Electrical – MOSFET as inrush current limiter (passthrough parasitic C?)

current-limitinginrush-currentmosfet

I have a circuit based on a P-FET which shall limit inrush current (20 mA).
However, when turning on the power supply there is always a current peak (30 mA, 5 ms) through the M1. Even if I tie its gate to the source.

My question is: What effect is causing that current peak?

  • Is the P-FET initially conducting?
  • Is there a capacitance in series with the P-FET which could be large enough to let that current pass?

Appreciate any hints.
If there are details missing in my description, my apology in advance.

schematic

simulate this circuit – Schematic created using CircuitLab

@WhatRoughBeast I have updated the FET type.


In order to detail my last comment about counteracting the condition which leads to initial FET conduction (capacitive voltage divider) I'd like to draw what I have in mind. Maybe that helps to understand and discuss about.

schematic

simulate this circuit

So theoretically one would need a charge pump in order to cancel the inrush current through Cgs so no significant (less than Vgs_th) Vgs would develop.
The charge pump would need to be very fast.

What do you/others think?

Best Answer

Since you dont have any specs, no solution is [perfect.] = will meet spec. Perhaps consider a Current sense cct amp. to drive the gate is what you need. These are just ideas, not proven ccts.
- i.e. extremely dependent on load, Vt and RdsOn.

schematic

simulate this circuit – Schematic created using CircuitLab

I changed it to a 240mA load.

But in your case, the ESR of your C1 is greater than the ESR of the Miller Capacitance of your FET

or try this instead to allow slow Vgs turn on.

Rev A

schematic

simulate this circuit