Coaxial power connector

Common DC power connectors

A coaxial power connector is a miniature power connector used for attaching extra-low voltage devices such as consumer electronics to external electricity. Also known as barrel connectors, concentric barrel connectors or tip connectors, these small cylindrical connectors come in an enormous variety of sizes.

The primary use of these plugs is a DC connector (or sometimes AC) on the cable connected to a power supply. The matching jack or socket is then mounted in the equipment to be powered. Some of these jacks contain a normally closed switch; the switch can disconnect internal batteries whenever the power supply is connected to avoid the risk of battery leakage or explosion posed by incorrect recharging of the batteries.

Connector construction

Some power plugs are merely subminature phone plugs pressed into service as power connectors. The two connectors on the left of the picture above are subminature and miniature phone plugs respectively, the subminiature size being 3/32 inch and the miniature being 1/8 inch. The original application of these connectors was for audio microphones and headsets. These connectors are typically 1/8 inch, 3/32 inch, 3.5 mm, or 2.5 mm in diameter. The original telephone plug was 1/4 inch in diameter. These connectors were not designed to carry power, and there is a possibility of shorting the power supply when mating the connector.

Some connectors have been specially designed as power connectors.

Cylindrical plugs generally have an insulated tip constructed to accept insertion of a pin (but note also the internal pin in the larger size EIAJ plugs). The outer body of the plug is one contact, most often but not always the negative side of the supply. A pin mounted in the socket makes contact with a second internal contact. The outer plug contact is often called the sleeve, and the inner the tip, although the tip itself is actually non-conductive.

Many different sizes

There are many different sizes of these connectors. (See below.)

Contact ratings vary from unspecified (and probably less than 1 A in practice) up to 5 A, with 2 A typical. Voltage is again often unspecified, up to 48 V with 12 V typical. The smaller types usually have lower ratings, both for current and voltage.

It is quite possible that new sizes will continue to appear and disappear. The most likely reason for a new size is that a particular manufacturer wishes to discourage use of third-party power supplies, either for technical reasons or to promote use of their own products or both.

Furthermore, sometimes there is no rhyme or reason to the choice of which connector is used in an application. One manufacturer might use one size connector for its 12V 1A product; a second manufacturer might use a different connector for its 12V 1A product. Although the power supplies are otherwise identical, they are not interchangeable because the connectors are different.

Standards

Some organizations have proposed standards to minimize the market complexity. In an ideal world, specifying a voltage and a current for a power supply would also determine the connector.

At least two different national standards exist, EIAJ in Japan and DIN in Germany. As well several conventions have been adopted by specific manufacturers, notably by Sony, to indicate voltage by plug size.

Some manufacturers use opposite polarity standards, and some generic power supplies cater for this by allowing the polarity to be reversed by use of a switch or an unpolarized two-pin plug and socket arrangement. These two-pin plugs seem to be standardized but official specifications are hard to find. The pins are 1.5 mm in diameter, 6 mm long and spaced 4.2 mm apart. (see Egston connector overview (pdf), page 6, number 230)

Universal power supplies

Power adapters (or wall warts) have become almost universal. They free product designers from worrying about some safety issues. The designer builds his product to run off a low voltage (obtained through the coaxial power connector) and does not have to worry about hazardous voltages. One disadvantage of power adapters is they get separated from the product. Consequently, there is a market for replacement adapters. Not only must the consumer match voltage and current requirements, but he must also match the connector.

Some power supplies allow the voltage to be switched. That eases the voltage matching problem.

Four-way X connectors or six-way star connectors, also known as spider connectors, with multiple plug sizes and types are common on generic power supplies. On others there are arrangements for changing the connector, with from four to nine different connectors available.

A six-way connector on a 'universal' DC power supply, consisting of a 4-way X connector and two individual connectors. The X-connector here provides 3.5 and 2.5 mm jack plugs and two sizes of cylindrical connector

EIAJ standards

Further information: EIAJ connector

Five plug and matching socket or jack designs are defined by the EIAJ standard RC-5320A (a.k.a. JEITA RC-5320A). Each of these plugs is used with a specified voltage range. Most manufacturers use a yellow insulating material to distinguish these plugs from other similar-looking DC plugs.

• EIAJ-01 for 0-3.15 V
• EIAJ-02 for 3.15-6.3 V
• EIAJ-03 for 6.3-10.5 V
• EIAJ-04 for 10.5-13.5 V (a.k.a. JSBP 4)
• EIAJ-05 for 13.5-18 V (a.k.a. JSBP 5)

Unlike most DC plugs, the larger two EIAJ sizes have an internal pin in the plug. The smaller three do not and are similar to the generic plugs in structure. The plug length is 9.5 mm in all cases, and current rating 2 A.

