What Is a DC Barrel Jack?
A DC barrel jack is a cylindrical (barrel-shaped) power connector used to take DC supply from a power adapter into a board.
Its Structure
The outer metal sleeve carries one polarity, the inner center pin the other. The inner and outer diameters (e.g. 5.5 mm outer / 2.1 mm inner) determine the connector's fit; a wrong diameter won't plug in or seats loosely.
| Property | Typical |
|---|---|
| Outer diameter | 5.5 mm (common) |
| Inner pin | 2.1 / 2.5 mm |
| Polarity | Usually center-positive |
Polarity
The most critical point is polarity. In most devices the center (inner pin) is positive and the outer sleeve is negative/ground. If the polarity symbol on the adapter label isn't followed, the device is damaged.
Where Is It Used?
Routers, cameras, LED-strip supply, development boards and all small electronic devices running on a desktop adapter.
Current Limit
Barrel jacks have a typical current limit (usually a few amperes). In high-current applications the jack heats up; so at high power a thicker connector or a terminal block is preferred.
Common Mistakes
- Reverse polarity: a center-negative adapter can damage a center-positive device.
- Wrong diameter: a 2.1 mm device stays loose/without contact with a 2.5 mm plug.
- Overcurrent: the jack's current limit must not be exceeded.
Frequently Asked Questions
How is center-positive understood?+
Is every 5.5 mm jack compatible?+
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