In my school notes I have been given a basic thyristor circuit. I would like to breadboard a similar circuit and have some questions about choosing a suitable capacitor type and value between points P and Q.
Assuming the thyristor is latched on and S2 is open, the voltage at P will be close to zero and at Q should equal Vs.
When S2 is closed, I am told to expect Q to immediately drop to 0V.
To quote my notes: "However, there has been no time for charge to move. As a result, Q must still be 12 V higher than P. In other words, when the voltage at Q dropped by 12 V from 12 V to 0 V, the capacitor forced the voltage at P down by the same amount, from 0 V to -12 V."
The thyristor is thus reverse biased and switches off; the voltage at P therefore returns to Vs, but if S2 has not been released Q remains at 0 V. When switch S2 is released, both P and Q will be at Vs.
Bearing in mind the reversal of charge on the capacitor, could you suggest a suitable capacitor type to breadboard this circuit? I assume a polarised capacitor (e.g. electrolytic) would NOT be suitable. Also, how would I calculate a suitable capacitor value? I presume that R2 must be at least 1K to minimise current flow when S2 is pressed. I have not been given a formula to use.
I intend to use a 12 V supply and thyristor C106DG.