Hi

Trying to get the hang of this pwm fancontroller.(For a computer fan). With the cap the fan stops at like 75% duty cycle while without the cap it stops at 10% but there's this buzzing sound.

The output on the mosfet looks weird aswell.

Two first shots are captured on the input on the drain-pin while the third one is captured on the drain pin.

Can anyone tell me what I've missed? :s

Edit: Crap, missed the schematic;

 

Have a look HERE under suppressing PWM noise on page 2 to adjust your gate RC.

 

I wouldnt have bothered with the RC. Just pulsing the motor will alter its speed. Also it means the FET is on or off rather possibly in its linear region which might cook it.

 

Most DC fans have controller IC's built in. If you mess around with trying to pulse the voltage or current into them, they won't work right.

 

Ye, without the RC there's this annoying noise from the PWM pulses aswell.

Thanks for answers anyway. I'm going to try different RC setups unless someone else has something to say.

 

Three problems..
1. What type of fan u are using.
2.What is the PWM frequency?
3.Remove RC at gate...just put a 47ohm resistor in series with gate only. Gate charge together with RC is driving the fan haywire.

{ed}
for q 2....around 1KHz... hey wizard, that is the audible range.