FET circuit: Output device connected to Ground

OK, here is my situation.

I am going to use my Arduino to control some motorcycle electronics.

My idea is to have all input and output devices connected to the motorcycle’s fram, which is mass (or earth or 0volts).

By doing this, I can ground any device to 0 Volt on one side, which is allways close and saves complex wiring.
And alos, I have to route only one wire from the Arduino to the output device.

But, I can only find MOS-FET circuits that have the output device connected to PLUS, and the other side to the FET.

I am sure I do not have to re-invent the wheel. Can anyone point me to an image that shows my solution?

Kind Regards,

Seems you want a high-side switch.
Look at this page.
The third diagram is a high-side switch.

Normally with a FET or transistor, the + Power is always connected and you switch the ground ([u]example[/u]).

The reason for that is, the MOSFET is turned on by a voltage difference between the Gate & Source and you have only 5V (Gate voltage relative to ground) from the Arduino.

If you want to switch the + side, you'll need a P-MOSFET and you'll have 12V on the Source. You'll need a 2nd MOSFET or transistor to drive the Gate to 12V (no voltage difference between the Gate & Source) to turn-off the power-MOSFET.

If you mount the MOSFET at the "far end", you can avoid running a ground wire, but you'll still need power and a control wire. That might make sense if you are controlling several things (like a lighting cluster) because you can run one shared power-wire, with a separate control-wire for each thing.

Another option would be relays or solid-state relays.

Hi Guys,

Thanks for the info. That is what I was looking for.

There is indeed some more parts involved. Will look into this further!

Cheers, Phrireho

If your application is for a motor vehicle, there are special Hi-side MOFETs designed for automotive low voltage applications.

google automotive high side switches

They usually have all the input circuitry on board to input from a gnd based output.

Tom... :slight_smile: