Telecode type laser remote control lighting switch

The circuit of the telecoded laser remote control lighting switch is shown in Figure 1-34. VD3~VD7, C2, and C3 form a simple capacitor
step-down bridge rectifier and voltage stabilizing circuit. After the power is turned on, a stable DC current of about 15V is output at both ends of C2 to supply
power to the entire electronic circuit. Normally, the transistor VTI^VT3 is in the cut-off state, the relay K is released, and its normally open contact k. t, k．
2 are both turned on, the lamp H does not emit light.
For example, if you click on the small laser flashlight, the photosensitive diode Vl will immediately show a low resistance state when illuminated by the light, VTI will be turned on, and
the power will be injected into the base of VT3 through VT1, VD1, and R2, causing VT3 to quickly turn on, and the relay K will be powered on. Close, its normally
open contacts kl and k-2 are closed. kl makes relay K self-locking, k-2 connects the power supply circuit of lamp H, and lamp H lights up.
At the same time, the light-emitting diode LED lights up to indicate the working status of the circuit. The other channel of the power supply charges the capacitor Cl through VTI and Rl
. Since the laser irradiates VI for a very short time, VT1 quickly returns to the cut-off state. Therefore, the voltage at both ends of C1 cannot be charged
to the door-opening level of VT2, and VT2 can still remain cut-off. status and has no effect on the circuit. When you need to turn off the light, just press and hold the small
laser flashlight for a long time until the voltage at both ends of cl is charged to about 0.65V. VT2 will enter the conducting state from the cut-off state.
The collector of VT2 will output a low level, and VT3 will be turned on. The conduction state enters the cut-off state, relay K loses power and is released, kl and k-2 open
, the light goes out, and the circuit returns to the original standby state.