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From: John Woodgate
Subject: Re: TRIAC "wears out" on dimmer circuit
Date: Thu, 24 Oct 2002 13:28:01 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Thu, 24 Oct 2002 12:50:59 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that John Harris
wrote (in ) about
'TRIAC "wears out" on dimmer circuit', on Thu, 24 Oct 2002:
>There is heavy interference on the AM radio band.
>I have a 240V 0.47uF capacitor connected across the triac output, but
>no inductor in series. I tried using inductors before and after the
>triac stage with no noticeable reduction in EMI. There is obviously a
>design flaw on my part and any suggestions would be appreciated.
The inductor between the supply and the triac is NOT only for emission
control. It reduces the rise-time of the current when the triac is
triggered. You need quite a big (physically) inductor for 240 W. They
are usually wound on lossy iron dust toroids. It is difficult to specify
or measure the inductance because it varies with applied voltage. The
usual 'design' method is to fiddle with the inductance until the rise-
time is as long as desired. In your case, 200 us is probably enough.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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