PHILIPS 12B310 /38L PHILETTA 310 CHASSIS TM7 INTERNAL VIEW.

A surently amazing chassis ! The PHILIPS CHASSIS TM7 is divided and realized in two main boards;
one for power / large signal and
one for signal processing / small signal

This chassis development remembers the Philips chassis series K9 and K11 and Km2 and Km4 which all of these you can see HERE.


The Line deflection output is with an AY102 and a BD160.


Power Supply: The examples chosen are taken from manufacturers' circuit diagrams and are usually simplified to emphasise the fundamental nature of the circuit. For each example the particular transistor properties that are exploited to achieve the desired performance are made clear. As a rough and ready classification the circuits are arranged in order of frequency: this part is devoted to circuits used at zero frequency, field frequency and audio frequencies. Series Regulator Circuit Portable television receivers are designed to operate from batteries (usually 12V car batteries) and from the a.c. mains. The receiver usually has an 11V supply line, and circuitry is required to ensure that the supply line is at this voltage whether the power source is a battery or the mains. The supply line also needs to have good regulation, i.e. a low output resistance, to ensure that the voltage remains constant in spite of variations in the mean current taken by some of the stages in the receiver. Fig. 1 shows a typical circuit of the power -supply arrangements. The mains transformer and bridge rectifier are designed to deliver about 16V. The battery can be assumed to give just over 12V. Both feed the regulator circuit Trl, Tr2, Tr3, which gives an 11V output and can be regarded as a three -stage direct -coupled amplifier. The first stage Tr 1 is required to give an output current proportional to the difference between two voltages, one being a constant voltage derived from the voltage reference diode D I (which is biased via R3 from the stabilised supply). The second voltage is obtained from a preset potential divider connected across the output of the unit, and is therefore a sample of the output voltage. In effect therefore Tr 1 compares the output voltage of the unit with a fixed voltage and gives an output current proportional to the difference between them. Clearly a field-effect transistor could do this, but the low input resistance of a bipolar transistor is no disadvantage and it can give a current output many times that of a field-effect transistor and is generally preferred therefore. The output current of the first stage is amplified by the two subsequent stages and then becomes the output current of the unit. Clearly therefore Tr2 and Tr3 should be current amplifiers and they normally take the form of emitter followers or common emitter stages (which have the same current gain). By adjusting the preset control we can alter the fraction of the output voltage' applied to the first stage and can thus set the output voltage of the unit at any desired value within a certain range. By making assumptions about the current gain of the transistors we can calculate the degree of regulation obtainable. For example, suppose the gain of Tr2 and Tr3 in cascade is 1,000, and that the current output demanded from the unit changes by 0.1A (for example due to the disconnection of part of the load). The corresponding change in Tr l's collector current is 0.1mA and, if the standing collector current of Tr 1 is 1mA, then its mutual conductance is approximately 4OmA/V and the base voltage must change by 2.5mV to bring about the required change in collector current. If the preset potential divider feeds one half of the output voltage to Tr l's base, then the change in output voltage must be 5mV. Thus an 0.1A change in output current brings about only 5mV change in output voltage: this represents an output resistance of only 0.0552.


PHILIPS  12B310 /38L  CHASSIS TM7 TV HORIZONTAL OSCILLATOR HAVING A STABILIZED AUXILIARY DC OUTPUT

A TV horizontal oscillator having an output transformer is arranged to supply a principal AC output to the horizontal deflection yoke of a picture tube. In order to provide stabilized DC voltage to other transistor stages in the TV receiver, an auxiliary winding of the transformer is connected in series with the parallel combination of a resistance and a capacitance. A voltage proportional to the difference between the voltage across at least a portion of the auxiliary winding and that across the resistance-capacitance combination is rectified and filtered. The resulting DC output is substantially insulated from changes in current through the output transformer caused, e.g., by beam-current induced changes in the width of the TV picture.



1. In a TV horizontal oscillator, an arrangement for generating a reference DC voltage that is stabilized against current changes through the transconductive path of the oscillator, which comprises:

2. An arrangement as defined in claim 1, in which the auxiliary winding is a tapped second primary winding of the transformer serially connected in the transconductive path, and in which the deriving means comprises, in combination, a rectifier and a second resistance serially connected between the tap of the second primary winding and the terminal of the first resistance most remote from the second primary winding, the voltage at the junction of the rectifier and the second capacitance constituting the reference DC voltage.

3. An arrangement as defined in claim 1, in which the auxiliary winding is a secondary winding of the transformer, in which the junction between the secondary winding and the first resistance is connected to a point in the transconductive path of the oscillator, and in which the deriving means comprises, in combination, a rectifier and a second capacitance connected across the serial combination of the secondary winding and the first resistance, the voltage at the junction of the rectifier and the second capacitance constituting the reference DC voltage.

4. In a TV horizontal oscillator, an arrangement for generating a reference DC voltage that is stabilized against current changes through the transconductive path of the oscillator, which comprises:

Description:

BACKGROUND OF THE INVENTION

The DC voltage supply for the picture tube and many of the transistorized stages of a TV receiver may be advantageously generated by suitably rectifying and filtering portions of the transformer output of the associated horizontal oscillator. Because of the extremely high frequency of the oscillator, such rectification and filtering may be done with much smaller and simpler components and configurations than have previously been necessary when such DC voltage was derived from the line frequency power transformer.

The horizontal oscillator AC output is conventionally coupled to the horizontal deflection yoke of the picture tube. In an attempt to minimize unwanted changes in width of the TV picture (caused, e.g. by changes in the picture tube beam current), a first resistance may be inserted in series with a primary winding of the transformer and the transconductive path of the horizontal oscillator. Consequently, any tendency of the picture to widen, and thus induce changes in current in the oscillator output, will be offset by a decrease in the oscillator current because of such first resistance. Such decrease, in turn, will decrease the deflection caused by the horizontal deflection yoke to narrow the picture to its normal width.

Unfortunately, such automatic variation of the current through the oscillator output transformer to compensate for beam width changes generates corresponding (and undesirable) changes in the DC voltage derived at the output of the oscillator.

SUMMARY OF THE INVENTION

In accordance with the invention, the DC voltage derived from the output of the horizontal oscillator may be stabilized notwithstanding variations in the oscillator supply current caused, e.g., by beam current variations. An auxiliary winding on the oscillator output transformer is serially connected with the parallel combination of a second resistance and a capacitance, whereby changes in voltage developed across such auxiliary winding due to current changes through the oscillator tend to be offset by voltage changes across the second resistance. The required stabilized DC voltage is derived by suitably rectifying and filtering a voltage proportional to the net difference of the voltages across the auxiliary winding and the second resistance.

In a first embodiment of the invention, the auxiliary winding constitutes a tapped second primary winding in the transconductive path of the oscillator. In this case, the above-described rectifying and filtering means are serially connected between the tap of the second primary winding and the terminal of the second resistance most remote from the second primary winding.

In an alternative embodiment, the auxiliary winding is a secondary winding of the transformer having a terminal coupled to the transconductive path of the oscillator. The rectifying and filtering means are connected across the serial combination of the last-mentioned secondary winding and the second resistance.

In another alternative embodiment, the auxiliary winding is a second primary winding serially connected with the transconductive path of the oscillator. Suitable circuitry is provided to derive the stabilized DC output as the algebraic sum of (a) the rectified and filtered output of the second primary winding and (b) a voltage proportional to the voltage across the second resistance.

PHILIPS  12B310 /38L  CHASSIS TM7 B-W TELEVISION DIAGRAM AND DEFLECTION CIRCUIT:

A unidirectional conductive device is coupled from a base terminal to a collector terminal of a horizontal deflection output transistor in a television receiver and poled in a direction to prevent the transistor from saturating when it is driven into its conductive state during a portion of each deflection cycle. Biasing means is coupled to the diode to preselect the desired operating voltage of the transistor during its conduction period.

1. In a television receiver, a deflection circuit comprising: 2. A circuit as defined in claim 1 wherein said transformer is an auto-transformer and said second terminal is intermediate said first and 3. In a television receiver, a deflection circuit comprising:

Description:

The present invention relates to transistorized deflection circuits utilized in television receivers.

