Practical delay light circuit (2)

It is a practical delay light circuit with no special requirements for components
, and the use effect is quite good. Normally, transistor VT1 is off, VT2 is on
, and the gate potential of thyristor VT3 is almost
zero, so VT3 is off and bulb
E does not light up. When you need to turn on the light, just press SB once
, and the pulsating DC output from VDl-VD4
will be transmitted through R. Current limiting,
vs stabilized voltage becomes 25V DC voltage
to quickly charge the capacitor C, vri is turned on immediately,
VT2 is cut off, and the blockade of wrz is released. The gate of VT3 passes through R, obtains the trigger current and turns on, and the lamp E lights
up. After releasing SB, since the charge stored in capacitor C can be discharged to the VT1 emission junction through R,
VT1 can still be maintained in the on state, so the lamp E continues to light up. Until the C charge is basically discharged and VT1 cannot be maintained
on, the circuit returns to its original state, that is, VT1 is turned off and VT2 is turned on. VT3 is turned off and the light F goes
out. The delay time
    of this circuit is mainly determined by the R: and C discharge time constants, and everyone can
adjust their values ​​as needed.