JPS5946471B2 - video circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises an image signal source and at least one luminance signal source connected thereto for generating a luminance signal for generating a video signal for displaying an image on an image screen. The present invention relates to a video circuit comprising a circuit and a protection circuit for protecting the image screen from burning out due to prolonged exposure to still images.

This type of video signal includes at least a Y luminance signal or an R-luminance signal. G- and B-luminance signals, or only the latter, are generated and used to display images of information sent from information processing devices, including teletext systems, view data systems, and even video games. Ru. These luminance signals can be applied directly to the corresponding input terminals of the display device, or they can be modulated and placed on a carrier wave before being applied to the antenna input terminal of the television receiver.

By the way, in such a case, a certain image is projected stationary on the image screen for a long time, and as a result, the bright parts of the image tend to burn out that part of the image screen locally at an accelerated rate. occurs often.

In particular, it often happens that the user forgets to switch off the video game, so that, for example, the pattern of the lines of a playing field continues to be displayed on the image screen all night. Attempts have therefore been made to provide protection circuits in the video path to eliminate the above-mentioned deleterious effects. One such attempt at a video circuit, such as that described at the beginning of the specification, is described in Canadian Patent Application No. 267,742. The video circuit protection circuit described here is
A temperature-dependent element is used to cause the displayed image to slowly move a certain distance on the image screen in response to changes in ambient temperature. However, with this method, for example, when using a heating device with temperature control in a room with doors and windows closed for a long period of time, once the temperature is set in the evening, the room temperature remains at a constant temperature for the entire night. may remain stationary and continue to be displayed at the same position on the image screen. SUMMARY OF THE INVENTION It is an object of the present invention to provide a video circuit of the type described above, which prevents image screen burnout under all circumstances, including these situations.

The video circuit of the present invention that achieves this purpose includes an electrical protection switch that completely or partially suppresses the luminance signal in the video circuit when the protection circuit is switched off, and a change in the electrical signal of the image signal source. The circuit consists of a detection circuit for detecting the above protection and a timer circuit, the detection signal output terminal of the detection circuit is connected to the start input terminal of the timer circuit, and the time signal output terminal of this timer circuit is connected to the time signal output terminal for the above protection. Connect to the control input terminal of the switch, and the detection circuit is tied. If no signal change is detected within a predetermined time by the master circuit, the protection switch is turned off. This is a surprisingly simple and inexpensive method to adjust the image brightness of all pixels on the image screen after a certain period of time determined by the timer circuit, when no new information is sent to the display device and the switch is not turned off. It can be reduced to zero or to such a low average level that burnout does not occur completely or substantially completely.

Note that the embodiments described in claims 2 to 13 are some possible examples of protection switches, detection circuits, and timer circuits, and these can be combined in any way. It is.

The invention will be explained with reference to the drawings.

In FIG. 1, a control device 1 is connected to an image signal source 2. In FIG.

The control device 1 typically includes one or more control elements known per se, for example a pushbutton touch control.
Equipped with a switch or rotary variable resistor. Note that variable resistors are sometimes operated with so-called "control rods." , the image signal source 2 serves to provide all the image information necessary for the selected purpose in each case. With this image information signal, image signal source 2
at least one luminance circuit 3 connected to the display device 4 to provide a luminance signal to the display device 4. In the case of a color image, generally speaking, three such luminance circuits 3 are prepared to provide so-called R-, G-, and B-luminance signals.

The link between the control device 1 and the image signal source 2 can be remote controlled if desired.

In that case, it would be a good idea to send the control signal using infrared radiation, for example. At least one signal from the image signal source 2 is applied to the detection circuit 5.

