Optotriac resistor selection

bitrex · 2016-10-30T17:11:03+00:00

I have a MOC3010 optotriac (from da junk box) that I'm trying to use to switch about 100VAC from a small inverter brick to a length of EL wire about a meter long. Right now I'm driving the internal infrared LED through a 1k resistor from a 3.7 volt supply. The meter shows that the chip is drawing about 3mA of current compared to when the pins are disconnected, so I'm assuming the LED is turning on, but it doesn't appear to be enough to fire the triac when it's hooked up to this load. Can anyone suggest a more appropriate value, or a way to calculate such?

Oct 30, 2016 23 Replies

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Benderthe.evilrobot 9 years ago

Not if the load current is less than the holding current....................

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Frnak McKenney 9 years ago

[...]

Gotcha. Thanks for the clarification.

Oh, and you're not alone in looking for a way to switch the HV AC for EL stuff: A search on "use arduino to switch electroluminescent wire AC" turned up:

Switching el wire from Arduino

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Optoisolator with EL wire won't turn off, TRIAC works fine. Why?

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Enjoy...

Frank

Factors other than random selection subdue the influence of [reason] on public affairs. For the chief of state under modern conditions, a limiting factor is too many subjects and problems in too many areas of government to allow solid understanding of any of them, and too little time to think between fifteen-minute appointments and thirty-page briefs. This leaves the field open to protective stupidity. Meanwhile bureaucracy, safely repeating today what it did yesterday, rolls on as ineluctably as some vast computer, which, once penetrated by error, duplicates it forever. -- Barbara Tuchman / The March of Folly

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bitrex 9 years ago

It seems the tricky part of using a TRIAC to accomplish dimming is that it presents a capacitive load, so with the I and V out-of-phase the technique of cutting in the AC voltage some of radians after the zero crossing to reduce the effective RMS voltage (as one would in an old-fashioned incandescent lamp dimmer) doesn't work properly.

Looks a lot of folks accomplish dimming then by modulating the inverter input low voltage, which appears to work but seems like an inefficient and clunky solution. And doesn't let you dim strands independently from the same inverter brick.

So rectify to pulsed DC and MOSFET? Or use some circuit to make the wire look resistive? Or use TRIACs with built in zero-crossing detectors and do some kind of "pulse swallowing" modulation?

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Lasse Langwadt Christensen 9 years ago

FET inside bridge rectifier or back-to-back fets

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