Add a switch between MOSFET drain and MOSFET source?

Other Hardware General Electronics
1

Hi,

I have an Arduino connected to a MOSFET (gate), the MOSFET is switching a 12v solenoid valve. This works fine but now I want to add a manual switch. Can I simply add the switch between MOSFET drain and MOSFET source?

If this is OK, are there an issues related to the gate status? This could be high or low when the manual switch is used.

2

MartynC:
Can I simply add the switch between MOSFET drain and MOSFET source?

Eh, what? lol.

You are describing the MOSFET itself. How can you put a manual switch inside a MOSFET?

Did you mean add a switch in series with the motor and the MOSFET? In the latter case, I would say yes, that would most likely work.

3

Sounds like he wants a manual switch in parallel (not series) to the MOSFET to bypass it.
In series would just mean he needs both to be on to be on.
In parallel would mean only one needs to be on to be on.

I don't see a problem if both are on in the parallel config.

4

I don't want to add the switch in series with the motor and the mosfet. I want to connect the switch to the mosfets source and drain pins.

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My concern is, is there any issue with this configuration when the gate connection is high?

5

Short answer, yes :slight_smile:

6

septillion:
Short answer, yes :slight_smile:

Is that yes will it will work,
or yes there an issue with this configuration when the gate connection is high?
:slight_smile:

7

Sorry, it's an answer to the original question. That will work just fine.

8

Yes, you can do so. If you close the switch Source and Drain potentials become the same, therefore no current will be flowing through the MOSFET.

9

Many thanks

10

And, more importantly, it doesn't short-circuit the Arduino output to ground or any other hard voltage rail. So it's safe for the Arduino until there's some extraordinary event like 220V getting shorted to the motor. Then everything disappears in a puff of magic smoke.

Remember that the full motor current will be flowing through your switch. With a large motor and a small switch, this may cause problems for the switch. Make sure it's rated for the voltage and current you're using.

11

MartynC:
Is that yes will it will work,
or yes there an issue with this configuration when the gate connection is high?
:slight_smile:

It will work. The fact the FET is on or off won't matter since Vds will be 0V when the switch is on,
the gate doesn't care.