Hi, fellow enthusiasts! I was trying to build a trigger circuit for a Xenon flashlamp (Yes, I know it is dangerous, I am taking significant precautions!).
The issue I'm facing is likely because I am not familiar with SCRs. See a circuit similar to what I'm trying to build in the attachment (comes from Les' lab teardown of this laser power supply
https://youtu.be/8khFcicKwJ4?si=zSY34p-erosQiF_e&t=522).
After building some simpler versions of this circuit (say, a low-voltage capacitor crowbar with the SCR), I'm facing the problem that the SCR remains latched after the trigger signal at the gate. As far as I understood, this is expected behavior and it's ok. The thing I'm not quite appreciating by reading the attached circuit is how the SCR is unlatched. If I gather correctly, I need to make the current between Anode and Cathode close to zero for it to unlatch. But the only thing that could do that is the TVS diode D1. But that diode will not conduct until the voltage between A&K exceeds 550V, so it should be open throughout the operation, is that not right?
I thought that maybe the trigger transformer would produce a negative voltage transient that would unlatch the SCR, but that doesn't happen in my circuit. I also tried at a higher voltage (1000V) and it triggers once, latches, and then the current through the SCR is so high that it breaks.
Perhaps you could point out what I'm missing here?
Thanks!