555 audio-visual equipment automatic power switching circuit

Published:2011/6/7 20:17:00 Author:TaoXi | Keyword: 555, audio-visual, equipment, automatic, power switching | From:SeekIC

As the figure 14-21 shows, the power supply automatic switch is composed of the comparator, the OR gate circuit and the monostable delay circuit, and it can be used in the television and the recording equipments, when there is no sound over 2 minutes, the circuit will cut off the power supply automatically. The comparative circuit is composed of the two operational amplifiers IC1 and IC2(uA741), the IC1's in-phase port pin-3 and the IC2's reversed-phase port connect with the reference level +6V, when the output signal of the televisions and the recording equipments is larger than +/-50mV, the comparator outputs the high electrical level, VT1 conducts, the capacitance C1 (the IC3's charging and discharging circuit) discharges, the 555's discharging port pin-7 has the low electrical level, the pin-3 has the high electrical level, VT2 conducts and J closes, the load gets the power to work.



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