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PICList Thread
'Motor control on-the-cheap'
1995\06\17@024652 by Mark G. Forbes

>I'm interested in controlling a 90-volt, 2.4 amp DC motor with a PIC
>using PWM. This is not a servo application, just simple but precise
>speed control in one direction with braking.

>Unfortunately, all of the books I have seen on power supplies seem to
>assume that any application over about 24 volts only requires current
>in the milliamps range. Can anyone suggest a good AC to DC conversion
>circuit, preferably without a transformer?

I'm working on something similar, but at 12 volts. *However*, the
technique may still be applicable.

I'm using an audio power op-amp, made by SGS Thomson. TDA2040....I think.
It's a 5-lead TO-220 package, grounded tab, good for about 3 amps
continuous. They sell these things in a variety of current and voltage
ratings. Hang an RC integrator on the front end and you've got a
PWM-to-DC driver. It sources, it sinks, it's bulletproof and it's cheap!

90 volts is a little higher than I'd go with the 2040, but you might
add a couple of power transistors on the output to beef up the voltage
capability. Or, they make higher-voltage parts, though I'm not sure
how *much* higher. Or, call Apex Microtechnology...they make POWER opamps
up to kilovolts/kilowatts. Serious oomph, serious dollars.

You may want to actively drive both leads, even though you want only
one-direction rotation. Ya know how fast you can *stop* a motor by
reversing the drive current? Yow! I've got sheared keys to prove it.
Mark G. Forbes
"Never ascribe to malice that which can be blamed on the engineer."

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