I have a simple 12V circuit with PIR, 555, couple of transistors and an outside 220mA LED light in a circuit powered from a 12V lead acid battery battery with long leads so am expecting LC spikes that could fry the lot.
I'm thinking of using a TVS diode to clamp the spikes but not sure how the reverse standoff voltage Vrwm, works with the clamp voltage Vc. They seem to work against each other.
e.g. a P6KE15A has Vrwm 12.8V which seems ideal but Vc 21.2V which may not be good for the circuit.
From my understanding Vrwm should be the normal working voltage of the circuit, i.e. around 12V. However, if the circuit cannot sustain a 21.2V spike, it seems the diode won't protect it. It would fry the 555 for a start.
I'm expecting spikes of 35-40V from the long wires from the 12V lead acid battery and cheap, large mechanical button.
I can see that breakdown occurs at 14.3V for this diode but with a 40V spike the circuit will see the max Vc of 21.2V.
Or have I misunderstood how TVS diodes work?