Isolated phase control using SCR

Dear all,

I'm trying to use a SCR for a phase control application. I have tried out the first circuit but I am not getting expected results. The second circuit is the one that I will be using later but due to lack of parts availability I have used the first setup.

Best regards !!!

Might be a bit soon in the am for me, surely the circuit will trigger when the opto led lights up, which looking at the cathode would be the falling adge as per your fig.
With the 10k as the load you could rig that up direct to the triac in the opto to see if thats working ok.

My original thought was that the 10K load possibly did not draw enough current for the circuit to latch on. But looking at your diagram you only expect conduction while the trigger pulse is active (Low) This may be just the way you have drawn the diagram with the rising edge of the trigger pulse being just before the zero crossing point in the first positive half cycle and exactly on the crossing point on the second one. When you say its does not work do you mean it does not conduct at all, it does not latch, it conducts on all of the positive half cycles or it conducts all of the time.

Les.