There are two other, less common, connectors defined by EIAJ; RC-5321 and RC-5322. The latter is designed for both 12 V and 24 V automotive applications.

DIN 45323 power connectors

The German national standard DIN (Deutsches Institut für Normung) DIN 45323 apparently defines two DC power plug sizes. The information below is inferred from catalog references, as the German standard has not been translated into English as of yet.

• 5.00 mm OD, 2.00 mm ID, 14 mm long?
• 6.00 mm OD, 1.98 mm ID [1]
• Connectors for coupling an external low-voltage power to portable entertainment equipment

Guidelines for selection

With more than 30 different designs of coaxial power connectors in existence and used to power electronic products, the lack of a clear starting point for selecting one has helped lead to the wide incompatibilities between power plugs and devices.

Here are some guidelines that can be drawn from the few power connector designs that have clear specifications associated with them.

• 1.5 V devices
  • EIAJ-01
• 3.0 V devices
  • EIAJ-01
• 4.5 V devices
  • EIAJ-02
  • EIAJ RC-5321
• 6.0 V devices
  • EIAJ-02
  • EIAJ RC-5321
• 7.5 V devices
  • EIAJ-03
• 9.0 V devices
  • EIAJ-03
• 10.5 V devices
  • EIAJ-03
• 12.0 V devices, including automotive electrical systems
  • EIAJ-04
  • ARINC 628/EmPower for automotive or airplane use
  • EIAJ RC-5322 for automotive use
• 13.5 V devices
  • EIAJ-04
  • EIAJ RC-5322 for automotive use
  • ARINC 628/EmPower for automotive or airplane use
• 15.0 V devices
  • EIAJ-05
  • ARINC 628/EmPower for automotive or airplane use
• 16.5 V devices
  • EIAJ-05
• 18.0 V devices
  • EIAJ-05

Generic types

Close-up of a yellow-tipped EIAJ connector

The most common plugs are 5.5 mm in outside diameter (OD) and 9.5 mm in length. Two pin sizes are common in the jacks for this size plug body, 2.1 mm and 2.5 mm, and the plugs should ideally match. Generic plugs are often named for the pin diameter they are designed to take, so these types will be seen described as 2.1 mm DC plugs and 2.5 mm DC plugs respectively. These two sizes are easily confused unless seen together.

Slightly smaller 5.0 mm OD plugs are sometimes used in both 2.1 mm and 2.5 mm pin sizes, as are longer or shorter 5.5 mm OD plugs. All are typically 8 mm to 14 mm in length. There are also 6.5 mm OD plugs taking a 3 mm pin, 3.8 mm OD plugs taking either a 1.35 mm or a 1.05 mm pin, 3.5 mm plugs for a 1.3 mm pin, and many less common sizes.

Use of a plug designed for a larger pin, for example a 2.5 mm pin plug in a 2.1 mm pin jack, may work perfectly depending on the design of the jack, but often the result is an unreliable contact or occasionally no contact at all. A pin that is too large for the plug will not allow insertion of the plug at all. Similarly, a larger plug body (OD) may not fit at all, a smaller one may fit but may not make a reliable contact. Length is less critical than the diameters but is sometimes a consideration, in general a longer plug is no great problem but a shorter one may fail to contact the pin reliably or at all.

After the two common 5.5 mm OD plugs the next most common size is 3.5 mm OD to take a 1.3 mm pin, commonly 9.5 mm in length but both longer and shorter versions also exist. These 3.5 mm OD plugs are normally used for lower voltages and currents.

Comprehensive listing of DC coaxial connectors

This list shows all known types, and is annotated with the manufacturers each is available from (based on those found in the Mouser and Digi-Key catalogs), since not all make all sizes. It should be further noted that a circular locking detent or high-retention feature is present on some of these barrel connectors, and its presence or absence should be a clue in distinguishing very similar sizes. This is not to be confused with the locking DC connectors which use threaded fittings to secure the connection between the plug and jack.

Some of these sizes always include a high-retention feature, while others feature it only in designs from certain manufacturers. Typically, this is a conical cut-back section of the tip, just behind the insulator that separates the inner from outer contact surfaces.

There are a number of sizes below that appear to be quite similar, and while the tolerances of these connectors is typically indicated as +/- 0.05 or 0.03 mm by the manufacturers, there is still sufficient ambiguity in whether two sizes differing by only 0.05 mm (or where the specification is only to the nearest 10^th of a mm) to warrant listing them separately here. Further work should be done to determine the original specification for the size, and then list the similar sizes that are intended to be compatible.

