Automatic emergency lighting circuit

The automatic emergency lighting circuit shown is very suitable for home
installation. Because the components used are smaller, the price is cheaper.
    When the mains power grid supplies power normally, the AC 220V mains voltage is compressed by
the capacitor CI ire.k, and then undergoes half-wave rectification by the diode VD1 and
filtering by the capacitor C2, and then charges the battery with a pulse current of about 90mA. At the same
time, because the base of transistor VT1 is in the on state due to the positive bias
, gates 1 and 2 are in the cutoff state, and the bulb EL does not light up. . Once the mains power
grid is powered off, the transistor VT1 changes from conduction to cutoff, VT2 changes from cutoff to conduction
, and the light bulb EL lights up. The function of diode VD2 is to isolate the battery
and the base of VT1 to ensure that the mains power is cut off. VT1 turns to 1 and stops. After the mains power is restored, VT1 is turned on, EI. Off, the circuit is reset.
    II in the figure. It is a small battery of 6.3V, 0.15A. The battery can be 4 No. 1 batteries or a 6V battery.