Practical delay light circuit (3)

It is a delay lamp controller with good performance. Like the previous two examples, the connection between the controller and the bulb
is also a two-wire system, so it is very convenient to install and use, and there are no particularly strict requirements on components.
    Normally, j-electrode VT2 is turned on due to
base bias current due to R:, and its collector is
low level, so the gate of thyristor VTI
is clamped at about 0 zv, so
VT1 is turned off and the lamp E does not light up. At this time,
2ZOV AC power is added to the voltage divider R through VD1~VD4 bridge
rectifier. ,R.
On, this can make the capacitor C. Charge with
a DC voltage of about 20V. VT3 is in cut-off state due to R; the right end is floating. When you need to turn on the light, just press
the button switch SB, and the G stored charge will quickly pass through SB to (1. Discharge the charge, and the c1 charge will pass through R; inject
the base of VT3 to turn on VT3 and cut off VT2, releasing the blockade of thyristor VT1. , VT1 is turned on because the gate
obtains a positive trigger current through R, and the lamp E lights up. After releasing SB, the bulb E can still keep lighting
up until c: When the charge is basically discharged and VT3 cannot be maintained on, the circuit After recovery, VT1 is turned off and the light E
goes out.