# LM317 adjustable regulator: 1.25 to 37 V, 1.5 A and the heat it makes

> A three-pin adjustable linear regulator: datasheet limits, how two resistors set the voltage, and why dropping a big voltage at high current needs a heatsink.

Canonical: https://roboticsengineering.in/components/lm317-adjustable-regulator/ | Published: 2026-11-03 | Updated: 2026-11-03

**The LM317 is a three-pin adjustable linear regulator: it gives an output from 1.25 V to 37 V at up to 1.5 A, set by two resistors, and has current limiting, thermal protection and safe-area protection built in.** It is a simple way to make an odd rail such as 6 V for servos from a higher battery. Because it is linear, it turns the voltage it drops into heat, so it suits low-current rails far better than motors. Figures are from the Texas Instruments LM317 datasheet SLVS044Z.

## Key specifications

| Output voltage | 1.25–37 V adjustable |
| --- | --- |
| Output current | 1.5 A |
| Input-output differential | 3–40 V |
| Line regulation | 0.01 %/V typical |
| Load regulation | 0.1 % typical |
| Protection | current limit, thermal overload, safe area |
| Packages | SOT-223, TO-263, TO-220 |

## What the datasheet promises

| Item | Datasheet value |
| --- | --- |
| Output voltage range | 1.25 V to 37 V, adjustable |
| Output current | 1.5 A |
| Input-to-output differential | 3 V to 40 V in the recommended operating conditions |
| Line regulation | 0.01 percent per volt, typical |
| Load regulation | 0.1 percent, typical |
| Protection | Internal short-circuit current limiting, thermal overload protection, output safe-area compensation (new chip) |
| Packages | SOT-223 (4 pin), TO-263 (3 pin), TO-220 (3 pin) |

The datasheet says the overload protection stays working even if the adjust pin is disconnected, and that capacitors are typically not needed unless the regulator sits more than about 6 inches from the input filter capacitors. It also describes an optional output capacitor to improve transient response, which is worth adding on a robot rail that sees motor noise.

## The heat problem

A linear regulator dissipates the voltage drop times the current. Dropping a 12 V battery to 6 V at 1 A makes 6 W of heat, far beyond what a bare TO-220 can lose to air; it needs a heatsink, and at that point a buck converter such as the [LM2596 module](https://roboticsengineering.in/components/lm2596-buck-converter/) wastes much less. The input must also stay at least 3 V above the output for the regulator to work, so a 7.4 V pack cannot give a stable 6 V rail at heavy load.

## Setting the voltage

The datasheet circuit uses a 240 Ω resistor R1 between the output and adjust pins and a second resistor R2 from the adjust pin to ground. The output is about 1.25 V times (1 + R2 divided by R1), plus a very small adjust-pin current term. For 6 V with R1 = 240 Ω, R2 comes to about 960 Ω; check the result with a multimeter before connecting a load, as in [checking for shorts before power on](https://roboticsengineering.in/fix/check-short-circuit-with-multimeter-before-power-on/).

## Sources and further reading

- [Texas Instruments LM317 datasheet (SLVS044Z)](https://www.ti.com/lit/ds/symlink/lm317.pdf) — the ranges, regulation and protection above.

Last reviewed: November 2026. The 6 V example is a calculation from the datasheet’s 1.25 V reference and 240 Ω R1, not a measurement. No price is quoted because it has not been checked.