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# LM1117 3.3V Regulator (TO-220)

TI's 800 mA low-dropout regulator in TO-220: a fixed 3.3 V from a 5 V or higher supply, with about 1.2 V of dropout.

Source page: https://www.tinkered.ai/components/lm1117t-3v3
Datasheet: https://www.ti.com/lit/ds/symlink/lm1117.pdf

## In short

The LM1117T-3.3 is a 3.3 V low-dropout linear regulator in a TO-220 package that delivers up to 800 mA with a typical dropout of 1.2 V at full load (TI LM1117 datasheet, p. 1). Looking at its front, pin 1 is GND, pin 2 (and the tab) is the 3.3 V output, pin 3 is the input, which takes up to 15 V (pp. 3, 4). Put a 10 µF capacitor on the output, required for stability, and another on the input (pp. 14, 15).

The LM1117 is a three-terminal low-dropout (LDO) linear regulator from Texas Instruments, made in adjustable and fixed 1.8 V, 2.5 V, 3.3 V and 5 V versions. The LM1117T-3.3 is the fixed 3.3 V version in the through-hole TO-220 package, which stands in a breadboard and bolts to a heatsink (TI LM1117 datasheet, pp. 1, 3).

It drops a higher voltage to a steady 3.3 V for up to 800 mA. Its dropout is 1.2 V typical at 800 mA, 1.1 V at 100 mA, so a 5 V USB rail or Arduino 5V pin is enough to run it; TI specifies the 3.3 V output from 4.75 V to 10 V in, and the input may go up to 15 V (pp. 4, 5, 6). Inside are current limiting at 1.2 A typical and thermal shutdown (pp. 1, 6).

Unlike a ready-made AMS1117 module, the bare LM1117 has no capacitors of its own. TI requires at least 10 µF on the output, a tantalum with an ESR between 0.3 Ω and 22 Ω, to keep the regulator stable, and recommends 10 µF on the input (pp. 14, 15). It is a linear regulator, so every volt it drops at the load current turns into heat in its tab.

## Agent rules

Follow these when you wire this part or write code for it.

- Do: A 10 µF capacitor from OUT to GND (and one from IN to GND): TI's datasheet requires the output one for stability; without it the regulator can oscillate.
- Do: IN 4.75-10 V, from a supply: a board's 5V or VIN pin, a 5 V rail (an MB102 side at 5 V), a 9 V battery, a 4xAA pack.
- Do: GND to the circuit's ground, shared with the board that talks to the 3.3 V part.
- Do: OUT feeds only 3.3 V parts. The tab is OUT too: nothing metal may touch it.
- Do: The supply goes to IN (pin 3), never to OUT: fed through OUT it regulates nothing.
- Do: Prefer the AMS1117 module when the user just needs 3.3 V on a breadboard (capacitors on board, fewer parts); use the LM1117 when they ask for it, or to learn how a bare regulator is wired.
- Never: No LM1117 without its output capacitor.
- Never: No IN above 15 V; NO OUT on a 5 V rail or a board's 5V pin.
- Never: No swapping the pins: pin 1 is GND, not IN (unlike the 7805's IN-GND-OUT).
- On an ESP32 DevKit V1: IN is on VIN, which gives about 5 V only while the board is powered from USB.
- On a Raspberry Pi Pico: IN is on VBUS, which gives about 5 V only while the board is powered from USB.

## Pinout

| Pin | Function | Type |
| --- | --- | --- |
| GND | 1 GND (ADJ/GND) | power in |
| OUT | 2 VOUT (3.3 V, also the tab) | power out |
| IN | 3 VIN (4.5-15 V) · 3.3 V (max 15 V) | power in |

## Wiring

### Arduino Uno

| LM1117 3.3V Regulator (TO-220) | Arduino Uno | Note |
| --- | --- | --- |
| IN | 5V |  |
| GND | GND |  |

### ESP32 DevKit V1

| LM1117 3.3V Regulator (TO-220) | ESP32 DevKit V1 | Note |
| --- | --- | --- |
| IN | VIN |  |
| GND | GND |  |

Warning: IN is on VIN, which gives about 5 V only while the board is powered from USB.

### Raspberry Pi Pico

| LM1117 3.3V Regulator (TO-220) | Raspberry Pi Pico | Note |
| --- | --- | --- |
| IN | VBUS |  |
| GND | GND |  |

Warning: IN is on VBUS, which gives about 5 V only while the board is powered from USB.

## Specifications

| Spec | Value | Source |
| --- | --- | --- |
| Output voltage | 3.3 V (3.267 V to 3.333 V at 10 mA, 25 °C) | TI LM1117 datasheet (SNOS412Q), p. 5 |
| Output current | 800 mA | TI LM1117 datasheet, p. 1 |
| Dropout voltage | 1.1 V at 100 mA, 1.15 V at 500 mA, 1.2 V at 800 mA (typical) | TI LM1117 datasheet, p. 6 |
| Input voltage | 15 V max recommended; 20 V absolute maximum | TI LM1117 datasheet, p. 4 |
| Current limit | 800 mA min, 1200 mA typical, 1500 mA max | TI LM1117 datasheet, p. 6 |
| Quiescent current | 5 mA typical, 10 mA max | TI LM1117 datasheet, p. 6 |
| Output capacitor | 10 µF minimum (tantalum), ESR 0.3 Ω to 22 Ω | TI LM1117 datasheet, p. 15 |
| TO-220 pinout | 1 ADJ/GND, 2 VOUT (and tab), 3 VIN | TI LM1117 datasheet, p. 3 |
| Junction temperature | 0 °C to 125 °C (LM1117); thermal shutdown built in | TI LM1117 datasheet, pp. 4, 18 |
| Dimensions | 10.16 × 4.57 × 28.7 mm | Tinkered component registry |
| Weight | 2 g | Tinkered component registry |

