Dependent switch for household appliances. Scheme, description

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Dependent switch for household appliances. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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We can say that now in Russia there is a flourishing of DVD technology. DVD players, recorders, home theaters and more are sold very affordable. But all this should work together with the TV.

Even if you decide to make an "audio center" by connecting a multi-format DVD player to a home-made powerful ultrasonic speaker with speakers, you still need a TV so that you can select tracks on its screen, view clips, and other things that are now accompanied by MP-3 recordings made on DVD.

My such "DVD-music center" was going gradually. First, a multi-format DVD player "UNITED-DVD-51" was purchased for the TV "Vityaz-6024ТЦ-1-7064", which can play not only DVD movies, but also MP-3 music, CDs and more. Stereo sound output with volume control and equalizer (from the DVD player remote control). Of course, the sound quality is standard. The TV's speaker system (two narrow speakers at the edges of the kinescope) left much to be desired.

Therefore, according to one of the publications in the journal, a stereo ULF was additionally assembled on an IC for automotive equipment, powered by a conventional transformer source. Now the task has become how to control this ULF so that it turns on and off at the same time as the TV.

As a result of reflections and experiments, the circuit shown in the figure appeared. This is a dependent switch on an automotive relay type 98.3777-10, sold in any auto shop as a "4-pin relay for VAZ", at a price of 40-50 rubles. Relay in a plastic case, with a winding for 12 V with a resistance of 70 Ohm. Of course, it is designed for switching low-voltage circuits, but its analogue SCB-1-M-1240, judging by the reference data from the Internet, can also operate at 220 V AC up to 5 A. So the relay was tested for switching 220 V and by me personally qualified.

Dependent switch for household appliances

The scheme works like this. TV "Vityaz-51ТЦ-6024-1" in the on state takes a power of 60 watts. In the "Stand-By" state, the power is less than 1 watt. This means that the current consumed by it in the switched on mode will be about 0..3 A, and in "Stand-By" about 5 mA. The relay winding has a resistance of 70 ohms, that is, at rated voltage, it takes a current of about 0,17 A, which corresponds to a TV power of 37 watts.

Thus, if a TV is connected through the relay winding in the "Stand-By" mode, the relay will not switch, but when it is on, its winding will easily burn out. The circuit on VD1 and VD2 selects a voltage of about 14 V from one of the half-waves of the voltage supplying the TV. This pulsating voltage is rectified by the VD3 diode and smoothed by the capacitor C1, after which it enters the relay winding.

If the TV is turned off, there is no current at all, and there is no voltage on the relay winding. If the TV is turned on in the "Stand-By" mode, that is, turned off from the remote control, then the supply current of the relay winding will be very low (about 5 mA), and the relay will also not switch, since it needs 170 mA. When you turn on the TV in the operating mode, the voltage and current increases. The relay is activated and turns on the ULF power. A powerful zener diode VD2 protects the relay winding from damage by limiting the voltage on it and removing excess current.

Now a few words about the application of this switch.

If the power of the TV or other "main consumer" is below 40 watts, look for another relay whose winding consumes less current. If the power consumption of the "main consumer" is much higher, for example, the system unit of a personal computer, then you need to turn on one or more zener diodes in parallel with the VD2 zener diode, taking 150 W of maximum power for each zener diode.

That is, for example, with a power of 250 W, you need two zener diodes in parallel, and with a power of 400 W, three in parallel.

Everything is located in a housing with three sockets for external wiring. One socket was dismantled, and in this part the circuit was assembled by volumetric installation. It turned out such an extension cord with two sockets: "Main" and "Dependent".

Author: Mezentsev A.A.

See other articles Section Clocks, timers, relays, load switches.

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