AC adapter

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A "wall wart" type AC adapter for a household game console Wall-Wart-AC-Adapter.jpg
A "wall wart" type AC adapter for a household game console
An AC adapter for Lenovo laptop Lenovo Power Adapter AC 65W 20V.jpg
An AC adapter for Lenovo laptop
Internal adapter circuitry Internal adapter circuit.jpg
Internal adapter circuitry

An AC adapter, AC/DC adapter, or AC/DC converter [1] is a type of external power supply, often enclosed in a case similar to an AC plug. Other common names include plug pack, plug-in adapter, adapter block, domestic mains adapter, line power adapter, wall wart, power brick, and power adapter. Adapters for battery-powered equipment may be described as chargers or rechargers (see also battery charger). AC adapters are used with electrical devices that require power but do not contain internal components to derive the required voltage and power from mains power. The internal circuitry of an external power supply is very similar to the design that would be used for a built-in or internal supply.


External power supplies are used both with equipment with no other source of power and with battery-powered equipment, where the supply, when plugged in, can sometimes charge the battery in addition to powering the equipment.

Use of an external power supply allows portability of equipment powered either by mains or battery without the added bulk of internal power components, and makes it unnecessary to produce equipment for use only with a specified power source; the same device can be powered from 120 VAC or 230 VAC mains, vehicle or aircraft battery by using a different adapter. Another advantage of these designs can be increased safety; since the hazardous 120 or 240 volt mains power is transformed to a lower, safer voltage at the wall outlet and the appliance that is handled by the user is powered by this lower voltage.

Modes of operation

An AC adapter disassembled to reveal a simple, unregulated linear DC supply circuit: a transformer, four diodes in a bridge rectifier, and an electrolytic capacitor to smooth the waveform Wall wart opened.JPG
An AC adapter disassembled to reveal a simple, unregulated linear DC supply circuit: a transformer, four diodes in a bridge rectifier, and an electrolytic capacitor to smooth the waveform

Originally, most AC/DC adapters were linear power supplies, containing a transformer to convert the mains electricity voltage to a lower voltage, a rectifier to convert it to pulsating DC, and a filter to smooth the pulsating waveform to DC, with residual ripple variations small enough to leave the powered device unaffected. Size and weight of the device was largely determined by the transformer, which in turn was determined by the power output and mains frequency. Ratings over a few watts made the devices too large and heavy to be physically supported by a wall outlet. The output voltage of these adapters varied with load; for equipment requiring a more stable voltage, linear voltage regulator circuitry was added. Losses in the transformer and the linear regulator were considerable; efficiency was relatively low, and significant power dissipated as heat even when not driving a load.

Early in the twenty-first century, switched-mode power supplies (SMPSs) became almost ubiquitous for this purpose. Mains voltage is rectified to a high direct voltage driving a switching circuit, which contains a transformer operating at a high frequency and outputs direct current at the desired voltage. The high-frequency ripple is more easily filtered out than mains-frequency. The high frequency allows the transformer to be small, which reduces its losses; and the switching regulator can be much more efficient than a linear regulator. The result is a much more efficient, smaller, and lighter device. Safety is ensured, as in the older linear circuit, because a transformer still provides galvanic isolation.

A linear circuit must be designed for a specific, narrow range of input voltages (e.g., 220–240 VAC) and must use a transformer appropriate for the frequency (usually 50 or 60 Hz), but a switched-mode supply can work efficiently over a very wide range of voltages and frequencies; a single 100–240 VAC unit will handle almost any mains supply in the world.

However, unless very carefully designed and using suitable components, switching adapters are more likely to fail than the older type, due in part to complex circuitry and the use of semiconductors. Unless designed well, these adapters may be easily damaged by overloads, even transient ones, which can come from lightning, brief mains overvoltage (sometimes caused by an incandescent light on the same power circuit failing), component degradation, etc. A very common mode of failure is due to the use of electrolytic capacitors whose equivalent series resistance (ESR) increases with age; switching regulators are very sensitive to high ESR (the older linear circuit also used electrolytic capacitors, but the effect of degradation is much less dramatic). Well-designed circuits pay attention to the ESR, ripple current rating, pulse operation, and temperature rating of capacitors. [2]