## Circuit notes

- Pin order is GND, OUT, IN from left to right on the front, not the IN, GND, OUT of a 7805, and the metal tab is the output (TI datasheet, p. 3). Keep the tab away from other metal or insulate it on a heatsink.
- Fit at least 10 µF from OUT to GND, close to the pins. TI asks for a tantalum with an ESR of 0.3 Ω to 22 Ω; more capacitance only improves stability (p. 15). A 10 µF capacitor on IN is recommended too (p. 14).
- Feed IN from 4.75 V up to 15 V for a fully specified 3.3 V output (pp. 4, 5): a 5 V rail, an Arduino's 5V or VIN pin, a 9 V battery or a 12 V adapter. From a 3.3 V or 3.7 V source the output follows the input minus the dropout and sags.
- Heat is (VIN minus 3.3 V) times the load current, plus VIN times the 5 mA ground current (p. 18). From 5 V at 500 mA it dissipates about 0.9 W; from 12 V at the same current, about 4.4 W, which needs a heatsink. The junction must stay under 125 °C, and thermal shutdown cuts the output if it does not.
- Share the regulator's GND with the microcontroller that talks to the 3.3 V part, and feed only 3.3 V parts from OUT.

## Common mistakes

- **Wiring it like a 7805.** The 7805 is IN, GND, OUT; the LM1117 is GND, OUT, IN (TI datasheet, p. 3). Swapping them feeds the supply into the output or ground and the part regulates nothing.
- **Leaving out the output capacitor.** The LM1117 needs at least 10 µF on its output, with an ESR between 0.3 Ω and 22 Ω, to stay stable (p. 15). Without it the output can oscillate and devices on the 3.3 V rail reset at random.
- **Using only a tiny ceramic on the output.** A small multilayer ceramic alone can have an ESR below the 0.3 Ω TI asks for (p. 15). Use a 10 µF tantalum, or an electrolytic of 10 µF or more, as the output capacitor.
- **Feeding it from 3.3 V or a single Li-ion cell.** With about 1.2 V of dropout at 800 mA (p. 6), the output cannot reach 3.3 V from a 3.3 V or 3.7 V source. Use 4.75 V or more in, or a lower-dropout regulator.
- **Pulling high current from 12 V without a heatsink.** All of the 8.7 V dropped from 12 V to 3.3 V turns into heat. At a few hundred milliamps that is several watts, enough to trip the thermal shutdown (p. 18). Add a heatsink or use a buck converter.

## Questions

### What is the LM1117T-3.3 pinout?

Facing the printed side with the leads down: pin 1 is ADJ/GND, pin 2 is VOUT (3.3 V) and pin 3 is VIN. The metal tab is also VOUT (TI LM1117 datasheet, p. 3).

### What input voltage does the LM1117 3.3 V need?

TI specifies the 3.3 V output from 4.75 V to 10 V in across the full load range, and the input may go up to 15 V (datasheet, pp. 4, 5). The absolute maximum is 20 V. Below about 4.5 V the output drops with the input.

### Can I power an ESP8266 or ESP32 from an LM1117 3.3 V?

Yes, from 5 V in. It delivers up to 800 mA (datasheet, p. 1), enough for the Wi-Fi bursts, as long as the 10 µF output capacitor is fitted and the input is 4.75 V or more. Add extra bulk capacitance near the module for its current spikes.

### Why is my LM1117 getting hot or its output oscillating?

Hot: it burns (VIN minus 3.3 V) times the current (datasheet, p. 18), so a high input voltage at a large load needs a heatsink or a buck converter. Oscillating or noisy: check the output capacitor, at least 10 µF with an ESR of 0.3 Ω to 22 Ω, placed close to the pins (p. 15).

### LM1117 vs AMS1117: what is the difference?

They share the 1117 pinout and job. TI's LM1117 is rated for 800 mA and 15 V of recommended input (TI datasheet, pp. 1, 4); AMS's AMS1117 is rated for 1 A with a 15 V absolute maximum input (AMS1117 datasheet, pp. 1, 2). Both need an output capacitor; small AMS1117 modules come with theirs fitted.

### LM1117 vs a buck converter like the LM2596?

The LM1117 is simple, quiet and cheap, but wastes the dropped voltage as heat. A buck converter switches instead: TI's LM2596 reaches 73 % to 90 % efficiency at 3 A in its datasheet's test circuits (LM2596 datasheet, p. 6). For large drops at high current, use a buck.

## Related parts

- [Electrolytic Capacitor (470µF)](https://www.tinkered.ai/components/capacitor-electrolytic-470uf.md): wired with it in its circuit
- [Red LED](https://www.tinkered.ai/components/led-red.md): wired with it in its circuit
- [220Ω Resistor](https://www.tinkered.ai/components/resistor-220.md): wired with it in its circuit
- [MB102 Breadboard Power Module](https://www.tinkered.ai/components/mb102-power-module.md): same job: regulates a supply
- [AMS1117 3.3V Regulator Module](https://www.tinkered.ai/components/ams1117-3v3-module.md): same job: regulates a supply
- [LM2596 Buck Converter Module](https://www.tinkered.ai/components/lm2596-buck-module.md): same job: regulates a supply

## Try it

Tinkered can design a circuit with the LM1117 3.3V Regulator (TO-220), draw its schematic and check it. Free to start at https://www.tinkered.ai.