The detection circuit 5 has a detection signal output terminal 6 from which an electrical detection signal DET is taken out. This detection signal has a pulse waveform and is generated when the signal sent from the image signal source 2 changes. Note that the signal applied to the detection circuit 5 can be extracted directly from the control signal applied to the image signal source 2, or can be extracted from a new signal generated as a result of processing this control signal by the image signal source 2. Of course, as soon as two or more signals are applied to the detection circuit 5 and at least one of these two or more shows a change, the detection signal DE
It is also possible to generate T. An example of such a circuit is given below in FIG. A detection signal output terminal 6 of the detection circuit 5 is connected to a (startup) input terminal 7 of a timer circuit 8 . Timer circuit 8 has a time signal output terminal 9. The timer circuit 8 itself is a known circuit plotter.
For example, it can be a monostable multivibrator circuit or a digital counting circuit. This timer circuit 8 receives a detection signal DETi sent from the detection circuit 5 on the input terminal 7 side.
l? - is set to the starting position, that is, the "O" position. Then, if no new detection signal DET occurs thereafter, the timer circuit 8 starts operating, e.g. the voltage on the capacitor increases monotonically as a function of time to a certain predetermined time determined by the time constant of the circuit program. After a certain period of time has elapsed, either by changing the state of the monostable multivibrator or under the control of a clock signal, the counting position is advanced until a certain predetermined maximum counting position is reached. When this predetermined time has elapsed, the timer circuit 8 outputs a time signal 0TC to its time signal output terminal 9. However, if a new detection signal DET appears before this predetermined time has elapsed, the timer circuit 8 returns to the "0" position again. The time constant of the timer circuit 8 is considerably longer than the time interval between changes in the information signal during normal use of the device, for example one minute or more. The time signal 0TC is generated only when no change is observed in the image information for a period longer than this predetermined time. The time signal output terminal 9 of the timer circuit 8 is connected to the (control) input terminal 10 of the protection switch 11. In this example, the protection switch 11 is directly connected to the luminance circuit 3.

This protection switch 11 completely or partially suppresses the luminance signal as soon as the timer circuit 8 reaches its maximum position and maintains this state until a restart command is given. Thus the calculator. When a bright reference line, etc. in a still image derived from data communication systems, video games, etc. is about to be displayed at a certain position on the screen with high brightness for a long time,
It is possible to prevent the image screen of the display device 4 from being burnt out. It should be noted that even a small difference in brightness will be a major eyesore when the screen is used the next time, precisely because burnout in one area of the screen does not cause burnout in other areas. The time diagram in FIG. 2 is for explaining the above process.

Here, a line 20 indicates a pulse of the detection signal DET, and a line 21 indicates a characteristic value of the timer circuit 8 that increases linearly from, for example, "0" to the maximum value [Max]. When the detection signal DET is sent at the instant Tnl, the timer circuit 8 is set to the "O" position. This is repeated at the instant t[Tl+1, etc., and the "Max" position is not yet reached. Only when nothing is recorded for a long time does the timer circuit 8 reach the "Max" position at the instant Tn, and remains at this 1rr1axJ position until a new detection signal DET is sent, for example at Ti. The line 22 shows the time signal 0TC of the timer circuit 8, but here, the normal state is temporarily shown as [ON], that is, "1", and the state at the "Max" position is shown as "0FF". When the time signal 0TC becomes "0FF", line 2
3, the protection switch 11 is set to the "0FF position", and the luminance signal Y displaying the monochrome image is completely or significantly suppressed during this instant Tn (5ti), as shown by the curve 24. The figure shows another embodiment.

In this FIG. 3 and the following figures, corresponding circuit summaries are given the same reference numerals as in FIG. 1. elements 1, 2, 3, 4,
5 and 8 have the same function as in FIG.

However, in the case of Fig. 3, a new power source 12 such as a battery, etc.
, which supplies the power supply voltage to other parts of the video circuit via the transistor 13, which is in a conductive state under normal conditions. The base of the transistor 13 corresponds to the (control) input terminal 10 of the protection switch.

While the time signal 0TC at the time signal output terminal 9 of the timer circuit 8 is "ON", the transistor 13 is in a conductive state and the power supply voltage is supplied to the video circuit.

