This NiCad baterry charger regulator circuit can charge 6 volts as well as 12 volts NiCd batteries. It uses a transformer which can deliver 4 to 5 A current between 12.6 and 15 V. Ordinary chargers select the charging voltage through a swith but the circuit featured here uses an automatic current regulator.

The charging current is automatically regulated to 4.2 amperes. Once the charging current reaches 4A, the voltage drop at R1 will be 600 mV. In this case the transistor T1 will conduct and supplies current to T2. continue reading…