Fan speed controller based on temp.

Discussion in 'General Electronics Chat' started by Zapnologica, Jul 9, 2012.

  1. Zapnologica

    Thread Starter Member

    Jun 15, 2012
    Howist guys,

    I have build me a circuit that uses a few voltage regulates that produce a fair amount of heat even with the heat sinks.

    Now i want to attach a fan to it, but i dont want it blasting away.

    Where can i get a schematic for a simple temp based fan controller?

    My original thoughts where just using a adjustable voltage regulator setup and replacing the potentiometer with a thermistor. i have had no experience with thermistor's but i think that the hotter they get the more resistance it is. so this will cause my voltage to drop as the heat goes up.

    But basically i want to put a sensor ( i heave read u can use diodes, non transistors etc) on each heat sink, there are 2 and then have them control the voltage of the fan.

    the ic would be receiving a 20v voltage.

    Im sure there is a better and more efficient way in doing it that i dont know of. please help me out :)

  2. paulktreg

    AAC Fanatic!

    Jun 2, 2008
    Buy one of these for £6.99?

    .. or just search on "temperature controlled fan circuit" for plenty of ideas?
  3. cork_ie

    Active Member

    Oct 8, 2011
    If you want a variable fan speed then the easiest (and most efficient) is a 555 timer based pwm circuit with the duty cycle proportional to temperature. The 555 timer will run in astable mode. Depending on the type of temp sensor and whether it has a positive or negative temp co-efficient you can vary the duty cycle by placing the sensor between either pin7 and positive line or pin 7 and Pins 2&6.

    the other option is to switch the fan full on at a particular temp. Using a voltage divider (with your temp sensor as part of the divider) and zener diode to trigger a transistor on or off.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Forget it.. Your circuit is going to change based on your other post about this "stepper driver" circuit.. You won't need a fan at all when you do it right. A NO
  5. Zapnologica

    Thread Starter Member

    Jun 15, 2012
    That is most likely correct, but to be honest the main reason i am doing this is just to learn electronics and get familiar with them. I dont really need half the things i have done, but i have just added features on so that i can learn how tp do them. So i just thought that it would be kwl to have a fan that changes its speed according to the temperature.

    And i will still need a heat sink for the voltage regulators that feed the power to the steppers?
  6. JMac3108

    Active Member

    Aug 16, 2010

    If you're just doing the fan speed controller for fun, then here is what you need.

    (1) A way to measure temperature.

    The LM35 is a very simple temperature measurement IC. Puts out a voltage proportional to the temperature.

    A thermistor is a resistor that varies its resistance based on temperature. Placed into a circuit it makes a good temperature sensor. The output is non-linear so the standard procedure is to put another resistor in parallel with it to linearize it.

    (2) A way to control the speed of the fan

    The easiest way is to PWM the fan. In other words, turn it on and off quickly. For example, if you had a 12V fan you could run it at half speed by applying 6V. However, if you turn the fan on and off with a 50% duty cycle then this is equivalent to running it at 6V.

    A simple transistor or MOSFET can be used to turn off and on the fan.

    (3) A way to tie parts 1 and 2 together to make a fan speed controller.

    I would use a microcontroller. Read the voltage from your temperature sensor using an ADC pin on the micro. Drive the transistor to PWM your fan using a digital I/O pin or timer output on the micro.

    Another option is to do it with a 555 timer as someone else mentioned. You have to figure out how to get the voltage output from your temperature sensor to modify the duty cycle output from the 555 timer.
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009