PWM radial blower, not starting till 50% duty cycle

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check with a scope what is happening on the Drain side of U4. Pin numbering suggests a power FET and these are normally slow switching, you need a fast switching FET to ensure you actually have a nice square wave on the speed regulation pin.

Also try with a PWM of 20KHz and ensure it actually is 20KHz with the scope. It is what the motor likes best according to the datasheet so start with that.

most simple thing is to first go to 0% and 100% duty cycle to see what the max fan speed is. then do a 50% duty PWM and see that you are actually about half way. The FEt is crucial as if it is not fast enough the dutycycle will not be anywere near what you at the moment think it is.

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Kartman wrote:

As I mentioned earlier, the MOSFET is not a suitable type and you most likely need a pullup to 5V for the PWM signal. Design involves a bit more than just using Altium.

 

I kept the same Mosfet as this the only one I have at the moment, but after some trials, I found that a 100R pullup resistor on the PWM wire made it work as intended. Now when I adjust the duty cycle, the fan speed does adjust accordingly.  In addition to that, the voltage measured on the PWM line also matches, the duty cycle, as shown in the datasheet graph(Post 5).

 

The only issue I have is at certain times you do hear small speed variation, which I guess is due to fact I am using software PWM/ I guess once on my new board with hardware PWM is done, this issue would not arise.

 

In addition to this, would be a good idea to add some extra components for filtering on my new design? Or would this not be necessary on a 4 wire fan/blower.

 

Thanks

 

 

 

Thanks

Regards

DJ

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meslomp wrote:

check with a scope what is happening on the Drain side of U4. Pin numbering suggests a power FET and these are normally slow switching, you need a fast switching FET to ensure you actually have a nice square wave on the speed regulation pin.

Also try with a PWM of 20KHz and ensure it actually is 20KHz with the scope. It is what the motor likes best according to the datasheet so start with that.

most simple thing is to first go to 0% and 100% duty cycle to see what the max fan speed is. then do a 50% duty PWM and see that you are actually about half way. The FEt is crucial as if it is not fast enough the dutycycle will not be anywere near what you at the moment think it is.

 

I got it working, now, my PWM at moment is 32Khz, as I am using timer 0, where I am not able to adjust the frequency. But on my new design, I will use a timer that lets me adjust the frequency beyond the pre-scalers. 

 

This is the FET i am using

FDC637BNZ: N-Channel PowerTrench<sup>®</sup> MOSFET, 2.5V Specified, 20V, 6.2A, 24mΩ (onsemi.com)

 

 

Thanks

Regards

DJ

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djoshi wrote:
I got it working, now

So what was the problem?

 

Don't forget to mark the solution.

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It seems like it just needed a 100ohm Pull resistor to 5V on the PWM wire. Is this a normal requirement?

 

But I would like to know, is it recommended add any addition passive components when controlling a 4 wire fan, so I can at least add the footprints in my next PCB.

Thanks

Regards

DJ

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djoshi wrote:
is it recommended add any addition passive components

Look at the manufacturer's recommendations that you yourself posted in #30 !

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Pulling the tact line to 3.3v will not work as your fan has allready pulled this line to +5V. You will need to use a FET or transistor to lvl shift this line for you

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You are needlessly making a big mistake...after your transistor put in an RC flter...that will turn your pwm into a voltage, which is what the fan actually uses (the fan DOES NOT actually use PWM).

Then you can use a low PWM freq,., like 1 KHz, or 3 KHZ, or maybe even 500 Hz, if your C is large enough.

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Thu. Nov 26, 2020 - 07:54 PM
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awneil wrote:

djoshi wrote:
is it recommended add any addition passive components

Look at the manufacturer's recommendations that you yourself posted in #30 !

 

As per my conversation with them on the phone, I have been told that this is the internal circuit within the fan, but it seems that might not be true based on my experiments. I need to get in contact with them again.

Thanks

Regards

DJ

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Kuch wrote:
Pulling the tact line to 3.3v will not work as your fan has allready pulled this line to +5V. You will need to use a FET or transistor to lvl shift this line for you

 

Yes, that makes sense

Thanks

Regards

DJ

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avrcandies wrote:

You are needlessly making a big mistake...after your transistor put in an RC flter...that will turn your pwm into a voltage, which is what the fan actually uses (the fan DOES NOT actually use PWM).

Then you can use a low PWM freq,., like 1 KHz, or 3 KHZ, or maybe even 500 Hz, if your C is large enough.

 

 

Ok, thanks.

 

I think I will make my new PCB with various options so that I experiment with the best solution.   Can I still use 2n3904 transistors , but obviously with resistor on the base?

 

But for now, I can see it working in principle with the mosfet.

 

 

Thanks

Regards

DJ

Last Edited: Thu. Nov 26, 2020 - 08:18 PM
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Can I still use 2n3904 transistors , but obviously with resistor on the base?

Yes that will work perfect for translating the logic signal from 3.3V to 5V (or even 12V if needed).  Remember, it will be upside down.   You could use 2 stages to  bring it rightside up, if you wanted (double inversion).

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:

Can I still use 2n3904 transistors , but obviously with resistor on the base?

Yes that will work perfect for translating the logic signal from 3.3V to 5V (or even 12V if needed).  Remember, it will be upside down.   You could use 2 stages to  bring it rightside up, if you wanted (double inversion).

 

Yes, I have done something like this in the past.

 

 

 

I guess I can also adjust by duty cycle accordingly e.g. 90%, now becomes 10%.

 

 

The circuit from the datasheet on post 30, does it look like that the circuit is the internal circuit within the fan or is something I need to add?

 

As my conversation with a member of the company, mentioned that circuit is within the fan, but after giving some thought I am starting to think I need to added on my PCB.

 

 

 

 

Thanks

Regards

DJ

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You seem to be struggling with basic electronics. It is clear that the circuit is internal to the fan - how else could it accept a voltage or pwm signal?

It is also clear that you either must actively drive the fan signal high or have a pullup resistor. 100R is going to consume some current.

Stop guessing - understand the basics well before thinking of doing a pcb.

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Lots of PWM fans have a "dead zone" in about the first 25% of the PWM range. Because of this, I prefer to make the fan controller provide whatever RPM I request. Then, the PWM duty cycle is of no concern to the programmer. The function simply returns an exit code "RPM set" or "RPM failed". This also conveniently detects stalled or locked rotor conditions.

 

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