N 3 . An oscillator circuit OSC is associated with the primary winding N 1 and the auxiliary winding N 3 to control the power supply from the commercial power source V to the primary winding N 1 .
A rectifying circuit E is connected to the commercial power source V for applying a rectified voltage to a capacitor C 1 . A negative terminal of the capacitor C 1 is grounded, and a positive terminal of the capacitor C 1 is connected to the collector electrode of a switching transistor Q 5 through the primary winding N 1 of the transformer T. The oscillator circuit OSC performs the oscillating operation when receiving a predetermined voltage, and develops a control signal toward the base electrode of the switching transistor Q 5 to control the switching operation of the switching transistor Q 5 . The switching transistor Q 5 functions to control the power supply to the primary winding N 1 , thereby controlling the power transfer to the secondary winding N 2 and the auxiliary winding N 3 .
The auxiliary winding N 3 is connected to a capacitor C 3 in a parallel fashion via a diode D 1 . A positive terminal of the capacitor C 3 is connected to the oscillator circuit OSC to supply a drive voltage Vc 3 . A negative terminal of the capacitor C 3 is connected to the emitter electrode of the switching transistor Q 5 and grounded. The positive terminal of the capacitor C 3 is connected to the primary winding N 1 via a diode D 2 and a capacitor C 2 in order to stabilize the initial condition of the oscillator circuit OSC.
The secondary winding N 2 functions to develop a predetermined voltage through the output terminal V 0 . A smoothing capacitor C 0 is connected to the secondary winding N 2 via a diode D 0 , and a series circuit of a resistor R 0 and a light emitting diode D i is connected to the smoothing capacitor C 0 in a parallel fashion. The light emitted from the light emitting diode D i is applied to a photo transistor Q 8 employed in the oscillator circuit OSC. The light emitting diode D i and the photo transistor Q 8 are preferably incorporated in a single package as a photo coupler.
The light amount emitted from the light emitting diode D i is proportional to the output voltage developed from the output terminal V 0 . The photo transistor Q 8 exhibits the impedance corresponding to the applied light amount. The oscillator circuit OSC is so constructed that the oscillation frequency is varied in response to variation of the impedance of the photo transistor Q 8 . Accordingly, the ON/OFF operation of the switching transistor Q 5 is controlled in response to the output voltage level, thereby stabilizing the output voltage level.
In the above constructed power supply voltage stabilizer, there is a possibility that an abnormal overvoltage is developed through the secondary winding N 2 and the auxiliary winding N 3 when the oscillator circuit OSC or the light emitting diode D i is placed in the fault condition.
FIG. 2 show
s an embodiment of the power supply voltage stabilizer of the present invention, which includes means for precluding occurrence of the above-mentioned overvoltage. Like elements corresponding to those of FIG. 1 are indicated by like numerals.
The power supply voltage stabilizer of FIG. 2 mainly comprises the transformer T, the oscillator circuit OSC, a driver circuit 1 including the switching transistor Q 5 , and an overvoltage detection circuit 3.
The positive terminal of the capacitor C 3 is connected to the driver circuit 1 and the oscillator circuit OSC to apply the driving voltage thereto. The positive terminal of the capacitor C 3 is also connected to the primary winding N 1 through the diode D 2 and a parallel circuit of the capacitor C 2 and a resistor R 2 in order to stabilize the initial start operation of the oscillator circuit OSC. The secondary winding N 2 is connected to an output level detector 2, which comprises the light emitting diode D i as shown in FIG. 1. The ON/OFF control of the switching transistor Q 5 is similar to that is achieved in the power supply voltage stabilizer of FIG. 1.
The secondary winding N 2 and the auxiliary winding N 3 are wound in the same polarity fashion and, therefore, the voltage generated through the auxiliary winding N 3 is proportional to that voltage generated through the secondary winding N 2 . The overvoltage detection circuit 3 is connected to receive the voltage at a point a as a power source voltage, and the voltage at a point b which is connected to the positive terminal of the capacitor C 3 . When the voltage level at the point b exceeds a reference level, the overvoltage detection circuit 3 develops a control signal for terminating the operation of the oscillator circuit OSC.
FIG. 3 shows a typical construction of the overvoltage detection circuit 3.
The voltage at the point a is applied to a series circuit of resistors R 3 and R 4 , and grounded. The voltage at the point b is applied to the connection point of the resistors R 3 and R 4 via a diode D 3 . The connection point of the resistors R 3 and R 4 is grounded through resistors R 5 and R 6 and a Zener diode Z 1 . A double-base diode (Trade Name Programmable Unijunction Transistor) P 1 is provided for developing the control signal to be applied to the oscillator circuit OSC. The anode electrode of the programmable unijunction transistor P 1 is connected to the connection point of the resistors R 3 and R 4 , the gate electrode of the programmable unijunction transistor P 1 is connected to the connection point of the resistors R 5 and R 6 , and the cathode electrode is connected to the oscillator circuit OSC.
When the voltage level of the point b exceeds a reference level VZ 1 , the programmable unijunction transistor P 1 is turned on to develop the control signal for terminating the oscillation operation of the oscillator OSC. In this way, the impending abnormal overvoltage is detected to protect the circuit elements. The ON condition of the programmable unijunction transistor P 1 is maintained as long as the main power switch is closed, because the overvoltage detection circuit 3 is connected to receive the voltage from the point a.
The voltage detection circuit 3 does not necessarily employ the programmable unijunction transistor. Another element showing the latching characteristics such as a negative resistance element can be employed instead of the programmable unijunction transistor.
FIG. 4 shows a typical construction of the oscillator circuit OSC.
The oscillation circuit OSC mainly comprises an astable multivibrator including transistors Q 1 , Q 2 and Q 3 , and an output stage including a transistor Q 4 . The astable multivibrator is connected to receive the voltage appearing across the capacitor C 3 , and develops an output signal of which frequency is determined by the circuit condition as long as the multivibrator receives a voltage greater than a predetermined level.
The output signal of the output stage is applied to the base electrode of the switching transistor Q 5 included in the driver circuit 1 in order to switch the switching transistor Q 5 with a predetermined frequency. A transistor Q 9 is interposed between the base electrode of the transistor Q 3 and the grounded terminal. The transistor Q 9 is controlled by the control signal derived from the overvoltage detection circuit 3. Accordingly, the transistor Q 3 is turned off to terminate the oscillation operation when the abnormal overvoltage is detected by the overvoltage detection circuit 3.
Now assume that a voltage Vc 3 is developed across the capacitor C 3 . When main power supply switch is closed, the voltage Vc 3 varies in a manner shown by a curve X in FIG. 5. When the voltage Vc 3 reaches a predetermined level, the astable multivibrator begins the oscillation operation. More specifically, the transistor Q 1 is first turned on because the base electrode of the transistor Q 1 is connected to a capacitor C 4 of which the capacitance value is relatively small. At this moment, the transistor Q 2 is held off.
Because of turning on of the transistor Q 1 , the capacitor C 4 is gradually charged through a resistor R 4 and the transistor Q 1 . Accordingly, the base electrode voltage of the transistor Q 1 is gradually increased and, hence, the emitter electrode voltage of the transistor Q 1 is also increased to turn on the transistor Q 2 . When the transistor Q 2 is turned on, the transistor Q 3 is also turned on. The base electrode voltage of the transistor Q 2 which is bypassed by a resistor R 1 is reduced and, therefore, the transistor Q 2 is stably on. At this moment, the transistor Q 1 is turned off.
When the transistor Q 3 is turned on, the transistor Q 4 is turned on to develop a signal to turn on the switching transistor Q 5 . Upon turning on of the transistor Q 3 , the charge stored in the capacitor C 4 is gradually discharged through paths shown by arrows in FIG. 4. Therefore, the base electrode voltage of the transistor Q 1 is gradually reduced. When the base electrode voltage of the transistor Q 1 becomes less than a predetermined level, the transistor Q 1 is turned on, and the transistor Q 2 , Q 3 and Q 4 are turned off. Accordingly, the transistor Q 5 is turned off. After passing the initial start condition, the driving voltage Vc 3 is held at a predetermined level as shown by a curve Y in FIG. 5 to maintain the above-mentioned oscillation operation.
The photo transistor Q 8 is disposed in the discharge path of the capacitor C 4 in order to control the discharge period in response to the impedance of the photo transistor Q 8 . That is, the oscillation frequency is controlled in response to the light amount emitted from the light emitting diode included in the output level detector 2.
FIG. 6 shows another em
bodiment of the power supply voltage stabilizer of the present invention, which includes means for precluding occurrence of an abnormal overcurrent. Like elements corresponding to those of FIG. 2 are indicated by like numerals.
In the power supply voltage stabilizer of FIG. 1, there is a possibility that an abnormally large current flows through the primary winding N 1 when the magnetic flux is saturated due to requirement of large current at the secondary winding side. The power supply voltage stabilizer of FIG. 6 includes an overcurrent detection circuit 4 for detecting an impending abnormally large current.
A resistor R 9 is interposed between the emitter electrode of the switching transistor Q 5 included in the driver circuit 1 and the grounded terminal. The overcurrent detection circuit 4 is connected to receive a signal from the connection point of the resistor R 9 and the emitter electrode of the switching transistor Q 5 , thereby developing a control signal for terminating the oscillation operation of the oscillation circuit OSC.
FIG. 7 shows a typical construction of the overcurrent detection circuit 4.
The voltage at the point a is applied to a series circuit of resistors R 10 and R 11 , and grounded. The collector electrode of a transistor Q 10 is connected to the connection point of the resistors R 10 and R 11 through resistors R 12 and R 13 . The emitter electrode of the transistor Q 10 is grounded. The base electrode of the transistor Q 10 is connected to the connection point of the resistor R 9 and the emitter electrode of the switching transistor Q 5 via a resistor R 14 .
When the switching transistor Q 5 is turned on, a current flows through the resistor R 9 . When the voltage drop across the resistor R 9 exceeds a predetermined value due to a large current, the transistor Q 10 is turned on to turn on the programmable unijunction transistor P 1 . That is, when a large current flows through the primary winding N 1 , the programmable unijunction transistor P 1 develops the control signal to terminate the oscillation operation of the oscillator circuit OSC.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.
The present invention relates to a power supply voltage stabilizer and, more particularly, to a power supply voltage stabilizer employing a switching system for controlling power supply to a transformer included in the power supply voltage stabilizer.
In the conventional power supply voltage stabilizer employing a switching system for controlling power supply to a transformer included in the power supply voltage stabilizer, there is a possibility that an abnormal overvoltage will be developed from an output terminal thereof and/or an abnormal overcurrent may flow through the primary winding of the transformer.
Accordingly, an object of the present invention is to provide a protection means for protecting the power supply voltage stabilizer from an abnormal overvoltage and/or overcurrent.
Another object of the present invention is to provide a detection means for detecting an impending overvoltage and/or overcurrent occurring within the power supply voltage stabilizer.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The
To achieve the above objects, pursuant to an embodiment of the present invention, an overvoltage detection circuit is connected to the auxiliary winding. The overvoltage detection circuit functions to compare a voltage created in the auxiliary winding with the rectified power supply voltage, and develop a control signal, when an impending overvoltage is detected, for terminating operation of the oscillator circuit, thereby precluding power supply to the primary winding.
In another embodiment of the present invention, an overcurrent detection circuit is provided for detecting an impending overcurrent flowing through the primary winding to develop a control signal for terminating operation of the oscillator circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention and wherein:
FIG. 1 is a circuit diagram of a basic construction of a power supply voltage stabilizer of the present invention;
FIG. 2 is a block diagram of an embodiment of a power supply voltage stabilizer of the present invention, which includes an oscillator circuit and an over voltage detection circuit;
FIG. 3 is a circuit diagram of an embodiment of the overvoltage detection circuit included in the power supply voltage stabilizer of FIG. 2;
FIG. 4 is a circuit diagram of an embodiment of the oscillator circuit included in the power supply voltage stabilizer of FIG. 2;
FIG. 5 is a waveform chart for explaining operation of the oscillator circuit of FIG. 4;
FIG. 6 is a block diagram of another embodiment of a power supply voltage stabilizer of the present invention, which includes an oscillator circuit and an overcurrent detection circuit; and
FIG. 7 is a circuit diagram of an embodiment of the overcurrent detection circuit included in the power supply voltage stabilizer of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
R
eferring now in detail to the drawings, and to facilitate a more complete understanding of the present invention, a basic construction of a power supply voltage stabilizer of the present invention will be first described with reference to FIG. 1. The power supply voltage stabillizer mainly comprises a transformer T including a primary winding N 1 connected to a commercial power source V, a secondary winding N 2 connected to an output terminal V 0 , and an auxiliary winding N 3 . An oscillator circuit OSC is associated with the primary winding N 1 and the auxiliary winding N 3 to control the power supply from the commercial power source V to the primary winding N 1 .
A rectifying circuit E is connected to the commercial power source V for applying a rectified voltage to a capacitor C 1 . A negative terminal of the capacitor C 1 is grounded, and a positive terminal of the capacitor C 1 is connected to the collector electrode of a switching transistor Q 5 through the primary winding N 1 of the transformer T. The oscillator circuit OSC performs the oscillating operation when receiving a predetermined voltage, and develops a control signal toward the base electrode of the switching transistor Q 5 to control the switching operation of the switching transistor Q 5 . The switching transistor Q 5 functions to control the power supply to the primary winding N 1 , thereby controlling the power transfer to the secondary winding N 2 and the auxiliary winding N 3 .
The auxiliary winding N 3 is connected to a capacitor C 3 in a parallel fashion via a diode D 1 . A positive terminal of the capacitor C 3 is connected to the oscillator circuit OSC to supply a drive voltage Vc 3 . A negative terminal of the capacitor C 3 is connected to the emitter electrode of the switching transistor Q 5 and grounded. The positive terminal of the capacitor C 3 is connected to the primary winding N 1 via a diode D 2 and a capacitor C 2 in order to stabilize the initial condition of the oscillator circuit OSC.
The secondary winding N 2 functions to develop a predetermined voltage through the output terminal V 0 . A smoothing capacitor C 0 is connected to the secondary winding N 2 via a diode D 0 , and a series circuit of a resistor R 0 and a light emitting diode D i is connected to the smoothing capacitor C 0 in a parallel fashion. The light emitted from the light emitting diode D i is applied to a photo transistor Q 8 employed in the oscillator circuit OSC. The light emitting diode D i and the photo transistor Q 8 are preferably incorporated in a single package as a photo coupler.
The light amount emitted from the light emitting diode D i is proportional to the output voltage developed from the output terminal V 0 . The photo transistor Q 8 exhibits the impedance corresponding to the applied light amount. The oscillator circuit OSC is so constructed that the oscillation frequency is varied in response to variation of the impedance of the photo transistor Q 8 . Accordingly, the ON/OFF operation of the switching transistor Q 5 is controlled in response to the output voltage level, thereby stabilizing the output voltage level.
In the above constructed power supply voltage stabilizer, there is a possibility that an abnormal overvoltage is developed through the secondary winding N 2 and the auxiliary winding N 3 when the oscillator circuit OSC or the light emitting diode D i is placed in the fault condition.
