The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: firstname.lastname@example.org (John Harris)
Subject: TRIAC "wears out" on dimmer circuit
Date: 24 Oct 2002 03:17:34 -0700
NNTP-Posting-Date: 24 Oct 2002 10:17:34 GMT
I built a circuit to fade a string of twelve 20W tungsten filament
light bulbs connected in parallel (for outdoor use). This translates
to a peak current of less than 2A at 240Vac (after the initial
switch-on surge). I used a TIC236D triac, which is rated for 12A at
400V. The circuit worked perfectly for a few days (around 60 hours of
operation), but then a fault developed, whereby the string would only
fade from fully on to around half brightness, instead of fully off.
When the opto-transistor that I used to trigger the triac (via a
capacitor) was disconnected from the driving signal, the lights
remained at half brightness instead of remaining off. When the circuit
was switched on from cold, it would work fine for a few minutes and
then the problem would re-appear, even though everything was well
heatsinked and the triac remained barely warm to the touch anyway. I
replaced the offending triac and the fault disappeared for another few
days before returning again. The string is around 10 metres long and
no bulbs have blown. 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.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup