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'PWM control of 90-volt, 2.4-amp DC motor'
1995\06\16@170614 by BBoles

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    Moto has some high voltage / high power  (1000V, 10A) MOSFET's with 5V
    gate inputs.  Real handy!  (Free samples, too. 800.441.2447)

    TTYL, Brian.                              spam_OUTbbolesTakeThisOuTspammicrochip.com


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Subject: PWM control of 90-volt, 2.4-amp DC motor
Author:  "BOWDEN; ANDREW V JR" <.....ABOWDENKILLspamspam@spam@SCANA.COM> at Internet_Exchange
Date:    6/16/95 11:25 AM


    Hi, all.

    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. :)

    Andrew

1995\06\17@222819 by Markus Imhof

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>     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
net).

>     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.

Bye
 Markus

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