AUTOVOX TVC2278 ALTAIR CHASSIS 100 POWER
Supply CONSTANT-VOLTAGE CONVERTER EMPLOYING THYRISTOR:
A constant voltage converter having a rectifier for rectifying AC power and with a thyristor connected between the rectifier and a filter for selectively passing therethrough a rectified output to an output terminal. There is a wave generator connected to the output of the rectifier for producing a first signal and an intergrator circuit connected to the output of the wave generator for producing an integral output in response to this first signal. In addition there is a detector circuit for detecting a fluctuation of the rectified output power and for producing second signal. A comparison circuit is connected between the intergrator circuit and the detector circuit for producing third signal in accordance with the comparison. A trigger circuit is connected between the comparison circuit and the control gate of the thyristor for supplying a phase control signal to the thyristor to thereby obtain a constant voltage output regardless of the fluctuation of the rectified output.
1. A constant voltage converter comprising an input of a power supply means, an output terminal, filter means, rectifier means connected to said input for rectifying a.c. power and for supplying output thereof to said output terminal, thyristor means connected between said rectifier means and said filter means for selectively passing therethrough a rectified output to the output terminal by way of said filter means, saw-tooth wave generator means connected between the output of said rectifier means and at least one integrator circuit means for producing an integral output in response to a saw-tooth wave produced, a first transistor in said saw-tooth wave generator, the input of said integrator circuit means being connected to a collector of said first transistor, detector circuit means connected to said output terminal for detecting a fluctuation of the rectified output power and for producing an output signal, said detector circuit means having a second transistor, pulse generator circuit means connected between said saw-tooth wave generator means and said detector circuit means for producing a trigger pulse to said thyristor through a trigger means, a third transistor in said pulse circuit generator means, the base of said third transistor being connected to the output of said integrator circuit means, the emitter thereof being connected to the emitter of said second transistor in said detector circuit means, and the collector thereof being connected to the gate of the thyristor means so as to supply a phase control signal thereto, thereby obtaining a constant voltage output regardless of the fluctuation of the rectified output.
Conventional constant-voltage converters of the type employing a thyristor are arranged to phase shift and full-wave-rectify an input a.c. power applied thereto and to maintain the output voltages constant by regulating the firing angle of the thyristor in comparison of the output voltages with the phase-shifted and rectified input a.c. power. When, however, these converters are connected to a common a.c. source having a relatively high internal impedance, the waveform of the phase-shifted and rectified a.c. input power is distorted thereby causing undesired operations of the converters.
It is therefore an object of the present invention to provide a constant-voltage converter which correctly operates notwithstanding the distortion of the input a.c. voltage.
Another object of the invention is to provide a constant-voltage converter which effectively suppress an undesired rush current.
Another object of the invention is to provide a constant-voltage converter having an improved feed-back circuit of a substantially constant loop gain .
In the drawings:
FIG. 1 is a schematic view of a converter according to the present invention;
FIG. 2 is a diagram showing a circuit arrangement of the converter of FIG. 1;
FIG. 3 is a diagram showing various waveforms of signals appearing in the circuit of FIG. 2;
FIG. 4 is a diagram showing various waveforms appearing in the circuit of FIG. 2 when an a.c. power is supplied to the circuit;
FIG. 5 is a diagram showing another circuit arrangement of the converter of FIG. 1;
FIG. 6 is a diagram showing waveforms of signals appearing in the circuit of FIG. 5; and
FIG. 7 is a diagram showing further another circuit arrangement of generator the of FIG. 1.
Referring now to FIG. 1, a constant-voltage converter 10 according to the present invention comprises a rectifier 11 having two input terminals 12 and 13 through which an a.c. power is supplied. The rectifier 11 is preferably a full-wave rectifier although a half-wave rectifier may be employed. An output 14 of the rectifier 11 is connected through a line 15 to an anode of a thyristor 16. The thyristor 16 passes therethrough the rectified a.c. power in only one direction from its anode to cathode when triggered by a trigger pulse through its gate. The cathode of the thyristor 16 is connected through a line 17 to an input of a smoothing filter 18. The smoothing filter 18 smoothes the power from the thyristor 16. An output of the smoothing filter 18 is connected through a line 19 to an output terminal 20. The output 14 of the rectifier 11 is also connected through a line 21 to a saw-tooth wave generator 22 which generates a saw-tooth wave signal having the same repetition period as the rectified input a.c. power. An output of the saw-tooth wave generator 22 is connected through a line 23 to one input of a trigger pulse generator 24. The other input of the trigger pulse generator 24 is connected through a line 25 to the line 19. An output of the trigger pulse generator 24 is connected through a line 26 to the gate of the thyristor 16. The trigger pulse generator 24 produces a trigger pulse on its output when the voltage of the saw-tooth wave signal reaches a level which is varied in response to the output voltage on the terminal 20. The trigger pulse generator 24 may be variously arranged and in this case arranged to comprise rectangular generator 27 having one input connected through the line 23 to the saw-tooth wave generator 22 and the other input connected through a line 28 to an output voltage detector 29. The detector 29 produces a reference signal representing the output voltage on the terminal 20. The pulse generator 27 is adapted to produces a rectangular pulse when the saw-tooth wave signal to the one input reaches a level which defined is in accordance with the reference signal. An output of the rectangular pulse generator 27 is connected through a line 30 to an input of a trigger circuit 31. The trigger circuit 31 is adapted to convert the rectangular pulse into a spike pulse. An output of the trigger circuit 31 is connected through the line 26 to the gate of the thyristor 16.