In present day transistor deflection circuits, for example, those used in the horizontal output stage of a television receiver; the output transistor is normally operated in a switching mode, that is, the transistor is driven into saturation during a trace interval of each deflection cycle and driven out of conduction during the retrace portion of each deflection cycle. By operating the transistor in its saturation region, average power losses are minimized. With saturated operation, however, the accumulation of minority carriers in the base region will effect a continuation in the flow of collector current after the trace interval during the initial portion of the retrace interval while the transistor is being driven into its non-conducting state. In addition to causing this undesirable delay time in turning off the transistor, losses occurring during this period may be localized in small areas commonly referred to as "hot spots." These losses are characterized in being regenerative and tend to cause second breakdown of the device. This effect is explained in greater detail in a paper authored by the present inventor and entitled "Thermal Regeneration in Power Dissipating Elements" which appeared in "The Electronic Engineer" publication in the January 1967 issue. Although operating the horizontal output transistor in its saturated region may reduce the average power dissipated in this device during its conduction interval, it increases the possibility of second breakdown during the turn-off time. With the advent of high voltage (1,500 volts) transistors, it is possible to develop the necessary output energy utilizing one of these transistors which can be operated in a non-saturated mode. The circuit of the present invention insures that the deflection output transistor will not be driven into saturation.

Certain low power transistor switching circuits, such as employed in computer applications, have utilized diodes in conjunction with resistive biasing means coupled between the base and collector terminals to prevent the transistor from saturating and thereby increase the maximum switching frequency of the circuit by reducing the turn-off time of the device.

In the solid state deflection art, however, it is desirable to reduce the turn-off time of the device not to increase the frequency of operation of the circuit, but rather to prevent second breakdown of the device as the relatively large inductive voltage pulse appears during the initial portion of the flyback interval, when current flowing through the deflection winding is interrupted to initiate the retrace portion of each deflection cycle.

The non-saturated operation of the deflection output transistor is achieved in circuits embodying the present invention by automatically holding the collector voltage above the saturation level by shunting excess base drive from the base to emitter junction into the collector circuit. Prior transistor deflection systems employ only the saturated operation of the deflection output device.

Circuits embodying the present invention include a deflection output transistor having a diode coupled between its base and collector terminals and poled to prevent the transistor from being driven into saturation during its conduction period of each deflection cycle.

The invention can be more fully understood by referring to the drawings together with the description below and the accompanying claims.

In the drawings:

FIG. 1 illustrates in block and schematic diagram form, a television receiver including a solid state deflection output stage embodying the present invention;

FIG. 2a is a waveform diagram of the voltage present at the collector terminal 55c of transistor 55 in FIG. 1;

FIG. 2b shows the drive current to terminal A in FIG. 1;

FIG. 2c is a waveform diagram of the current in diode 56 in FIG. 1;

FIG. 2d is a waveform diagram of the base current flowing in transistor 55 of FIG. 1;

FIG. 3 is a schematic diagram of an alternative embodiment of the present invention;

FIG. 4a is a waveform diagram of the voltage appearing at the terminal 366 in FIG. 3;

FIG. 4b is a waveform diagram of the drive current to terminal A in FIG. 3;

FIG. 4c is a waveform diagram of the current in diode 356 in FIG. 3; and

FIG. 4d is a waveform diagram of the base drive current to transistor 355 in FIG. 3.

Referring specifically to FIG. 1, an antenna 10 receives television signals and couples these signals to a tuner 12 which selects the desired radio frequency signals of a predetermined broadcast channel, amplifies these signals, and converts the amplified radio frequency signals to a lower intermediate frequency (I.F.). The tuner 12 is coupled to an I.F. amplifier 14 which amplifies the intermediate frequency signals. The I.F. amplifier 14 is coupled to a video detector 16 which derives video information from the I.F. signals. The video detector 16 is coupled to a video driver stage 18 which amplifies the video signals. The video driver stage 18 is coupled to a video output stage 20, an automatic gain control stage 25 and a synchronizing separator stage 42. An output signal from video driver stage 18 may also be coupled to a sound channel (not shown) to reproduce the audio portion of the transmitted television program. The video output stage 20 couples amplified video information to a control element, such as a cathode 28, of a kinescope 30.

The automatic gain control stage 25 operates in a conventional manner to provide gain control signals which are applied to a radio frequency amplifier included in tuner 12 and to the I.F. amplifier 14. Sync separator 42 separates the synchronization information from the video information and also separates the horizontal synchronizing information for the vertical synchronizing information. The vertical synchronizing pulses derived from sync separator 42 are applied to the vertical deflection system 44 which provides the required deflection current to a vertical deflection winding 43 associated with kinescope 30 by means of the interconnection Y--Y. The horizontal synchronizing pulses from sync separator 42 are applied to an automatic frequency control detector 45 which serves to synchronize a horizontal oscillator 46 with the horizontal synchronizing pulses. The horizontal oscillator stage 46 is coupled to a horizontal driver stage 48 which develops the required drive signal and may be coupled by means of an output transformer in stage 48 (not shown) to a transistorized horizontal output stage 50. The transformer secondary, coupled to terminal A, provides a direct current path for the drive current.

