IT is a circuit for a battery charger with automatic overload protection feature.
The power supply is 9V and is stabilized by a voltage regulator IC LM317.
The regulator output is used to charge the 6V battery.
Once the battery is fully charged (ie the voltage across the battery is 6V) enters the zener diode biased and starts conducting, which gives a positive voltage to the base terminal of BC548 loading.
Battery Charger with Protection Circuit Diagram