OD (mm)	ID (mm)	Center Pin Dia (mm)	Barrel Length (mm)	Adaptaplug	Standard	Volts	Plug Part Numbers	Jack Part Numbers	Notes
2.35	0.70		9.5	A	EIAJ-01	0–3.15 V
2.40	0.70						Egston 212		Possibly a rounded-off representation of EIAJ-01
2.40	0.80						Egston 213
3.00	1.00
3.00	1.10			G			Egston 214
3.40	1.30			H			KOBICONN
3.40	1.35						Egston 218 Medical, 220
3.40	1.40				NES/J 135
3.50	1.30						Egston 238
3.50	1.35						CUI Inc. P7 KOBICONN Egston 215
3.60	1.15						Egston 216
3.80	1.10			I			CUI Inc. P9 but with 1.05 mm ID
3.80	1.30						Egston 217
3.80	1.35						CUI Inc. P8
4.00	1.70		9.5	B	EIAJ-02 [1]	3.15–6.3 V
4.75	1.70		9.5	C	EIAJ-03 [2]	6.3-10.5 V
4.75	?.??		2.5 protruding	C	EIAJ RC-5321
4.80	1.70		2.5				KOBICONN
5.00	1.50			J
5.00	2.00				DIN 45323?		Egston 206, 207, 219
5.00	2.10			K			CUI Inc. P3
5.00	2.50			L			CUI Inc. P4
5.50	1.50		1.80	S
5.50	2.10			M			CUI Inc. P5 KOBICONN		2.1 mm DC plug
5.50	2.10						CUI Inc. P10 locking
5.50	2.50			N			CUI Inc. P6 KOBICONN Egston 222		2.5 mm DC plug
5.50	2.50						CUI Inc. P11 locking
5.50	2.80			O
5.50	3.30	1.00	9.5	D	EIAJ-04, JSBP4	10.5-13.5 V			Microsoft XBOX 360 HD DVD drive
5.50	3.80	1.80		P
6.00	1.98				DIN 45323?
6.30	3.00			Q
6.50	?.??				EIAJ RC-5322
6.50	3.00
6.50	3.10	1.00					Philmore 285
6.50	4.10/3.10	1.00		U					same as Philmore 285?
6.50	4.30			T	EIAJ-05,JSBP5 [3]	18.0 V			OD is of ring at tip
6.90	4.20	0.70		R
7.00	??	1.00					Philmore 48-412

RadioShack Adaptaplug conversion matrix

RadioShack sells adapter plugs that convert from the above-described two-pin non-polarized connector to various DC power plugs. RadioShack, in particular, has assigned a single-letter code to each plug, but has not provided the official name for each plug, nor often their complete specifications on barrel and pin diameter. Here is a complete list:

Adaptaplug	Outside Diameter	Inside Diameter	Pin Diameter	EIAJ Type	EIAJ Range	Ring Color	Radio Shack Part Number
A	2.35 mm	0.70 mm		EIAJ-01	up to 3.15 V	Yellow	273-1704
B	4.00 mm	1.70 mm		EIAJ-02	3.15 to 6.3 V	Yellow	273-1705
C	4.75 mm	1.70 mm		EIAJ-03	6.3 to 10.5 V	Yellow	273-1706
D	5.50 mm	3.30 mm	1.0 mm	EIAJ-04	10.5 to 13.5 V	Yellow	273-1707
E	2.50 mm (3/32" submini plug)					Black	273-1708
F	3.50 mm (1/8" mini plug)					Black	273-1709
G	3.00 mm	1.10 mm				Turquoise	273-1710
H	3.40 mm	1.30 mm				Orange	273-1711
I	3.80 mm	1.10 mm				Pink	273-1712
J	5.00 mm	1.50 mm				Red	273-1713
K	5.00 mm	2.10 mm				Purple	273-1714
L	5.00 mm	2.50 mm				Dark Green	273-1715
M	5.50 mm	2.10 mm				Navy	273-1716
N	5.50 mm	2.50 mm				White	273-1717
O	5.50 mm	2.80 mm				Brown	273-1718
P	5.50 mm	3.80 mm	1.80 mm			Not Specified	273-1719
Q	6.30 mm	3.00 mm				Yellow-Green	273-1720
R	6.90 mm	4.20 mm	0.70 mm			Not Specified	273-1721
S	5.50 mm	1.50 mm	1.80 mm			Gray	273-1722
T	6.50 mm	4.30 mm	1.40 mm	EIAJ-05	13.5 to 18.0 V	Yellow	273-1723
U	6.50 mm	4.10 mm / 3.10 mm	1.00 mm			Light Yellow	273-1724

References

• Digi-Key Catalog #T053; September-December 2005
• Mouser Electronics Catalog #624; November 2005–January 2006
• Mouser catalog page [2]
• RadioShack Web site (online descriptions of Adaptaplugs)
• Simple low voltage connection basics for everybody[3]
• Understanding the Radioshack Adaptaplug System*
• Hosiden
• [4]
• [5]
• [6]
• [7]
• [8]
• [9] shows a connector not yet covered here.
• inline adapters to convert from 2.1 mm plugs