Many inexpensive switched-mode AC adapters do not implement adequate filtering and/or shielding for electromagnetic interference that they generate. The nature of these high speed, high-energy switching designs is such that when these preventative measures are not implemented, relatively high energy harmonics can be generated, and radiated, well into the radio portion of the spectrum. The amount of RF energy typically decreases with frequency; so, for instance, interference in the medium wave (US AM) broadcast band in the one megahertz region may be strong, while interference with the FM broadcast band around 100 megahertz may be considerably less. Distance is a factor; the closer the interference is to a radio receiver, the more intense it will be. Even WiFi reception in the gigahertz range can be degraded if the receiving antennae are very close to a radiating AC adapter. A determination of if interference is coming from a specific AC adaptor can be made simply by unplugging the suspect adapter while observing the amount of interference received in the problem radio band. In a modern household or business environment, there may be multiple AC adapters in use; in such a case, unplug them all, then plug them back in one by one until the culprit or culprits is found.


External AC adapters are widely used to power small or portable electronic devices. The advantages include:

AC adapter supporting four different AC plug systems Steckernetzteil mit Adaptern IMGP2309 smial wp.jpg
AC adapter supporting four different AC plug systems


"Power brick" in-line configuration, with detachable AC cord Notebook-Computer-AC-Adapter.jpg
"Power brick" in-line configuration, with detachable AC cord

A survey of consumers showed widespread dissatisfaction with the cost, inconvenience, and wastefulness of the profusion of power adapters used by electronic devices. [3] Science fiction author and satirist Douglas Adams wrote an essay bemoaning the profusion and confusion of power adapters, and calling for more standardization. [4]


Millions of still-usable AC power adapters are thrown out annually, because of poor or unknown compatibility with new equipment. Steckernetzteile.jpg
Millions of still-usable AC power adapters are thrown out annually, because of poor or unknown compatibility with new equipment.

The issue of inefficiency of some power supplies has become well known, with U.S. president George W. Bush referring in 2001 to such devices as "Energy Vampires". [5] Legislation is being enacted in the EU and a number of U.S. states, to reduce the level of energy wasted by some of these devices. Such initiatives include standby power and the One Watt Initiative.

But others [ who? ] have argued that these inefficient devices are low-powered, e.g., devices that are used for small battery chargers, so even if they have a low efficiency, the amount of energy they waste is less than 1% of household consumption of electric energy.[ citation needed ]

Considering the total efficiency of power supplies for small electronic equipment, the older mains-frequency linear transformer-based power supply was found in a 2002 report to have efficiencies from 20–75%, and have considerable energy loss even when powered up but not supplying power. Switched-mode power supplies (SMPSs) are much more efficient; a good design can be 80–90% efficient, and is also much smaller and lighter. In 2002 most external plug-in "wall wart" power adapters commonly used for low-power consumer electronics devices were of linear design, as well as supplies built into some equipment.

External supplies are usually left plugged in even when not in use, and consume from a few watts to 35 watts of power in that state. The report concluded that about 32 billion kilowatt-hours (kWh) per year, about 1% of total electrical energy consumption, could be saved in the United States by replacing all linear power supplies (average efficiency 40–50%) with advanced switching designs (efficiency 80–90%), by replacing older switching supplies (efficiencies of less than 70%) with advanced designs (efficiency of at least 80%), and by reducing standby consumption of supplies to not more than 1 watt. [6]

Since the report was published, SMPSs have indeed replaced linear supplies to a great extent, even in wall warts. The 2002 report estimated that 6% of electrical energy used in the U.S. "flows through" power supplies (not counting only the wall warts). The website where the report was published said in 2010 that despite the spread of SMPSs, "today's power supplies consume at least 2% of all U.S. electricity production. More efficient power supply designs could cut that usage in half". [7]

Since wasted electrical energy is released as heat, an inefficient power supply is hot to the touch, as is one that wastes power without an electrical load. This waste heat is itself a problem in warm weather, since it may require additional air conditioning to prevent overheating, and even to remove the unwanted heat from large supplies.

