DC Barrel Jack 5.5x2.1 Pinout
Common 5.5 mm OD / 2.1 mm ID coaxial DC power connector for adapters and dev boards.
Overview
The 5.5 x 2.1 mm barrel (coaxial) connector carries DC power over two concentric conductors: a center pin (2.1 mm bore) and an outer barrel sleeve (5.5 mm outer diameter). The standard plug is a tip-positive male.
On the common center-positive convention the inner pin is positive and the outer sleeve is ground/negative. Many panel jacks add a switch terminal tied to the sleeve, opened when a plug is inserted.
Pinout
| Pin | Name | Function | Description |
|---|---|---|---|
| TIP | Center (+) | POWER / SIGNAL | Center pin, 2.1 mm bore - positive supply on the standard center-positive convention |
| SLEEVE | Barrel (-) | GND | Outer 5.5 mm sleeve - ground / negative return |
| SW | Switch | GND | Optional normally-closed switch lug (panel jacks) tied to sleeve, opened when a plug is inserted |
Notes
- Center-positive is most common, but polarity is not guaranteed - check the device's polarity symbol.
- 5.5 mm is the outer barrel diameter, 2.1 mm the inner pin bore; a 5.5x2.5 mm variant looks identical.
Reference: CUI Devices - barrel jack datasheet· verified 2026-06-27