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From: email@example.com (John Harris)
Subject: Re: TRIAC "wears out" on dimmer circuit
Date: 29 Oct 2002 07:21:57 -0800
NNTP-Posting-Date: 29 Oct 2002 15:21:57 GMT
firstname.lastname@example.org (John Harris) wrote in message news:...
Thank you all for your useful input. I now know a little more about
TRIAC circuits. From my observations and some ideas that I have
investigated based on your information, my plan is as follows:
1. Remove the 0.47uF capacitor at the output.
2. Include a 50-100uH inductor in series with the load to reduce
current surges. I've read in app notes that the inductor must not
saturate during the maximum current peak, else its inductance would
collapse and it would no longer limit the dI T /dt. An air-core
inductor is therefore recommended although I suspect that this would
have to be physically huge to obtain 50uH at the desired current
rating, so I will investigate this further.
3. Adjust the circuit so that the lights are still powered with a
"warming" current when they appear to be off. This should prolong bulb
and TRIAC life.
4. Although the TIC236D should be more than capable of driving my 240W
load (I've seen example dimmer apps using a lower spec TRIAC to drive
1000W of incandescent bulbs), I will replace it with a BTA16-600CW
TRIAC for the following reasons:
a) This device has a built-in snubber (i.e. it's a "snubberless"
device), which will enable me to replace the 0.47uF capacitor with a
proper RC solution while saving space in my housing to make room for
the physically large inductor.
b) It has superior electrical specifications, being rated for an RMS
on-current of 16A @ 600V, with a non-repetitive peak surge of 160A.
Because the lights are connected in parallel, I hope that these
improved capabilities will add a further level of robustness to the
circuit in the event of a bulb blowing.
c) It's pin-compatible with the TIC236D, hence avoiding a new PCB
d) It's only a few pence dearer and this is only a 'one-off' project.
5. I will reduce the value of my quick-blow fuse from 5A to 2A to
minimise the risk of frying the TRIAC if a bulb blows.
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