# IRL Z44N FET not playing nice.

HI guys.

I’m working on a small vaporizer project as the cheap ones I have right now are rather crap.

I have some IRL Z44N FETs which (from what I understand ) should be able to be switched directly from an Arduino (and pulsed to vary the output)

I’ve verified that the circuit and sketch works with an LED and multi meter and I can vary the brightness/voltage with PWM. However I cannot seem to get it to switch from the 5v from the Arduino with any substantial load on it (2.2ohm on 12v). If I apply 12v to the gate it switches the load fine.

Any help would be greatly apriciated

What is the intent of your 330 Ohm resistor?

Granted... you should still get around 4.6 volts at the gate pin.

I seem to remember reading somewhere that its a good idea to have a small current limiting resistor (120ohm) between gate and the Arduino pin, however I only had a couple 330s lying around.

330 would be fine, you're just trying to limit the IO exposure to the gate capacitance of the MOSFET, which looks like a charged or discharged cap when IO voltage level changes.
Worse case: 5V/.035A = 145 ohm, so 330 ohm will limit current to 5V/330ohm = 15mA.

So two people have responded and avoided your real question...

Why? Because you really should not be having an issue with a logic level mosfet.

Vgs = 4V (4.5?) may be to low. Take a look at Fig 3. here

Seems to be working now. I think that Arduino I was using was on its last legs.

The other Arduino you were using wasn't a 3.3volt version was it? (so the output to the FET would be 3 volts or so instead of close to 5v)

tekkninja:
I seem to remember reading somewhere that its a good idea to have a small current limiting resistor (120ohm) between gate and the Arduino pin, however I only had a couple 330s lying around.

It doesn’t make much difference, but it is wrong to put the 10k resistor on the FET side of R2 as it ever so slightly reduces the drive voltage.

Since the concern is that if the Arduino is in input/ reset mode it will not definitively control the gate, the correct approach is to put the 10k resistor across the Arduino output. This is even more critical if you wish to put a base pull-down on a bipolar transistor.