Battery Discharger

The battery discharger published in the June 1998 issue of this magazine may be improved by adding a Schottky diode (D3). This ensures that a NiCd cell is discharged not to 0.6–0.7 V, but to just under 1 V as recommended by the manufacturers. An additional effect is then that light-emitting diode D2 flashes when the battery connected to the terminals is flat.The circuit in the diagram is based on an astable multivibrator operating at a frequency of about 25 kHz. When transistor T2 conducts, a current flows through inductor L1, whereupon energy is stored in the resulting electromagnetic field.