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I want to use a digital potentiometer, however, the digital potentiometer has a power limit, which means I can't apply the voltage for my application.

I am looking for a circuit which functions as an "resistance follower": depending on the resistance you input (that resistance should draw low current through it), the voltage source will "see" a resistance equal to that resistance. In other words, the current will follow Ohm's law. (PD: The impedance can be just proportional and not just equal to the input resistance).

I was thinking of a voltage-controlled current source, where the voltage is proportional to the input resistance, something like this:

enter image description here

In this circuit Vinput/Iinput is proportional to Potentiometer R4 (in my understanding). An additional problem is the big voltage created at the output of U1.

The details are as follows: The voltage input will be maximum ~25 V, PWM of max 20 Hz. Resistance can be 100-5000 Ω. Digital pot = AD5292.

To be more specific on the application, as requested: I want to use the AD2592 with a voltage of 25 V which is above its current limit of 3 mA (using a 100 Ω value). Ideally this digital pot should withstand 250 mA.

ocrdu
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Eduardo Ramírez Gómez
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    Can you be more specific about the application? What are you really trying to accomplish? The reason I ask is that most of the times I see a request for a resistance follower, it turns out to be an XY problem that can better be solved with more conventional approaches. – evildemonic Feb 02 '23 at 21:19
  • Unsaturated BJTs can act like variable resistors, that's how they follow voltage. – dandavis Feb 02 '23 at 22:24
  • Being more specific on the application: I want to use a digital pot (AD5292) but with a current >3mA (Max current for that digital pot. Ideally a max current of 250mA. My best guess was to use a resistance follower. – Eduardo Ramírez Gómez Feb 02 '23 at 22:35
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    You're still looking at the trees. We need you to look at the forest, please. What is the **ultimate** problem you need to solve? Please read this: https://xyproblem.info/ – Davide Andrea Feb 02 '23 at 23:06
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    What do you intend to use this resistance for? – evildemonic Feb 02 '23 at 23:07
  • @Eduardo Do you expect this to operate in two quadrants? Also, a VCCS doesn't seem right from what you say about it acting like a resistance. A resistor will vary its current based upon variations of the applied voltage. But a VCCS won't act like that. I must be missing something. – periblepsis Feb 03 '23 at 18:59

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