FIG. 2 illustrates a preferred circuit arrangement of the converter shown in FIG. 1 which comprises a rectifier 11 of a full-wave rectifier consisting of rectifiers 40, 41, 42 and 43. Inputs of the rectifier are connected to terminals 12 and 13 through which an a.c. power is applied. The output 14 of the rectifier 11 is connected through a line 15 to an anode of a thyristor 16. A cathode of the thyristor 16 is connected through a line 17 to a smoothing filter 18 which includes a capacitor C4 having one terminal connected to the line 17 and the other terminal grounded. The output of the smoothing filter 18 is connected through a line 19 to an output terminal 20.
The saw-tooth wave generator 22 includes a resistor R 1 having one terminal connected to the line 21 and the terminal connected through a junction J 1 to one terminal of a resistor R 2 . The other terminal of the resistor R 2 is grounded. The junction J 1 is connected through a coupling capacitor C 1 to a base of a transistor T 1 of PNP type. An emitter of the transistor T 1 is connected through a resistor R 3 to the line 21. A resistor R 4 is provided between the emitter and the base of the transistor T 1 so as to apply a bias potential to the base. A collector of the transistor T 1 is grounded through a parallel connection of a resistor R 5 and capacitor C 2 . To the emitter is connected a capacitor C 3 which is in turn grounded and passes therethrough only a.c. signals to the ground.
The rectangular pulse generator 27 comprises a transistor T 2 of PNP type having a base connected through a resistor R 6 to the collector of the transistor T 1 . An emitter of the transistor T 2 is connected through a resistor R 7 to the emitter of the transistor T 1 . A collector of the transistor T 2 is grounded through a resistor R 8 and connected through the line 30 to one terminal of a capacitor C 4 of the trigger circuit 31. The other terminal of the capacitor C 4 is connected through a line 26 to the gate of the thyristor 16.
The output voltage detector 29 includes a transistor T 3 of NPN type having an emitter grounded through a zener diode ZD. A collector of the transistor T 3 is connected through a line 28 to the emitter of the transistor T 2 and, on the other hand, connected through a capacitor C 5 to the grounded. A base of the transistor T 3 is connected to a tap of an adjustable resistor R 9 connected through a resistor R 10 and a line 25 to the line 19 and connected, in turn, to the ground through a resistor R 11 .
When, in operation, an a.c. electric power is applied through the input terminals 12 and 13 of the rectifier 11, a full-wave rectified power as shown in FIG. 3 (a) appears on the output 14. The rectified power is applied through the line 15 to the anode of the thyristor 16. The thyristor 16 passes therethrough the rectified power while its firing angle is regulated by the trigger signal applied to the gate. The rectified power passed through the thyristor 16 is applied through the line 17 to the smoothing filter 18. The smoothing filter smoothes the power by removing the ripple component in the power. The smoothed power appears on the line 19 which is to be supplied to a load through the output terminal 20. The smoothed power on the line 19 is, on the other hand, delivered through the line 25 to the resistor R 10 of the output voltage detector 29. The resistor R 10 constitutes a voltage divider in cooperation with the resistors R 9 and R 11 . The output of the voltage divider is applied through the tap of the resistor R 9 to the base of the transistor T 3 . When the potential of the base of the transistor T 3 exceeds the zener voltage of the zener diode ZD, a base current flows through the transistor T 3 so as to render the transistor T 3 conductive. The potential of the collector of the transistor T 3 then varies in accordance with the voltage of the smoothed output power on the line 19. The potential variation at the collector of the transistor T 3 is then applied through the line 28 to the trigger pulse generator 27 and utilized to regulate the triggering timing of the thyristor 16.
The full-wave rectified power is, on the other hand, applied through the line 21 to the saw-tooth wave generator 22. Since the resistors R 1 and R 2 consistute a voltage divider to reduce the voltage of the full-wave rectified power to a potential at the junction J 1 , a charging current to the capacitor C 1 flows from the emitter to the base of the transistor T 1 whereby the transistor T 1 repeats ON-OFF operation in accordance with the voltage of the rectified power. If the transistor T 1 is conductive when the voltage of the full-wave rectified power is lower than a threshold voltage v 1 as shown in FIG. 3(a), then the potential at the collector of the transistor T 1 is varied as shown in FIG. 3 (b) due to the charge and discharge of the capacitor C 2 . The variation of the potential at the collector of the transistor T 1 is supplied through the line 23 to the resistor R 6 of the trigger pulse generator 27.
As long as the voltage of the smoothed power on the line 19 equals to the rated output voltage, the transistor T 2 is adapted to become conductive when the voltage of the saw-tooth wave signal falls below a threshold value v 3 shown in FIG. 3(b). Therefore, a potential at the collector of the transistor T 2 varies as shown in FIG. 3(c). The potential variation, that is, a pulse signal at the collector of the transistor T 2 is supplied through the line 30 to the capacitor C 4 of the trigger circuit trigger 31. The trigger circuit 31 converts the pulse signal into a spike pulse or a trigger pulse shown in FIG. 3(d) which is then applied through the line 25 to the gate of the thyristor 16. Upon receiving the spike pulse, the thyristor 16 becomes conductive until the voltage of the rectified power on the line 15 falls below the cut-off voltage of the thyristor 16.
When the voltage of the smoothed power on the line 19 exceeds the rated output voltage, the collector current of the transistor T 3 increases with the result that the current flowing through the resistor R 7 increases. The threshold voltage of the transistor T 2 therefore reduces to a voltage v 2 as shown in FIG. 3(b). At this instant, leading edge of the pulse signal delays as shown by dot-and-dash lines in FIG. 3(c), so that each trigger pulse delays as shown by dot-and-dash line in FIG. 3(d). When on the contrary, the voltage of the smoothed signal on the line 19 lowers below the rated output voltage, the collector current of the transistor T 3 decreases whereby the threshold voltage rises to a voltage v 4 in FIG. 3(b). Each leading edge of the signal pulse now leads as shown by dotted line in FIG. 3(d). Being apparent from the above description, the appearance timing of each trigger pulse is regulated in accordance with the voltage of the smoothed power on the line 19 so that the voltage of the output voltage at the terminal 20 is held substantially constant.
Referring now to FIG. 4, start operation of the converter 10 is discussed hereinbelow in conjunction with FIG. 2. When an a.c. voltage is applied to the input terminals 12 and 13, the capacitor C 3 begins to be charged by the voltage on the line 15, and the capacitor C 5 also begins to be charged through the resistors R 3 and R 7 . It is important that the time constant of power supply circuit constituted by the resistor R 3 and the capacitor C 3 is selected to be much larger than that of the time constant of another power supply circuit constituted by the resistor R 7 and the capacitor C 5 . Thus, the emitter potential of the transistor T 1 is built up more quickly than that of the transistor T 2 . Upon completion of the charging of the capacitor C 3 , the saw-tooth wave generator 22 begins to generate saw-tooth wave signal as shown in FIG. 4(b). Since the capacitor C 5 is, on the other hand, slowly charged, the emitter voltage of the transistor T 2 slowly rises as shown in FIG. 4(c), so that, the threshold voltage of the transistor T 2 gradually rises as shown by a dotted line in FIG. 4 (b). Accordingly, the trigger pulses is produced on the gate of the thyristor 16 as shown in FIG. 4(d), whereby the firing angle of the thyristor 16 is gradually reduced as shown in FIG. 4(a) which illustrates the voltage at the output terminal 14 of the rectifier 11. The output voltage on the output terminal 20 therefore gradually rise up as shown in FIG. 4(e). It is to be understood that since the output voltage of the converter 10 starts to gradually rise up as shown in FIG. 4(e), an undesired rush current is effectively suppressed.
FIG. 5 illustrates another form of the converter 10 which is arranged identically to the circuit arrangement of FIG. 1 except that an integrator 50 is interposed between the output of the saw-tooth wave generator 22 and the input of the trigger pulse generator 27. The integrator 50 includes a resistor R 12 having one terminal connected to the output of the saw-tooth wave generator 22 and the other terminal connected to the input of the rectangular pulse generator 27, and a capacitor C 7 having one terminal connected to the other terminal of the resistor R 12 and the other terminal grounded.
In operation, the saw-tooth wave generator 22 produces on its ouput a saw-tooth wave signal having decreasing exponential wave form portion as shown in FIG. 6 (a), although the saw-tooth wave signal ideally is illustrated in FIG. 3. This saw-tooth wave signal is converted by the integrator 50 into another form of saw-tooth wave having a increasing exponential wave form portion as shown in FIG. 6(b).
It should be noted that the saw-tooth wave signal of FIG. 6(a) has a smaller inclination near 180°. Hence, when the integrator 50 is omitted and the saw-tooth wave signal as shown in FIG. 6(a) is applied to the trigger pulse generator 27, the rate of change of the output voltage of the converter 10 become larger at a firing angle near to 180°. On the other hand, it is apparent from FIG. 6(c) that the rate of change the output voltage of the thyristor 16 with respect to the firing angle become large at a firing angle near to 180°. Therefore, the loop gain of the trigger pulse generator 24 increases when the firing angle of the thyristor 16 is near to 180°. It is apparent through a similar discussion that the loop gain of the trigger pulse generator 24 decreases when the firing angle is near to 90°. Such non-uniformity of the loop gain of the trigger pulse generator invites a difficulty of the regulation of the output voltage of the converter. It is to be noted that the saw-tooth wave signal shown in FIG. 6(b) has a large inclination at an angle near 180°. Therefore, when the saw-tooth wave signal of FIG. 6(b) is applied to the trigger pulse generator 24, the loop gain of the trigger pulse generator 24 is held substantially constant, whereby the output voltage of the converter is effectively held constant.
FIG. 7 illustrates another circuit arrangement of the converter according to the present invention, which is arranged identically to the circuit of FIG. 2 except for the trigger circuit 31 and the smoothing circuit 18.
