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Barrel Jack

DC Barrel Connector

Standard: EIAJ (some sizes), otherwise de facto Last updated: 2025-01-21

Barrel connectors are one of the most frustrating connector types due to complete lack of standardization. Dozens of sizes exist, polarity varies by manufacturer, and voltage ranges from 3V to 48V. The only way to know compatibility is to check all specifications. Despite this chaos, they remain common because they're cheap, simple, and adequate for low-power DC applications. USB-C Power Delivery is slowly replacing them.

Quick Specifications

Max Speed

0 Mbps

Max Power

120W

Pins

2

Reversible

No

⚠️ Common Confusion Points

  • 5.5x2.1mm and 5.5x2.5mm look nearly identical but 2.1mm plugs are loose in 2.5mm jacks
  • Center positive vs center negative - ALWAYS check polarity before connecting, wrong polarity can destroy devices
  • Voltage is not standardized - a 12V device on a 19V adapter will likely be damaged
  • Same size connector does NOT mean compatible - check voltage, current, AND polarity
  • Barrel jacks have no keying or protection against wrong polarity/voltage
  • EIAJ standardized sizes exist but most manufacturers ignore them
  • Many universal adapters come with multiple tips but selecting wrong voltage is dangerous

Protocols & Versions

Protocol Data Rate Power Max Length
5.5x2.1mm (5.5x2.1mm) DC Power Typically 12V-24V, up to 5A Varies by voltage/current
5.5x2.5mm (5.5x2.5mm) DC Power Typically 12V-24V, up to 5A Varies by voltage/current
3.5x1.35mm (3.5x1.35mm) DC Power Typically 5V, up to 2A Varies by voltage/current
EIAJ-4 (Yellow Tip) (EIAJ-4) DC Power 10.5V-13V nominal Varies by voltage/current

5.5x2.1mm Features

Most common size Center positive (usually)

Cable requirements: 5.5mm outer, 2.1mm inner diameter

5.5x2.5mm Features

Slightly larger inner pin Common on laptops

Cable requirements: 5.5mm outer, 2.5mm inner diameter

3.5x1.35mm Features

Smaller devices USB hubs, small electronics

Cable requirements: 3.5mm outer, 1.35mm inner diameter

EIAJ-4 (Yellow Tip) Features

Standardized voltage range Yellow tip indicates EIAJ-4

Cable requirements: 4.75mm outer, 1.7mm inner

Connector Specifications

Shape
cylindrical coaxial
Pins
2
Width × Height
5.5 × 5.5 mm
Depth
9.5 mm
Reversible
No

Electrical Specifications

Max Voltage
48V
Max Current
5A
Max Power
120W

Compatibility

Can Adapt To

  • USB-C PD (with voltage conversion)
  • Other barrel sizes

Can Adapt From

  • USB-C PD (trigger boards)
  • AC adapters

Common Uses

  • Laptops (older models)
  • Routers and modems
  • LED strips
  • CCTV cameras
  • Audio equipment
  • Arduino and electronics projects
  • External hard drive enclosures
  • Monitors
  • Network switches

Buying Guide

ALWAYS match voltage (exact), polarity (center positive/negative), current (adapter must meet or exceed device requirement), AND physical size. When in doubt, measure your existing adapter with calipers. Universal adapters are convenient but risky - triple-check settings. Consider switching to USB-C PD for new projects.

Also Known As

Barrel jack DC jack Barrel plug Coaxial power connector

Data Sources