Universal power adapters

A six-way connector on a "universal" DC power supply, consisting of a four-way X connector and two separate individual connectors (one is the nine-volt battery connector). The X-connector here provides 3.5 and 2.5 mm phone plugs and two sizes of coaxial power connector Dcxconnector.jpg
A six-way connector on a "universal" DC power supply, consisting of a four-way X connector and two separate individual connectors (one is the nine-volt battery connector). The X-connector here provides 3.5 and 2.5 mm phone plugs and two sizes of coaxial power connector

External power adapters can fail, and can become separated from the product they are intended to power. Consequently, there is a market for replacement adapters. The replacement must match input and output voltages, match or exceed current capability, and be fitted with a matching connector. Many electrical products are poorly labeled with information concerning the power supply they require, so it is prudent to record the specifications of the original power supply in advance, to ease replacement if the original is later lost. Careful labeling of power adapters can also reduce the likelihood of a mixup which could cause equipment damage.

Some "universal" replacement power supplies allow output voltage and polarity to be switched to match a range of equipment. [8] With the advent of switch-mode supplies, adapters which can work with any voltage from 110 VAC to 240 VAC became widely available; previously either 100–120 VAC or 200–240 VAC versions were used. Adapters which can also be used with motor vehicle and aircraft power (see EmPower) are available. [9]

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. Other replacement power supplies have arrangements for changing the power connector, with four to nine different alternatives available when purchased in a set. RadioShack sells universal AC adapters of various capacities, branded as "Enercell Adaptaplug", and fitted with two-pin female sockets compatible with their Adaptaplug connector lineup. This allows many different configurations of AC adapters to be put together, without requiring soldering. Philmore and other competing brands offer similar AC adapters with interchangeable connectors.

The label on a power supply may not be a reliable guide to the actual voltage it supplies under varying conditions. Many low-cost power supplies are "unregulated", in that their voltage can change considerably with load. If they are lightly loaded, they may put out much more than the nominal "name plate" voltage, which could damage the load. If they are heavily loaded, the output voltage may droop appreciably, in some cases well below the nominal label voltage even within the nominal rated current, causing the equipment being supplied to malfunction or be damaged. Supplies with linear (as against switched) regulators are heavy, bulky, and expensive.

Modern switched-mode power supplies (SMPSs) are smaller, lighter, and more efficient. They put out a much more constant voltage than unregulated supplies as the input voltage and the load current vary. When introduced, their prices were high, but by the early 21st century the prices of switch-mode components had dropped to a degree which allowed even cheap supplies to use this technology, saving the cost of a larger and heavier mains-frequency transformer.

Auto-sensing adapters

Some universal adapters automatically set their output voltage and maximum current according to which of a range of interchangeable tips is fitted; tips are available to fit and supply appropriate power to many notebook computers and mobile devices. Different tips may use the same connector, but automatically supply different power; it is essential to use the right tip for the apparatus being powered, but no switch needs to be set correctly by the user. The advent of switch-mode power supplies has allowed adapters to work from any AC mains supply from 100 to 240 V with an appropriate plug; operation from standard 12 V DC vehicle and aircraft supplies can also be supported. With the appropriate adapter, accessories, and tips, a variety of equipment can be powered from almost any source of power.

A "Green Plug" system has been proposed, based on USB technology, by which the consuming device would tell the external power supply what kind of power is needed. [10]

Use of USB

Common sizes of USB AC adapters USB AC Adapters.JPG
Common sizes of USB AC adapters

The USB connector (and voltage) has emerged as a de facto standard in low-power AC adapters for many portable devices. In addition to serial digital data exchange, the USB standard also provides 5 VDC power, up to 500 mA (900 mA over USB 3.0). Numerous accessory gadgets ("USB decorations") were designed to connect to USB only for DC power and not for data interchange. The USB Implementers Forum in March, 2007 released the USB Battery Charging Specification which defines, "...limits as well as detection, control and reporting mechanisms to permit devices to draw current in excess of the USB 2.0 specification for charging ...". [11] Electric fans, lamps, alarms, coffee warmers, battery chargers, and even toys have been designed to tap power from a USB connector. Plug-in adapters equipped with USB receptacles are widely available to convert 120 VAC or 240 VAC power or 12 VDC automotive power to 5 VDC USB power (see photo at right).

The trend towards more-compact electronic devices has driven a shift towards the micro-USB and mini-USB connectors, which are electrically compatible in function to the original USB connector but physically smaller.

In 2012, a USB Power Delivery Specification was proposed to standardize delivery of up to 100 watts, suitable for devices such as laptop computers that usually depend on proprietary adapters.


