DC Fan speed control

Hello,

I have a noob question. Here is a 5V,0.75W DC FAN - MF40200V1-1000U-A99. I want to control its speed using microcontroller.
Would it be enough if I use a mosfet as shown below to drive the fan using 1kHz PWM? I don't know if this topology would work fine for a dc fan and hence posting the question.


Datasheet Links:

STP90NF03L
BC-847
BC-857

Hi,

why all this circuitry?
Why not drive the MOSFET´s gate directly from microcontroller?

Whether the fan can be controlled by PWMing the power supply .. and which frequency to use: contact the fan manufacturer.
Some fans don´t like this.

Klaus

It should work but the STP90NF03 is a low gate charge device and has a logic level threshold so you probably don't need the driver stages. It could be driven directly from the microcontroller but a single transistor current booster would be advised.

You drive PWM pulses directly to the motor, that's fine if it is simply a brushed motor but if it has any internal electronics you need to check with the manufacturer, you might be resetting it's internal speed regulator 1,000 times per second!

Note that you have no feedback to regulate the speed and the torque will be very small when the average voltage is low. You might find the motor doesn't start at all until the PWM ratio is high then suddenly speeds up. Don't expect a linear PWM to speed control.

Brian.

KlausST said:

Whether the fan can be controlled by PWMing the power supply .. and which frequency to use: contact the fan manufacturer.

Click to expand...

Ok. Thanks for clarification. I'll contact the manufacturer.

betwixt said:

It should work but the STP90NF03 is a low gate charge device and has a logic level threshold so you probably don't need the driver stages.

Click to expand...

Thanks for the info.

Just switching the output MOSFET is not the suited approach at all due to the huge inductive impedance characteristic of the Fan,. You should consider adding capacitor at the base of the gate in order to low-pass filter the PWM fundamental frequency and control the speed as much linearly as possible through a DC-like current. I'm not sure if doing with a BJT would be better doing this instead with a MOSFET.