FIG. 2 show
s an embodiment of the power supply voltage stabilizer of the present invention, which includes means for precluding occurrence of the above-mentioned overvoltage. Like elements corresponding to those of FIG. 1 are indicated by like numerals. The power supply voltage stabilizer of FIG. 2 mainly comprises the transformer T, the oscillator circuit OSC, a driver circuit 1 including the switching transistor Q 5 , and an overvoltage detection circuit 3.
The positive terminal of the capacitor C 3 is connected to the driver circuit 1 and the oscillator circuit OSC to apply the driving voltage thereto. The positive terminal of the capacitor C 3 is also connected to the primary winding N 1 through the diode D 2 and a parallel circuit of the capacitor C 2 and a resistor R 2 in order to stabilize the initial start operation of the oscillator circuit OSC. The secondary winding N 2 is connected to an output level detector 2, which comprises the light emitting diode D i as shown in FIG. 1. The ON/OFF control of the switching transistor Q 5 is similar to that is achieved in the power supply voltage stabilizer of FIG. 1.
The secondary winding N 2 and the auxiliary winding N 3 are wound in the same polarity fashion and, therefore, the voltage generated through the auxiliary winding N 3 is proportional to that voltage generated through the secondary winding N 2 . The overvoltage detection circuit 3 is connected to receive the voltage at a point a as a power source voltage, and the voltage at a point b which is connected to the positive terminal of the capacitor C 3 . When the voltage level at the point b exceeds a reference level, the overvoltage detection circuit 3 develops a control signal for terminating the operation of the oscillator circuit OSC.
FIG. 3 shows a typical construction of the overvoltage detection circuit 3.
The voltage at the point a is applied to a series circuit of resistors R 3 and R 4 , and grounded. The voltage at the point b is applied to the connection point of the resistors R 3 and R 4 via a diode D 3 . The connection point of the resistors R 3 and R 4 is grounded through resistors R 5 and R 6 and a Zener diode Z 1 . A double-base diode (Trade Name Programmable Unijunction Transistor) P 1 is provided for developing the control signal to be applied to the oscillator circuit OSC. The anode electrode of the programmable unijunction transistor P 1 is connected to the connection point of the resistors R 3 and R 4 , the gate electrode of the programmable unijunction transistor P 1 is connected to the connection point of the resistors R 5 and R 6 , and the cathode electrode is connected to the oscillator circuit OSC.
When the voltage level of the point b exceeds a reference level VZ 1 , the programmable unijunction transistor P 1 is turned on to develop the control signal for terminating the oscillation operation of the oscillator OSC. In this way, the impending abnormal overvoltage is detected to protect the circuit elements. The ON condition of the programmable unijunction transistor P 1 is maintained as long as the main power switch is closed, because the overvoltage detection circuit 3 is connected to receive the voltage from the point a.
The voltage detection circuit 3 does not necessarily employ the programmable unijunction transistor. Another element showing the latching characteristics such as a negative resistance element can be employed instead of the programmable unijunction transistor.
FIG. 4 shows a typical construction of the oscillator circuit OSC.
The oscillation circuit OSC mainly comprises an astable multivibrator including transistors Q 1 , Q 2 and Q 3 , and an o
utput stage including a transistor Q 4 . The astable multivibrator is connected to receive the voltage appearing across the capacitor C 3 , and develops an output signal of which frequency is determined by the circuit condition as long as the multivibrator receives a voltage greater than a predetermined level. The output signal of the output stage is applied to the base electrode of the switching transistor Q 5 included in the driver circuit 1 in order to switch the switching transistor Q 5 with a predetermined frequency. A transistor Q 9 is interposed between the base electrode of the transistor Q 3 and the grounded terminal. The transistor Q 9 is controlled by the control signal derived from the overvoltage detection circuit 3. Accordingly, the transistor Q 3 is turned off to terminate the oscillation operation when the abnormal overvoltage is detected by the overvoltage detection circuit 3.
