Portable devices used ni- cd auto battery charger

To use portable devices such as digital camera, wireless headphone, pocket radio, etc, which they operates with two "AAA" size batteries, using rechargeable Ni-Cd batteries is a conscionable way to reduce cost.

The circuit presented in the above schematic has been designed to charge automatically two series 350mAh "AAA" size batteries. Set the 20KOhms multiturn potentiometer to get a 2.78V on the 3rd pin of the LM311 which is a comparator. So if the net voltage of batteries reaches at 2.81V, the output of the LM311 goes high and then the state of the transistor becomes off, resulting in charging operation stops. When the red LED is lighted, it indicates that the charging is in the progress, and vice versa.

S:newcircuits.com