# Am I using the right P-channel MOSFET for my high side switch?

#### Zurn

Joined Mar 4, 2019
79
Hi everyone,

I'm using a microcontroller to control power to my system with a p-channel MOSFET. The uC is an ATTiny85 and the MOSFET is an NDP6020P.

As of now my system is runs between 12 and 16V and everything works fine - however, when I charge the batteries everything jumps up to 24V. Could this be a problem for my MOSFET?

Here's my circuit:

The load is a bunch of things: special uCs, voltage regulators, and some hydrophones.

I've had some problems in the past with misreading MOSFET data sheets, so I figured it would be wise to get a second opinion.

#### Alec_t

Joined Sep 17, 2013
11,517
The Absolute Maximum Vgs is given as ±8V for that FET. You are using Vgs = 24*10/15 = 16V. Also, maximum rated Vds is only -20V. Houston, I think you have a problem (or two)!

#### Zurn

Joined Mar 4, 2019
79
The Absolute Maximum Vgs is given as ±8V for that FET. You are using Vgs = 24*10/15 = 16V. Also, maximum rated Vds is only -20V. Houston, I think you have a problem (or two)!
Ah yes, I accidentally swapped the resistors in my voltage divider calculation (I did 24*5/15 = 8V). I guess if I swap those resistors around I'll only have one problem.

Now to find a logic controlled P-MOSFET with a Vds of -24V...

Thanks for the input.

#### djsfantasi

Joined Apr 11, 2010
6,714
Ah yes, I accidentally swapped the resistors in my voltage divider calculation (I did 24*5/15 = 8V). I guess if I swap those resistors around I'll only have one problem.

Now to find a logic controlled P-MOSFET with a Vds of -24V...

Thanks for the input.
Or more. Perhaps one with a Vds of 30V would work? That’s what I used in a 12V system.

#### Zurn

Joined Mar 4, 2019
79
Yea... this one looks right (SQP50P03-07).

Is there any advantage to using something with a much bigger Vds, such as this FQP27P06?

#### Alec_t

Joined Sep 17, 2013
11,517
SQP50P03-07
That one and the FQP27P06 are rated at Vgs=-10V to turn on fully. You might need to play with your voltage divider again.

#### Sobhanjahaniparast

Joined Dec 13, 2019
9
Connect one zener diode between gate and source.