Need a Triac; haven't got one!

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high,

I've

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somewhere near 50mA or more, forget about using a TRIAC because you're not going to meet it's holding current requirements. Use a relay instead, and the relay will need to be snubbed too.

worry about the holding current. How often does a bell get turned on/off an yway? Driving one EM with another EM device is a more harmonious and simpli fied fit.

Not for the kind of engineering you do...

.

What was he using to drive TRIAC?

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bloggs.fredbloggs.fred
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Spehro Pefhany 
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Reply to
Spehro Pefhany

You risk breaking the insulation on the coils, as it is prepared to get only 100V across the coil.

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-TV
Reply to
Tauno Voipio

Well they've since tested good at 240VAC, so that's that AFAIC. :->

Reply to
Julian Barnes

Whoosh!

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Rick C
Reply to
rickman

I'm not familiar with that manufacturer. Can you provide a link?

Reply to
bloggs.fredbloggs.fred

I know you now have a triac but here are two possible ways to use two SCRs whereby one is slaved to the other and triggering is referenced to one supply rail:

piglet

Reply to
piglet

Thank you for that, Piglet. I shall take a good, hard look at it for future reference.

Reply to
Julian Barnes

That is an interesting concept. But you can also connect two SCRs in series, cathode to cathode, with anti-parallel diodes across each, and drive both gates from a single source. Here's an LTSpice simulation:

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Paul

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  • C:\Users\paul_000\Documents\PSTECH\LTSpice\Two_SCR_Series.asc V2 N004 N006 SINE(0 170 60 0 0 0 120) XU2 N001 N002 0 MCR8SN D1 0 N001 MUR460 D3 0 N006 MUR460 R1 N003 N004 20

XU1 N006 N005 0 MCR8SN V1 gate 0 PULSE(0 5 50m 10u 10u 100m 200m 1) R2 gate N002 50 R3 N005 gate 50 .model D D .lib C:\PROGRA~2\LTC\LTSPIC~1\lib\cmp\standard.dio .tran 0 200m 0 1u startup uic .inc MCR8SN.sub .backanno .end

Reply to
P E Schoen

o

es,

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and you can do the same with fets, except then you can skip the diodes and you can turn off when ever you want

I've used it as a fast "fuse" switch off to protect a number of triac contr olled output from shorts

-Lasse

Reply to
Lasse Langwadt Christensen

Good idea! ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

[snip LTSpice ASCII]

Thanks. The disadvantage is having the diode drop along with the forward voltage drop of the SCR. Most SCR based SSRs and high power SCR controllers use two SCRs connected anti-parallel, so you eliminate two diodes and their voltage drop. But the gate control becomes more complex, usually requiring trigger transformers, opto-isolators, and DC-DC converters.

The systems I work with operate on 480 VAC mains and often draw currents well over 1000 amps for short durations. The load is a transformer with a

6-20 volt output connected to large industrial circuit breakers up to 6000 amp frame and instantaneous trip of 10x or more. For such highly inductive loads it is necessary to trigger the SCRs initially at about 60 to 90 degrees to reduce current surges from DC offset. And for very light loads or open circuit conditions the gates must be driven with continuous DC, so pulse transformers don't work.

Paul

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P E Schoen

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Michael A. Terrell

Good Lord!!

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Julian Barnes

Those were used in PBX phone systems for decades. I still have a couple good spares., and one five line system with the KTU cards.

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Michael A. Terrell

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