Author Topic: MOSFET problem in PWM fan controller  (Read 8564 times)

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Offline ZeroResistance

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Re: MOSFET problem in PWM fan controller
« Reply #25 on: December 22, 2016, 06:16:49 pm »
That circuit doesn't use the fan's PWM pin. It's a buck converter which varies the fan's supply voltage, which may not work well with four wire fans.

That circuit uses 2 modes of operation for 4 wire fan it goes into PWM mode where the PWM signal is provided by the PIC18F, for other type of fans it goes into buck converter mode.

It seems like you're overcomplicating things.

You don't need a MOSFET or any other switching transistor because MCU is more than capable of driving the current/voltage on the fan's PWM input. All you need is a small signal diode (1N4148 (silicon) or BAT54 (Schottky whcih should be even better), connected positive side to the fan's PWM input and negative side to the MCU output. This will convert the MCU output to an open drain output. There may be some tiny spikes when switching but the fan should be able to cope with them.
That's a brilliant idea Hero999 that should work out for the OP...
« Last Edit: December 22, 2016, 06:19:32 pm by ZeroResistance »
 

Online Zero999

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Re: MOSFET problem in PWM fan controller
« Reply #26 on: December 22, 2016, 06:21:47 pm »
That circuit doesn't use the fan's PWM pin. It's a buck converter which varies the fan's supply voltage, which may not work well with four wire fans.

That circuit uses 2 modes of operation for 4 wire fan it goes into PWM mode where the PWM signal is provided by the PIC18F, for other type of fans it goes into buck converter mode.
I see it now. Pins 12 & 13 are PWM outputs. It will work if the fan has a 5V tolerant input, otherwise it may damage the fan. A diode or perhaps even a current limiting resistor should enable it to drive a fan with a 3V input safely.
 

Offline tehtehteh

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Re: MOSFET problem in PWM fan controller
« Reply #27 on: December 22, 2016, 08:38:03 pm »
It seems like you're overcomplicating things.

You don't need a MOSFET or any other switching transistor because MCU is more than capable of driving the current/voltage on the fan's PWM input. All you need is a small signal diode (1N4148 (silicon) or BAT54 (Schottky whcih should be even better)), connected positive side to the fan's PWM input and negative side to the MCU output. This will convert the MCU output to an open drain output. There may be some tiny spikes when switching but the fan should be able to cope with them.
sounds promising! I don't have any suitable diodes, but I might be able to get a 1n4148 or a 1n4448 tomorrow
 

Offline 97hilfel

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Re: MOSFET problem in PWM fan controller
« Reply #28 on: December 26, 2016, 07:16:31 pm »
Well I just wire the MCU 25kHz output to the fan, also currently building a fan controller, you dont really need a driver between because 4 pin fans should already have that build in and the PWM has ro provide only the signal. (I use a 5V MCU and everything works fine)
 


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