Re: PWM DC motor circuit?

From: Gordon Youd (gordon_at_Zgyoud.demon.co.uk)
Date: 07/15/04 

Date: Thu, 15 Jul 2004 12:19:48 +0100

Terry,
MFACOMO DRILLS sell a PWM module which allows infinitely variable motor RPM
to be set.

 About 1 inch cube, 2 wires in, 2 wires out with a screw to set the speed.

Rapid electronics also sell them, they are about £8.00.

Hope this helps.

Regards, Gordon.

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"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:badve05nj0avdhtq06qipbn7sd1mipp9hu@4ax.com...
> 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
>

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