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LM317 Ideal Resistor Divider Voltage

The ideal divider model uses a 1.25 V reference and ignores adjustment-pin current: Vout=1.25(1+R2/R1). R1 connects output to adjustment; R2 connects adjustment to ground.

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

Worked example: voltage = 5. See the assumptions for units and model limits.

voltage=1.25*(1+(R2/R1))

Worked example

Enter these known values and leave the other values blank.

Resistor (R1)
240 Ω
Resistor (R2)
720 Ω
Output voltage
5 V

Assumptions and limitations

  • The ideal divider model uses a 1.25 V reference and ignores adjustment-pin current: Vout=1.25(1+R2/R1). R1 connects output to adjustment; R2 connects adjustment to ground.
  • Actual operation also depends on input headroom, reference tolerance, minimum load, heat, compensation and device ratings in the manufacturer datasheet. This computes the nominal divider relation only.

Common questions

What does this model assume?

The ideal divider model uses a 1.25 V reference and ignores adjustment-pin current: Vout=1.25(1+R2/R1). R1 connects output to adjustment; R2 connects adjustment to ground.

Can I solve for a different value?

Clear the desired editable unknown and enter sufficient independent known values. Unit selectors preserve quantities; singular or unsupported inverse branches remain incomplete.

References

Replace external illustrative media with authored accessible descriptions of all relationships and beat-unit variants, preserving original identities and conditions.

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