Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

PWM fan speed controller

Status
Not open for further replies.

makr

New Member
I'm hoping to convert some leftover 140mm PWM case fans (standard 4-pin computer connector) to a quiet room air circulator, with proper pulse-width speed control instead of voltage based.

I haven't found much on exactly what the supply needs to be, i.e. ground, +12v, pwm, rpm sense, but what does the pwm signal need to look like? Best I have gathered so far is it's a 21 kHz 12v square wave signal where the ratio of how long the signal stays at +12 within the cycle determines the fan speed.

My thought was to use one side of a 556 to supply the 21 kHz to trigger the other side to hold output high for an adjustable time, feeding the output to a power transistor to drive the 4 fans.

Does this seem reasonable, or am I in the wrong ballpark?
 
I'm hoping to convert some leftover 140mm PWM case fans (standard 4-pin computer connector) to a quiet room air circulator, with proper pulse-width speed control instead of voltage based.

I haven't found much on exactly what the supply needs to be, i.e. ground, +12v, pwm, rpm sense, but what does the pwm signal need to look like? Best I have gathered so far is it's a 21 kHz 12v square wave signal where the ratio of how long the signal stays at +12 within the cycle determines the fan speed.

My thought was to use one side of a 556 to supply the 21 kHz to trigger the other side to hold output high for an adjustable time, feeding the output to a power transistor to drive the 4 fans.

Does this seem reasonable, or am I in the wrong ballpark?
556's are not quite enough Umph for Hi or low side. since they drop 2~3V at 200mA

Whatever you use to drive the Fans should be < 0.5V @ 350mA or RdsOn=< 1 Ohm preferred low side (Nch) or high side (PCh.)

You can also bias a Schmitt inverter oscillator with a pot to and a few R's and Cap to input ground to shift the input waveform and output dutycycle to drive a FET.at 20kHz
 
Frequency probably isnt important, the line has a pullup so default is 100%.
As Ian says voltage probably isnt important too 5 or 12v.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top