However, for example, at the instant Tn, the time signal 0TC becomes "0".
When it becomes "FF", transistor 13 is cut off,
After cutting off the power supply voltage, the time signal 0TC should remain at this "0FF" position until the instant Ti. Therefore, the timer circuit 8 must have a holding function. For this purpose, it is sufficient to simply turn off the power supply voltage of the timer circuit 8.
However, it is better to turn off all power. This will extend the life of the battery if it is used as a power source. When using a television receiver as the display device 4, another advantage is provided if the luminance signal is modulated and arrives on a carrier wave at the antenna input terminal 14 of the receiver. When the power supply voltage goes out, the carrier wave goes out in response, and many receivers then hit, producing an audible alarm for the user. Another option is to provide the receiver with a so-called "standby" switch, which is placed in the "standby" position as soon as the mains voltage is removed. In FIG. 3, the circuit of the transistor 13 is schematically shown (C
only shown.

Although designing a suitable circuit is outside the scope of this invention,
This is no doubt obvious to those skilled in the art. If not only the timer circuit 8 but also the image signal source 2 and the detection circuit 5 are switched off as shown, it is not possible to automatically restart them with a new control signal.

In this case, the transistor 13 must be set briefly into a conductive state by means of a switch 15 (here included in the control device 1). This switch 15 can, for example, share a push-button switch already present as a control cable for other purposes, with its second contact connected to the base of the transistor 13. FIG. 4 schematically shows the video circuit 20, which includes an image signal source and a luminance circuit collectively represented by a block 21, and a synchronization signal circuit 22.
and a mixer circuit (modulation circuit) 23.

A modulated video signal carried on a carrier wave is sent out from an output terminal 24 of a mixer circuit (modulation circuit) 23. There are two control devices 30 and 31 outside the video circuit 20, which are connected to the control signal input terminal of the image signal source 2 and also to the two VC detection circuits 32 and 33. Here, the occurrence of a control operation is detected. The output terminals of the detection circuits 32 and 33 are connected to the corresponding input terminal 3 of the 0R gate 36.
The output terminal 37 of the 0R gate 36 is connected to the input terminal 38VC of the timer circuit 8. Timer circuit 8 has a time signal output terminal 9. The luminance signal appearing at the output terminal 40 of the luminance circuit 21 is sent to the mixer circuit (modulation circuit) 23 via an AND gate for the time period when the time signal 0TC at the time signal output terminal 9 of the timer circuit 8 is "ON". If it is passed through the timer circuit 8, the time signal will be 0T even after restarting because it corresponds to the retrace period of a monostable multivibrator with a large time constant.
If it is inconvenient that C is not 0NJ, an 0R gate 43 may be provided as shown in the figure, and the detection signal DET may be directly applied to the AND gate 42VC.However, the 0R gate 43 is indispensable. Instead, the time signal output terminal 9 of the timer circuit 8 is directly connected to one input terminal (control input terminal) of the AND gate 42.
It is also possible to connect to Obviously time signal 0TC
As soon as the signal becomes "0FF", the AND gate 42 cuts off the luminance signal. 5a to 5e are simplified time diagrams of various signals, FIG. 5a is a synchronization signal, and FIG. 5b is an image information signal, both of which are modulated together by a modulation circuit 23, A video signal (Fig. 5e) is sent out on a carrier wave.

FIG. 5c shows that the detection signal DET ends at the instant T, and FIG. 5d shows that the time signal 0TC changes to "0FF" at the instant T2 after a long time has elapsed since then.

