Two-way touch switch (3)

VDI --VD4 and vs form the main circuit of the switch , VT1, R4 and Ml form the touch "on" control loop, VT2,
R5 and M2 form the touch "off" control loop.
    Normally, the transistors VT1 and VT2 are in the cut-off state, the thyristor VS is in the blocking state, and the light H does not light up. At this time,
the alternating current passes through lamp H (because the current is in the order of microamps, so the lamp will not light up), VDI ~ VD4 bridge rectifier, Rl, R2
divide the voltage, and obtain about 8.8v DC voltage at both ends of cl for the control loop operation. The static power consumption of the entire switch is only tens of mW,
which can be ignored. When a human hand touches the electrode sheet M1, the human body leakage AC current is injected into the base of VT1 through R4, causing VTI
to conduct. Therefore, a trigger current is injected into the gate of the thyristor vs through VT1, causing vs to turn on, and the lamp H lights up. After vs
is turned on, there is a leakage current at the gate of vs. Since the resistance of resistor R3 is designed to be small, this leakage current charges to C2 through R3.
Even when the human hand leaves the electrode sheet M1, an amplitude can still be generated at both ends of C2. It is a DC voltage of about 0*75V
. This voltage puts the switch in a self-protection state, ensuring that vs always remains on after the human hand leaves M1. When you need to turn off the light
, just touch the electrode sheet M2 with your hand. At this time, VT2 is turned on, short-circuiting the voltage at both ends of C2, and VS loses the "self-protection"
touch voltage. When the alternating current crosses zero, the switch is turned off and the light H goes out.