24V FAN management issue


I’m completely puzzled by the following issue and I would be very interested in someone’s helping hand on this :

I developped a PCB on the basis of a Pro Mini (ATMEGA 328P 16Mhz 5V) and I added the capability to drive a 24V brushless DC FAN from Sanyo Denki (Ref 9GA0424P3J001).

I have a MOSFET (NXP PMV20EN) which gate pin is connected to a ATMEGA digital pin (non PWM).
I have a 150Ohm resistance in serie between the Arduino pin and the Gate pin.
I also have a 10K pulldown resistance at the gate pin.
There is also a diode in parallel of the FAN pins.

I have the following behavior which is strange :

Case 1 : When I set pin to HIGH, the FAN keeps on reacting for a moment (just as if it was starting running) and then stopping. When I measure the voltage on the Gate PIn, the value sways around 0V despite the HIGH value.

Case 2 : If I unplug the FAN and then I set the gate pin to HIGH : I normally get continous 5V.
And after several seconds, if I pulg the FAN back, the FAN works fine.

How come the fact that the FAN is plugged or not can change the behavior of the MOSFET?

Case 3 : while in case 1 or not, if I put external 5V to the gate pin, the FAN starts running fine.

Is anybody have an idea where the problem comes from?

Could it be related to the Gate capacitance or something? The MOSFET seems ok if we consider case 3… However seems to be more that there is something wrong in the relation between arduino pin and mosfet?

Thanks for your support

Can you provide your code and your circuit (clear schematics preferred, or in-focus photos).

Its important to show how you are powering the Arduino and the fan. You do have grounds commoned?


Actually it is quite difficult to provide a general drawing or photo.

What I can say is : 1. FAN and chipset are on the same GND level. 2. The power supply comes from an LDO regulator (LDK715M50R from ST Micro) with 24V input and 5V output. Normally able to supply up to 85mA.

The schema is very much the same as the ones you can get from any web site : gate pin on digital pin through a resistor in serie (150Ohms). FAN P+ linked to 24V source, P- to MOSFET drain pin and source pin to GND.

The MOSFET is NXP PMV20EN 30V Nchannel with Vgate threshold of 1.5V, Gate resistance of 1.7Ohm, Gate capacitance of 435pF.

COncerning the program, this appears with the simple button example from arduino IDE.

Do you think that would come from the 5V power supply? If so, how come when I turn HIGH the gate while no FAN is connected and I connect the FAN afterwards it works?

Thanks for your support.

The key parameters for a MOSFET are the Rds(on) @ Vgs = 5V and the maximum Vds voltage. For PWM the total gate charge at Vgs=5V is important too.

Can you post the code you are actually using please, I've already asked for it. Its much much more useful if you draw a schematic of your circuit and take a photo and post it, words are not an efficient way to describe circuits.