JPS6112427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates in particular to a horizontal oscillation frequency control device for a television receiver.

In television receivers, when the DC power supply voltage rises abnormally due to a failure in the power supply circuit, or when the resonance capacity of the horizontal output circuit decreases, the horizontal output pulse increases and the voltage on the high voltage side becomes excessive. Nari X
In order to prevent such problems, an overvoltage protection device is provided to stop the horizontal oscillation circuit to the horizontal output circuit. However, when receiving a VTR signal, if the horizontal synchronization signal of the received signal changes temporarily, causing the frequency to become too low and the horizontal pulse increases, the above-mentioned overvoltage protection circuit will operate and the receiver will A practically inconvenient situation occurs in which the operation of the device is stopped. Furthermore, if the horizontal oscillation frequency becomes too high, the horizontal amplitude becomes too small, causing problems such as a black frame around the periphery.

In order to avoid the above-mentioned problems, the present invention provides an upper limit of the phase detection output voltage to be applied as a control voltage for controlling the oscillation frequency to the horizontal oscillation circuit on the output side of the phase detection circuit that controls the horizontal oscillation frequency. The purpose is to prevent the overvoltage protection circuit from malfunctioning by connecting a constant voltage diode that limits the lower limit and the lower limit to a predetermined limit voltage, respectively, to prevent the horizontal oscillation frequency from becoming higher or lower than a certain range. be.

Hereinafter, the present invention will be explained in detail with reference to the embodiments shown in the drawings.

Generally, in a television receiver, a phase detection circuit 2 is connected to a sync separation circuit 1 that separates a sync signal from a composite video signal, and the phase detection output of the phase detection circuit 2 is applied to a horizontal oscillation circuit 3 to generate a horizontal oscillation frequency. A horizontal drive circuit 4, a horizontal output circuit 5, and a flyback transformer 6 are sequentially connected to the output side of the horizontal oscillation circuit. and,
The output pulses of the flyback transformer 6 are supplied to an overvoltage protection circuit 8 via a rectifier circuit 7, and the output of the overvoltage protection circuit 8 is applied to the horizontal oscillation circuit 3 to control the horizontal oscillation operation. Further, the output pulse of the flyback transformer 6 is applied to the integration circuit 9, and the sawtooth wave output from the integration circuit 9 is fed back to the phase detection circuit 2, and the output synchronous signal of the synchronous separation circuit 1 and the phase The phases are compared in the detection circuit 2.

The present invention further includes a constant voltage power source 11 connected to the phase detection output side via a constant voltage diode 10 to limit the phase detection output within a certain range.

Next, the operation of the phase detection circuit 2 will be explained with reference to FIGS. 2, 3, and 4. In Fig. 2, a is the synchronization signal output from the synchronization separation circuit 1, b is the sawtooth wave signal output from the integration circuit 9, and by comparing the phase difference between these signals a and b, the phase of c is determined. Obtain the detection output. Then, it is taken out as the phase detection average output of d and applied to the horizontal oscillation circuit 3 to control the horizontal oscillation frequency.

Now, the horizontal oscillation frequency is the center value and the synchronization signal a
When the phase difference between the signal b and the sawtooth wave signal b shown by the solid line is 0, the phase detection output c is equal in positive and negative as shown by the solid line, and the average phase detection output d is equal to the reference voltage Vo shown by the solid line.
become. Next, when the horizontal oscillation frequency becomes higher and the phase of the sawtooth wave advances by Δφ1 as shown by the broken line in b, the positive and negative values of the phase detection output c are A difference occurs, and the phase detection average output d becomes the voltage V1 shown by the broken line, which is changed by ΔV1 from the reference voltage Vo.The horizontal oscillation circuit 3 is controlled so that the horizontal oscillation frequency is lowered, and the horizontal oscillation frequency is returned to the original center horizontal oscillation frequency. return.

Next, in FIG. 3, a, b, c, and d are the same signal waveform diagrams as in FIG. 2, respectively. Synchronization signal a
If the central horizontal frequency shown by the solid line becomes a lower frequency shown by the broken line and a phase delay occurs by Δφ2, the voltage V2 shown by the broken line changes by ΔV2 from the reference voltage Vo shown by the solid line d. , the horizontal oscillation circuit 3 is controlled to have a frequency lower than the center horizontal frequency.