The trigger circuit 31 of FIG. 7 comprises a transformer TR with primary and secondary coils. One terminal of the primary coil is connected to the resistor R 7 of the pulse generator 27. The other terminal of the primary coil is connected to a collector of a transistor T 4 of NPN type. The secondary coil has terminals respectively connected to the gate and cathode of the thyristor 16. An emitter of the transistor T 4 is grounded through a resistor R 13 . A base of the transistor T 4 is grounded through a resistor R 14 and connected through a capacitor C 8 to the collector of the transistor T 2 of the pulse generator 27.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
IF VIDEO DEMOD + AMPL + SOUND IF unit (Motorola TBA120C) (Motorola CA270BE) VIF STAGE
- CHROMINANCE unit (PHILIPS TBA570 + TBA540 + TAA630S)
- LUMINANCE + SYNCHRONIZATION unit (TBA920)
- Color difference amplifier + Luminance amplifier stage unit
- Line deflection output unit. (Texas Instruments BU208A)
- Frame deflection output unit. ( 2 x Motorola BD142-4 )
- E/W Correction output unit. (RCA BD182)
The Luminance and the chrominance are amplified and performed in separate way until the CRT MATRIX (CRT DEMATRIXING)
TBA920 line oscillator combination
The line oscillator combination TBA920 is a monolithic
integrated circuit intended for the horizontal deflection of the black and white
and colour TV sets
OPTIONAL NOISE INVERSION
GENERATION OF A LINE FREQUENCY VOL-
TAGE BY MEANS OF AN OSCILLATOR
PHASE COMPARISON BETWEEN SYNC-
PULSE AND THE OSCILLATOR WAVEFORM
PHASE COMPARISON BETWEEN THE OS-
CILLATOR WAVEFORM AND THE MIDDLE OF
THE LINE FLY-BACK PULSE
AUTOMATIC SWITCHING OF THE VARIABLE
TRANSCONDUCTANCE AND THE VARIABLE
TIME CONSTANT TO ACHIEVE NOISE SUP-
PRESSION AND, BY SWITCHING OFF, POS-
SIBILITY OF TAPE-VIDEO-REGISTERED RE-
SHAPING AND AMPLIFICATION OF THE OS-
CILLATOR WAVEFORM TO OBTAIN PULSES
FOR THE CONTROL OF DRIVING STAGES IN
HORIZONTAL, DEFLECTION CIRCUITS
USING EITHER TRANSISTORS OR THYRISTORS,
npn transistors,pnp transistors,transistors
Category: NPN Transistor, Transistor
MHz: <1 MHz
HIGH VOLTAGE CAPABILITY
JEDEC TO-3 METAL CASE.
The BU208A, BU508A and BU508AFI are
manufactured using Multiepitaxial Mesa
technology for cost-effective high performance
and use a Hollow Emitter structure to enhance
* HORIZONTAL DEFLECTION FOR COLOUR TV With 110° or even 90° degree of deflection angle.
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VCES Collector-Emit ter Voltage (VBE = 0) 1500 V
VCEO Collector-Emit ter Voltage (IB = 0) 700 V
VEBO Emitter-Base Voltage (IC = 0) 10 V
IC Collector Current 8 A
ICM Collector Peak Current (tp < 5 ms) 15 A
TO - 3 TO - 218 ISOWATT218
Ptot Total Dissipation at Tc = 25 oC 150 125 50 W
Tstg Storage Temperature -65 to 175 -65 to 150 -65 to 150 oC
Tj Max. Operating Junction Temperature 175 150 150 °C
AUTOVOX TVC2278 ALTAIR 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
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
1. A transformerless output vertical deflection circuit, comprising a vertical oscillator circuit for generating a vertical pulse train in response to vertical synchronizing pulses applied thereto, a sawtooth signal generator for generating a series of sawtooth signals, each cycle of said sawtooth signal including a pulse component, a vertical output circuit coupled to said sawtooth generator for amplifying said sawtooth signal including said pulse component and loading a vertical deflection coil, and stabilizing means connected between said vertical oscillator and said sawtooth signal generator for varying the width of the pulse component which is to be fed to said vertical output circuit in response to the average level of DC output voltage fed from the vertical output circuit. 2. A transformerless output vertical deflection circuit claimed in claim 1, wherein said stabilizing means comprises a control circuit means for receiving a series of pulses from the vertical oscillator and a feedback signal from the vertical output circuit and for varying the width of the pulse which is to be fed to the vertical output circuit in response to a DC control signal proportional to the width of the pulse component included in the vertical output signal and smoothing circuit means connected between said vertical output circuit and said stabalizing means for smoothing said feedback signal. 3. A transformerless output vertical deflection circuit claimed in claim 2, wherein said control circuit comprises a charging capacitor which is parallel to a transistor, said transistor being switched on in response to pulses fed from the vertical oscillator wherein said capacitor is charged by the voltage fed from said smoothing circuit, and discharged in response to conduction of the transistor, a differential amplifier circuit which receives the voltage on said capacitor and a fixed voltage, and a gating circuit for producing a pulse which has a width equal to the difference between the width of the pulse fed from the vertical oscillator circuit and the width of pulse fed from the differential amplifier circuit. 4. A transformerless output vertical deflection circuit claimed in claim 2, wherein said control circuit comprises a capacitor which is charged by a fixed power source and is discharged by means of a switching transistor operated by the pulses fed from the vertical oscillator circuit and a differential amplifier circuit receiving the voltage on the capacitor and the output of said smoothing circuit. 