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Thread: [EE] ? : Controlling a load with a variable voltage.
www.piclist.com/techref/power.htm?key=voltage
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face BY : Mike Hardwick email (remove spam text)



>Hi all, have a question for you.  I need to control a load using a PIC that
>will take a variable voltage.  It is a simple variance, I only want it to
>have either +7V or +12V.  Also 0V (off) will be needed.  I know I'll need 2
>pins per load on this, perviously I used a power mosfet to provide only +12
>and it worked great, so I'm looking for options.

If you want output voltage flexibility, try power amp chips. A single PIC
pin with PWM output drive can give you a variable voltage output (after
filtering), including zero volts. National's LM1875 audio power amp,
ferinstance, can handle up to 3A, is protected much like a regulator IC,
and doesn't cost much. Voltage gain has to be >=10, and you'll need a
low-current negative power supply to accommodate the amplifier's input
common mode range.

If you need multiple outputs, you can produce PWM briefly at each pin in
turn, just long enough to control a simple R/C integrator. Switch those
pins to input mode when they're not driven. Refresh/update the charge
periodically...

Mike Hardwick
Decade Engineering
http://www.decadenet.com

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