Therefore, as shown in FIG. 1, the control voltage applied to the horizontal oscillation circuit is controlled by the clamp voltage V3 indicated by the dashed-dotted line in FIG. It is clamped and controlled so that the horizontal oscillation frequency does not fall below a certain value.

FIG. 4 shows the phase difference Δφ and the change ΔV in the phase detection average output in the operation of the phase detection circuit 2 described above.
Indicates the relationship between When the phase difference is Δφ1, the voltage change is ΔV1, and when the phase difference is Δφ2, the voltage change is ΔV2.
It's getting old.

FIG. 5 shows the relationship between the phase difference Δφ and the phase detection average output V. When the phase difference is Δφ1, the phase detection average output should be V1, and when the phase difference is Δφ2, the phase detection average output should be V2, but because it is limited by the clamp voltage V3, the phase difference becomes Δφ3 or more. Even if the phase detection average output is not lower than V3.

FIG. 6 shows the control relationship between the phase detection average output V and the horizontal oscillation frequency. Here, the phase difference is Δφ2
When , the horizontal oscillation frequency is the phase detection average output V2
The clamping voltage should be controlled by
Since it is limited by V3, it will stay at a frequency lower than the horizontal center frequency o, but relatively higher than the very low frequency 2. In this case, the horizontal oscillation frequency 3 is set by the overvoltage protection circuit 8 to prevent problems such as abnormally high voltage and component destruction.
It is necessary to determine the clamp voltage V3 so that it is higher than the value at which the horizontal synchronization occurs due to temperature changes, power supply voltage changes, component variations, etc.

Furthermore, contrary to the above case, the phase detection circuit 2
If the output voltage of the phase detection circuit 2 is too large, the oscillation frequency in the horizontal oscillation circuit 3 will become too high, causing problems such as insufficient horizontal amplitude. The horizontal oscillation frequency is prevented from becoming excessive by clipping at the total voltage of the constant reverse voltage and the voltage of the constant voltage source 11.

As described above, according to the present invention, a horizontal synchronizing signal can be generated by connecting a constant voltage diode that limits both the upper and lower limits of the control voltage applied from the phase detection circuit to the horizontal oscillation circuit to a predetermined voltage. This effectively prevents the horizontal oscillation frequency from becoming too low due to temporary changes in the voltage, causing the overvoltage protection circuit to operate and stopping the receiver, or preventing the horizontal oscillation frequency from becoming too high and causing insufficient horizontal amplitude. It is something that can be done.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a television receiver according to an embodiment of the present invention, Fig. 2 is a waveform diagram showing the operation of the phase detection circuit when the horizontal oscillation frequency changes from the center value, and Fig. A waveform diagram showing the operation of the phase detection circuit when the horizontal synchronization signal changes from the center value. Figure 4 shows the relationship between the phase difference between the synchronization signal and the sawtooth wave comparison signal and the changing voltage of the phase detection circuit output. Figure 5 is a graph showing the relationship between the phase difference and the average output of the phase detection circuit and the relationship between the clamp voltage, similar to Figure 4, and Figure 6 is a graph showing the relationship between the average output of the phase detection circuit and the horizontal oscillation frequency. It is. 2... Phase detection circuit, 3... Horizontal oscillation circuit, 1
0... Constant voltage diode, 11... Constant voltage power supply.

Claims (1)

[Claims] 1. A horizontal oscillation circuit, and a phase detection circuit that compares the phase of a signal obtained by integrating the output pulse of the flyback transformer and a horizontal synchronization signal, and applies the phase detection output to the horizontal oscillation circuit as a control voltage for horizontal oscillation frequency control. and limiting both the upper and lower limits of the control voltage to a range such that the oscillation frequency of the horizontal oscillation circuit does not become lower than the frequency that operates the overvoltage protection circuit and does not become higher than the frequency that causes the screen amplitude to become insufficient. A television receiver in which a constant voltage diode is connected between the output terminal of the phase detection circuit and a constant voltage source.