Peltier Element BJT Driver

Discussion in 'The Projects Forum' started by lijoostenk, Dec 15, 2013.

  1. lijoostenk

    Thread Starter New Member

    Jan 25, 2013
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    0
    Hello.
    Currently Iam working on a project, part of which requires me to design a temperature controller using peltier element. I have almost completed the design but I would like to clarify whether the peltier driver that I've used is correct before proceeding towards final implementation.
    Since applying a PWM may damage a peltier element, I've chosen a Quasi complementary push pull class B amplifier using BJT's for delivering the required power to the peltier element from the output of a PID processor. The driver consists of Darlington & Feedback pairs, the circuit of which is shown below. Photo1809.jpg Is there any problem in implementing this circuit & How am I supposed to design the two resistors?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Why the elaborate circuit? Just use a single N-MOSFET as a switch.
     
  3. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I could be wrong but I think PWM is ok as long as the voltage is below the peltier rating. I'm thinking you need to heat and cool with the same device?
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    PWM is okay for Peltiers and gives higher efficiency. For best efficiency and maximum cooling effect when driving a Peltier with PWM you should use an inductor in series with the element and a free-wheeling diode to ground to smooth out the pulses and reduce I-squared-R loss in the Peltier.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Peltiers also require a minimum frequency if you want to drive them with PWM direct to reduce thermal mehcanical shock that kills them, from memory I think it requires >2000 Hz.

    Likewise if you are switching them on/off with a simple controller it helps to ramp the on/off currents over 100mS or so to again reduce the thermal shock.
     
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