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Floating Voltages Causing Damage?

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J_M_B

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Hi All

I am working on a circuit with multiple mosfets connected in weird and wonderful ways.

My knowledge on floating voltages only goes so far.

Could there ever be a case where a floating voltage causes damage to a part by floating up/down to a voltage which is outside the spec of the part?
e.g. drain of mosfet connected to GND, floating source floats to voltage above the parts max source drain voltage?

I am thinking about the floating source voltage being affected by environmental EMI.
Probably a silly question, forgive my ignorance!


Any thoughts would be much appreciated
 

KlausST

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Hi,

on a PCB and inside of an enclosure i don´t think there is a problem.
But as soon as wires go outside and they may be touched, either by human, animals or any other thing you have to protect the circuit.
For a hobby project you can do anything, but for professional use i´d call this a must.

Even the brush of a vacuum cleaner may be statically charged to very high voltage. If it touches the wire then the overvoltage goes to the FET. Even if the other side (drain) is not connected to earth potential there will be capacitive current. This may not destroy the FET at once, but it will hurt the FET inside isolation barrier. Maybe all is fine for years... then maybe the leakage current increases and soon the FET destryos itself.

Klaus
 

J_M_B

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Hi Klaus

Thats great, really helped broaden my understanding.


Thanks a lot

Jamie
 

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