USB circuit which resistor/s needed?

[richie25]

Hi all,

I have a 5v fan rated at 0.36Amps. i have wired this into the usb port and it works great but it's very loud and i'm wanting to decrease the voltage so it's quieter. now i have done a little digging but i'm still not 100% sure what i need as i don't want to blow the usb port by demanding too much current as the port runs upto 500miliamps.

So any ideas which resistor i need to say lower the voltage to 3v? and perhaps 2v?

Thank you

 

[Ian Rogers]

Use a 555 to vary the 5v by frequency or PWM...

https://freecircuitdiagram.com/2009/02/01/pwm-motor-control-circuit/

 

[diy didi]

keep it simple. Try a resistor between 5 and 12 ohms. Pwm is best but large circuit, and switching freq of pwm can induce its own noise

 

[richie25]

Thanks for your replies.

That's exactly what i needed, i think i'll start from 5ohms and work my way up.

I'm making it for my laptop. the inbuilt fan is constantly turning on and off and it's very annoying. so i thought i'd use the usb port via the motherboard pins and run it from there so the fan is constantly going and at a lower rate too.

 

[Ian Rogers]

Most Bios software allow fan speed modifications.... If your fan is switching on and off regularly... You need to sit the laptop on a firm surface ( laptop tray) as its overheating... I hardly hear the fan on mine.... But mine is always on the table... ( plenty of circulation ).

BTW... They are not called Laptops anymore ( for this reason ) They are now called notebooks...