LM317 Reference Tables, Pins & Specifications

Pin reference

Signal names, electrical functions and connection guidance

TO-220

Physical pin numbers3 pins

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LM317 pin functions and connections
Signal	Type	Function & connection
ADJUST	Feedback reference	The control loop holds approximately 1.25 V between OUTPUT and ADJUST. Connection guidance Connect R1 from OUTPUT to ADJUST and R2 from ADJUST to the load return. Adjustment current flows out of this pin; include IADJ × R2 when estimating output voltage. This is not a ground pin.
OUTPUT	Regulated output	Supplies the load and the external feedback divider. The metal tab is also OUTPUT. Connection guidance Connect the load and the top of R1 here. Keep the R1 connection close to the output lead. The exposed TO-220 tab and D²PAK thermal pad are electrically live at output voltage; isolate a grounded heatsink where needed.
INPUT	Unregulated input	Feeds the pass stage from a DC voltage sufficiently above the requested output. Connection guidance Place a 0.1 µF input bypass close to the device when required by the supply wiring. The 40 V absolute limit is input-to-output differential, not a recommended operating input or an unconditional output range.

Operating characteristics

ST LM317 · not LM217 or LM317B

Manufacturer-referenced values5 parameters

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Parameter	Value	Conditions / notes
Output adjustment	1.2–37 V	Requires input headroom, load and suitable cooling
Reference voltage	1.2 / 1.25 / 1.3 V	Minimum / typical / maximum; Table 4 conditions
Junction temperature	0–125°C	Selected LM317 grade
Minimum load at 40 V differential	3.5 mA typical; 10 mA maximum	Output may rise if the load is insufficient
Adjustment current	50 µA typical; 100 µA maximum	Include its contribution through R2

Base conditions: VIN − VOUT = 5 V, IOUT = 500 mA, IMAX = 1.5 A, PMAX = 20 W unless stated. These are test conditions, not a package dissipation guarantee.

Regulation and rejection

Manufacturer conditions retained

Manufacturer-referenced values5 parameters

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Parameter	Value	Conditions / notes
Line regulation at 25°C	0.01%/V typical; 0.04%/V maximum	VIN − VOUT = 3–40 V
Line regulation over temperature	0.02%/V typical; 0.07%/V maximum	VIN − VOUT = 3–40 V
Load regulation, output ≤5 V	5 mV typical; 25 mV maximum	25°C; IOUT = 10 mA to IMAX
Ripple rejection without CADJ	65 dB typical	120 Hz; 25°C
Ripple rejection with CADJ	66 dB minimum; 80 dB typical	CADJ = 10 µF; 120 Hz; 25°C

The adjustable output and test load affect which row applies; consult Table 4 for complete conditions.

A nominal 5 V supply

9 V input · 120 Ω / 360 Ω divider

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
R1 · OUTPUT to ADJUST	120 Ω	Reference current ≈ 1.25 / 120 = 10.42 mA
R2 · ADJUST to GND	360 Ω	Nominal resistor ratio 3:1
Ideal output	5.00 V	1.25 × (1 + 360 / 120)
Including typical IADJ	5.018 V	Adds 50 µA × 360 Ω = 18 mV
Input bypass	0.1 µF	Place close to the input and return
Output capacitor	1 µF tantalum	Illustrative transient improvement from manufacturer guidance

Use resistor and capacitor ratings appropriate to the circuit. The drawing omits optional adjustment bypass and its associated protection diode.

Headroom and thermal design

Current ratings require cooling

Manufacturer-referenced values5 parameters

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Parameter	Value	Conditions / notes
Pass-stage estimate	PD ≈ (VIN − VOUT) × IOUT	Include divider current in IOUT
TO-220 RθJC	5°C/W	Package reference; actual mounting matters
D²PAK RθJC	3°C/W	Package reference; actual PCB copper matters
Overload protections	Current, thermal and safe-area protection	Do not use protection as normal regulation
High differential voltage	Available current decreases	See manufacturer curves and operating limits

The LM317 is a linear regulator: excess voltage is dissipated rather than efficiently converted.

Package and stress limits

LM317T · TO-220

Manufacturer-referenced values5 parameters

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Parameter	Value	Conditions / notes
Connections	1 ADJUST · 2 OUTPUT · 3 INPUT	Follow the selected package orientation
Tab / thermal pad	OUTPUT · pin 2	Not GND
Input-to-output absolute maximum	40 V	Stress rating; not a normal design target
Storage temperature	−65 to +150°C	Unpowered
Lead pitch	2.54 mm	Verify the selected manufacturer drawing

The same three numbers have different functions from a 7805. Do not substitute without checking connections.