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The bistable circuit with optocoupler and transistor

2016-05-06 23:53  
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The bistable circuit with optocoupler and transistor
In the initial state with the power turning on, the transistor VT is cutoff, the circuit outputs high potential. When the input terminal is coupled with a positive pulse, the collector current of VT increases, photocoupler light emitting diode emits light, and the collector-emitter resistance of phototransistor becomes smaller, then the base current of VT increases to form a positive feedback, so that VT quickly be saturated, and it changes to 0 from 1 . When it is input the negative pulse, the collector current of VT becomes small, thereby enabling light emitting diode darken, and VT's base current becomes small, causing the collector current of VT to be further reduced, the VT quickly become the OFF state, the light emitting diode does not emit light, the phototransistor is turned off, so that VT is stable in the off state, the state of flip-flop changes from 0 to l .