How Do I Select an AC/DC Power Adapter?

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ac dc power adapters at parts express

How Do I Select an AC/DC Power Adapter?

In the US, electricity available from a wall outlet is 110 volts alternating current (AC). Many electronic devices require much lower voltage to operate, and most of those require direct current (DC). Adapters that are used to supply proper voltage and current to electronic devices are referred to as AC/DC adapters or power supplies.

Using an improper power adapter can result in the device not working, becoming damaged, or worse. To select the proper power adapter for your device, you'll have to narrow down the available choices. This process will be much easier if you have the original adapter that came with the device. If you don't, some specifications may be on the device near the power
jack, or you may have to contact the manufacturer.


The details you must determine:

Output voltage and current type

Voltage and current type will be expressed as a number and current designation. For example, a converter with a 12 volt DC output might be labeled 12V DC, 12VDC, or 12 VDC. Most home electronics run on DC, but don't take it for granted. If you don't see an AC or DC designation, consult the device manufacturer. Making the wrong choice may cause your device not to work or damage it.


AC power adapter



Regulated or unregulated

Regulated AC/DC power adapters keep voltage and current potential constant. Failure to use them can damage some devices. On the other hand, using a regulated AC/DC power adapter will never hurt a device designed for an unregulated AC/DC adapter. "Brick" adapters that operate inline with the power cord are more often regulated than "wall wart" adapters that plug directly into the wall, but this is far from an absolute rule. If you have doubts about which type of adapter your device requires, contact the manufacturer.


"Brick" and "wall wart" power adapters



The device's current draw, measured in Amps or Milliamps (A or mA)

Never use an adapter with a lower current rating than the adapter that came originally with the device. Using an unregulated adapter with a higher than required current rating can cause damage to the device, but exceeding the original current rating with a regulated adapter will work fine.


Current rating from AC adapter



The power connector's style, shape, and polarity

Of a cylindrical plug's three relevant dimensions, the most critical is the diameter of the round opening in the center. There are many sizes, but 2.1 mm and 2.5 mm are the most common. Differentiating between them is difficult by eye, so it's best to measure with a micrometer or contact the device manufacturer. The other measurements are the cylinder's outside diameter (typically 5.5 mm) and the length of the cylinder, which should match the depth of the socket.


Hollow cylindrical plugs are more common than solid plugs


Other similar styles of adapter plug may include 2.5 mm and 3.5 mm mono (TS) phone connectors, as are often seen on audio equipment.


Polarity Diagram (on back of AC/DC adapter)


Determining proper polarity is important. Often, there will be a diagram on the device. Popular convention is to make the center positive, but this is not universal. Choosing the wrong polarity may cause the device not to work or damage it.


Universal plug and tip


Many of our power adapters are "universal," in that their cords end in a socket that accepts many different styles of plug. Some even have selectable output voltage. When selecting a plug for one of these universal adapters, it's sometimes easiest to buy several that you think are likely candidates. It's inexpensive insurance against buying the wrong one and having to order again.

If the connector does not look like a barrel plug or a phone plug, it may be USB or a proprietary connector. If you have concerns about which type of adapter plug your device requires, contact the manufacturer.


Is it USB?

Universal Serial Bus (USB) was developed as a cable standard for computer peripherals. Its popularity has soared, however, as a method of powering and charging all kinds of electronic devices. When supplying USB power from a wall outlet, there are two options: The first is to use a USB cable and an adapter with a USB port.


Adapter with USB port


The second is to buy an adapter with a captive USB cord.

In either case, the adapter will output a regulated 5 VDC.

USB plugs used for power typically come in three varieties; standard USB, Mini USB, and Micro USB. When you buy a USB cable or adapter with captive USB cord, be sure that the plug will fit your needs.

Most USB devices do not require a current capability beyond 1000 mA. More recent USB devices, including some tablets, require as much as 2000 mA. These may not charge properly with a 1000 mA USB power source and will require a 2000 mA adapter.



If, at this point, you're confused or unsure of which AC adapter to buy, contact a Parts Express Technical Advisor or your device's manufacturer.

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