JPS5834845Y2 - tv jiyeonji yuzouki - Google Patents

Description

[Detailed description of the invention] This invention particularly improves the S/N ratio in a television receiver that detects the presence or absence of a synchronization signal and automatically stops its operation after a certain period of time after a television broadcast ends. The purpose of this is to prevent malfunctions caused by thermal noise.

When television broadcast waves are not present, the tuner's high-frequency amplifier generally operates at high gain, which tends to generate thermal noise in the synchronization separation circuit.

When thermal noise occurs, a television receiver that detects the presence or absence of a synchronization signal and shuts off the output of the DC power supply circuit after the television broadcast ends, will continue to operate even after the Ten Vision broadcast ends. may not stop.

Conventionally, as a means to solve this kind of problem, it has been considered to provide a suitable time constant circuit in the control grid of the discharge tube for detecting the presence or absence of a synchronization signal.

However, with this measure, when the thermal noise level is significant under weak electric field reception conditions, the bias of the control grid of the discharge tube is affected.

That is, even after the broadcast signal stops, the bias change in the control grid of the discharge tube becomes small due to the direct current component of thermal noise, and the operation of the discharge tube continues in the same state as during reception of the broadcast signal.

Therefore, the intended purpose cannot be achieved.

Further, if continuous pulse noise comes, the above-mentioned malfunction may occur, which is undesirable.

This proposal was proposed to solve the above-mentioned problem, and includes a pulse generator that operates only in response to horizontal and vertical synchronizing signals that are higher than a predetermined reference potential.
A DC stabilized power supply circuit is controlled by a DC voltage obtained by converting this pulse output into DC voltage.

FIG. 1 is an example of a well-known DC power supply stabilization circuit to which the present invention is applied, in which 1 is a DC voltage input terminal, 2 is a stabilization circuit,
3 is an output terminal.

Further, 4 is a control transistor, 5 is a drive transistor, 6 is a Zener diode, 7 is an error amplification transistor, and 8 is a variable resistor for adjusting the power supply voltage, and these constitute the stabilizing circuit 2.

The DC voltage stabilized by the stabilizing circuit 2 is supplied to necessary parts of the television receiver from the output terminal 3.

FIG. 2 is a diagram showing an embodiment of the present invention, in which 9 is a synchronizing signal input terminal, 10 is a transistor 11, 12, and a resistor 22.
13 is a rectifying and amplifying transistor, 14 and 15 are resistors and a capacitor that constitute a smoothing circuit, 16 and 17 are resistors that constitute a time constant circuit together with the capacitor 15, and 18 and 20 are switching circuits. The double-amplifying transistor 19 is a switch having contacts a r b.

Here, terminal A in FIG. 2 is connected to the input terminal of the stabilizing circuit 2 in FIG. 1, terminal B is connected to the base of the error amplifying transistor 7 in FIG. It is connected to the output terminal of the conversion circuit 2.

First, the operation of the circuit shown in FIG. 2 will be described in the case where the movable piece of the switch 19 is connected to the contact a.

When television broadcasting is being performed, a signal as shown in FIG. 3A is supplied to the terminal 9 from a synchronous divider circuit (not shown).

In FIG. 3A, 24 is, for example, a composite synchronization signal of negative polarity;
25 is noise mixed into the input signal.

The synchronizing signal 24 containing this noise 25 is supplied to a Schmitt trigger circuit 10 having a well-known configuration, and is supplied to a resistor 2 as a trigger.
Only the synchronizing signal 24 having an amplitude exceeding the bias level or trigger level of the transistor 12 determined by 2°23 is extracted to the collector of the transistor 12;
Noise 25 does not appear as shown in FIG.

The negative synchronization signal 24 from which the noise 25 has been removed is rectified, amplified, and phase-inverted by the transistor 13, and a positive synchronization signal is generated at the collector of the transistor 13.

This voltage is converted into a DC voltage by a resistor 14 and a capacitor 15, and the positive DC voltage generated across the capacitor 15 is delayed for a certain period of time by a time constant circuit consisting of a resistor 16, 17 and a capacitor 15, and is then supplied to the base of a transistor 18. be done.

This keeps transistor 18 on and transistor 20 cut off.

As mentioned above, the collector terminal B of the transistor 20 is connected to the base of the error amplification transistor 7 in FIG.
Since the emitter of the transistor 20 is grounded, the transistor 20 has no relation to the operation of the stabilizing circuit 2 shown in FIG. 1, and the stabilizing circuit 2 operates normally.

Next, when the television broadcast ends and no synchronizing signal is supplied to the terminal 9, the transistor 11 is turned on and the transistor 12 is turned off, and the collector potential of the transistor 12 rises.

