Power switches used in automotive are usually rated to withstand clamped load dump events, of the 35 - 40 V peak variety. AFAICT there are two main clamping mechanisms - first one for the logic part and second one for the MOSFET DS channel within. These power switches will generally (re)open the DS channel once the second clamping mechanism has engaged.

Since manufacturers do not boast about their power switches being able to withstand full (unclamped) load dumps it must be the case that the FETs within won't take that kind of energy / peak power.

Worst case as per ISO 16750-2: Ri = 0.5 ohm, Vs = 79 V, tr = 5 ms, td = 400 ms. Could I use some TVS diodes effectively for protecting against this ?

My targeted power switches Rds(on) = 30 - 40 mohm and for a led light of 200 mA normal draw @ 12V I would throw in 60 ohm of dynamic reistance even for voltage spikes (?).

My targeted TVS dynamic resistance Rd = 1/Pdc +/- 50% ~= 1/8 = 125 mohm (formula pricked up from here). Multiply that by 3 for a stack of 3 TVS diodes -> 375 mohm.

It appears at a first glance that the TVS stack is sufficient to help out a power switch make it through load dump events unharmed. Of course, the logic part must also tolerate the clamping voltage of these 3 series TVS diodes. Does anything escape my thinking ?

edit Diagram:

posted 9 months ago

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9mo ago

kellogs‭

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