P-channel MOSFET and driver component selection

Question

I am working on a project where I need to switch 12 V, 10 A high side using a P-channel MOSFET. I understand how to construct a P-channel MOSFET 3.3 V logic-level driver using an NPN transistor which controls the MOSFET, but I'm having difficulty figuring out how to select components that will work. Are there tools like LTpowerCAD that can be used for this?

I vaguely understand the different properties of transistors and MOSFETs that are important, but I think I'm most confused on what properties I need to look at for the transistor and MOSFET to work together.

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

That is a simple circuit that should work for your needs. A 3V logic level will drive the 1.2 ohm load at 10A.

(edit) The PMOS device is chosen to operate on 12V gate, and capable of 10A current. R1 is to keep the gate off until a voltage is applied through 1k resistor R2 and NPN transistor Q1. 1k resistor R3 is chosen to limit base current to about 2.3 mA at 3V logic level drive. None of these components are critical.

(edit2) The MOSFET has an ON resistance of 70 mOhms, so it will dissipate 7W at 10A, and will need an appropriate heat sink. Other MOSFETs with lower resistance are available, like the FQP50N06.

Answer 2

Most likely, the only parameter of importance will be Rds(on) of the PMOS. You want to make sure Rds(on) does not cause too high of a voltage drop with 10 Amps. Also, you want to make sure the power dissipation of the PMOS is reasonable at 10A. Probably you are looking for Rds(on) of around 1 mOhm or so.

Of course, Vds max must be > 10 V. And Vgs max must be > 10 V. Sometimes on PMOS the ratings have a negative sign. But I am talking about the magnitude of Vds and Vgs.

No need for special tools.

Any small signal NPN will do.