This turns off transistors 13 and 18,
Transistor 20 is turned on, and current flows from terminal A in FIG. 1 through resistor 21 and the base and emitter of transistor 20.

Therefore, the potential of terminal B in FIG. 1, that is, the base potential of error amplification transistor 7, becomes almost ground potential, transistor 7 is cut off, transistors 4 and 5 are also cut off, and the potential of output terminal 3 is zero. The television receiver will automatically stop operating.

However, even after the television broadcast ends and the synchronization signal disappears, various noise components actually arrive.

Since the AGC circuit continues to operate in the receiver even after the broadcast ends, the gain increases and the thermal noise generated internally is amplified and reaches the terminal 9.

In addition, in the city, even when broadcasting ends at night, external noises from neon signs, cars, high-frequency equipment in factories operating at night, etc. mix in.

If the noise applied to terminal 9 does not exceed the reference level, ie, the trigger level of Schmitt circuit 10, as shown in FIG. 3C, circuit 10 will not respond and will not generate a pulse.

Therefore, as described above, the DC stabilized power supply circuit is cut off.

Generally, the components that determine the average value of noise exist below the trigger level, as shown in FIG. 3C, but there may also be some components with peak values that exceed the trigger level.

However, it is also true that the pulse width of components above that level is extremely narrow compared to the synchronization signal.

If a noise pulse with a component exceeding the trigger level arrives, the Schmitt circuit 10 responds only to the component above the reference potential and generates a pulse.

This pulse has a much lower average value than the synchronization signal.

Therefore, when the DC voltage is rectified, smoothed, and integrated by a time constant circuit that performs delay, the DC voltage applied to the base of transistor 18 is extremely small and is not sufficient to turn on transistor 18.

In other words, the DC power supply stabilizing circuit can be kept in a cut-off state.

Once the video camera stops operating, current continues to flow through the base-emitter circuit of the transistor 20 from terminal A in Figure 1 through the resistor 21, and the potential at the output terminal 3 of the stabilizing circuit 2 is kept at zero. Therefore, even if television broadcasting starts again, the operation of the receiver remains stopped.

However, when the movable piece of switch 19 is switched to the contact point,
The base potential of the transistor 20 becomes the ground potential, the transistor 20 is turned off, the stabilizing circuit returns to its normal state, and the receiver starts operating.

When the normal state is restored, the movable piece of the switch 19 is switched to contact a again to prepare for the end of the next television broadcast.

As described above, the present invention is configured so that the synchronization signal exceeds the trigger level of the Schmitt trigger circuit and the average value of the noise component does not exceed this level, so that it responds only to signals that exceed this reference potential. ing.

Therefore, noise components smaller than a predetermined reference potential are completely removed by this Schmitt trigger circuit.

In addition, for noise components exceeding the reference potential, it is equipped with a DC voltage generation circuit that performs rectification, smoothing, and delay operations.
By averaging this component and suppressing it to a negligibly low potential, malfunctions are prevented.

That is, the present invention includes a circuit that will not malfunction due to various noise components even if the synchronization signal disappears after the television broadcast ends.

Moreover, since the present invention maintains the DC voltage by delay operation, even if broadcast waves are temporarily interrupted due to channel switching, etc., there is no malfunction of turning off the power, making it extremely practical.

In the embodiments described above, a Schmitt trigger circuit is used as a pulse generator that operates only in response to a signal exceeding a predetermined reference potential, but it goes without saying that other amplitude selection circuits may be used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a DC power supply stabilizing circuit to which the present invention is applied, in which 1 is an input terminal, 2 is a stabilizing circuit, 3 is an output terminal, and 7 is an error amplification transistor. FIG. 2 is a diagram showing an embodiment of the present invention, in which 9 is a synchronizing signal input terminal, 10 is a Schmitt trigger circuit, 13 is a rectifying and amplifying transistor, 14 to 17 are resistors and capacitors constituting a smoothing and time constant circuit, 18 and 20 are switching transistors. FIG. 3 is a diagram for explaining the present invention.

Claims (1)

[Scope of utility model registration request] A pulse generator that responds and generates an output pulse only when an input signal exceeds a predetermined reference potential, a DC voltage generation circuit that rectifies and smoothes and delays the output pulse of this pulse generator, and this DC voltage. and a switching circuit that cuts off the output of the DC power supply stabilizing circuit in response to a change in the DC voltage of the generation circuit, using horizontal and vertical synchronization signals obtained during television broadcasting as input signals exceeding the reference potential, Further, the average value of noise components generated during and at the end of television broadcasting is set so as not to exceed the reference potential, and when the synchronization signal disappears, the output pulse disappears, the DC voltage shifts, and the switching A television receiver characterized in that the DC power supply stabilizing circuit is cut off by a circuit.