Double button light switch circuit (1)

The double-button touch light switch circuit is shown in Figure 91. It is mainly composed of a transistor switch circuit , a relay control circuit
and a power supply circuit.
    VDl-VD4, bar, etc.
form a simple capacitor step-down bridge rectifier
and voltage stabilizing circuit.
After power on, C and II D output
a DC voltage of about 12V for the entire switch
. Normally, the transistors
VTl-VT3 are all in the cut-off
state, the relay K does not move
, its movement and closing will cause an electric shock, and the lamp F will not light up. You need to turn on the light||d Just touch the microchip M1. The human body leakage
i Ll d is injected into the base of VT2, and is amplified by VT2 and VT3, which is enough to make VT3 saturated and conductive. Relay
K closes the dynamic contact kl of the electric suction table, allowing the VT2 base to pass through R. Connect to the power supply under J to make the circuit
in a self-locking state. Ⅱ After the human hand leaves M1, VT2 and VT3 can still maintain the conductive state. The other moving contact point k-? of K
is connected, causing the bulb E to glow.
    When you need to turn off the light, you only need to touch the electrode sheet M2, and the human body leakage current will flow through n to the wri curve base,
causing VT1 to quickly flip from the cut-off state to the on-state, and its collector, the base of VT2, will suddenly change to a low level. VT2
and VT3 immediately flip from the on state to the off state. Relay K is released when it loses power, its contacts kl and k2 are reset,
the self-locking is reset, and the controlled lamp F also loses power and goes out.
    f1, in the rLl path, the towel mainly plays the role of damping. When the IU capacitor C1_ is canceled, if the electrode piece Ml is held for a long time
, the relay K will generate vibration with a frequency of joH7 .