'PWM control of 90-volt, 2.4-amp DC motor'
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Subject: PWM control of 90-volt, 2.4-amp DC motor
Author: "BOWDEN; ANDREW V JR" <SCANA.COM> at Internet_Exchange ABOWDEN
Date: 6/16/95 11:25 AM
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?
Second, can anyone suggest a proper interface circuit that will allow
the PIC to perform PWM. In other words, perhaps control of a MOSFET
that does the switching with proper protection for the PIC.
Any assistance would be eagerly and gratefully received. BTW, I have
the capability to handle attached graphics files if anyone wants to
include a schematic. :)
> in the milliamps range. Can anyone suggest a good AC to DC conversion
> circuit, preferably without a transformer?
Sorry ? Could you plese explain what for (Input/Output parameters) ? At
least I didn't understand the connection of that problem with a DC motor
control (unless it's related to getting the 90 Volts DC from a 115/230 V AC
> Second, can anyone suggest a proper interface circuit that will allow
> the PIC to perform PWM. In other words, perhaps control of a MOSFET
> that does the switching with proper protection for the PIC.
If you want to do breaking, you'll need some possibility of electronically
short-circuiting the motor. With a full bridge it's easy, but that requires
4 power transistor vs. 1 for a simple speed control.
For the power part: at that current/voltage I'd use a bipolar transistor.
High voltage mosfets tend to be more difficult to organize. Anyway, the
power part of this circuit (without breaking) could be: optocoupler for PIC
protection, pull-up resistor and a pnp (perhaps darlington) between motor
and positive supply. Should work, but try it beforehand.
> Any assistance would be eagerly and gratefully received. BTW, I have
> the capability to handle attached graphics files if anyone wants to
> include a schematic. :)
If you need one, drop me a line - I don't think we should handle schematics
on the list, but in case I talk complete gibberish, the other people here
are bound to provide some corrective feedback.
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