DC Barrel Jack Symbol
Definition: The DC Barrel Jack symbol represents a coaxial power connector—consisting of a cylindrical sleeve (negative/ground) and a central pin (positive)—used to supply DC power to electronic equipment; it is shown in schematics as a two-terminal connector block with a Center (+) pin and a Sleeve (−) pin, with the most common size being the 5.5 mm outer-diameter / 2.1 mm inner-pin variant.
Also known as: barrel connector, DC barrel connector, coaxial power connector, DC power jack, barrel plug, 5.5/2.1 connector, 5.5/2.5 connector.
What the DC Barrel Jack symbol means
The DC Barrel Jack symbol denotes the mechanical DC power connector found on the majority of consumer and hobbyist electronics equipment such as Arduino boards, benchtop power supplies, routers, and audio equipment. The jack (socket, female) is the board-mounted receptacle and the plug (male, attached to the power adapter cable) mates with it to deliver low-voltage DC power.
In a schematic, the DC barrel jack symbol marks the primary power entry point of the circuit. The center pin carries the positive supply voltage and the outer sleeve carries the return (negative or ground). Polarity convention is critical: the vast majority of modern DC barrel connectors follow centre-positive polarity, but centre-negative connectors do exist (particularly in older guitar effects pedals), making polarity marking essential on every schematic.
How to identify the DC Barrel Jack symbol
The DC Barrel Jack symbol is a two-terminal connector block labelled 'DC Barrel Jack' or 'PWR'. Two pins are shown: Center (+) representing the inner positive pin, and Sleeve (−) representing the outer cylindrical ground sleeve. Some schematic tools use a coaxial connector glyph—a circle with an inner dot for the centre pin and a ring for the sleeve—to represent the jack. The symbol is always annotated with polarity markings to prevent incorrect power adapter connection.
Function in a circuit
The DC barrel jack provides a quick-connect mechanical interface for DC power supply to a PCB or device. The centre pin and sleeve make simultaneous contact when the plug is fully inserted, supplying the DC rail. Switched variants include a third pin (normally-closed switch) that opens when the plug is inserted, commonly used to disconnect an internal battery when an external supply is connected.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60130-10 covers coaxial connectors; DC power barrel connectors are also addressed in IEC 61076-2. The most common barrel sizes follow IEC and EIAJ standards: EIAJ RC-5320A defines voltage-coded barrel connector sizes used in Japanese consumer electronics. |
|---|---|
| ANSI/IEEE 315 | There is no dedicated ANSI Y32.2 / IEEE 315 symbol for a DC barrel jack. It is represented as a generic two-terminal connector in IEEE 315, with pin labels identifying the function. |
| Key difference | Neither IEC 60617 nor IEEE 315 defines a unique standardised glyph for the DC barrel jack; both treat it as a labelled connector. The mechanical size standards (EIAJ RC-5320A, IEC 60130-10) govern the physical dimensions rather than the schematic symbol. |
Terminals / pins
| Pin | Name |
|---|---|
| center | Center (+) |
| sleeve | Sleeve (-) |
Typical values
Common outer diameters: 5.5 mm (most common), 6.3 mm, 3.5 mm, 2.5 mm. Common centre pin diameters: 2.1 mm, 2.5 mm, 1.7 mm, 1.35 mm, 0.7 mm. Voltage range: 3–24 V DC typical (rated up to 48 V DC for some variants). Current rating: 1–5 A depending on connector size and contact material. Polarity: centre-positive (most common in modern equipment) or centre-negative (some audio/guitar equipment).
Where the DC Barrel Jack symbol is used
- Arduino Uno and Mega boards (5.5/2.1 mm, 7–12 V input to onboard regulator).
- Raspberry Pi 4 uses USB-C for power; older models (Pi 2/3) used micro-USB; Pi accessories use barrel jacks.
- Benchtop variable power supplies with standard 5.5/2.1 mm output barrel sockets.
- CCTV cameras and IP cameras powered by 12 V DC via 5.5/2.1 mm barrel connectors.
- Laptop power adapters and chargers with proprietary barrel sizes (Dell, HP, Lenovo older models).
