LM317 vs LM317L — Full Comparison & Selection Guide | ICMASS

LM317 vs LM317L: Side-by-Side Comparison

Key Differences

Output Current: 15x Apart, With a Middle Tier

TI's own family runs LM317 at 1.5A, LM317M at 0.5A, LM317L at 100mA. And the LM317L's current limit is a band — 100mA min, 300mA max. A batch can land anywhere inside, so you design to 100mA and treat extra as margin, never as spec.

Minimum Load: 10mA vs 5mA Is the Sneaky One

Both regulators return their internal bias current through the output pin, so an idle output floats up without a minimum load. The LM317L needs 5mA worst case; the LM317 needs 10mA. The classic 240Ω divider pulls only 5.2mA — fine for the “L”, short for the big one.

Dissipation: The “L” Runs Out of Watts Before Milliamps

The SOIC-8 LM317L is rated 625mW. At a 40V differential that allows roughly 15mA — the 100mA rating only lives at small input-output gaps. The heatsinked TO-220 is where actual watts belong.

Temperature and Footprint: The Small Part Wins One

The TI LM317L-N is rated −40 to +125°C, colder than the LM317's own 0°C floor — useful for outdoor nodes and cold-start gear. Watch the vendor, though: onsemi's commercial LM317L stays at 0 to +125°C. And the footprints never interchange: three TO-220 legs versus an SOIC-8 fan-out.

When to Choose LM317 / When to Choose LM317L

Choose the LM317 when the rail must source more than 100mA, when a heatsink is already in the mechanical design, when you charge batteries or run a bench supply, and when the 240Ω divider plus a real load keeps the 10mA minimum honest.

Choose the LM317L when the load is under 100mA and the board is dense, when the supply is a 4-20mA transmitter or op-amp rail that idles near zero, when you need −40°C cold starts, and when dual-sourcing matters — TI and onsemi LM317L parts are pin-for-pin.

Frequently Asked Questions

Q1: Are the LM317 and LM317L the same chip?

A: No — same control loop, different output stage. Both hold a 1.25V reference and use the same Vout = 1.25(1 + R2/R1) formula, but the LM317 sources 1.5A from TO-220 while the LM317L tops out at 100mA in SOIC-8 or TO-92.

Q2: Can I replace an LM317 with an LM317L?

A: Only below 100mA and inside the SOIC-8's 625mW ceiling — at a 40V differential that means roughly 15mA of output. And the packages differ, so you're relaying out the board, not swapping a footprint.

Q3: Can I replace an LM317L with an LM317?

A: Electrically yes, and it's the common quick fix — but the full-size part brings a 10mA worst-case minimum load (the “L” needs only 5mA) and a TO-220 footprint. On a 15mA bias rail it's more iron than the job needs.

Q4: Why does the LM317 need 10mA of minimum load?

A: Its internal bias current returns through the output pin, so regulation needs a minimum load or the output floats up. Worst case is 10mA. The classic 240Ω divider pulls only 5.2mA — designs that idle below 10mA drop R1 toward 120Ω.

Q5: Do they share a pinout?

A: No. The TO-220 LM317 runs ADJ on pin 1, OUT on pin 2, IN on pin 3. The SOIC-8 LM317L puts VIN on pin 1, VOUT on 2/3/6/7, ADJ on 4, NC on 5/8. The “L” itself is pin-for-pin between TI and onsemi — that swap works.

Q6: Which one has lower dropout?

A: Neither wins. The LM317 is about 2V typical (2.5V worst case), and the LM317L datasheet only says “up to 2.5V” with no published curve — TI's E2E forum confirms the full characteristic was never characterized. If dropout is the deciding spec, you want an LDO, not either of these.

Q7: Which one suits a 4-20mA transmitter?

A: The LM317L. Loop currents max out at 20mA, so a 1.5A regulator is dead weight, and the SOIC-8 fits DIN-rail modules. Published 4-20mA converter designs built on the LM317L claim 0.02% linearity.

Q8: Is the LM317M a third option?

A: Yes — TI's tiering runs LM317 at 1.5A, LM317M at 0.5A, LM317L at 100mA. If your rail sits between 100mA and 500mA, the “M” is the honest middle instead of forcing a 1.5A part onto a 300mA rail.