The horizontal output stage 50 includes an output transistor 55 having a base, a collector and an emitter terminal 55b, 55c and 55e, respectively. A resistor 52 and a capacitor 53 are coupled in parallel between the horizontal driver stage 48 and the base terminal 55b of transistor 55.

The output stage includes a unidirectional conductive device such as a diode 56 coupled between the base and collector terminals 55b and 55c of transistor 55. Stage 50 also includes a damper diode 57 coupled across transistor 55, a retrace capacitor 58 coupled across transistor 55 and the series combination of a horizontal deflection winding 59 and an S-shaping capacitor 60 also coupled across transistor 55. Output stage 50 also includes a flyback transformer 61 with a primary winding 61p coupled from a source of operating potential (B+) to the collector terminal 55c of transistor 55. A secondary winding 61s on transformer 61 develops high voltage pulses which are coupled to a high voltage rectifier 63 to provide the ultor voltage for application to a terminal 32 on kinescope 30. Flyback transformer 61 may also include additional windings (not shown) for providing, for example, keying pulses to the AGC stage 25.

The output stage 50 in FIG. 1 is a conventional shunt fed trace driven circuit with the exception of the diode 56 and the bias network including resistor 52 and capacitor 53. Beginning at the center of the trace interval of the deflection cycle, the yoke current is zero and capacitor 60 has a maximum charge. The drive signal applied to the base terminal 55b of transistor 55 turns this device on, thereby completing the conduction path for yoke current which includes capacitor 60, yoke 59 and the collector to emitter current path through transistor 55. During this portion of scan the yoke current is supplied by the charge on capacitor 60 and increases to a maximum value in one direction at which time scan retrace is initiated by driving transistor 55 out of conduction by applying an appropriate signal from the driver stage 48 to the base 55b of transistor 55. During the latter portion of the trace interval when the magnitude of the yoke current is increasing, the output transistor of prior circuits is normally driven into saturation and is in this conduction state at the instant retrace is initiated. During the first portion of retrace, the yoke current is at a maximum and resonates with the retrace capacitor 58 by charging capacitor 58 in a polarity to reverse bias the damper diode 57. As the yoke current decreases to zero, capacitor 58 has a maximum charge impressed upon it; and during the second portion of retrace, the capacitor (58) drives current through the yoke in a reverse direction until it is discharged and the voltage across it reverses sufficiently to forward bias damper diode 57. Diode 57 then conducts during this first portion of trace to complete the current path for yoke current which is, at this instant, at a maximum value in a direction in yoke 59 to charge capacitor 60 and is increasing toward zero. At the mid-point of trace the yoke current has reached zero and the cycle is completed by driving transistor 55 into conduction once again.

Turning now to the operation of the circuitry of FIG. 1 including the present invention, reference is made to the waveform diagrams of FIG. 2. The initial portion of trace is represented in FIG. 2 by the time period between t ₀ and t ₁ in the figure. It is recalled that during this period damper diode 57 is conducting. The voltage at collector terminal 55c of transistor 55 is represented by the voltage waveform (V _c ) in FIG. 2a and is equal to the forward voltage drop across diode 57 which is of the order of -0.7 volts. At some non-critical time before t ₁ , the horizontal driver 48 provides a drive current (I _A ), as is shown in FIG. 2b. This current flows through diode 56 as is illustrated in FIG. 2c, since the diode is forward biased. [The cathode of diode 56 is at the same voltage as collector terminal 55c (-0.07 volts) and the drive current produces a positive voltage at point A which is at the anode of diode 56.] As time t ₁ (the center of trace) is reached, damper diode 57 turns off allowing the collector voltage on transistor 55 to increase as shown in FIG. 2a. At the same time, a portion of the drive current flowing into terminal A is conducted by the now forward biased base to emitter junction of transistor 55 as is illustrated by the waveform of FIG. 2d. Transistor 55 is now conducting the increasing yoke current during the latter portion of scan represented by the period from t ₁ to t ₂ in FIG. 2. As the magnitude of the yoke current increases during the t ₁ to t ₂ interval, the base current in transistor 55 increases as shown in FIG. 2d. Diode 56 conducts as illustrated in FIG. 2c to shunt the remaining portion of the applied drive current at terminal A. It is noted that the sum of the currents shown in FIGS. 2c and 2d will equal the current shown in FIG. 2b. The values of resistor 52 and capacitor 53 can be selected to hold the transistor collector voltage at a preselected value sufficient to prevent saturation of the transistor 55. If, for example, the voltage across capacitor 53 is 5.3 volts, the voltage at terminal A with respect to ground will be approximately 6 volts (5.3 volts plus the forward voltage drop across the base-emitter junction of transistor 55). The collector voltage will then be approximately equal to the voltage at terminal A less the forward voltage drop across diode 56. It is desirable to choose values of resistor 52 and capacitor 53 to operate transistor 55 near but not into the saturation region of conduction during the latter portion of each trace interval.

At time t ₂ retrace is initiated by applying a relatively large negative drive signal as shown in FIG. 2b to the base terminal of transistor 55. During the retrace interval (t ₂ to t ₀ in FIG. 2), the collector voltage increases in a typical manner as illustrated in FIG. 2a. At time t ₀ the cycle is again repeated.

The circuit modification illustrated in FIG. 3 is another embodiment of the invention which reduces the change in voltage applied to the yoke 59 of FIG. 1 at time t ₁ . As shown in FIG. 2a, when diode 57 turns off and transistor 55 conducts, the voltage at the collector terminal 55c of transistor 55 changes by as much, for example, as 6 volts. This voltage change, which is coupled to the yoke 59, will vary the rate of change of yoke current during the center of trace and may, in certain circuits, cause an undesirable non-linearity in the scanning rate. As FIG. 4a illustrates, the circuit of FIG. 3 reduces this change in voltage at the mid-point of trace (t ₁ ).

Referring to FIG. 3, the circuit elements which correspond to those of FIG. 1 are prefaced by the numeral 3. In explaining FIG. 3, it is helpful to refer to the waveform diagrams of FIG. 4. Transformer 364 in FIG. 3 is a tightly coupled auto-transformer wherein the tap point 365 may be, for example, at the 5 percent point on the transformer. That is, the segment between terminals 365 and 366 contain 5 percent of the total number of windings on transformer 364. Transformer 364 may also include a secondary winding such as the high voltage winding which is not shown in the figure. In operation, as drive current is applied at sometime prior to t ₁ as is shown in FIG. 4b, damper diode 357 is conducting and the voltage at terminal 366 is therefore at approximately -0.7 volts. Drive current flowing into terminal A as represented in FIG. 4b will be conducted by diode 356 during this interval as indicated by the diode current waveform in FIG. 4c. At the middle portion of trace (t ₁ ), the damper diode turns off and voltage at terminal 366 is thereby allowed to go slightly positive (less than 0.7 volts). The collector voltage of transistor 355 is held at a value of approximately 5 volts (assuming, for example, the B+ voltage is equal to 100 volts and the collector is coupled to the tap 365 on transformer 364 at a 5 percent point). At this instant, the base to emitter junction will be forward biased and transistor 355 conducts. It is seen that the anode voltage of diode 356 is at approximately +0.7 volts and its cathode which is coupled to terminal 366 is at a less positive voltage. Diode 356 begins to conduct during the latter portion of trace as illustrated by the current waveform diagram shown in FIG. 4c.

During the latter portion of trace, the transistor tends to saturate and the collector voltage at terminal 355c tends to decrease. As this occurs, more current will flow from the B+ terminal through the upper portion of transformer 364. Due to the relatively tight coupling of the segments of transformer 364, terminal 366 experiences a decrease in voltage which controls the forward bias applied to diode 356 to shunt sufficient drive current to hold the transistor 355 out of saturation. The collector voltage of transistor 355 is thus held at some preselected value depending on the location of tap point 365 on transformer 364. Since transformer 364 is utilized, terminal 366 will remain at a low voltage during the latter portion of trace as shown in FIG. 4a, and diode 356 will be forward biased during the application of a positive drive signal to terminal A. As before, the base drive current will increase and diode 356 conduction will decrease generally as shown in FIGS. 4c and 4d during the latter portion of trace. At time t ₂ in FIG. 4, a negative drive pulse is applied to the circuit which initiates the retrace interval of the deflection cycle.

Although the specific embodiments of the invention are illustrated in the horizontal deflection output stage of a black and white television receiver, the invention has equal applicability to other deflection systems and may be utilized in a color television receiver.