High side 12v driver from Arduino?

[jbickerton]

Hi all,

(Please be gentle, I'm a mechanical engineer with schoolboy electronics trying to achieve an end goal...)

I'm going crosseyed trying to design a circuit: I want to drive a 12v-14v inductive load on a car - they're solenoids to run air suspension (with a built-in controller which takes +12v continuous as a trigger), as well as controlling a compressor (up to 10A 12V). It makes sense to use power electronics to run these loads - I can use a low-side N channel MOSFET for the compressor (with a diodes etc for the inductive load), but the solenoid controller has me foxed.

There's a reference to a high-side controller using a P channel MOSFET here:
https://forum.arduino.cc/index.php?topic=555862.0

jremington:
For high side switch use a P-channel MOSFET, like this:

Pololu makes some nice high side, high current switch modules that can be controlled either by an MCU or an on board switch.

But further down the thread it suggests the FET gate needs to be ~10v higher than Vcc, which I can't do easily on the car. I can use the Pololu controller but then it's getting more expensive. Should I just use a sealed through-hole 5v relay and have done with it?

All help gratefully received!

[Wawa]

You misunderstood.
The gate of a P-channel fet must be lower (not higher) than source.
Q3 pulls the gate 12volt lower than the source, so that's ok.

This is a 'dangerous' circuit for in a car.
A supply voltage spike higher than the fet's absolute max gate/source voltage (20volt?) could kill the fet.
See diagram four on this page.
Leo..

[jremington]

Automotive electronics require circuitry to suppress electrical noise, handle voltage dropouts and reversals, and protect from voltage spikes >120 V.

This application note explains and suggests solutions.