5. A transformable output vertical deflection circuit comprising a vertical oscillator for generating a vertical pulse train in response to vertical synchronizing pulses applied thereto, a sawtooth signal generator for generating a series of sawtooth signals each cycle of said sawtooth signal including a pulse component, a vertical output circuit for amplifying said sawtooth signal including said pulse component and loading a vertical deflection coil, and pulse stabilizing means coupled between the vertical oscillator circuit and the sawtooth signal generator, said stabilizing means comprising a capacitor which is charged by a fixed power source and discharged by means of a discharging means operated in response to the vertical pulse fed from the vertical oscillator, a circuit means for generating a train of output pulses each starting at the time when the voltage appearing on the capacitor exceeds a predetermined value and terminating in synchronism with termination of the pulse fed from the vertical oscillator, and gating means for generating pulses having a width equal to the difference between the width of the pulse fed from the vertical oscillator and the width of the output pulse of the circuit means. 6. A transformerless output vertical deflection circuit, comprising a vertical oscillator circuit for generating a vertical pulse train in response to vertical synchronizing pulses applied thereto, a sawtooth signal generator for generating a series of sawtooth signals, each cycle of said sawtooth signal including a pulse component, a vertical output circuit coupled to said sawtooth generator for amplifying said sawtooth signal including said pulse component and loading a vertical deflection coil, and stabilizing means, comprising a control circuit connected between said vertical output circuit and said vertical oscillator circuit for varying the width of each pulse produced by the vertical oscillator circuit in response to a DC control signal having a value corresponding to the width of the pulse component applied to the vertical deflection coil of the vertical output circuit for controlling the pulse width of the output of said vertical oscillator circuit and thereby the pulse width of said pulse component.
AUTOVOX TVC2278 ALTAIR CHASSIS 100 Amplifier suitable for use as a color kinescope driver:
A color kinescope matrix amplifier has a first input coupled through a capacitor to a source of color difference signals. Another input is coupled to a source of luminance signals. The matrix amplifier includes a cascode output stage direct current coupled to a cathode of a kinescope. A portion of a direct voltage developed at the cascode output amplifier is coupled to one input of a comparator circuit. The other input of the comparator circuit is coupled to a temperature compensated direct voltage reference source. The comparator is rendered operative during horizontal retrace intervals to provide a current to either charge or discharge the input capacitor in accordance with the difference between the voltage at the output of the cascode output amplifier and the reference voltage to compensate for voltage variations at the output of the cascode amplifier due to power supply variations and the like. To compensate for droop caused by the discharge of the input capacitor during the scanning interval, one input of a differential amplifier is included between the input capacitor and the input of the cascode output stage. Negative signal feedback is provided from the output stage to the other input of the differential amplifier via a capacitor arranged to be charged during the horizontal retrace interval. The two capacitors discharge at substantially the same rates during the scanning interval. By virtue of the common mode operation of the differential amplifier droop effects are minimized.
1. In a television receiver including an image reproducing device, a source of chrominance signals, a source of luminance signals and a source of horizontal blanking pulses, said horizontal blanking pulses occurring during the time interval during which said image reproducing device is horizontally retraced, the apparatus comprising:
AUTOVOX TVC2278 CHASSIS 100 ALTAIR receiver tuning circuit in which without operation of extra switches a change-over can be made from tuning by means of a continuously varying tuning voltage to tuning by means of one of a number of adjusted tuning voltages by using a capacitor controlled by an automatic tuning correction current source circuit for obtaining said voltage, and an automatic switch for applying the desired tuning voltages to this capacitor.
1. A receiver tuning circuit comprising a tuning section having a tuning input, a capacitor means coupled to said tuning input for applying a tuning voltage thereto, a controllable current source coupled to said capacitor, a tuning correction signal detector means coupled between said tuning section and said current source for applying an automatic tuning correction signal to said capacitor means through said current sourc
2. A receiver tuning circuit as claimed in claim 1, wherein said switch comprises a current source which can be influenced by an operating signal, said source being coupled to two parallel branches the first of which includes a transistor having an emitter coupled to said current source, a base coupled to an input of the switch, and a collector, a current mirror circuit having an input coupled to said collector and an output, the second branch including a pair of series connected diodes coupled to the current source and to said output of the current mirror circuit, and output of the switch being coupled to the pair of diodes.
3. A circuit as claimed in claim 1, further comprising a manually operable second switch means for obtaining a continuous coupling between said potentiometer means and said capacitor.
4. A circuit as claimed in claim 1 further comprising a supply circuit means for obtaining a desired tuning voltage, said memory means being independent of said supply circuit, said first switch further comprising a second time constant circuit means coupled to said supply circuit means for temporarily applying a tuning voltage determined by the potentiometer to said capacitor when the supply voltage is switched on.
