A high efficiency Ni-Cd battery charger using stepwise monitoring

A circuit design for accomplishing high efficiency Ni-Cd battery charging for portable electronic appliances is presented. The proposed method uses a stepwise mV monitoring to trace the battery voltage to determine the state of charging. The control strategy of this charger senses the most important negative delta voltage characteristic of the Ni-Cd batteries. It ensures full recharging under various residual conditions, and maintains battery lifetime. A constant current power supply is applied; this extends the charging capability for different battery voltages. The recharging efficiency was tested and shown to reach above 97% to 105% of the rated specification. The recharging failure rate is approximately 0 to 200 sample tests within 6 months. The proposed circuit design has been fabricated into an integrated circuit.