Re: [TCML] IGBT variac dimmer?

[David Petzer <davepetzer@xxxxxxxxx>]

Hi Scott,

IGBTs (or fets or transistors) could definitely do the job of a variac, that is to produce a sinusoidal voltage at mains frequency  of variable magnitude. One circuit topology would be to rectify the mains AC then use an IGBT half bridge to produce the desired sinusoid.

You could do more with the IGBTs as well because you would be able to vary the magnitude and frequency of your sinusoidal out put, or even produce non sinusoidal functions like ramp or square waves these could produce some interesting results for Tesla coil outputs.

As for protecting from over load there are a host of solid state methods for protecting the switching devices from this.

As an aside I believe that the humble dimmer switch contains a thyristor (SCR) so the wave form which it produces is a chopped version of the mains AC, not a sinusoid of lower magnitude.

David Petzer


________________________________
From: Scott Bogard <sdbogard@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Friday, 16 September 2011 4:35 AM
Subject: [TCML] IGBT variac dimmer?

Greetings all,
     Just wondering if anybody has played with the idea of using IGBTs to
build a sort of solid state variac that would function like a dimmer
switch.  I can't imagine it would be that difficult, and IGBTs have proven
their worth in TCs, so it would just be a matter of using external
ballasting to keep the current levels acceptable for the IGBTs even at full
power.  This might actually be cheaper than trying to source super big
variacs for pole type coils, if one can find cheap used IGBTs as is
seemingly the case on eBay.  Any thoughts?

Scott Bogard.
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