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phase control thyristor as AC switch

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Jun 17, 2011
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I am trying to make a circuit to control mains AC. I want to control a heating elment (e.g. soldering iron, water heater). I have a thermostat control which will switch up to 50 mA at 9-24V. I was planning on using a relay, but don't have one on hand, and reading up on it a little, it seems that a triac would be a better choice. I have a bunch of heavy duty phase control thyristors around, and I was wondering if I could use one as my switch. My heating elements are much larger than necessary, so using only part of the AC cycle would be more than adequate. Am I right in thinking that supplying a positive signal from the thermostat to the thyristor gate will allow a part of the forward-biased current to be conducted, and removing the signal would cause the thyristor to stop conducting at the end of that half-cycle? I'm hoping to achieve temperature control within a few degrees, so the timing is of no consequence. I have e.g. some CS16-12IO2 rated at 1200 V 30 A.

Just looking for a quick heads up. Thanks!

Hi, thanks for that. I guess what I'm not sure about is how exactly the phase control thyristor works, what the difference is between a basic thyristor and a "phase control" thyristor. Your application note uses a triac as a switch (bi-directional), which would be ideal, if I had one at hand. The phase control thyristor will only pass current for a portion of the phase, but I don't understand how it's triggered; specific voltage or dv/dt? Anyway, maybe I'll just have to try it and see what happens. :smile:

Looks voltage triggered

Pict. 2 & 9.

Look pict. 13 & 14 how to connect non-sensitive / sensitive gate SCR

for sesitive gate add resistor and diode (between g-k)


I am trying to make a circuit to control mains AC. I want to control a heating elment (e.g. soldering iron, water heater)...

Depending on thermal capacity of target object, is not strictly required a phase control.
If time base of heating be much larger than sinewave period, you can manage the power by ON/OFF control.
( note that thermostat performs that control )


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