Temperature Dependent Current Control

Discussion in 'General Electronics Chat' started by iONic, Dec 9, 2010.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    I'm looking to keep part count low, lower than a 555 PWM circuit as well as eliminate the need for manual adjustment of current to a cooling fan.

    In other words I would like to sense the temperature and with increases in temperature, increase the speed of the motor, and with decreases in temperature, decrease the current to the cooling fan. I'd like therefore, to maintain a temperature. It would be a 12V fan running off 500mA and less. A somewhat arbitrary temperature would be around 110 deg F +/- %10.
    The goal is to do this with as little or fewer parts that are necessary than a 555 PWM circuit. The minimum current needed to make the fan is unknown at present. Would a thermistor or LM34Z temp sensor into a comparator with some hysteresis be a viable option and would it be the most compact (fewest part count)?

    Perhaps the LM34 with the ATTINY13. Ideally I'd like the fan on at the minimum state. But when the temp is increased by +10% increase the current by X , if after 20 seconds the temp 1s still higher than the trigger point, increase by x again...
    until temp is stable. When below the temperature set-point, decrease current by x...repeat until set-point is reach or the min fan current is reached.

    Any ideas? I don't know that there are IC options to do just this or not, I will be checking into this soon, just thought I offer this up for discussion.

    Last edited: Dec 10, 2010
  2. tyblu

    Active Member

    Nov 29, 2010
  3. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    Didn't know that...of course I don't know how to program them either...yet. A very good piece of info though!

    The positioning of the temperature sensing circuitry MAY need to be further away than where I might need the sensor, not sure yet.