AMS1117 vs LM317: Which Linear Regulator Should You Use?
2026-10-09 · PartVane Electronics
Two regulators show up on a huge share of 3.3 V and 5 V boards: the fixed-output AMS1117-3.3 LDO and the adjustable LM317T. They are not drop-in swaps. This comparison uses only the Advanced Monolithic Systems AMS1117 datasheet and the Texas Instruments LM317 datasheet (SLVS044Z).
Key differences from the datasheets
| Item | AMS1117 | LM317 |
|---|---|---|
| Output type | Adjustable or fixed (1.5/1.8/2.5/2.85/3.3/5.0 V versions) | Adjustable, 1.25 V to 37 V |
| Output current | Up to 1 A | 1.5 A |
| Dropout | 1.3 V max at 0.8 A load (higher above 0.8 A) | See the datasheet curves; higher input headroom is needed than for an LDO |
| Input voltage | 15 V absolute maximum | 40 V max input-output differential |
| Minimum load | 10 mA max (adjustable version) | 10 mA max, 3.5 mA typical |
| Packages | SOT-223, TO-252, SO-8 | SOT-223, TO-263, TO-220 (varies by chip) |
| Junction temperature | -40 °C to 125 °C | See datasheet for the grade you buy |
When to pick the AMS1117-3.3
- You need a fixed 3.3 V rail from 5 V with no resistors, as in the datasheet's 5 V to 3.3 V application.
- Load is below 1 A and the input is under 15 V.
- Low dropout matters: the datasheet guarantees operation down to about 1 V input-to-output differential.
When to pick the LM317
- You need an output other than the fixed steps, set by two resistors (VOUT = 1.25 V x (1 + R2/R1) + IADJ x R2).
- You need up to 1.5 A, or a higher output up to 37 V.
- You need strong ripple rejection: the datasheet quotes 80 dB at 120 Hz with a 10 µF bypass on the ADJUST pin (new chip).
Heat is the real limit
Both are linear regulators, so dissipation is (VIN - VOUT) x IOUT. The AMS1117 datasheet gives 90 °C/W junction-to-ambient for SOT-223 and notes guaranteed power of 1.2 W for that package. Dropping 5 V to 3.3 V at 0.5 A is about 0.85 W, so copper area matters. Above that, use a switching converter.
Need either part? Check the part pages for AMS1117-3.3 and LM317T, then send an RFQ with your quantity and package.