LM317 Pinout
LM317 Adjustable Regulator · Adjustable linear regulator, 1.25V reference; two external resistors set the output 1.25–37V.
🛑 TO-220 with the front (printed face) toward you and the pins down, left to right is ADJ-OUT-IN — a different order from the 78xx series (IN-GND-OUT), which is the most common wiring mistake. The heatsink tab is connected to OUT (not ground).
| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | ADJ · Adjust | Control | Adjust pin (connects to the divider resistors that set the output) |
| 2 | OUT · Vout | Output | Output (connected to the heatsink tab) |
| 3 | IN · Vin | Power | Input voltage (≥3V above the output) |
How to read the LM317 pinout
- 01
Find pin 1
One end of the chip has a half-circle notch or a dot; with the notch facing up, the top-left pin is pin 1.
- 02
Count counter-clockwise
Count counter-clockwise from pin 1: go down the left side first, then up the right side from the bottom.
- 03
Check the table below
Look up each pin's function by number in the table below; power/ground are color-coded, and alternate-function signals are in parentheses.
Frequently asked questions
What is the LM317 pin order?
With the front (printed face) toward you and the pins down, left to right is ADJ-OUT-IN. Note the metal heatsink tab is connected to OUT, not ground.
How do I compute the output voltage?
Vout ≈ 1.25 × (1 + R2/R1), with R1 between ADJ↔OUT (typically 240Ω) and R2 between ADJ↔GND.
Can the LM317 and 7805 be swapped directly?
No! Their pin definitions differ (the 317 is ADJ-OUT-IN, the 7805 is IN-GND-OUT), and the 317 needs external resistors to set the voltage.
Pinout data comes from TI LM317 datasheet (standard TO-220 numbering). Refer to the actual device datasheet as authoritative for the pinout.