Note that this is a compressed representation, and in reality the instant t
There are multiple synchronization pulses between T1 and T2. The image information signal is applied to the modulation circuit 23 through the AND gate 42 up to the instant T2. After instant T2, AND gate 42
blocks the image information signal sent from the block 21, so that the modulation circuit 23 receives only the synchronization signal sent from the synchronization signal circuit 22, and the image on the display screen becomes dark. Sometimes you don't want to suppress the image completely, but just reduce it to a harmless brightness level. It has been found that no noticeable burnout phenomenon occurs if the brightness level is lowered to approximately 50% of the maximum brightness level. FIG. 6 shows an embodiment in which only the brightness level is lowered in this way. Here, the modulation circuit 23 has a resistor 5
0, 51, and 52 are used to symbolically show an example, and the carrier wave oscillator is not shown in order to make the drawing easier to see. The modulation circuit 23 functions in a manner known per se.
In the embodiment of FIG. 6, the AND gate 42 of FIG.
4, and a protection circuit (corresponding to a protection switch) 53 consisting of a side in which a variable resistor 55 and a diode 56 are connected in series.
has been replaced by The anode of the diode 56 is connected to the variable resistor 55, and the cathode is connected to the output terminal of the 0R gate 43 or directly to the time signal output terminal 91fC of the timer circuit 8.
Connecting. As a starting point, choose the power supply voltage of the video circuit to be positive. In the normal state, the potential of the cathode of the diode 56 becomes a positive potential when the time signal 0TC is "0N", the diode 56 is cut off, and the luminance signal passes only through the resistor 54 and is sent to the mixer circuit (modulation circuit) 23VC. enter. As soon as the time signal 0TC becomes "0FF", the diode 56
conducts and the luminance signal is reduced by the additional load formed by the series connection of variable resistor 55 and diode 56.

The resistors 54 and 55 can also be combined into one adjustable variable resistor. In addition, in both Figures 4 and 6, 0
Connect one output terminal 60 of the video circuit to the output terminal of the R gate 43, and if the video circuit is built in the television receiver, connect the output terminal of the 0R gate 43 from now on.
The output signal can be extracted and used to switch the receiver to television reception mode. If the 0R gate 43 is omitted, this output terminal 60 is connected to the timer circuit 8.
It can be directly connected to the time signal output terminal 9 of.

FIG. 7 schematically shows the detection circuit 71 and the control device 30. The control device 30 is a touch control type, and the voltage change caused by touching the control device 30 is sent to the timer circuit through the detection circuit 71. It can be sent to 8.

FIG. 8 shows an embodiment slightly different from the above.

Although there are two detection circuits 74 and 75 in FIG. 8, in this case they are included in the video circuit 20, and each input terminal 76 and 77 connects to the output of the corresponding control device 30 and 31, respectively. connected to the terminal. On the other hand, output terminals 78 and 79 of the detection circuits 74 and 75 are connected to input terminals 35 and 34 of the 0R gate 37, respectively. FIG. 9 shows an embodiment of the detection circuits 74 and 75.

An impedance matching circuit (121a, 121b, respectively) is provided on the input side (76, 77, respectively) of each detection circuit, and a pair of comparison circuits (122a and 123a, 122b, 123b, respectively) is provided at the subsequent stage, resulting in a total of four outputs. The terminals are connected to the four corresponding input terminals of 0R gate 36. In each comparison circuit pair consisting of two comparison circuits, two pairs of input terminals of opposite polarity are interconnected, and one of them (128a, 128b, respectively) is connected to a first RC circuit (128a, 128b, respectively).
24a and 125a, 124b and 125b) to the output terminals of the impedance matching circuits 121a and 121b, and the other set (129a and 129b, respectively)
RC circuits (126a and 127a, 126b and 12, respectively)
7b) also via an additional 1C impedance matching circuit 1
Connect to the output terminals of 21a and 121b.

This also passes through the additional second RC circuit, so 12
The total delay time between 1 and 129 will be greater than the total delay time between 121 and 128. For example, if there is a change in the input signal at the input terminal 76 of the detection circuit 74, the comparison circuit 12
An output signal is provided from either 2a or 123a that brings about the "0FF" state, which appears at the output terminal 3711C of the 0R gate 36, which temporarily becomes "ON".

If the control device is left without any operation, the input signal will not change as described above, and the comparison circuits 122a, 12
The potentials of all the input terminals of 3a, 122b, and 123b become equal, and the output voltage of the 0R gate 36 becomes equal to "0". Note that if the time constant of the second RC circuits 126 and 127 is made sufficiently large, for example, 1 minute or more,
Since this RC circuit performs the function of the timer circuit 8, the output terminal 37 of the 0R gate 36 is directly connected to the 0R gate 43. In some cases, it may be sufficient to directly connect the AND gate 42VC.

