TV automatic switch. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Consumer electronics
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The TV's circuit breaker turns off the TV after broadcasts have ended. It is controlled by constant or pulsed voltage signals, which can be taken from the fractional detector of the audio channel, from the control grid of the amplitude selector lamp, from the video amplifier (video signal), from the amplitude selector (sync pulses), etc.
The TV set has two buttons: S2 "On" and S1 "Off". When the S2 button is pressed, power is supplied to the device and the TV, a constant voltage appears at the output of the rectifier VI and V2 and relay K.2 is activated, opening its normally closed contact K2.1. Capacitor C4 starts charging, relay K1 is activated and the power button is blocked by contacts K1.1 until capacitor C4 is fully charged. This time is enough to warm up the TV and receive a video signal at the input of the device. The signal selected by the L1C2 circuit, which is tuned to the horizontal sync pulse frequency, opens the transistor V3 with a negative half-wave and the current through the relay winding K1 does not stop even after the capacitor C4 is charged. After the end of the transmission, the video signal disappears, the transistor V3 closes, and at the end of the discharge time of the capacitor C4, the relay K1 opens its contacts, turning off the TV. The S1 button is used to turn off the TV manually.
Details. Transformer T1 is made on the magnetic circuit Ш12X15. Winding I contains 6000 turns of wire PEV-2 0,1, winding II - 600 + 600 turns of wire PEV-2 0,12; coil L1 is wound with PEV-1 0,23 wire on a cylindrical paper frame with an inner diameter of 8,5 mm, 35 mm long and contains 1200 turns with taps from the 812th and from the 120th turns, counting from the end connected to the common wire , the core of the coil is a rod cylindrical ferrite grade 700 NM, 50 mm long and 8 mm in diameter.
The device is adjusted by connecting the resistor R1 to the anode (collector) of the output lamp (transistor) of the video amplifier. The emitter of transistor V3 is disconnected from the circuit and connected to the common wire of the device. Using a voltmeter, control the voltage on the circuit and adjust the core of the L1C2 circuit until the maximum voltage is obtained. Then, having restored the circuit, the emitter of the transistor V3 is connected in turn to the 12th, 11th, 10th, 9th and 8th turns of the circuit, the generation of the circuit is disrupted (self-excitation is evidenced by the closed contacts K1.1 of the relay K1 in the absence of a video signal).
Author: Yu. Gunchenko
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