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Is it possible to output LM317 in a parallel circuit where there are 2 voltage and has a different output voltage where one is 12V constant and the other is adjustable using potentiometer?

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    \$\begingroup\$ The LM 317 requires a 2 volt or so "headroom" (minimum voltage drop between input and output) so, with a 36 volt output, you won't be able to get more than about 34 volts output (probably lower at higher currents). \$\endgroup\$ – Peter Bennett Jul 24 '19 at 2:41
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    \$\begingroup\$ your question is not clear. Obviously a single LM317 regulator can only give you a single regulated voltage. You can have a switch to flip between a constant 12V and a variable voltage. This switch would allow the adjust pin to select either the potentiometer or a fixed resistor. R1 is usually kept constant because it is also current limiting resistor. \$\endgroup\$ – Indraneel Jul 24 '19 at 2:57
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There is no problem connecting two or more voltage regulators to a common source, so you could have one LM317 set up as a fixed 24 volt (for example) regulator, and another LM317 as an adjustable regulator both connected to your 36 volt source.

You must provide appropriate heat sinks to deal with the power dissipation in each regulator, and ensure that the total current drawn from the two regulators does not exceed the capabilities of the 36 volt source.

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  • \$\begingroup\$ What I mean about that is only using one voltage regulator (LM317) and output 2 different voltage at once, not two or more voltage regulators. \$\endgroup\$ – unknown Jul 24 '19 at 5:25
  • \$\begingroup\$ @unknown It is not rational to expect multiple regulated voltages from a single source without using multiple voltage regulators. What gave you the notion that this might be possible? They do not have to be the same type of regulator. \$\endgroup\$ – Sparky256 Jul 24 '19 at 6:10
  • \$\begingroup\$ @sparky26 I was thinking about the parallel circuit implementation, so I thought of giving it a go for the lm317 voltage regulator, two outputs, one is a constant 12V and for the other one is adjustable, I wouldn't mind if the adjustable wouldn't reach its maximum voltage. the 12v is for the fan to keep heat sink cool and the adjustable is for the Arduino or other module. \$\endgroup\$ – unknown Jul 24 '19 at 7:20
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If you want 2 separate regulated voltages, then you will need 2 regulators as the LM317 has only one output. The circuit shown in your question provides an adjustable output using a potentiometer. You can get a fixed 12 volt output by using a 12 volt zener diode fed from the input source feeding the LM317. However it will not be as well regulated as it would if derived from a LM317.

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