10, 11 and 12 show the case of color image display, but the parts not related to color are almost the same as the circuits in FIGS. 4, 8 and 6, respectively.

In the case of these FIGS. 10, 11 and 12, three protection switches 42a, b, c or an equivalent protection circuit 53 are used.
a, b, and c are R.
It is provided between the three output terminals for G and B and the modulation circuit 400 in accordance with, for example, the PAL system or the SECAM system.

A synchronization signal circuit 300 is also connected to the modulation circuit 400 separately. The output terminal 100 of the modulation circuit 400 can be linked to the antenna input terminal of a television receiver. Among other things, video input terminals R, G, B and SYN are provided, as is common today, in order to be able to connect a video recorder.
Obviously, in the case of a television receiver in which C is provided separately, the modulation circuit 400 can be omitted. The example shown in FIG. 13 shows a very simple solution in the case of color display, in which the protection circuit is constructed by three exclusive OR circuits 110, 111 and 112 (their output terminals 113,
114 and 115 respectively. G and B signals are output) and one NOR gate 116.

In a simple video circuit, color information is provided by three 1-bit signals SR, SG, and SB, and eight colors including white and black are formed by various combinations of their "O" and "1" signals. These 1-bit signals SR, SG and SB are applied to first input terminals 120, 121 and 122 of exclusive OR circuits 110, 111 and 112, respectively. Second human terminal 13 of each exclusive OR circuit 110, 111 and 112
0,131 and 132 are one VC. NOR after summarizing
Output terminal 1331/C connection of gate 116. This N
During the period when the output of the OR date 116 is "0", R, G and B match SR, SG and SC, respectively.
The above-mentioned time signal 0TC and clock signal CLK are set to NO.
is applied to the input terminal of R gate 116. During the period when the time signal 0TC is "0N" during regular use, the NOR gate 16
The output is "0FF". However, when the time signal 0TC becomes "0FF", the NOR gate 116 follows the clock signal CLKVC, and accordingly, the output alternately takes "0N" and "0FF" according to the period of the clock signal. Every time the output of the NOR gate 116 becomes 0NJ, R
, G and B are SR, SG and S, respectively.
The bit combination of B is exactly reversed (for example, 00
0 is replaced with 111, 011 is replaced with 100), and the output of NOR Gero 16 is alternately "
0FF" and "ON", a color signal determined by SR, SG, and SB and a color signal complementary thereto are alternately sent to the R, G, and B terminals. If one of these color signals continues to be "1", the result is that "0" and "1" are repeated alternately, and the average brightness level of each color signal is the maximum brightness level. 50 (fl). FIG. 14 is a time diagram showing this relationship with respect to R, for example, and the time axis is aligned with that in FIG. 2. The signal SR is sent as is to the R terminal until the instant Tn.

Note that the signal SR is represented in the form of a multi-bit signal for ease of understanding. At the instant Tn, the time signal 0TC becomes "
At 0FFJ, all bits of the luminance signals of all three colors are switched over and all bits are connected to the clock signal C.
The period C of LK is therefore periodically inverted and the three colors are inverted all at once. As a result, R alternately takes values such as a and Max'''-a, and the average value becomes 1'Max'''' according to the following formula. The same can be said for other colors other than R.

The resulting pattern is visible on the screen,
The average brightness has dropped significantly. The clock frequency can be chosen arbitrarily within a wide range.

For example, it is also possible to drive a clock in the device with an AC voltage of 50H2 from a commercial power source, and use the second signal as the clock signal. Figure 15 is a very simple and inexpensive method for video games.
This is an example of an effective detection circuit.