- Guitar effects pedals (often centre-negative, 5.5/2.1 mm, 9 V DC).
- LED strip driver modules and DC power distribution boards with multiple barrel sockets.
Example
An Arduino-based sensor node uses a DC barrel jack (5.5/2.1 mm) as its sole power connector. The schematic shows the Barrel Jack symbol with Center (+) connected to the Arduino VIN pin through a Schottky diode (reverse-polarity protection), and Sleeve (−) connected to GND. A 9 V, 1 A wall-wart adapter with a centre-positive 5.5/2.1 mm plug connects to the jack, powering the board's onboard 5 V regulator.
Key facts
- The DC Barrel Jack is a coaxial power connector with a Centre (+) inner pin and a Sleeve (−) outer conductor; the most common size is 5.5 mm outer diameter with a 2.1 mm centre pin.
- Centre-positive polarity (positive on the centre pin) is the modern standard for most hobbyist and consumer DC equipment; centre-negative polarity exists and must be verified before connecting any adapter.
- The two schematic pins are Center (+) for the positive supply and Sleeve (−) for the ground/negative return.
- Switched barrel jacks include a third, normally-closed contact that disconnects an internal battery when an external power plug is inserted—a key feature in portable equipment designs.
- Common voltage and current ratings for 5.5/2.1 mm connectors are 2–24 V DC and 1–5 A; exceeding the current rating causes overheating and contact failure.
- Neither IEC 60617 nor IEEE 315 defines a unique standardised glyph for the barrel jack; both represent it as a labelled generic connector with pin designations.
- EIAJ RC-5320A specifies colour-coded barrel connector sizes used in Japanese consumer electronics: each physical size corresponds to a specific voltage range to prevent misconnection.
Frequently asked questions
What does the DC barrel jack symbol look like on a schematic?
The DC barrel jack symbol is a two-terminal connector block labelled 'DC Barrel Jack' or 'PWR Jack'. It shows two pins: Center (+) for the inner positive contact and Sleeve (−) for the outer ground sleeve. Some tools render it as a coaxial glyph (concentric circle with centre dot).
What is the polarity of a DC barrel connector?
The vast majority of modern DC barrel connectors are centre-positive: the inner pin carries positive voltage and the outer sleeve is ground. However, centre-negative connectors exist—notably on many guitar effects pedals—where the outer sleeve is positive. Always verify polarity markings on the equipment label or schematic before connecting.
What is the most common DC barrel connector size?
The most common DC barrel connector size is 5.5 mm outer diameter with a 2.1 mm centre pin, widely used on Arduino boards, CCTV equipment, and 12 V DC power supplies. The 5.5/2.5 mm variant (2.5 mm centre pin) is also common; plugging a 2.1 mm plug into a 2.5 mm socket (or vice versa) may result in a loose, unreliable connection.
What are the two pins of the DC barrel jack?
The DC barrel jack has two electrical pins: Center (+), which is the inner cylindrical pin that carries the positive DC supply, and Sleeve (−), which is the outer cylindrical shell that carries the ground or negative return.
What standard defines the DC barrel jack connector?
The mechanical dimensions of barrel connectors are governed by IEC 60130-10, IEC 61076-2, and the EIAJ RC-5320A voltage-coding standard. The schematic symbol is treated as a generic labelled connector per IEEE 315 / ANSI Y32.2 and IEC 60617; there is no dedicated barrel-jack schematic symbol in either standard.
How do I protect against reverse polarity on a DC barrel jack?
Common protection methods include a series Schottky diode between the Centre (+) pin and the power rail (low V_F drop, fast response), a P-channel MOSFET in series with the positive rail (low on-resistance, minimal voltage drop), or a crowbar circuit with a fuse. The Schottky diode method (e.g. 1N5819) is the simplest and most common in hobbyist designs.
What is a switched DC barrel jack?
A switched barrel jack has a third pin—a normally-closed (NC) switch contact—that is connected to the negative return of an internal battery. When no plug is inserted, the NC contact completes the battery circuit, powering the device from the battery. When a DC plug is inserted, it mechanically opens the NC contact, disconnecting the battery and transferring power to the external supply.
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