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LM317 Adjustable Regulator Output Calculator — result sheet
Estimate an LM317-style adjustable regulator output from the reference voltage, resistor divider, and adjust-pin current, then check available input headroom.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Vout = Vref(1 + R2/R1) + IadjR2; divider current = Vref/R1; input headroom = Vin − Vout.
The resistor divider sets the adjustable regulator's nominal output, while the adjust-pin current adds a small error term. Headroom is reported so a mathematically valid output is not mistaken for proof that regulation will hold under load.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Input voltage — V; minimum 1.0E-6; maximum 1000
- Reference voltage — V; minimum 1.0E-6; maximum 100
- R1 from output to adjust — Ω; minimum 1.0E-6; maximum 1000000000
- R2 from adjust to ground — Ω; minimum 0; maximum 1000000000
- Adjust-pin current — μA; minimum 0; maximum 1000000
Worked example
| Input | Value |
|---|---|
| Input voltage | 12 |
| Reference voltage | 1.25 |
| R1 from output to adjust | 240 |
| R2 from adjust to ground | 720 |
| Adjust-pin current | 50 |
Vout ≈ 5.036 V, divider current ≈ 5.208 mA, and input headroom ≈ 6.964 V.
Assumptions and limits
- The reference voltage, resistors, and adjust current represent the chosen LM317 operating point.
- R1 is the resistor from output to adjust and R2 is from adjust to ground, matching the stated convention.
- Dropout margin, load regulation, thermal limits, ripple, protection, and the manufacturer's tolerance limits require a separate design check.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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