OT: Variable current supply schematic ?

Hi,

I apologize for the OT but need some help finding a schematic of a power supply with a pot for varying the current from 0 to about 6 amps.

I've built many fixed and variable voltage supplies with LM78XX and LM317's before but I don't know how to build a variable current one.

I did Google for this and didn't find what I was looking for so if you know of any please let me know.

Thanks,

Sam

Check for LM338K, or LT1083

Connect the HPWM output of a PIC to a low pass filter to develop a variable DC voltage. Use that DC value on the base of a power NPN transisitor configured as an emitter follower current amplifier. With the emitter connected to ground, and your load between the collector and your positive supply, you can vary the collector current with the PWM. Just remember to set the "knee" of your low pass filter to about 1/10th to 1/5th of your PWM output frequency. You might also consider putting a high wattage sense resister between the emitter and ground and reading the voltage on the emitter with the A/D of the PIC for some feedback.