Classic 3-terminal adjustable positive-voltage linear regulator in a TO-220 package. It holds a 1.25 V reference between OUT and ADJ, so two resistors set any output from 1.25 V to 37 V, delivering up to 1.5 A. Only two external resistors are needed (plus optional caps), and it has internal current limiting and thermal shutdown. The default adjustable bench-and-board regulator; set VOUT = 1.25 V x (1 + R2/R1).

Pinout

Pin	Name	Type	Function
1	ADJ	input	Adjustment pin. Ties to the midpoint of the external R1/R2 divider between OUTPUT and GND to program VOUT = 1.25V x (1 + R2/R1) + I_ADJ x R2. Internal reference holds this pin at 1.25V below OUTPUT. Typical adjustment-pin current is 50 μA (100 μA max).
2	OUT	power_out	Regulated output. Delivers up to 1.5A over VOUT = 1.25V to 37V (VIN-VOUT differential 3V to 40V). Also electrically bonded to the package TAB for heatsinking. Optional 1 μF output capacitor improves transient response.
3	IN	power_in	Unregulated input supply. Recommended 3V to 40V above VOUT (absolute max input-to-output differential 40V). Add a 0.1 μF input bypass if the device sits more than 6 inches from the input filter capacitors.

Key specifications

Parameter	Value
Type	Adjustable positive linear regulator
Output voltage	1.25-37 V (VREF 1.25 V)
Output current	1.5 A
Input voltage	up to 40 V (VIN-VOUT <= 40 V)
Dropout	~2 V typ
Protection	Current limit + thermal shutdown
Package	TO-220
Body (L×W×H)	10.3 × 4.6 × 15.9 mm (TO-220)

Ordering variants

Same part, different packaging or reel option.

LM317T (TO-220)
LM317KTTR (TO-263)

CAD (KiCad official)

Symbol: Regulator_Linear:LM317_TO-220
Footprint: Package_TO_SOT_THT:TO-220-3_Vertical
3D model: TO-220-3 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Texas Instruments datasheet (44 pp, sha256 323ec64a58515090, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude) — every pin and dimension is cited to a datasheet page; refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF