JPS5952865B2 - Television receiver constant voltage circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator type constant voltage circuit used in a television receiver.

A switching regulator that stabilizes unstable DC voltage by controlling the conduction period of a switching element that switches in synchronization with the horizontal scanning cycle to obtain the constant DC voltage necessary to operate a television receiver. A type constant voltage circuit is sometimes used.

Hereinafter, a conventional constant voltage circuit of a television receiver will be explained using FIG.

A DC power supply 1 whose power supply voltage is unstable is connected to a switch element 3 via a primary winding 2A of a transformer 2, and the switch element 3 switches the output of a pulse width modulator 10 through an exciter 11. The voltage induced in the secondary winding 2B connected in reverse phase is rectified and smoothed by the diode 4 and the capacitor 5, and then supplied to the horizontal deflection circuit 7 and other load circuits 6 other than the horizontal deflection circuit 7. The pulse width modulator 10 includes:
A sawtooth wave formed by waveform-shaping the retrace pulse voltage generated in the horizontal deflection circuit 7 and the output of the error amplification circuit 9 corresponding to fluctuations in the DC output voltage supplied to the load circuit 6 and the horizontal deflection circuit 7 are input, Pulse width control is performed to turn on and off the switch element 3. In such a constant voltage control circuit, when the switching element 3 changes from a conductive state to a cutoff state, an oscillating voltage is generated by the leakage inductance and distributed capacitance between the primary winding 2A and the secondary winding 2B of the transformer 2. do. Since this oscillating voltage has an extremely high frequency, it interferes with the signal circuit of the television receiver, and if the cut-off time of the switch element 3 is within the horizontal scanning period, vertical streaks will appear on the screen. It has the disadvantage that it appears as The purpose of the present invention is to
It is an object of the present invention to provide a constant voltage circuit for a television receiver that can eliminate the appearance of interference on the screen of the television receiver due to the oscillating voltage when the above-mentioned switch element is cut off.

In the present invention, in order to eliminate the disturbance that appears on the screen when the switch element is cut off, the switch element is switched from the conductive state to the cut-off state during the retrace period of horizontal scanning.

The present invention will be explained below with reference to FIGS. 2 and 3.

2 is a circuit diagram showing an embodiment of a constant voltage circuit of a television receiver according to the present invention, and FIG. 3 is a voltage waveform diagram of main points in FIG. 2.

FIG. 3a shows the retrace pulse voltage generated in the horizontal deflection circuit 7. This pulse voltage is waveform-shaped by the waveform shaping circuit 8 into a sawtooth waveform voltage as shown in FIG. 3B. A voltage as shown in FIG. 3C is generated at the collector of transistor 12 of pulse width modulation circuit 10. Therefore, the collector voltage of the transistor]3 of the excitation circuit 11 becomes as shown in FIG. 3D. Excitation circuit 11
The output waveform of is transmitted through a transformer 14 connected in reverse phase to
The transistor 3A, which is the switch element 3, is switched. FIG. 3E shows the collector voltage waveform of transistor 3A. Since the transistor 3A changes from a conductive state to a cut-off state within the horizontal blanking period, the influence of vibration does not appear during the horizontal scanning period. As described above, the switch element 3 changes from the conductive state to the cutoff state during the horizontal retrace period, and the disturbance due to the oscillating voltage generated at this time does not appear on the screen.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a constant voltage control circuit of a conventional television receiver, FIG. 2 is a circuit diagram showing an embodiment of a constant voltage control circuit of a television receiver according to the present invention, and FIG. It is a voltage cross-section diagram of the main points in the figure. 1...DC power supply, 2...Transformer, 3
......Switch element, 4...Diode, 5...Capacitor.

Claims (1)

[Claims] 1 Connect the primary winding of a transformer and a switch element in series between the two electrodes of an unregulated DC power supply, turn the switch element on and off in a horizontal cycle, and control the ratio of the on period to the off period. In the constant voltage circuit of a television receiver, which stabilizes the DC output voltage obtained by rectifying and smoothing the pulse voltage generated in the secondary winding of the transformer, the above switching element is switched from on to off during the horizontal blanking period. A constant voltage circuit for a television receiver characterized by switching to.