Present television receivers are adapted to receive both high frequency (VHF) and ultrahigh frequency (UHF) television broadcast signal bands. The VHF tuner generally is of a rotary preset channel tuning type and covers the 12 broadcast channels (2 to 13) in the lower frequency VHF band. This tuner may be manually operated or motor driven and includes a rotary mechanical control element, such as a control shaft, movable in steps progressively through detent-controlled channel tuning positions over a full rotational range of movement in either direction.
The UHF tuners generally employed also are of a rotary type but, instead of being detent controlled, are of the continuous tuning type, covering the 70 broadcast channels (14 to 83) in the higher frequency UHF band. Tuners of this type have a control shaft for continuous rotational tuning movement but of less than one full rotation of the shaft.
In order to switch between the VHF and UHF bands, it is necessary to set the VHF tuner to a UHF position (the channel 1 position). In this position the VHF tuner is disconnected from the receiver, and the UHF tuner is connected; so that control of the channels being received is under the control of the setting of the UHF tuner. Whenever the VHF tuner is in any of its other positions, the UHF tuner is disconnected from the receiver or is disabled; so that control of the received channel then is effected by the setting of the VHF tuner.
In addition, the mechanical VHF and UHF tuners are relatively large and cumbersome and are subject to the problems of wear and adjustment normally associated with mechanical devices of this type. The construction of these mechanical tuners is sufficiently complicated to make the tuners relatively expensive to manufacture thereby resulting in an increased cost of the television receiver.
A tuning circuit of the kind described above is known from German Offenlegungsschrift No. 2,025,369 in which the said capacitor is optionally connected to a tuning potentiometer by means of a push-button switch for applying a voltage determined by said potentiometer to said capacitor as long as the push-button switch is operated, whereafter a tuning frequency thus selected is corrected with the automatic tuning correction signal through the current source circuit and the charge of said capacitor.
It is an object of the invention to enhance the comfort of operation of such a tuning circuit.
To this end a tuning circuit of the kind described in the preamble is characterized in that the operating device includes a memory for storing the last adjusted state of said operating device, and a signal generator which upon operation of the operating device applies a signal to an output thereof, which output is coupled to a time-constant circuit coupled to said switch for maintaining said switch switched on for a period determined by the time-constant circuit independently of the operating duration of the operating device.
Due to the step according to the invention it is possible at any moment to ascertain, by means of the state of the memory, the last operating action of the operating device, maintaining the advantage of a temporary tuning voltage supply to the capacitor so that subsequently other functions such as, for example, a tuning correction device or a search tuning device can become active on said capacitor through the current source circuit.
The invention will now be described with reference to the drawing.
FIG. 1 shows by way of a block-schematic diagram a receiver tuning circuit according to the invention;
FIG. 2 shows by way of a principle circuit diagram a possible embodiment of part of the receiver tuning circuit according to the invention.
In FIG. 1 a tuning section 1 has an input 3 to which a received RF signal is applied and an output 5 from which an IF signal is obtained. This IF signal is applied to an input 7 of an IF amplifier 9 and derived in an amplified form from an output 11 thereof and applied to an input 13 of a tuning correction signal detector 15 and an input 17 of a signal amplitude detector 19.
Furthermore, the tuning section 1 has an input 21 which receives a tuning voltage from a capacitor 23. The charge of the capacitor 23 can be changed with the aid of a current source circuit 25 for which purpose an output 27 thereof is connected to the capacitor 23 whose other end is connected to ground.
An input 29 of the current source circuit 25 is controlled by a tuning correction signal originating from an output 31 of the tuning correction signal detector 15. This correction signal can be rendered inactive with the aid of a switch-off device 33 incorporated in the connection between the output 31 and the input 29, and with the aid of signals applied to an input 35 or 37 thereof.
For this purpose the input 35 of the switch-off device 33 is connected to an output 39 of a station finder 41 two outputs 43, 45 of which are connected to inputs 47, 49 of the current source circuit 25. Thus, the station finder 41 can continuously bring about a charge or discharge of the capacitor 23 when the automatic tuning correction is switched off so that the tuning section 1 is continuously detuned. When a station is found, a signal is produced at the output 31 of the tuning correction signal detector 15, which signal causes stop signal at an input 55 of the station finder through a polarity correction circuit 51 and a delay circuit 53, and this for a certain period, for example, 1.5 seconds so that station finding is temporarily discontinued and the automatic tuning correction is activated. As a result, tuning is effected immediately and correctly at the frequency of the received station. If this station is not desired, further station finding can be continued after 1.5 seconds.
The capacitor 23 providing the tuning voltage for the tuning section 1 may be controlled not only by the current source circuit 25, but also by an output 57 of a switch 59 an input 61 of which is connected to an output 63 of an operating device 65.
A voltage originating from one of a plurality of tuning potentiometers 67, 69, 71 can be temporarily applied to the capacitor 23 with the aid of the operating device 65. When the device 65 is operated a signal is obtained to that end from a signal generator 73. This signal is applied through an output 75 of the operating device to an input 77 of a time-constant circuit 79. The time constant circuit 79 is coupled to the switch 59 and closes it for a certain time so that the capacitor 23 assumes the desired voltage of a selected potentiometer 67, 69 or 71.
