Voltage regulator

[Raymond C Drouillard]

On Sat, 02 Jan 1999 17:20:40 PST "Bill the arcstarter"
<arcstarter at hotmail.com> writes:
>It was written:
>
>>>Using PWM control is better yet, as it does NOT reduce the peak
>>>voltage/torque at all - it just modulates it. PWM control on a DC 
>>>type motor reduces speed without APPRECIABLY reducing torque.
>>
>>To claim that there is not enough inductance in the motor windings to
>>smooth out the highs and lows of the PWM voltage notches is living in
>>dreamland or a sign of having ingested too much egg-nog!!
>
>Actually you can (and will) instantaneously change the voltage across an

>inductor (motor winding) w/o an instantaneous change in the current.  
>Nothing in physics says otherwise.
>
>I suppose the question is one of *what* damages the motor - rapid force 
>oscillations (caused by rapid changes in current - something which is 
>limited/prevented by the self-inductance of the windings) or some form 
>of (?) dielectric breakdown across the windings caused by rapid voltage 
>fluctuations... ?
>
>The big boys do use specially insulated magnet wire on the larger (1-10 
>hp) motors designed specifically for use with chopper drives.  I'm not 
>sure if a smaller motor (like a fuel pump) would care one way or the
other.
>
>If you build such a chopper - be sure to include a flyback or snubber 
>circuit to prevent your fet/transistor from going POOF due to the 
>inductive kickback. :-)
>
>-Bill
>(building a 10000 watt phase controlled SCR driver for my stick 
>welder)
>Wanna know how to turn OFF an SCR?  See my page:
>http://www.geocities.com/CapeCanaveral/Hangar/6160/hvtank/hvtank.html

I would take a lesson from the switching regulater designs.  Put a diode
across the source that'll be reverse biased when the "chopper" transister
is on.  When the transister turns off, the energy stored in the inductor
would forward bias the diode.  That way, the current will decay more
slowly and not produce the inductive "kick".

Also, I would use a high frequency.  That way, the current wouldn't decay
much when the transister is turned off.  This would reduce the amplitude
of the mechanical vibrations.

Ray Drouillard

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