Triac circuit explanation

[hey_poolboy]

I did a search for the term triac, but did not find a thread that actually explained the way a triac circuit works.

I have no real use for this information, I have seen them used in speed controls, and so forth, and am curious to know how they function.

thanks,
mike

 

[electricman2]

Re: Triac circuit explanation

A triac is sort of like two SCR's connected in parallel in opposite directions with only one gate terminal. Go Here for a good tutorial.

 

[suemarkp]

Re: Triac circuit explanation

Try a search for SCR or silicon controlled rectifier. A triac is effectively two SCR's -- each conducting in opposite directions. A DC circuit would use an SCR and an AC circuit needs a triac unless you want only half the waveform.

Think of an SCR as a solid state relay. You apply a small current at the gate and the SCR conducts. Take the gate current away and it stop conducting. Speed controls can be made by keeping the conduction time very short but repetitive. So short, that the full waveform of the applied voltage is not applied. This makes a normal 60 Hz sinewave look more like shark fins. A mechanical relay can't respond fast enough to work this way.

 

[hey_poolboy]

Re: Triac circuit explanation

John,
thanks, that was a very good tutorial.

mike

 

[rattus]

Re: Triac circuit explanation

Important point:

When an SCR or Triac is triggered, the gate electrode no longer has any effect; the device remains ON until the voltage is reversed.