9 Volt Battery Chargers

0 - 160 mA Adjustable Charge Rate Battery Charger

This circuit uses a potentiometer and an op-amp to make a 0 - 160 mA adjustable constant current source. A transistor is used to boost the output current of this circuit.

The current flowing through the transistor is limited only by the control signal from the op-amp.

R5 is not a current limiting resistor. R5 is a sense resistor.

R5 is far too small to limit current to protect the transistor.

Divide the voltage drop across R5 to get charging current.

Use 1 ohm or 10 ohms or 100 ohms for the value of R5. This makes for very easy calculation.

I used a 2N2222A NPN transistor from Radio Shack. Any NPN transistor will work if it can handle the voltage, current and power.

Salvage a large high voltage transistor complete with large heat sink from a dead TV.

Use star grounding.

• Connecting the Emitter to ground.
• Connecting V+ to Base.
• Opamp control circuit applying V+ to the Base .