JPS6117192B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit used in a television receiver.

FIG. 1 is a block diagram of a conventional power supply circuit.
1 is an AC power supply, 2 is a rectifier circuit, 3 is a smoothing circuit that smoothes the rectified uncontrolled DC voltage, 4 is a voltage control circuit that controls the uncontrolled DC voltage to obtain a stable output voltage, 5 is an output terminal, 6 is a gate amplifier circuit that supplies a stable control input signal to the voltage control circuit 4;
7 is a comparison circuit, 8 is an output voltage feedback circuit that feeds back the output voltage to the comparison circuit 7, 9 is a reference voltage generation circuit that generates a reference voltage, and 10 is a synchronization pulse input terminal.

In the conventional power supply circuit, the comparison circuit 7 compares the output voltage and the reference voltage, generates a pulse voltage with a time delay corresponding to the output voltage with respect to the synchronization pulse, and based on this pulse voltage, the voltage control circuit 4 The circuit configuration was designed to control the output voltage and keep the output voltage stable.

In such a circuit configuration, in order to increase the suppression rate of the ripple component of the AC power cycle appearing at the output terminal 5, the AC loop gain in the output voltage feedback circuit 8 and the comparison circuit 7 must be made sufficiently large. Therefore, it was difficult to obtain an inexpensive circuit configuration.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power supply circuit which eliminates the drawbacks of the conventional circuit described above and which can sufficiently suppress the ripple component of the AC power cycle with an inexpensive circuit configuration.

FIG. 2 is a block diagram of the power supply circuit of the present invention. In this figure, the same numbers as in FIG. 1 indicate the same contents. Note that 9' is a reference voltage generating circuit that integrates a horizontal synchronizing pulse (hereinafter referred to as a synchronizing pulse) and superimposes it on a specific reference voltage. In the present invention, the output of the smoothing circuit 3 is applied to the comparison circuit 7, the synchronization pulse from the synchronization pulse input terminal 10 is applied to the reference voltage generation circuit 9, and the output of the reference voltage generation circuit 9' is applied to the input of the comparison circuit 7. Other connections are the same as in FIG.

An embodiment of the present invention will be described in detail below. FIG. 3 shows a part of the power supply circuit according to the present invention, and FIG.
FIG. 3 is an explanatory diagram showing voltage waveforms at various parts in the figure. In FIG. 3, 33 is a rectified output terminal, which is grounded through a capacitor 11. The input terminal of the voltage control circuit 4 is connected to the rectified output terminal 33, and the output terminal thereof is connected to the output terminal 5. The rectifier output terminal 33 is connected to the cathode of a Zener diode 13 via a resistor 12, and the anode of the Zener diode 13 is grounded via a parallel circuit of a resistor 14 and a capacitor 15.
It is connected to the synchronous pulse input terminal 10 via a series circuit of a capacitor 26. The cathode of the Zener diode 13 is connected to the emitter of a transistor 20, the collector of the transistor 20 is grounded via a resistor 21, and the base of the transistor 20 is grounded via a resistor 19.

The rectified output terminal 33 is grounded through a series circuit of a resistor 16 and a resistor 17, and the base of the transistor 20 is connected to a connection point between the resistors 16 and 17 via a capacitor 18. The collector of the transistor 20 is connected to the base of a transistor 23 via a capacitor 22, and the base of the transistor 23 is grounded via a resistor 24. The emitter of the transistor 23 is grounded, and the collector of the transistor 23 is connected to one of the primary windings of the pulse transformer 29.
The other side of the primary winding is connected to the rectified output terminal 33 via a resistor 27, and at the same time is grounded via a capacitor 28. Pulse transformer 29-2
One of the secondary windings is connected to the output terminal 5, and the other to the other input terminal of the voltage control circuit 4. Further, the output terminal 5 is connected to the base of the transistor 20 through a resistor 30.

In the power supply circuit configured in this way, when a synchronizing pulse as shown in FIG. 4A is applied to the synchronizing pulse input terminal 10, the resistor 25,
The signal is shaped into a sawtooth wave by an integrating circuit composed of a capacitor 15 and a resistor 14, and is applied to the anode of a Zener diode 13. Therefore, a sawtooth wave superimposed on the Zener voltage Vz appears at the cathode of the Zener diode 13, as shown at 31 in FIG. 4B.

