Hi All

I have a 24V FAN, which has four wires. VCC,GND, PWM and TACT.

The FAN requires a voltage between 0-4.5-5V on PWM to vary its speed.

The FAN has an internal pullup on the PWM line to 4.5V, whereby if the PWM is not connected to anything, the FAN runs at the maximum speed as the voltage on PWM is about 4.5V.

My microcontroller is working on 3.3V. Therefore I would need to use either a MOSFET or transistor.

Is there a certain parameter I should keep in mind when selecting MOSFET or transistor for PWM?

At the moment, we are using the 2N3904 but found that we had to use an additional pull-up to 5V; otherwise, when the PWM varied, it was not adjusting FAN proportionally. It was as if the transistor was drawing more current from the PWM than supplied by the fan internal pullup. Maybe I am wrong.

Is there a 3 pin transistor or Mosfet which would be recommended?

 

Hi DJ,
These modules are useful.
E
https://www.amazon.co.uk/Youmile-Ch...S,B0887Y6GMX,B09296334D,B088LMJR5K,B07TX64C12

 

Thanks

I want to avoid have 5V power rail, as this is only necessary for the PWM signal, which already has a pullup.

With those modules, you still need to add a 5V line.

 

Try one of these .........
.
.
.

 

How did you have your transistor connected? That should have worked, generally speaking. Also, how much current can the pull-up supply?

 

There is 10K internal pullup, as shown in the diagram below. Transistor collector pin was connected to wire

 

Do you want to use a transistor that is controlled by the ESP8266 to control your fan? If so, how much current does the fan draw?

From what you are saying, we will be ignoring the tachometer signals and running the fan at full speed when on.

 

I have simple AVR outputting a PWM signal from its PIN. The fan draws about 0.5A at full speed.

At moment I am finding that I need to add an additional pullup on my transistor, other wise its does not work with internal pull up alone.

 

What do you have between the pull-up and the fan?

What is in the gray box? The Arduino?

 

hi DJ,

This is one option, no phase reversal
E

 

This is my current design.

The Collector is connected to the PWM wire.

My PCB is board is powered with 12V and I am using Zener diode to create a 5V for the pull up. Its working well for now. But I have found that a 5V pullup is needed even though that Fan has it own internal pullup.

If I can get it working with only internal pull up it would be great.

With out the additional pullup, the PWM signal seems to be a little distorted and speed of FAN is not proportional to duty cycle as specified in the datasheet.

I am thinking can it be my choice of transistor, which could causing the issue.

 

hi DJ,
That will invert your PWM sense.
E

 

hi DJ,

This is one option, no phase reversal
E
View attachment 253954

I will try this as well.

What difference between having AVR control the Emitter in comparison to the base?

 

hi DJ,
That will invert your PWM sense.
E

Yes, it already compensated in my firmware.

 

What difference between having AVR control the Emitter in comparison to the base?

ho DJ,
No signal inversion.
The component count is less than your option.
E

 

Yes, I guess i would need a 5V source?

 

The FAN has an internal pullup on the PWM line to 4.5V, whereby if the PWM is not connected to anything, the FAN runs at the maximum speed as the voltage on PWM is about 4.5V.

hi.
No, that 5V is the voltage that you see on that wire from the fan.

E

 

HI,

The 5V is internal to the fan, you do not see that on the wire. PWM wire is the port connected to the 1K resistor. The datasheet is a little confusing.

 

hi DJ,
Does this make it easier to follow.
E

 

Thanks I will give this a go.