The operating device 65 has a memory which is symbolically shown in the figure as a block 81. This memory 81 ensures that it can always be seen which potentiometers 67, 69 or 71 is interconnected to the output 63 of the operating device 65, while due to the action of the time-constant circuit 79 the voltage originating from this potentiometer is not continuously present at the capacitor 23. The said memory 81 may be either a mechanical or an electrical memory. When using a mechanical memory, the signal generator 73 may be an AFC switch which is present on many operating devices. When using an electrical memory, as is common practice with touch controls in the operating device 65, any change of state of this memory may be converted in a simple manner into a signal applied to the output 75.
The switch 59 has an output 83 which applies a signal to the input 37 of the switch-off device 33. This signal renders the automatic tuning correction inactive as long as the switch 59 is closed, as is the case when a tuning voltage is applied to the capacitor 23 with the aid of the operating device 65. The tuning correction is active again immediately when the switch 59 is open so that tuning is effected immediately and correctly when a selected station is received.
To be able to adjust the potentiometers 67, 69 or 71, easily, a switch 85, which can be operated manually, is connected to a further input 87 of the switch 59 which can be maintained closed with the aid of the manually operated switch 85 as long as is desired for adjustment.
Coupled to the switch 59 is a further time-constant circuit 89 which has an input 91 connected to an output 93 of a supply circuit 95. Thus, whenever the receiver is switched on, the switch 59 is maintained closed for some time so that firstly the station to which the operating device 65 is adjusted is tuned to, even if the station finder 41 were switched on. In that case the operating device 65 must have, for example, a mechanical memory 81, which is independent of the supply voltage, in order to maintain its adjustment also when the supply voltage is switched off.
Furthermore, the switch 59 has an input 97 which is connected to an output 99 of the signal amplitude detector 19. When the signal received by the receiver becomes too weak, the switch 59 can be closed via this path so that tuning to a frequency selected by the operating device 65 is maintained and is stil present when the received signal becomes stronger again. A further possibility, which may be particularly attractive for motorcar radios, is to incorporate a switch which can be operated in this manner between the capacitor and an output of a memory which can be coupled to that capacitor. When the field strength is sufficient, this memory may be written in with the voltage on the capacitor and when the field strength is insufficient, an output of this memory may be coupled to the capacitor for transferring the memory voltage to the capacitor. This memory may be, for example, a motor adjusting a potentiometer and operated with the aid of a control system. When the supply voltage drops out, the last adjusted state of the potentiometer is maintained.
It will be evident that the switch tuning may be omitted, if desired.
FIG. 2 shows a possible embodiment of the switch 59 and, coupled thereto, the time-constant circuits 79 and 89 of the receiver tuning circuit of FIG. 1. The inputs and outputs have the same reference numerals as the corresponding inputs and outputs in FIG. 1.
The input 61 of the switch 59 is connected to the base of a npn transistor 201. The emitter of this transistor 201 is connected through a diode 203 to the collector of an npn transistor 205 arranged as a current source whose emitter is connected to the output 83 and is furthermore connected to ground through a resistor 207.
The collector of the transistor 201 is connected through a diode 209 to the input 91 to which the supply voltage is applied. The diode 209 shunts the base-emitter path of a pnp transistor 211 which together with the diode 209 constitutes a current mirror circuit. The collector of the transistor 211 allows a current to flow through a series arrangement of two diodes 215, 217, which current has substantially the same intensity as the current flowing through the diode 203. Furthermore, the diode 217 is connected to the collector of the transistor 205, while the junction of the collector of the transistor 205 and the diode 215 is connected to the output 57.
The base of the transistor 205 is connected to a tap on a potential divider 219, 221 between the supply voltage and ground. This potential divider will raise the voltage at the base of the transistor 205 to such an extent that it produces a current, which is further determined by the emitter resistor 207, equally distributed over the collector branches with the diode 203 and the transistor 201 and with the diodes 217 and 215, respectively. When the circuit is designed in a integrated form, it can be achieved in a simple manner that the output 57 will always assume the same voltage as the input 61. Since the output 57 is connected to the capacitor 23, both a discharge and a charge of this capacitor 23 is possible. Charging is effected through the transistor 211 and discharging is effected through the diodes 215, 217. The circuit is independent of temperature influences. The diode 203 and consequently the diode 217 are provided to prevent a too large voltage difference at the base-emitter junction of the transistor 201.
The current source 205 can be turned off by connecting the base of transistor 205 to ground with the aid of a npn transistor 223 connected across the resistor 221. This is effected when the base of this transistor receives a voltage from a potential divider comprising three resistors 225, 227, 229. However, when the base of the transistor 223 receives a low voltage through the input 87 or the input 97, the transistors 223 is cut off and the transistor 205 conducts so that the switch 59 is closed.
The voltage at the base of the transistor 223 remains low for some time after switching on the supply voltage because a capacitor 231, which is connected to the junction between the resistors 225 and 227, must firstly be charged. Thus, the switch 59 is closed during that period.
Furthermore, the voltage at the base of the transistor 223 may be decreased by discharging the capacitor 231 through a resistor 233 to the input 77 when this input is earthed for a moment during operating device 65. The voltage at the capacitor 231 will subsequently increase in accordance with a certain time constant and after a certain time the transistor 223 conducts again and the switch 59, which was closed when the transistor 223 was cut off, will be open again.
The input 97 is interconnected to the input 87 so that the transistor 223 is also cut off and the switch 59 starts to conduct when the voltage at the input 97 becomes low upon a drop-out of a transmitter signal.
The switch 59 in this embodiment also acts as an amplifier so that the adjustments of the tuning potentiometer 67, 69 or 71 do not have any influence on the rate at which the charge of the capacitor 23 is changed.
An automatic fine tuning (AFT) circuit is provided which generates an AFT control signal in response to a video intermediate frequency (I.F.) signal. The I.F. signal is supplied to the inputs of two buffer amplifiers, which couple signals of like phase relationship to two inputs of a discriminator network. The discriminator network is tuned to the desired frequency of the video I.F. signal, and is responsive to the buffered I.F. signals for causing respective signal voltages to be developed at its inputs which vary differentially in magnitude in response to the frequency deviation of the I.F. signals from the desired I.F. frequency. The differentially related signals are detected by two peak detector networks for use as AFT control signals. The buffer amplifiers and peak detectors may be conveniently fabricated on a single I.C. chip. The discriminator network is coupled to the buffer amplifiers by two external I.C. terminals.
AUTOVOX TVC2278 ALTAIR Switching arrangement for picking up stored constant voltages:
A circuit arrangement for recalling stored, constant electric voltages such as tuning voltages for fixed transmitter selection in communication devices with capacitance diode-tuning in which the tuning voltages for the capacitance diodes are adapted to be picked off by means of an adjustable voltage storer, the arrangement including a common differential amplifier stage connected with the circuit to be tuned or adjusted, the common differential amplifier circuit being oppositely selectively coupled through at least one further, adjustable, uni- or multi-stage differential amplifier with each of voltage storers. The further uni- or multi-stage differential amplifier preferably has a symmetrical output which is connected with the inputs of the common differential amplifier.
It is known to read off the tuning voltages which are stored in the potentiometer circuits for fixed transmitter selection by manually actuable switches. In such known devices the voltages are picked off from the individual potentiometers for changing the tuners or oscillators of the tuning circuit, and the means for activating the pertinent switch is placed at the capacitance diodes of the corresponding tuning circuits or oscillators.
It is furthermore known to switch the tuning voltages electronically by means of so-called sensor scanners which are contactless switching members actuated by energizing fields. In a known embodiment the individual contacting fields act directly with an integrating circuit (IC), the outputs of which are connected with the individual potentiometers of the voltage storer. With the contacting of an individual sensor key a corresponding switching order is given to the integrated circuit, whereby the corresponding potentiometer is subjected to the desired voltage. The picked off voltage is conducted in the usual manner to the capacitance diode for tuning the HF-circuit.
A substantial drawback with this type of switching arrangement is that the temperature coefficient enters as a disturbing factor into the manually actuable switch as well as into the electronic switch, so that for the optimal tuning a post-adjusting must be carried out after the switching operation. The temperature coefficient fluctuates in known switching arrangements between 100 to 300 mV/°C. This variation in voltage causes an additional frequency drift during tuning. Also, in switching arrangements wherein the release of the tuning voltage is not effected via a sensor circuit, there is present a frequency drift as a result of the temperature-dependent electrical reference elements.
In order to avoid these drawbacks, it has already been proposed to incorporate in the device temperature compensating circuits, which compensate the voltage changes which result as a consequence of warming up the device, and thereby to make possible an optimum tuning. These types of temperature compensating circuits make the control circuits substantially more costly, and only are limited in providing an optimum tuning.
This object is attained in accordance with an embodiment of the invention by a combination of a differential amplifier stage which is connected with the controlled circuit to be adjusted, and with at least one oppositely connected, adjustable single or multi-stage differential amplifier which is connected to a voltage storer.
In a preferred embodiment of the circuit of this invention, there is provided an electronic switch for the electrical connection of the individual voltage storers to the corresponding differential amplifiers. In one embodiment of the invention the differential amplifier is controlled via a current generator which can be switched by means of an electronic sensor circuit via contacting fields or a manually actuable switch.
As the current generator is switched on the differential amplifier is simultaneously put into operation, whereby the current generator, by means of an emitter opposing coupling and its defined maintained base voltage, limits the differential amplifier current. The DC key input voltage range is very high with this differential amplifier due to the current generator. By this it is to be understood that the voltage at both inputs of the differential amplifier can be continuously increased in the same sense through a large range without the working points of both transistors being thereby displaced.
In a further embodiment of the invention there are provided a plurality of further similar differential amplifiers connected in parallel, there is arranged for each such further differential amplifier a separate voltage storer, the symmetrical outputs of the further differential amplifiers being connected with the inputs of a common differential amplifier stage, whereby the further differential amplifiers are individually switchable via a switching member. The further differential amplifiers preferably consist of equal-paired transistors, so that a uniform basic construction and equal electrical properties are available. It is thus possible to arrange the common differential amplifier stage with the oppositely coupled further differential amplifiers in an integrated circuit.
According to a further feature of the invention, the output of the common differential amplifier stage is connected with an amplifier, the output of which is connected with the input of the post-connected "user" circuit, that is, the circuit to be controlled, and with the input of the oppositely coupled inputs of the further differential amplifiers which are connected in parallel relative to each other.