In order to detect the position of the potentiometer 150 (this sliding terminal 151 is connected to the image signal source SIG),
This sliding terminal 151 is also connected to SR differentiation circuits 153 and 154. The differentiated signal is sent to the pulse shaping circuit 15.
Sent to 5. As the pulse shaping circuit, for example, an 0R gate, an AND gate with mutually connected AND input terminals, or an inversion circuit can be used. When the sliding terminal 151 slides, the pulse shaping circuit 155 will give a "1" pulse when the voltage taken out from the potentiometer increases if it is of the previous two types, or if it is an inverting circuit. A "1" pulse is given when the voltage drawn from the potentiometer drops. If the video circuit is for a video game played by two players, this detection pulse (the "1" pulse) is applied to the other party's potentiometer. The detection pulse derived from the yometer is combined with the 0R gate 156 to create the detection signal DET, which is taken out from the output terminal 157 of the 0R gate 156 and applied to the timer circuit 8VC. For example, in the case of a video game played by only one player, such as in the case of a card game, a potentiometer is always connected.

Just as in the case of two players, in the case of a single player, the player will operate his own potentiometer, changing direction several times per minute.

In this case, it is generally not necessary to provide the second potentiometer in the detection circuit. In that case, the 0R gate 156 may be omitted or left in place, and this second input terminal 1
Other control elements, such as touch controls, may also be connected to 58.

Finally, FIG. 16 is an example of a simple timer circuit formed using a digital counting circuit 160. Here 1
61 is a clock signal input terminal, 162 is a counting stop signal input terminal, 163 is a reset signal input terminal, and 164 is a counting output signal output terminal.

Clock signal input terminal 161 is connected to a clock signal source, for example 1H2, as described with reference to FIG.

The reset signal input terminal 163 is connected to the output terminal 6 of the detection circuit 5.
Each time the detection signal DET is sent from there, the counting circuit 160 is set to the "0" position, and then the stepping operation is performed again at the clock cycle.
When the counter information is not sent at all, the counting position finally reaches the maximum position, and a signal obtained by decoding the counter information at that time is taken out from the output terminal 164 as a counting output signal.

For example, when the highest counting position is reached, a carry signal may appear at the output terminal 164. In the case of a 6-bit counter with a clock frequency of 1H2, the highest counting position is reached after a period of time somewhat longer than 1 minute, unless the detection signal DET is subsequently sent. "111111
” After that, the counter did not continue counting [000000
”, the output terminal 164 is connected to the counting stop signal input terminal 162, and the signal CA is 0E.
As soon as the value becomes "0FF", the counting operation is immediately stopped.

However, as soon as the detection signal DET is sent again, the counter is reset. An example of such a digital counting circuit is Type 54161 manufactured by Signetics.
You can use some known counters like . If a higher number of bits than 4 bits is desired, two or more such counters can be connected in cascade.

The output signal CA of the output terminal 164 of the counter 160 (at the same time, the other becomes the time signal 0TC. The emitter side of the transistor 13 in FIG. 3 is connected to the positive voltage side 1 of the power supply 12,
The base of this transistor 13 can be driven by an inverter circuit consisting of a switching transistor 165.

The collector resistance of the switching transistor 165 is set to 16
6, and its tip 167 is connected to the base of the transistor 13. When the time signal 0TC is [0FF], no base current flows into the base of the transistor 13, so the transistor 13 is cut off. On the other hand, when the time signal 0TC is "0N" under normal conditions, the switching transistor 165 is conductive and the transistor 13 receives the base current. Note that this base current varies greatly depending on the resistance value of the collector resistor 166. In the circuit of FIG. 16, restarting can be accomplished by shunting transistor 165 with restart contact 168.

The examples described above are merely given to explain the idea of the invention, and the claims of the present invention are not limited thereto.

Various combinations of detection circuits, timer circuits, and protection circuits are also possible.

