# Turning off servos with a MOSFET

I'm trying to limit power used by servos. The application is such that I don't mind if the servo's position drifts a bit, so I just use an N-MOSFET to shut it off when not in use. A conversation on an Arduino forum brought up the following concern:

Blocking the current flow path on the ground lead may force voltage/current to flow back thru the servo control wire back thru the Arduino to the common ground between the Arduino and servo power supply. If the servo starts to heat up or behave erratically, this might be the reason. I haven't tried it, but a P-MOSFET on the servo power supply might be another choice.

I am seeing some erratic servo behavior, though I think it has more to do with some sort of reset not happening when I bring power back on. Is the logic in the quote sound? Here's a snippet of the current servo control circuit:

simulate this circuit – Schematic created using CircuitLab

• Does your arduino run from 6V? May 27, 2014 at 7:37
• yeah, it does.. May 27, 2014 at 14:17
• @kolosy has your circuit worked with the N-mosfet? Aug 13, 2015 at 19:02
• @Sathees The circuit above worked. The erratic behavior I was seeing was due to a specific Arduino issue, not the n-mosfet. Aug 14, 2015 at 3:24
• Why do you need the diode? May 4, 2020 at 19:50

If you want to be extra sure set the Arduino pin as an input when you turn off the mosfet: little or no current can flow in a microcontroller input, so there would be no path for current that would come from $V_{cc}$ to go anywhere.