By adjusting its Adjust pin, output voltage and current can beregulated. VR is placed between the adjust pin and ground to provide an output voltage of 9 volts tothe battery. Resistor R3 Restrict the charging current and diode D2 prevents discharge ofcurrent from the battery. Transistor T1 and Zener diode ZD act as a cut off switch whenthe battery
is full. Normally T1 is off and battery gets charging current. When the terminal voltage of the battery rises above 6. 8 volts, Zener conducts andprovides base current to T1.