Transistor as a variable resistor

[JerryG]

I am looking to design a circuit, most likely with a transistor, to act as a voltage controlled rheostat. The controlling voltage can range from 0 - 3.3 v and I am trying to get a resistance range of about 200 - 5500 ohms. The circuit should have fairly high input impedance since it will be controlled by a DAC. Does anyone know of such a design?

 

[johncameron]

I have not tried yet but you can try yourself on the bread board. Either your circuit works for this design or not or need some extra component for that. So better way is go ahead with your design and check the output.

 

[MisterX]

Search for "FET as voltage controlled resistor."

 

[Antiphon]

Yes, the FET with negative feedback from drain to gate makes an excellent linear resistor with gate voltage. The impedance will not be super high due to tge negative feedback network but it's plenty high enough to be driven by analog ICs. The ohmic range will extend from near zero to near open circuit.

 

[Jiggy-Ninja]

I haven't used them, but there are ICs that act as digitally controlled potentiometers.

 

[likephysics]

Yes, the FET with negative feedback from drain to gate makes an excellent linear resistor with gate voltage. The impedance will not be super high due to tge negative feedback network but it's plenty high enough to be driven by analog ICs. The ohmic range will extend from near zero to near open circuit.

Antiphon, do you have a circuit diagram w/negative feedback?