The ITU published Recommendation ITU-T L.1000, "Universal power adapter and charger solution for mobile terminals and other hand-held ICT devices", which specifies a charger similar in most respects to that of the GSMA/OMTP proposal and to the European Common external power supply. The ITU recommendation was expanded and updated in June, 2011. [12] The hope is to markedly reduce the profusion of non-interchangeable power adapters.

The European Union defined a Common external power supply for "hand-held data-enabled mobile phones" (smartphones) sold from 2010, intended to replace the many incompatible proprietary power supplies and eliminate waste by reducing the total number of supplies manufactured. Conformant supplies deliver 5 VDC via a micro-USB connector, with preferred input voltage handled ranging from 90 to 264 VAC.

In 2006 Larry Page, a founder of Google, proposed a 12 V and up to 15 A standard for almost all equipment requiring an external converter, with new buildings fitted with 12 VDC wiring, making external AC-to-DC adapter circuitry unnecessary. [13] [14]

IEC has created a standard for interchangeable laptop power supplies, IEC 62700 (full name "IEC Technical Specification 62700: DC Power supply for notebook computer"), which was published on February 6, 2014.

See also

Related Research Articles

Uninterruptible power supply Electrical device that uses batteries to prevent any interruption of power flow

An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery run-time of most uninterruptible power sources is relatively short but sufficient to start a standby power source or properly shut down the protected equipment. It is a type of continual power system.

Mains electricity Type of lower-voltage electricity most commonly provided by utilities

Mains electricity is the general-purpose alternating-current (AC) electric power supply. It is the form of electrical power that is delivered to homes and businesses, and it is the form of electrical power that consumers use when they plug items such as domestic appliances, televisions and electric lamps into wall outlets.

Power supply electronic device that converts or regulates electric energy and supplies it to a load

A power supply is an electrical device that supplies electric power to an electrical load. The primary function of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power.

Power inverter Device that changes direct current (DC) to alternating current (AC)

A power inverter, or inverter, is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC).

Switched-mode power supply Widely used type of power supply used to power electronic devices

A switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a DC or AC source to DC loads, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. A hypothetical ideal switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight.

A DC connector is an electrical connector for supplying direct current (DC) power.

Power cord power cable for connecting an appliance to a wall socket (including both captive and detachable cables)

A power cord, line cord, or mains cable is an electrical cable that temporarily connects an appliance to the mains electricity supply via a wall socket or extension cord. The terms are generally used for cables using a power plug to connect to a single-phase alternating current power source at the local line voltage—(generally 100 to 240 volts, depending on the location). The terms power cable, mains lead, flex or kettle lead are also used. A lamp cord is a light-weight, ungrounded, single-insulated two-wire cord used for small loads such as a table or floor lamp.

Power strip block of electrical sockets

A power strip is a block of electrical sockets that attaches to the end of a flexible cable, allowing multiple electrical devices to be powered from a single electrical socket. Power strips are often used when many electrical devices are in proximity, such as for audio, video, computer systems, appliances, power tools, and lighting. Power strips often include a circuit breaker to interrupt the electric current in case of an overload or a short circuit. Some power strips provide protection against electrical power surges. Typical housing styles include strip, rack-mount, under-monitor and direct plug-in.

In electrical engineering, power engineering, and the electric power industry, power conversion is converting electric energy from one form to another such as converting between AC and DC; or changing the voltage or frequency; or some combination of these. A power converter is an electrical or electro-mechanical device for converting electrical energy. This could be as simple as a transformer to change the voltage of AC power, but also includes far more complex systems. The term can also refer to a class of electrical machinery that is used to convert one frequency of alternating current into another frequency.

A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low to very high.

Voltage regulator regulator, designed to automatically maintain a constant voltage level;may: use a simple feed-forward design or include negative feedback, use an electromechanical mechanism or electronic components

A voltage regulator is a system designed to automatically maintain a constant voltage level. A voltage regulator may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.

Adapter Accessory for adapting or connecting two devices or two workpieces

An adapter or adaptor is a device that converts attributes of one device or system to those of an otherwise incompatible device or system. Some modify power or signal attributes, while others merely adapt the physical form of one connector to another.

