I need to be able to adjust the speed of my fans in the computer. I hear that PWM is an efficient way to adjust the speed of the fans. I need to adjust the speed of 4 fans. Is this a good circuit? Also is there a way to lower the number of components?

 

Take a look at my "Simple PWM Circuit" in the Projects Collection forum.
http://forum.allaboutcircuits.com/showthread.php?t=9016

 

9 components? not bad.
http://www.allaboutcircuits.com/vol_6/chpt_6/9.html

i think you need to choose the frequency carefully. i know for heavy inductor fans (automotive cooling fans) we drive them around 30Hz. pc fans may like to be driven at 100Hz, etc. experiment and see.

 

9 components? not bad.
http://www.allaboutcircuits.com/vol_6/chpt_6/9.html

If you look at the link to my simple PWM circuit, you would see that it has only six components not including the load, and all except for the power MOSFET are quite basic components.

 

Arthur, are your fans brushless motors? I think that many small fans such as those used in computers are brushless.

If they are brushless, I don't know if PWM will work as well as a variable DC drive such as an one based in LM317.

Sgtwookie, is that your understanding?

hgmjr

 

If you look at the link to my simple PWM circuit, you would see that it has only six components not including the load, and all except for the power MOSFET are quite basic components.

the 9 had transistor driver in the count...

6 or 9, does it really matter, still a low count of parts....

 

Arthur, are your fans brushless motors? I think that many small fans such as those used in computers are brushless.

If they are brushless, I don't know if PWM will work as well as a variable DC drive such as an one based in LM317.

Sgtwookie, is that your understanding?

hgmjr

Yes they are brushless.

 

If they are brushless, I don't know if PWM will work as well as a variable DC drive such as an one based in LM317.

Sgtwookie, is that your understanding?

Actually, I'm not sure offhand.

National's datasheet for the LM317 has a couple of switched-mode supply schematics. Those would be more efficient than simply using an LM317 by itself - but actually, a DC-DC converter would be more efficient than that.

OTOH, one could always build a comparator circuit to control a MOSFET to keep the voltage across a cap in an approximate range. A stripped-down switching power supply, if you will.