PWM DC motor circuit?

From: Terry Pinnell (terrypinDELETE_at_THESEdial.pipex.com)
Date: 07/10/04 

Date: Sat, 10 Jul 2004 11:09:37 +0100

Could someone kindly save me a bit of time in finding a suitable
circuit for driving a DC motor with PWM please? My first hour of
googling has found many threads, but so far no specific relevant
schematics.

The DC motor is from a cordless screwdriver, used originally with two
NiCad C cells, and duly marked as '2.4V'. I ran it briefly at 5V and
assume it would tolerate that, giving me higher torque potential. It's
geared, and (unloaded with 2.4V applied) gives 250 rpm. That's too
fast for my curtain control application so I want to be able to reduce
it. Hence PWM.

I'll probably use limit switches and a C/O relay for the
forward/reverse/off control, at least while getting the challenging
mechanicals sorted (as per separate thread). So I don't need to
consider the complications of combining PWM with an H-Bridge.

My first thoughts are to use a 5V supply (derived from a convenient
fairly heavy duty 12V supply I have nearby) with a variable duty cycle
555 (or maybe a 4001/4011 equivalent), directly driving a medium power
MOSFET, with the motor between its drain and 5V. I'll breadboard that
shortly, but meanwhile:
- will that simple approach be reliable?
- any snags or protective measures to watch out for?
- is there an 'optimum' frequency range?
- if I designed a *high* duty cycle from 555, which I recall makes it
easier to achieve a wide d/c range, what is most efficient way to
configure the output MOSFET stage?
- I happen to have a 2N3055 (or similar) already neatly mounted on a
h/sink, from a previous project; any major reason why I shouldn't use
that instead of a MOSFET?

As mentioned in the curtain thread, I'd like to build this asap, as
the full-speed motor action is adding to my design and testing
problems.

TIA. 

-- 
Terry Pinnell
Hobbyist, West Sussex, UK

Relevant Pages

  • PWM DC motor circuit?
    ... The DC motor is from a cordless screwdriver, ... Hence PWM. ... fairly heavy duty 12V supply I have nearby) with a variable duty cycle ... MOSFET, with the motor between its drain and 5V. ...
    (sci.electronics.design)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... with our ideal motor and ideal PWM, then the power from the 20 volts ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... the PWM is switching the motor drive between 20 volts and 0 volts. ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... the PWM is switching the motor drive between 20 volts and 0 volts. ...
    (sci.electronics.basics)
  • Re: Do you think NI can fix my PLL?
    ... It seems like you may need a much higher bandwidth than the typical servo amp provides. ... I am assuming there is some digital circuitry in the servo amp (has to be at least a PWM ... The PM motor was driven with a linear amp, a transistor boosted power op-amp, like you speak of below. ... The PLL loop compensation filter took care of the rest. ...
    (sci.electronics.design)