When is a TRIAC more appropriate to use than an SSR when controlling mains?

[crazy_steve]

Hi all,

I hope this question is not too broad to answer...

I was wondering when an optically isolated TRIAC circuit setup would be more appropriate to use vs. an SSR for controlling devices running off mains.

If the the triac circuit is a zero-crossing setup, then I can't think of a scenario where the ssr would be a poorer choice.

If the triac circuit is random-crossing then I can see that it could be useful in light dimming applications were the SSR would be pretty useless

Am I overlooking something? Perhaps something with quick toggling on/off and lifespan?

 

[sreein]

If you are more familer to triac please give me some circuit and web link .I want to know more about triac please help me dear

 

[lw1ecp]

As far as I know, the power device in most SSRs is a TRIAC. So, same as a TRIAC, a SSR can be triggered anywhere in the wave, but you have to wait until current reduces to zero in order to achieve turn off.
The main reason for using a SSR instead of a TRIAC (which is cheaper) is when you need to isolate the control circuit from the load. In fact, the SSR has built-in optical isolation. And some of them include added circuitry to delay turn-ON until the next zero voltage crossing (synchronous SSR).
More on this: www.omega.com/temperature/z/pdf/z124-127.pdf
Is this what you needed?.

 

[crazy_steve]

Yep, that answers that. I was under the impression an ssr did not contain triacs.. that they used two scrs along with some other magic which could cause them to have different properties. Thank you