I'm planning to use potentiometer in a circuit. I know when potentiometer reaching low resistance, big current/power could burn potentiometer. How could I select correct resistor to protect my potentiometer? What are they key factors need to be considered?
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3\$\begingroup\$ You select it so that you don't exceed the power rating of the potentiometer. For an actual answer, please specify which potentiometer you will use, and how, in what kind of circuit, because it depends what kind of protection it needs and why. \$\endgroup\$– JustmeCommented Aug 10, 2023 at 19:53
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1\$\begingroup\$ Show your preferred schematic. Related: electronics.stackexchange.com/questions/126204/… \$\endgroup\$– Andy akaCommented Aug 10, 2023 at 20:02
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1\$\begingroup\$ Whether a series resistor is needed depends on what you have connected to the potentiometer. So a schematic will help. \$\endgroup\$– StainlessSteelRatCommented Aug 10, 2023 at 22:04
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2 Answers
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In general it's a bad idea to pull substantial DC current through the wiper if you can avoid it.
If no maximum wiper current is stated in the datasheet, you can estimate the absolute maximum rheostat-connected wiper current as:
\$I_M = \sqrt{P/R_T}\$ where P is the power rating of the pot and \$R_T\$ is the element resistance.
But do not exceed 100mA in any case unless the datasheet says it is permissible.
So if you're putting a resistor in series with a 750mW 10kΩ rheostat connected pot connected in series with a 12V supply (and the output can be shorted) you would have to limit the wiper current to 8.6mA so you'd need a series resistor of about 1.4kΩ.
Note that the dissipation of the pot will be much less than the rated 750mW when it is near minimum resistance but at maximum permissible wiper current since only a small portion of the element is in use.
answered Aug 10, 2023 at 20:02
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It all depends how you plan to use your potentiometer.
If you use it to generate a variable voltage (ie you connect one end to ground, one end to your supply, and the middle point to your "load/sensor"), then often you don't need to add any extra resistor (I say often, because there are still special cases where the load can draw too much current if the potentiometer is near one end, for example if it is a LED without series resistor).
If you use the potentimeter as a variable resistor (ie you use the central point and only one end), then the resistance of the potentiometer can go down to nearly zero. In some circuits, this can lead to huge currents (in others it is no problem). If it leads to big (unwanted) currents, then you need to know the maximal current (the limiting factor can be the potentiometer or the rest of the circuit). Then you compute the minimum resistor you need to keep the current acceptable when the potentiometer is zero.
If you want a more specific answer, please provide the schematics of your circuit and the datasheet of your potentiometer.
