# A way to automatically adjust a variable resistor?

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?

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.

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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.

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?

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?