Battery charging circuit with reverse connection display a

In addition to the reverse connection display, this circuit also has a special feature: when the battery is connected to the charger
and charging starts, once the battery is disconnected, there will be no voltage at the output terminal of the charger . The trigger circuit of this circuit uses a relaxation oscillator
    composed of a programmable unijunction transistor (PRT), resistors R4 ~ Rs and capacitor C.
The basic charging circuit can adopt single-phase half-controlled rectification