NiCd Charger 15mA and 45mA
This simple NiCd battery charger provides constant current charging using a transistor. It is suitable for 1.5V and 9V rechargeable NiCd batteries.
Circuit Operation
- The charger uses a BD140 medium-power transistor configured as a constant current source.
- The voltage across two 1N4148 diodes biases the transistor's base. The combination of the transistor’s base-emitter voltage and the diode forward voltage ensures a relatively stable charging current.
- The charging current can be set to approximately 15 mA or 45 mA by using a switch.
Key Features
- Constant current NiCd battery charger
- Selectable charging current: 15 mA or 45 mA
- Uses BD140 transistor and 1N4148 diodes for stable operation
- Suitable for 1.5V and 9V rechargeable NiCd batteries
- Simple, low-cost, and reliable design
Construction Notes
- Use a small heatsink for the BD140 transistor if charging multiple batteries simultaneously.
- Ensure correct polarity when connecting batteries.
- Keep the diodes and transistor close together to minimize voltage drift due to temperature.
- Optional: add a series resistor to fine-tune the charging current if needed.
