LM317 adjustable regulator module: specs and pinout
An adjustable linear voltage regulator module built around the LM317 type. This page covers the LM317 chip; the module board (potentiometer, input diode, connectors, current rating) is not covered by an official document.
Specs
| Spec | Value | Source |
|---|---|---|
| Output voltage range | 1.25 V to 37 V, set with two resistors | source Features p.1; Recommended Operating Conditions p.6 |
| Output voltage formula | VOUT = 1.25 V x (1 + R2/R1) + IADJ x R2 | source Typical application (Equation 1), p.1 |
| Input-output differential | 3 V minimum to 40 V maximum | source Recommended Operating Conditions, p.6 |
| Output current | 0.01 A minimum load to 1.5 A maximum | source Recommended Operating Conditions, p.6 |
| Reference voltage | 1.25 V typ (1.2 V min, 1.3 V max) | source Electrical Characteristics, p.7 |
| Minimum load current | 3.5 mA typ, 10 mA max | source Electrical Characteristics, p.7 |
| Adjustment pin current | 50 uA typ, 100 uA max | source Electrical Characteristics, p.7 |
| Load regulation | 0.1% of VOUT typ, 0.5% max (10 mA to 1.5 A, 25 C) | source Electrical Characteristics, p.7 |
| Protection | Internal short-circuit current limiting, thermal overload and safe-area protection | source Features, p.1 |
| Junction temperature | 0 C to 125 C operating | source Recommended Operating Conditions, p.6 |
Power
| Value | Source | |
|---|---|---|
| Supply | Input must be at least 3 V above the output; up to 40 V differential | source Recommended Operating Conditions p.6; Electrical Characteristics p.7 |
| Current | Minimum load 3.5 mA typ (10 mA max) must be drawn for regulation | source Recommended Operating Conditions p.6; Electrical Characteristics p.7 |
Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.
The pins above are the bare LM317. The module board is not covered by an official document. The module's terminal names, current rating and how the output is adjusted are not verified.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| ADJUST (1) | Output voltage adjustment pin | Connect to a resistor divider to set VOUT | source Pin Functions, p.5 | |
| OUTPUT (2, tab) | Output voltage pin | The metal tab is connected to OUTPUT | source Pin Functions, p.5 | |
| INPUT (3) | Input voltage pin | source Pin Functions, p.5 |
Build with it
Project ideas for the LM317 adjustable regulator module. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Adjustable bench supply: The 12 V input leaves at least 3 V headroom for outputs up to about 9 V; the regulator burns (input - output) x current as heat, so keep the load small or add a heatsink. The INA226 and Uno only read the output.
- Constant-current LED test: The sheet shows one resistor of 1.25 V divided by the wanted current sets a constant current. The input must be at least LED forward voltage + 1.25 V + 3 V (the sheet's comparison table gives 4.25 V as the lowest input voltage). Only possible if the module exposes the adjust pin; the module is not documented, so otherwise use a bare LM317. The 10 mA minimum load is met by a 10-20 mA LED current. Learning project; size the resistor's power rating from the same sheet.
- Linear 5 V supply for a breadboard: 9 V in leaves 4 V of headroom over 5 V, above the 3 V minimum; the sheet requires at least 10 mA load, so a small bleed load may be needed with tiny logic circuits.
Common mistakes
- Running with the input less than 3 V above the output: the sheet's minimum input-output differential is 3 V, so a 5 V output needs at least 8 V in (source)
- Running with no load: the sheet gives a minimum load current (3.5 mA typ, 10 mA max) and the lowest recommended output current is 10 mA (source)
- Ignoring heat: dissipation is (input - output) x current and the sheet's limit is junction temperature 125 C, so a large drop at high current needs a heatsink (source)
Not covered by the official source
- Module board undocumented: current rating, input diode and potentiometer value unknown.
- Dropout and ripple values beyond the table rows used are not given here.
Sources
- link (TI LM317, SLVS044Z, Sept 1997 revised Apr 2025; maker)