On the other hand, a DC voltage obtained by dividing the output voltage by a resistor 30 and a resistor 19 is applied to the base of the transistor 20, and the emitter voltage waveform is shown in FIG.
It is sliced by the voltage of the resistor 19 as shown in 32. Then, a collector voltage having a waveform shown in FIG. 4C appears at the collector of the transistor 20. This collector voltage is differentiated by the capacitor 22 and the resistor 24, resulting in a waveform as shown in FIG. 4D, and is applied to the base of the transistor 23. Since the emitter of transistor 23 is grounded, transistor 23 is ON only when the base voltage is positive.
The secondary winding of the pulse transformer 29 is shown in Fig. 4E.
A voltage waveform like this is induced. This induced pulse operates the voltage control circuit 4 to control the output voltage.

Now consider the case where the output voltage increases. When the output voltage increases, the base voltage of the transistor 20 also increases, so that the time for the transistor 20 to turn on is delayed, and the emitter voltage waveform becomes as shown by the broken line B. At the same time, the collector voltage waveform also becomes as shown by the broken line C, and the broken base voltage waveform of the transistor 23 also lags as shown by the broken line D. Therefore, the voltage induced in the secondary winding of the pulse transformer 29 is also delayed as shown by the broken line E, and the voltage control circuit 4
The operating timing changes, the output voltage decreases, and the output voltage is kept constant.

The ripple voltage appearing at the rectified output terminal 33 is then compressed by the resistors 16 and 17 and applied to the base of the transistor 20 via the capacitor 18. In this case, since the frequency of the synchronizing pulse is much larger than the frequency of the ripple appearing at the rectified output terminal 33, the voltage at the base of the transistor 20 (waveform 32 in FIG. 4B) due to the integration effect
The change appears as a nearly DC change within the synchronous pulse period. That is, when the voltage at the rectified output terminal 33 increases, the base voltage of the transistor 20 also increases, the slice voltage of the emitter voltage also increases, and as described above, the timing at which the transistor 20 turns on is delayed. transistor 20
If the timing of turning on is delayed, the voltage control circuit 4 operates to lower the output voltage, so the ripple voltage that appears at the rectified output terminal 33 does not appear at the output terminal 5, and the output voltage is stabilized. Ru.

As explained above, according to the present invention, it is possible to sufficiently remove ripples in the power supply cycle using an inexpensive comparator circuit, and the capacitor for smoothing the rectified output voltage can also be relatively small. , an inexpensive and high-performance power supply circuit is provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional power supply circuit, FIG. 2 is a block diagram showing a power supply circuit according to the present invention,
FIG. 3 shows a part of a specific circuit example according to the present invention, and FIG. 4 is a voltage waveform diagram of each part for explaining the operation of FIG. 3. 1: AC power supply, 2: Rectifier circuit, 3: Smoothing circuit,
4: Voltage control circuit, 5: Output terminal, 7: Comparison circuit, 8: Output voltage feedback circuit, 9': Reference voltage generation circuit, 10: Synchronous pulse input terminal.

Claims (1)

[Claims] 1. A reference voltage generation circuit that integrates a horizontal synchronizing pulse and superimposes it on a specific reference voltage; An output voltage feedback circuit that detects the output voltage of the power supply circuit and feeds it back to the comparison circuit described below; The reference voltage generation circuit A first input voltage, which is the output voltage of the output voltage feedback circuit, and a second input voltage, which is formed by AC coupling a voltage proportional to the voltage obtained by rectifying the input AC voltage to the output voltage of the output voltage feedback circuit.
the first input voltage and the second input voltage.
a comparator circuit that outputs a time-delayed control pulse according to a voltage difference between the input voltage of the comparator; and a voltage control circuit that controls an uncontrolled DC voltage to a safe output voltage using the control pulse obtained from the comparator circuit A power supply circuit for a television receiver, characterized by comprising: