Hi,
thank You all for your replies.

My 20uS figure is actually due to the load (a motorbike coil whose
DC resistance is around 0.1ohm) which acts (at least on my 'scope)
quite like a constant current sink. I've made real world measurements
on it.

The capacitor I'm using is pulse-rated and can withstand that dI/dt
rate.

Of course the DC resistance of the coil doesn't say much, as it's
just the primary of a pulse transformer, then we have the secondary,
a resistor and a spark plug with a built in second resistor.

But if I pretend to be a transistor and ground it, on my 'scope I can
see that the capacitor discharges in 20uS, hence the calculation of
the pulse current that the switch has to widthstand. True, I could
have hacked together a current probe and measure it, but I just
thought why not calculate it.

If You think I better measure it, due to the uncertainty of the coil
inductance, capacitor ESR, etc.. I will definitely do it!

Thanks again.

With kind regards,
Mario

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