Controlling fan speed via PWM

Projects General Guidance
21

Thanks.
What about the protection diode you have in your diagrams. Are diodes rated for current too? Can you also recommend a diode that'll work with the motor I listed please? I've never purchased a diode before and I'm not sure if like resistors you have to watch out for things like wattage/current rating.

Speaking of diode, do they have a fixed 0.7 V voltage drop when forward biased? (I know there are different types of diode with different voltage drops, but that's not what I'm asking) In another word, the power dissipated at the diode is directly proportional to current when forward biased? (power = VI)

Speaking of fixed voltage drop and power dissipation, is that also true for the base emitter voltage of the Darlington transistor?

It seems the MOSFET you have in your diagram (for PWM) is a N type enhance mode correct?

Thanks

22

In the electronics section of these forums Perry Bebbington has a very good writeup about flyback diodes and why you need them. You want to give that a read. Hopefully it will answer some of your questions.

Ron

23

Will does diode work? It states a current of 3A ( Current - Average Rectified (Io)). Is that the max current?

24

In the PWM setup, should there also be capacitors and resistors in series with the flyback diode?

25

I dont remember any reference to a particular project parts list.
We are at post 24 - would you like to share a link to the project?

26

The part list is a PDF from a Discord group, not a URL, so I do not know how to share it here. But it's not important since I'm doing it a bit differently than the parts list. In the parts list, they use a dedicated board to control the fan speed, I'm trying to do it using PWM, which is why I had a few questions on your tutorial page.

I think the MOSFET in your PWM diagram is a N channel, enhancement MOSFET, is that correct?

I also would like to know if it's necessary to include a resistor and capacitor in series with the flyback diode.

Can you advise if this diode is suitable please:

Thanks

27

Still working years later.

28

Can you show the schematic you are referring to? Ive never seen that configuration

29

No and the flyback diode goes across the load reverse polarity. Post #22 I gave a link to flyback diode and why you need one. Read the link.
A RC (Resistor Capacitor) series network is what is known as a "snubber" you can read about snubber circuits here.

Ron