Two-way touch switch (4)

After the power is turned on, the 220V AC power is stepped down by the transformer T, VDI~VD4 bridge rectifier and Cl filtered, and outputs about
10V DC voltage for the Darlington switch circuit and relay control circuit. Darlington tubes VTI and VT2 are both in the cut-off
state, the two normally open contacts kl and k2 of relay K are both open, and the lamp H does not light up. When turning on the light, just
press the electrode piece M2 with your finger , and the DC voltage will inject the base current into VT2 through the finger resistor and R2. VT2 is turned on, the relay
K is powered on, and the contacts kl and k2 are closed. K2 connects the lamp H circuit to make the lamp H energized and glows. kl connects the resistor R3
to the circuit to make the circuit self-locking. In this way, when the finger leaves M2, due to The access relay of R3 still maintains the suction stage state, and the light H
always shines. When turning off the light, just press the electrode pad Ml with your finger. At this time, the Darlington tube VTI quickly saturates and conducts, causing
VT2 to cut off because the base potential drops to zero. The relay K loses power and is released. Its normally open contacts kl and k2 jump open, and the lamp H goes out
.