On Sun, 08 Jun 2008 09:21:49 GMT, PCPaul wrote:

On Sat, 07 Jun 2008 12:31:54 -0500, John Fields wrote:

On Sat, 07 Jun 2008 12:01:47 -0500, John Fields
wrote:

On Sat, 07 Jun 2008 11:06:59 -0500, John Fields
wrote:


Also, that cap is going to be pretty pricey.

http://www.newark.com/jsp/search/
browse.jsp;jsessionid=PYIT2ONBRZU42CXDUZ1G3PQ?N=5 00003+1001309+148378
+182171&Ntk=gensearch_001&Ntt=mallory&Ntx=&_reque stid=209120

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Here's a better deal:

http://search.digikey.com/scripts/Dk....dll?Selection

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Oops...
That didn't come out right.

Go to the Digi-Key website then find aluminum electrolytic capacitors
and narrow the search down to 2000 to 2400µF and 360 to 450V.


That circuit is more like it.. the random phase trigger simplifies things
somewhat. Wonder if I can just sample it ;-)

I guess the cap needs to be that big to keep the optocoupler LED lit for
100s or so..

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180 seconds.
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Since I don't really need the isolation, is there a way to do it that
uses a scaled down RC circuit to switch a transistor based trigger
instead?

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Yeah, there is.

I thought about it after I posted the other circuit, but didn't get
around to updating it.

I'll get on it sometime today...
---


I'd guess you could do that with a few uA instead of the 60mA
the optocoupler needs.

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The optocoupler only needs 5mA to start, and it'll keep the output
conducting until the LED current drops to 300µA.


JF