General > General Technical Chat

Quick TVS diode question. Vclamp < Vbreakdown

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kellogs:
So the thing will protect against negative 220 spikes as well, looks like a winner then! Why don't they make it more clear in the datasheet... :D
Just one more question about these surge stoppers, will they also protect fast Schotky diodes in series with them, when such diodes are placed before the protector IC, in line with the two power mosfets ?

Sir, copy pasting is what all great engineers do, not only the rookies; perhaps the source of confusion. I thought it was pretty obvious my level was not that high with all these questions.

P.S. - would have never thought to arrange Q3's Zener that way  :-+

T3sl4co1l:
What do you need a schottky for if you have back-to-back MOSFETs?

Tim

kellogs:
I want some energy to run the MCU a bit after 12V went away. I guess I can put the storage cap + diode after surge stopper too, but probably same deal since they are in series.

T3sl4co1l:
Oh in a separate path, that's fine.  The diodes won't care, but you get the full load dump out there so probably need a depletion MOS style voltage limiter.

Tim

kellogs:
Hello,
Tim, sir, can i have a bit more help please ?

I want to take this diagram:



And adapt it to also guard against +100V load dumps besides negative -220 spikes. Peeking at:



i would make the following changes:

- replace FETs with some 250V capable ones

- keep the SMAJ58CA but use it like the SMAT70A from the second diagram, together with an 1W resistor

- replace Rsns with a 6 mohm value and a max current of 50 mV / 6 mohm ~= 8.33 A

Any obvious faults ?
Thanks

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