i have a question which i want to ask from you peoples
1) why we use inductor in series with the thyristor??
2) why we use diode parallel with the supply??

 

I don´t do either of those. Can you post the circuit?

 

Putting an inductor in series with a triac or SCR is to limit the dI/dt because they have that kind of limit. Too fast burns the semiconductor due to hot spots.

As for the diode...depends on the circuit.

 

Maybe the diode is being used as a back EMF shunt for use in an inductive load? Or even a clamp to help protect a circuit?
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Either way, we are arguing apples vs oranges, and or grapefruit vs bananas without a schematic...
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For an example of a bypass diode, check out "this" power regulator link:::
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http://www.phoenixcomputerlabs.com/All-About-Mixers/LM317.html
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Dave
Phoenix, AZ