Touch Delay Lighting Switch (2)

Diodes VDI-VD4 and 1 thyristor VS form the main circuit of the touch switch, R1, LED and VD5 form the secondary circuit, and
the control circuit is composed of transistors VT1 ~ VT3 and other components. The LED lights up normally to indicate the position of the touch switch, making it easy
to find the switch at night . The collector of VT3 is clamped by VD5 at about 8v, VT1-VT3 are all in the cut-off state, and VS has no trigger
voltage and is in the off-state, so the lamp H does not light up. When you need to turn on the light, you only need to touch the touch electrode M with your finger. Because the human
body leakage current is divided by R5 and R4 and then injected into the base of the transistor VT3, so that VT3 is quickly turned on, and the 8v DC current flows
through the ce pole of VT3. The capacitor C2 is charged, and VT2 is turned on via R2, and VTI is quickly turned on. VS
is turned on because the gate receives a positive trigger current, and the lamp H is lit. After the human hand leaves the electrode sheet M, the charge stored in C2 is
discharged to the emitter junction of VT2 through R2, so the conduction of VT2, VTI and vs can still be maintained, and the lamp H is still lit.
Until the C2 charge is basically discharged, vr2 changes from on to off. VT1 also cuts off, and vs loses the trigger current. When
the alternating current crosses zero, it turns off and the light goes out. Changing the values ​​​​of R2, R3 and C2 can adjust the length of time the lamp is lit each time.
Using the graphic data, every time the electrode sheet M is touched, the lamp H can light up for about 60 seconds.