# Mosfet Maximum On Time

Hi guys i have a quick question. Can a mosfet be used as a relay? I want to control a simple solenoid valve that could pull as much as 2 amps. I want to activate it using my arduino and was wondering if i could use a IRLZ44N Mosfet to control the low side. I dont want to control it via pwm just simple on off.

Here is a link to the mosfet spec sheet. www.irf.com/product-info/datasheets/data/irlz44n.pdf

Thanks

Mitch

mitchedwards:
Hi guys i have a quick question. Can a mosfet be used as a relay? I want to control a simple solenoid valve that could pull as much as 2 amps. I want to activate it using my arduino and was wondering if i could use a IRLZ44N Mosfet to control the low side. I dont want to control it via pwm just simple on off.

Here is a link to the mosfet spec sheet. www.irf.com/product-info/datasheets/data/irlz44n.pdf

That MOSFET can handle 2 amps, no problem.

MOSFETS can handle large amounts of DC. The only time you really need a relay is when you have switch AC.

That is why i chose this mosfet so i dont need to worry about a heat sink. So you think it is ok for the mosfet to be on for say 30 minutes straight as if it were a relay but controlling the low side?

Thanks

Mitch

That MOSFET has an Ron of 0.025 ohms when the gates given 5V drive, you can
calculate the heat dissipation directly from P = I^2 R.
2 * 2 * 0.025 = 0.1W, so no heatsink needed.

Great thanks guys! I just wasnt sure if a mosfet could remain on for long periods of time like a relay. I though mosfets were only used for things like PWM.

Make sure that the gate to source voltage is at least 9V. That will put it in the saturation region, where the mosfet resistance is minimum. This will cause it to generate minimum heat and is a good practice than keeping the fet in the linear region where it offers a degree of resistance.

sreedevk:
Make sure that the gate to source voltage is at least 9V. That will put it in the saturation region, where the mosfet resistance is minimum. This will cause it to generate minimum heat and is a good practice than keeping the fet in the linear region where it offers a degree of resistance.

That would be sound advice for a MOSFET that isnâ€™t logic level, however
the IRLZ44N is logic level and has a Rds(on) specified for Vgs down to 4V
so 5V is absolutely fine. In fact the gate-source breakdown voltage is 16V so
you would not want to use this from a 12V gate driver, the margin of safety is
too low.

One thing to note about MOSFETs are they are very sensitive to overvoltage. Since you are connecting it to a solenoid, make sure you have a kickback protection diode in place, or your MOSFET will probably go pop after a while. Inductive loads can have a nasty voltage kick every time you turn them on and off.

The mosfet specified in this case hs internal protection diodes....so no need to worry abt that...

mirith:
One thing to note about MOSFETs are they are very sensitive to overvoltage. Since you are connecting it to a solenoid, make sure you have a kickback protection diode in place, or your MOSFET will probably go pop after a while. Inductive loads can have a nasty voltage kick every time you turn them on and off.

Actually the 'voltage kick' only occurs when turning off where the collapsing magnetic field creates a voltage across the windings. Turning on has no such effect.

Lefty

mitchedwards:
Great thanks guys! I just wasnt sure if a mosfet could remain on for long periods of time like a relay. I though mosfets were only used for things like PWM.

A MOSFET does not "wear out" - you can turn it on, and have it turned on from now till the end of time, and it will be just fine. Even if it got hot, as long as you had a heat-sink on to keep it below too-hot, it would last almost forever.

// Per.