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Re: electronic PWM variac

Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

How often have you had a circuit work by sheer luck Steve?
As Samuel Goldwyn said, "The harder I work, the luckier I get". I had constant monitoring of the spikes on the CRO and had snubber and MOV's in place. It was driven by a PCM motor speed controller from a TL494 and had output transistors in the driver.
I guess you lose a lot of power in the snubber ?up to 50%, but I didn't blow an IGBT.
I wasn't seriously expecting this to work well. If it was this easy clever people would have already designed a simple circuit on a small board that can be made for a few cents in China and everyone would be selling their variacs on eBAY.

Peter
http://tesladownunder.com/

Original poster: Steve Conner <steve@xxxxxxxxxxxx> 

>Re  "electronic variac" using a bridge rectifier and a
> single PWM FET.

If this circuit works with inductive loads, then it's
only by sheer luck. There is no path for the current
to free-wheel when the FET is off, so you wind up
either destroying it, or having to use an oversized
snubber that wastes a lot of power to keep it alive...

Steve Conner