Emergency power system independent backup source of electrical power that supports important electrical systems on loss of normal power supply

An emergency power system is an independent source of electrical power that supports important electrical systems on loss of normal power supply. A standby power system may include a standby generator, batteries and other apparatus. Emergency power systems are installed to protect life and property from the consequences of loss of primary electric power supply. It is a type of continual power system.

Battery charger device that charges a rechargeable battery by forcing current through it

A battery charger, or recharger, is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.

Standby power, also called vampire power, vampire draw, phantom load, ghost load or leaking electricity, refers to the way electric power is consumed by electronic and electrical appliances while they are switched off or in standby mode. This only occurs because some devices claimed to be "switched off" on the electronic interface, but are in a different state from switching off at the plug, or disconnecting from the power point, which can solve the problem of standby power completely. In fact, switching off at the power point is effective enough, there is no need to disconnect all devices from the power point. Some such devices offer remote controls and digital clock features to the user, while other devices, such as power adapters for disconnected electronic devices, consume power without offering any features. All of the above examples, such as the remote control, digital clock functions and—in the case of adapters, no-load power—are switched off just by switching off at the power point. However, for some devices with built-in internal battery, such as a phone, the standby functions can be stopped by removing the battery instead.

A voltage converter is an electric power converter which changes the voltage of an electrical power source. It may be combined with other components to create a power supply.

Power supply unit (computer) internal computer component that provides power to other components

A power supply unit converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage.

Automobile auxiliary power outlet Circular power outlet for electrically powering accessories inside a vehicle.

An automobile auxiliary power outlet in an automobile was initially designed to power an electrically heated cigarette lighter, but became a de facto standard DC connector to supply electrical power for portable accessories used in or near an automobile, directly from the vehicle's electrical system.

The Universal Power Adapter for Mobile Devices (UPAMD), codename IEEE 1823-2015, is an IEEE standard for power supply design intended to cater to the power range of 10–130 W for mobile devices like laptop computers. The power supply was required to have an output capacitive energy of less than 15.1 µJ and an inductive energy at disconnect of less than 5.3 µJ.

Most of the terms listed in Wikipedia glossaries are already defined and explained within Wikipedia itself. However, glossaries like this one are useful for looking up, comparing and reviewing large numbers of terms together. You can help enhance this page by adding new terms or writing definitions for existing ones.


  1. Lee, Richard M.L. "U.S. Patent 5245220". USPTO. Google Patents.
  2. Article on capacitor ESR and its effects
  3. Morrison, David. "Survey Finds Consumers Grow Weary of Wall Warts". Power Electronics Technology. Penton Media, Inc. Archived from the original on 15 July 2011. Retrieved 2011-06-03.
  4. Adams, Douglas. "Dongly things". The Digital Village, Ltd. Archived from the original on 11 June 2011. Retrieved 2011-06-03.
  5. Bush Takes Aim at "Wall Warts" Archived 2007-11-13 at the Wayback Machine   Extreme Tech article
  6. Calwell, Chris and Travis Reeder (2002), Power Supplies: A Hidden Opportunity for Energy Savings, Natural Resources Defense Council, pp. 4–9. Retrieved 2010-02-19.
  7. Efficiency of Power Supplies in the Active Mode
  8. Computer Times: 2006 review of a satisfactory third-party universal AC adapter Archived 2014-10-13 at the Wayback Machine
  9. Andrew Ku (September 2, 2011). "Universal Laptop Power Adapters For The Air, Road, And Wall". Tom's Hardware.
  10. Green Plug tries to replace the worry warts Engadget May 2008
  11. "USB-IF Enhances Battery Charging Capabilities with New Spec" (PDF). 2007-04-17. Archived from the original (PDF) on 2011-07-28. Retrieved 2011-02-21.
  12. "Universal power adapter and charger solution for mobile terminals and other hand-held ICT devices". International Telecommunications Union. 2011-06-13. Retrieved 2013-03-23.
  13. Markoff, John (September 26, 2006). "Google to Push for More Electrical Efficiency in PC's". New York Times. Retrieved 2011-06-03.
  14. Alter, Lloyd. "Google Pushes for PC Electrical Efficiency; Side Effect: No More Wall-Warts". Discovery Communications, Ltd. Archived from the original on 17 July 2011. Retrieved 2011-06-03.
  15. Dixon-Warren, Sinjin (16 July 2019). "AC Adapters: GaN, SiC or Si?". EE Times . Retrieved 21 December 2019.