[Brief explanation of drawings]

FIG. 1 is a simplified block diagram showing the entire system of the video circuit of the present invention provided with a protection circuit for suppressing the luminance signal;
Figure 2 is a time diagram showing important electrical signals in each part of the protection circuit, Figure 3 is a simplified block diagram of a video circuit with a protection switch that cuts off the power supply voltage, and Figure 4 is black and white. A block diagram of a video circuit with a brightness signal suppression type protection circuit for a television, Figure 5 is a time line diagram to explain the video circuit of Figure 4, and Figure 6 is a block diagram of a video circuit with a brightness signal suppression type protection circuit for a black and white television. FIG. 7 is a schematic illustration of the case where touch control is used in the video circuit of FIG. 4 or FIG. 6; FIG. 8 is a diagram of another embodiment of the video circuit of the present invention; FIG. Figure 9 is a wiring diagram of a detection circuit that also has a built-in timer circuit; Figures 10 to 13 are diagrams showing four embodiments of a video circuit with a protection circuit for color television;
Figure 4 is a time diagram for explaining the circuit in Figure 13;
FIG. 5 is a circuit diagram of a simple detection circuit, and FIG. 16 is a simplified block diagram when a timer circuit is constructed with a digital counting circuit. DESCRIPTION OF SYMBOLS 1... Control device, 2... Image signal source, 3... Luminance circuit, 4... Display device, 5... Detection circuit, 6
... Output terminal of the detection circuit, 7... Input terminal of the timer circuit, 8... Timer circuit, 9... Output terminal of the timer circuit, 10... Control input terminal of the protection switch, 11.
・・Protection switch, DET・・Detection signal, 0TC・・
・Time signal.

Claims (1)

[Scope of Claims] 1. An image signal source, at least one luminance circuit connected thereto for generating a luminance signal, for generating a video signal for displaying an image on an image screen; a protection circuit for preventing the image screen from being burnt out by still images, the protection circuit comprising: a detection circuit for detecting a change in the electrical signal of the image signal source; A time signal having an activation input terminal connected to a detection signal output terminal of the image signal source, and causing a predetermined time delay and switching to a suppressed state if no change in the electrical signal of the image signal source is detected during the time delay. a timer circuit whose output is generated from a time signal output terminal; a control input terminal connected to the time signal output terminal; A video circuit comprising: a protection switch having a switching input terminal and a switching output terminal connected within the circuit. 2. The video circuit according to claim 1, characterized in that a protection switch is disposed on the video signal line of the luminance circuit. 3. Video circuit according to claim 2, characterized in that it comprises a restart circuit for connecting the power input terminal of the timer circuit to the power input terminal of the luminance circuit and for switching on the protection switch again. 4. A video circuit according to claim 1, characterized in that a protection switch is arranged in series with the luminance circuit for completely or partially suppressing the luminance signal in the switched-off state. 5. The video circuit according to claim 1, which comprises a carrier wave oscillator and a modulation circuit, modulates a given video signal, puts it on a carrier wave, and sends it to an antenna input terminal of a television receiver, when the video circuit is in a switched off state. A video circuit characterized in that a protection switch is arranged in series with a carrier wave oscillator to suppress the carrier wave. 6.Equipped with a carrier wave oscillator, a modulation circuit, a transmitting antenna input terminal, a transmitting antenna spare input terminal, and an antenna changeover switch, which modulates the video signal, puts it on the carrier wave, and outputs it to the antenna input terminal of the television receiver. When transmitting, by switching the antenna changeover switch, the output terminal of the modulation circuit is connected to the transmitting antenna input terminal in the first switch state, and to the transmitting antenna preliminary input terminal in the second switch state. In the video circuit according to any one of items 1 to 5, when the protection switch is in the on state, the antenna selection switch is set to the first switching state, and when the protection switch is in the off state, the antenna selection switch is set to the first switching state. A video circuit characterized in that an antenna selector switch is connected to a protection switch for setting the second switch state. 7 Claim 1, characterized in that the timer circuit is a restartable monostable multivibrator circuit.
The video circuit according to any one of items 1 to 6. 8 The timer circuit is composed of a digital counting circuit, which has a reset signal input terminal corresponding to the start signal input terminal of the monostable multivibrator timer circuit, and a final counting position corresponding to the time signal output terminal of the monostable multivibrator timer circuit. 8. The video circuit according to claim 1, further comprising a signal output terminal.