Need a Triac; haven't got one!

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Hi,

I need a triac but all I have in my junk box is a pile of these:

http://www.onsemi.com/pub_link/Collateral/C106-D.PDF

I've read in various books that a triac is just two of these devices  
wired back to back, but is that strictly true? Is it possible to make up  
a triac from two SCRs that will perform as well as a discrete triac?

I'm really short of time on this project and don't want to have to order  
a triac if I can simply nail two of these other things together and  
achieve the same result.

It's a light load, btw (a 4k ohm exterior telephone bell which requires  
240VAC) so doesn't need much current.

Any thoughts?

Re: Need a Triac; haven't got one!
On Mon, 8 Aug 2016 20:31:38 -0000 (UTC), Julian Barnes

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Your problem is that the two SCR's back-to-back don't have a
common-potential GATE, each will have to be triggered relative to its
own cathode.

You can probably avoid that with transformers for each gate, but you
probably don't have transformers on hand, do you ?>:-}
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Need a Triac; haven't got one!
On Mon, 08 Aug 2016 13:39:16 -0700, Jim Thompson wrote:

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Got *hundreds* of them! Particularly if you mean the little audio  
matching transformers that come less than one cubic inch in overall size  
- the ones you used to find in old transistor radios. Would they suffice?

Still not sure what you mean, though. Are you saying the fact that the  
proper triacs are 'carved' out of a single chunk of multi-layer  
semiconductor means they don't suffer from the problem identified?

Re: Need a Triac; haven't got one!
On Mon, 8 Aug 2016 22:16:16 -0000 (UTC), Julian Barnes

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Maybe.  Probably won't support the proper risetime.

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Yep.
        
                                        ...Jim Thompson
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Re: Need a Triac; haven't got one!
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No, you can't trust the isolation unless they're made for it. If your doodad puts mains voltage to the phoe line, screws up teclo equipment and they can prove it they'll be all over your ass.  

Re: Need a Triac; haven't got one!
On Mon, 08 Aug 2016 16:11:35 -0700, jurb6006 wrote:

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I should perhaps mention that isolation for the phone line is NOT an  
issue here. None of this will be connected to the phone line in any way.


Re: Need a Triac; haven't got one!
On Mon, 08 Aug 2016 13:39:16 -0700, Jim Thompson

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Since you need isolation between mains and telephone line, the other
alternative would be to use two opto-SCRs in antiparallel and putting
the isolator inputs in series. Alternatively, use ordinary SCRs with
two opto-couplers.
  
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Re: Need a Triac; haven't got one!
On Tue, 09 Aug 2016 10:31:31 +0300, upsidedown wrote:

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No I don't!!! I'm using this phone bell for completely different purposes  
nothing to do with the phone system!


Re: Need a Triac; haven't got one!
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It's possible to make SCRs and indeed triacs ( and unijunctions) out of  
discrete transistors .

http://electronicsterms.com/triac/

I've done SCRs and unijunctions that way, but not triacs.

TBH with next day delivery from a lot of component suppliers, I'd just  
order the proper thing and have done with it.

Brian
--  
Brian Howie

Re: Need a Triac; haven't got one!
Den mandag den 8. august 2016 kl. 22.31.42 UTC+2 skrev Julian Barnes:
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thyristor and bridge rectifier?

Re: Need a Triac; haven't got one!
On Mon, 8 Aug 2016 14:08:50 -0700 (PDT), Lasse Langwadt Christensen

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There you go!
        
                                        ...Jim Thompson
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Re: Need a Triac; haven't got one!
On Mon, 08 Aug 2016 15:22:20 -0700, Jim Thompson

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Although, thinking about it, it might not turn off, depending on
holding current... since there will be no reverse voltage.
        
                                        ...Jim Thompson
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Re: Need a Triac; haven't got one!
Den tirsdag den 9. august 2016 kl. 01.15.45 UTC+2 skrev Jim Thompson:
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I don't remember ever using thyristor, but shouldn't going below holding current be enough?

-Lasse

Re: Need a Triac; haven't got one!
On Mon, 8 Aug 2016 17:15:50 -0700 (PDT), Lasse Langwadt Christensen

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Not necessarily... but I presume this is at 50/60Hz (since the OP is
trying to emulate a TRIAC) so it should be OK.  (It's a swept charge
removal timing thing.)
        
                                        ...Jim Thompson
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Re: Need a Triac; haven't got one!
On 8/8/2016 8:15 PM, Lasse Langwadt Christensen wrote:
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I thought about that for a moment and realized the voltage drop across  
the diodes gives a brief deadband where there is virtually *zero*  
current guaranteed.  I don't know how this would *not* turn off the  
SCR... unless the load were inductive.

--  

Rick C

Re: Need a Triac; haven't got one!
On Mon, 8 Aug 2016 20:58:01 -0400, the renowned rickman

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Sounds like an inductive load so it's a valid concern. A triac may not
turn off without a snubber with such a load, but at least triacs tend
to be ornery with large trigger/holding currents. The thing the OP has
is the son of the late GE C106B1 SCR, which has notoriously low
trigger and holding current (like 20uA typically) so it doesn't take
much to keep it on.  

The original horrible C106 package looked like this:  
<http://pdf1.alldatasheet.com/datasheet-pdf/view/616877/NJSEMI/C106Y1/+415889VlHS.xKdhBBDfv+/datasheet.pdf
The leads are 0.05" wide nominally.  

The diodes he's likely to use will take away another 5-10usec of the
zero crossing with their sloth-like turn-off characterists so it could
get dicey, especially at high temperatures.  

Alternistors are better- more like back-to-back SCRs in their
commutation behavior.  

It might be possible to use an MOC3021 type opto directly, it's only
60mA, but the turn-off problem exists and I don't think they're
available with higher than 400V PIV rating which is pretty marginal.

Another trick is to use a small mains transformer primary in series
with the load, say 24VAC, and connect a bridge rectifier and MOSFET or
whatever on the secondary. Turn the MOSFET on and the series reflected
impedance drops greatly. THe MOSFET and diodes have to handle
proportionally more current, of course.  

--sp  

--  
Best regards,  
Spehro Pefhany
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Re: Need a Triac; haven't got one!
On 09/08/2016 08:18, Spehro Pefhany wrote:
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MOC3061 is multi-sourced, cheap and has 600V PIV.

piglet


Re: Need a Triac; haven't got one!
On Mon, 08 Aug 2016 20:58:01 -0400, rickman wrote:

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For breadboarding purposes, I'm using a Solid State Relay instead of a  
triac. The control voltage on the SSR is either 12V or 0V, it never goes  
negative, yet the SSR has no issues turning off. Mind you, a SSR might be  
more 'intelligent' than a triac for all I know.
"Why don't you just use that SSR", then I hear you say. Well, it's too  
good for this app. It's an expensive 40 amp device and this bell only  
requires 60mA.

Re: Need a Triac; haven't got one!
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there's cheaper SSRs
digikey.http://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/CPC1972GSTR/CLA273CT-ND/1277147

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This email has not been checked by half-arsed antivirus software  

Re: Need a Triac; haven't got one!
On Thu, 11 Aug 2016 12:28:18 +0000, Jasen Betts wrote:

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circuits-division/CPC1972GSTR/CLA273CT-ND/1277147

Do these things have snubbers built-in? (I'm guessing they don't right?)


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