Schematic Wanted

Aug 31, 2013 6 Replies

Several decades ago I ran across a circuit as follows:



Uses a unijunction (not a PUT) to trigger a triac.



Input is mains 120vac. No transformer isolation. Isolation is not needed for my application.



Output is a single full sinewave with a long dead-time to the next full sinewave. As a potentiometer is adjusted, additional full sinewaves fill in the dead-time until full mains is output.



There is a slight dead-time at the start of each sine before the triac fires.



I am trying to find the schematic for this circuit. The circuit was published.


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I did that sort of thing to dim neon, back in my disco days in the early '80's... after frying several neon transformers with a phase-controlled drive >:-]

I didn't use a unijunction. I vaguely recall some optical thingy.

It's BC (before CAD) so I'll have to search my file cabinets for a paper drawing. I'll post if I find it. ...Jim Thompson

| James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.

Nobody would use a UJT these days, we have zero crossing detector opto coupler triac drivers...

Sounds like he wants pot-controlled variable duty cycle with full-cycle zero-switched output. Sort of like a solid-state infinite heat control.

Pretty trivial to do. It's possible to do reduce the periodic variations with a more modern approach (eg. sigma-delta).

Infinitesimal heat control? ;) Sort of, except that if he's doing integral cycle switching he'll never quite get there.

Aren't solid state light dimmers about six bucks ?

Actually they might just get cheaper because the work on incandescent lamps mainly.

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