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I'm looking to create a variable current regulator with the LM317 using 1-turn pots. I know that I am going to need to have a resistance of 1.25 Ohms to have a current of 1A, which I want to be my max; however, all of the pots that I have (barring trimpots) have a resistance of around 1.8 ohms when at their minimum setting, and I want to use 2 in series (for fine and coarse adjustment) which would bring total resistance to 3.6 ohms. Is there any way to get around this?

Thanks, Michael

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  • \$\begingroup\$ Hmm, I don't believe your 1.8 ohm number. Most of that (I'm guessing) is in the DMM. To measure low resistances use some current source.. it could be a voltage source and large resistance, and then measure the voltage drop. I'm guessing (again) you'll want to add some small resistance to the wiper of your pot. \$\endgroup\$ – George Herold Apr 10 '15 at 1:09
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Do not put 1A through the wiper on the pot. Put a resistor in series with the output, pot element in parallel, and tap the adj voltage from the wiper. The pot resistance is not critical- 1K would work fine.

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You can put a resistor is parallel.

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