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 the op-amp.

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 and lets far too much current through before it starts to limit current.

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.

VOM Reading	R5	I Charging Current
1 volt	1 ohm	1 amp
1 volt	10 ohm	100 ma
1 volt	100 ohm	10 ma

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 .