What Is the AMS1117? 3.3V LDO Regulator: Pinout and Uses
The AMS1117 is a low-dropout (LDO) linear voltage regulator, extremely common on development boards especially for producing 3.3 V from 5 V. With ~1.1 V dropout it regulates even when the input-output difference is small (which the 7805 cannot). It needs an output capacitor of ≥ 22 µF for stability; being linear, it heats up at a large difference/high current.
The AMS1117 is a low-dropout (LDO) linear voltage regulator, extremely common on development boards (ESP, STM32, sensor modules) especially for producing 3.3 V. It comes in fixed versions (3.3 V / 5.0 V / 1.8 V) and an adjustable version. For the concept, see what is a voltage regulator.
What is the AMS1117 used for?
Its most typical use is producing 3.3 V from 5 V (e.g. powering an ESP8266/ESP32 from 5 V USB). Thanks to its low dropout it can regulate even when the input-output difference is small — something the 7805 cannot do.
AMS1117 pinout (SOT-223, fixed version)
| Pin | Function |
|---|---|
| 1 | GND |
| 2 | OUTPUT (Vout) |
| 3 | INPUT (Vin) |
| Tab | OUTPUT (Vout) |
On the adjustable (ADJ) version, pin 1 is the ADJ (feedback) pin instead of GND.
Key electrical specifications
| Parameter | Typical value |
|---|---|
| Output | Fixed 3.3 / 5.0 / 1.8 V or adjustable |
| Output current | up to ~1 A |
| Dropout | ~1.1–1.3 V (at 1 A) |
| Maximum input | ~15 V (absolute ~18 V) |
Output capacitor for stability
The AMS1117 needs an output capacitor to work stably — typically ≥ 22 µF (tantalum or a good ceramic/electrolytic). Otherwise the output can oscillate. An input capacitor is also recommended.
Limitations
- It is linear; at a large difference/high current it heats up (e.g. 5 V→3.3 V at 1 A ≈ 1.7 W). For efficiency use a buck (LM2596).
- Unstable without an output capacitor.
- ~1.1 V dropout; the input must be that much above the output.
AMS1117 equivalents and alternatives
- LD1117 / LM1117: very close equivalents.
- MCP1700 / HT7333: very low quiescent 3.3 V LDOs (for battery).
- LM2596: an efficient buck.
Find it in our catalog
To compare price and stock for the AMS1117 and its alternatives, use the AMS1117 search.