High-rise residential walkway lighting control circuit

Press the button switch Sl-Sn, the light will turn on, and the power supply of the transformer T is turned on at the same time. The low-voltage alternating current stepped down by the secondary winding
is filtered by the bridge rectifier and the capacitor Ci, and then a DC voltage is output at the negative end of c1. This voltage is The relay winding K and the normally open contact of the relay are connected, and
the two branches of resistor R] and turtle C2 are added to the base of transistor vri, and VT1 is positively biased. then. The composite tube quickly becomes saturated
and conducts, current flows through the relay group, and its normal contacts close, forming a self-locking state. This way, even if SI releases the button, the light will still be on. While
the normally open contact is closed, the other normally closed contact is
opened, and the power supply continues to charge cz through the relay winding.
Since the base turtle current of \rri is small and the voltage at both ends of C2
cannot change suddenly, The potential can rise slowly, so Cui is
the relay axis at this time. The signal will continue to maintain the voltage; when c2 is charged
to the release voltage of the winding, the voltage difference between the two ends of the relay winding
is very small; it is not strong enough to maintain the pull-in, so K is disconnected,
the light goes out, and the relay winding is in contact with the grinding Detach. The residual voltage on c2
is quickly discharged through the discharge circuit composed of VT1 and Rz to prepare for the next delay.