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> Ac Relay, simple delay on
Sch3mat1c
Posted: July 02, 2010 10:04 pm
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Zeners do have a bit of negative resistance, but it's quite small. This is easy to observe when driven from a low current: the zener noise looks like ramps with a constant rising slope (current charges the diode capacitance) and a random falling slope (it turns on, dumps a gob of charge, then realizes it's gone too far and turns off).

Transistors have more, since they aren't made for zener duty. You can run a 2N3904 at ~100V and make a passable relaxation oscillator. Curiously, it switches in a mind-boggling fraction of a nanosecond.

At any rate, you can make a trigger diode by combining a zener with an SCR. If you want an AC device, you might as well buy a DIAC, since you end up needing a zener and SCR for each direction...

Tim


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MacFromOK
Posted: July 03, 2010 12:37 am
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QUOTE (Sch3mat1c @ July 02, 2010 04:04 pm)
At any rate, you can make a trigger diode by combining a zener with an SCR. If you want an AC device, you might as well buy a DIAC, since you end up needing a zener and SCR for each direction...

One direction is all that's necessary in this case. It just has to briefly trigger the relay which then latches itself.

Thanks for the info Tim. beer.gif


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tekwiz
Posted: July 03, 2010 06:07 pm
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QUOTE (MacFromOK @ July 02, 2010 03:37 pm)
QUOTE (Sch3mat1c @ July 02, 2010 04:04 pm)
At any rate, you can make a trigger diode by combining a zener with an SCR.  If you want an AC device, you might as well buy a DIAC, since you end up needing a zener and SCR for each direction...

One direction is all that's necessary in this case. It just has to briefly trigger the relay which then latches itself.

Thanks for the info Tim. beer.gif

You still need to halt current flow to turn an SCR off. On pure DC, they are self latching.


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MacFromOK
Posted: July 03, 2010 06:12 pm
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Does that matter since the relay stays latched on anyway?


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