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A way to automatically adjust a variable resistor?

  1. Jan 11, 2009 #1
    Is there a device or method for automatically (non manually) varying a resistor?

    Basically we have A thermoelectric with an internal resistance, hooked up to a load resistor, and we want peak power (which is when the load resistance matches the internal resistance). Right now we are manually (rheostat) changing the load resistance by turning a knob, but would like to have a method that automatically matches the load resistance with the internal resistance.

    Any ideas?
  2. jcsd
  3. Jan 11, 2009 #2


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    Last edited by a moderator: Apr 24, 2017
  4. Jan 11, 2009 #3
    The channel of a junction FET (source to drain) acts as a variable resistor controlled by the reverse biased gate - source junction.

    """The result is that the FET acts more like a voltage controlled resistor which has zero (well, low?) resistance when Vgs = 0 and maximum "ON" resistance (Rds) when the gate voltage is very negative."""

    http://www.electronics-tutorials.ws/transistor/tran_5.html [Broken]

    IGFET or MOSFET (more likley to have high power handling) might also work in a simliar way.
    Last edited by a moderator: May 3, 2017
  5. Jan 11, 2009 #4
  6. Jan 12, 2009 #5
    The FET idea is by far the easiest, depending upon load issues... ie if its high current, you will blow a lot of parts while debugging. In that case, a motor driven potentiometer such as used in some automated audio consoles may be a lot simpler and cheaper in the long run.
  7. Jan 15, 2009 #6
    Can you explain what a thermoelectric is and the range of its internal resistance? What kind of power source are you using - AC, DC, 120 V, 12V?
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