Reply-To: "George Gonzalez"
From: "George Gonzalez"
Subject: Re: TRIAC "wears out" on dimmer circuit
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
NNTP-Posting-Date: Thu, 24 Oct 2002 13:45:32 GMT
Organization: AT&T Broadband
Date: Thu, 24 Oct 2002 13:45:32 GMT
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.
If you open up one of the better light-dimmers, you'll see something like a
PI network filter, with the capacitors on the order of 0.02uf, then
inductor, abour 6 to 10 turns on a 1/4 inch core.
Your 0.47uf capacitor is going to draw some pretty hefty current spikes from
the triac as the triac turns on, that could be slowly wearing away at the
triac's safe operating area.
A capacitor that big may also be counterproductive on the EMI front-- it may
slow the voltage rise time, but the BIG internal current pulse may radiate
EMI magnetically just as well. Actually better, as you can filter voltage
EMI with a PI filter, magnetic EMI requires substantial metal.
That's why there's an inductor in those light dimmers. Thery wouldnt
splurge on a 30 cent inductor if they didnt absolutely have to!