Now assume that a voltage Vc 3 is developed across the capacitor C 3 . When main power supply switch is closed, the voltage Vc 3 varies in a manner shown by a curve X in FIG. 5. When the voltage Vc 3 reaches a predetermined level, the astable multivibrator begins the oscillation operation. More specifically, the transistor Q 1 is first turned on because the base electrode of the transistor Q 1 is connected to a capacitor C 4 of which the capacitance value is relatively small. At this moment, the transistor Q 2 is held off.
Because of turning on of the transistor Q 1 , the capacitor C 4 is gradually charged through a resistor R 4 and the transistor Q 1 . Accordingly, the base electrode voltage of the transistor Q 1 is gradually increased and, hence, the emitter electrode voltage of the transistor Q 1 is also increased to turn on the transistor Q 2 . When the transistor Q 2 is turned on, the transistor Q 3 is also turned on. The base electrode voltage of the transistor Q 2 which is bypassed by a resistor R 1 is reduced and, therefore, the transistor Q 2 is stably on. At this moment, the transistor Q 1 is turned off.
When the transistor Q 3 is turned on, the transistor Q 4 is turned on to develop a signal to turn on the switching transistor Q 5 . Upon turning on of the transistor Q 3 , the charge stored in the capacitor C 4 is gradually discharged through paths shown by arrows in FIG. 4. Therefore, the base electrode voltage of the transistor Q 1 is gradually reduced. When the base electrode voltage of the transistor Q 1 becomes less than a predetermined level, the transistor Q 1 is turned on, and the transistor Q 2 , Q 3 and Q 4 are turned off. Accordingly, the transistor Q 5 is turned off. After passing the initial start condition, the driving voltage Vc 3 is held at a predetermined level as shown by a curve Y in FIG. 5 to maintain the above-mentioned oscillation operation.
The photo transistor Q 8 is disposed in the discharge path of the capacitor C 4 in order to control the discharge period in response to the impedance of the photo transistor Q 8 . That is, the oscillation frequency is controlled in response to the light amount emitted from the light emitting diode included in the output level detector 2.
FIG. 6 shows another em
bodiment of the power supply voltage stabilizer of the present invention, which includes means for precluding occurrence of an abnormal overcurrent. Like elements corresponding to those of FIG. 2 are indicated by like numerals. In the power supply voltage stabilizer of FIG. 1, there is a possibility that an abnormally large current flows through the primary winding N 1 when the magnetic flux is saturated due to requirement of large current at the secondary winding side. The power supply voltage stabilizer of FIG. 6 includes an overcurrent detection circuit 4 for detecting an impending abnormally large current.
A resistor R 9 is interposed between the emitter electrode of the switching transistor Q 5 included in the driver circuit 1 and the grounded terminal. The overcurrent detection circuit 4 is connected to receive a signal from the connection point of the resistor R 9 and the emitter electrode of the switching transistor Q 5 , thereby developing a control signal for terminating the oscillation operation of the oscillation circuit OSC.
FIG. 7 shows a typical construction of the overcurrent detection circuit 4.
The voltage at the point a is applied to a series circuit of resistors R 10 and R 11 , and grounded. The collector electrode of a transistor Q 10 is connected to the connection point of the resistors R 10 and R 11 through resistors R 12 and R 13 . The emitter electrode of the transistor Q 10 is grounded. The base electrode of the transistor Q 10 is connected to the connection point of the resistor R 9 and the emitter electrode of the switching transistor Q 5 via a resistor R 14 .
When the switching transistor Q 5 is turned on, a current flows through the resistor R 9 . When the voltage drop across the resistor R 9 exceeds a predetermined value due to a large current, the transistor Q 10 is turned on to turn on the programmable unijunction transistor P 1 . That is, when a large current flows through the primary winding N 1 , the programmable unijunction transistor P 1 develops the control signal to terminate the oscillation operation of the oscillator circuit OSC.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.
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