about the circuit reverse protection by P-fet

Thread Starter

LAOADAM

Joined Nov 21, 2018
899
Hi all.
the picture shown the circuit, that has a zener to protect P-fet.
question:
1. is this circuit suite for a 5V supply unit or only for higher power unit like 15V of the drawing used to?
2. how to calculate the voltage of D1?
Thanks.
Adam

p fet.JPG
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
899
For a 5V source you need a logic-level type MOSFET (Vgs(th) max ≤2V).
The MOSFET you show needs a Vgs of 10V to be fully on.
thank you. seems not easy to find p-fet logic-level type MOSFET.
The VP2206 got: Vgs(th): -1.0 ~ -3.5, is it OK?
AO3401 got: -0.5v ~-1.3v better?
 

crutschow

Joined Mar 14, 2008
34,679
The VP2206 got: Vgs(th): -1.0 ~ -3.5, is it OK?
AO3401 got: -0.5v ~-1.3v better?
They both should work but the AO3401 is better.

Look at the Vgs voltage used for the Rds(on) in the spec sheet.
If it's measured at a Vgs of 5V or less, then it's a logic-level type MOSFET (below for VP2206):
Which to use depends upon the maximum load current and how much voltage drop you can tolerate at that current.

1713017005991.png
 
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