Power supplies
A power supply, which is also sometimes known as a power supply unit (PSU), is a device that supplies, most commonly, electrical energy to an output load (a device connected to the output of a circuit) or group of loads.
Basically a power supply is something that converts one form of energy into another form of energy, for use by other devices. In virtually all instances the phrase is used to describe a device that converts electrical energy.
There are a number of issues to consider with a power supply, these include, but are not limited to; how much energy they can supply, how long they can supply it before needing recharging, how stable is the output voltage or current under varying load conditions and does it provide continuous power or power pulses.
The voltage regulation of power supplies is done by incorporating circuitry to tightly control the output voltage and/or current of the power supply to a specific value. The specific value is closely maintained despite variations in the load presented to the power supply’s output, or any reasonable voltage variation at the power supply’s input.
Electrical power supplies
This term covers the mains power distribution system together with any other primary or secondary sources of energy such as:
- Conversion of one form of electrical power to another desired form and voltage. This typically involves converting 120 or 240 volt AC supplied by a utility company (see electricity generation) to a well-regulated lower voltage DC for electronic devices. For examples, see switched-mode power supply, linear regulator, rectifier and inverter (electrical).
- Batteries
- Chemical fuel cells and other forms of energy storage systems
- Solar power
- Generators or alternators (particularly useful in vehicles of all shapes and sizes, where the engine has rotational power to spare, or in semi-portable units containing an internal combustion engine and a generator) (For large-scale power supplies, see electricity generation.) Low voltage, low power DC power supply units are commonly integrated with the devices they supply, such as computers and household electronics.
Computer power supply
The top cover has been removed to show the internals of a computer PSU.A computer power supply typically is designed to convert 110 V or 230 V AC power from the mains to usable low-voltage DC power for the internal components of the computer. The most common computer power supplies are built to conform with the ATX form factor. This enables different power supplies to be interchangeable with different components inside the computer. ATX power supplies also are designed to turn on and off using a signal from the motherboard (PS-ON wire), and provide support for modern functions such as the Standby mode of many computers.
Computer power supplies are rated for certain wattages based on their maximum output power. Typical rated wattages range from 200 W to 500 W, although units used by gamers and enthusiasts usually range from 500 W to 800 W, with the highest end units going up to 1 kW.
Most computer power supplies have a large bundle of wires emerging from one end. One connector attached to the opposite end of some wires goes to the motherboard to provide power. The PS-ON wire is located in this connector, and is usually green. The connector for the motherboard is the largest of all the connectors. There are also other, smaller connectors, most of which have four wires: two black, one red, and one yellow. Unlike the standard electrical wire color-coding, each black wire is a Ground, the red wire is +5 V, and the yellow wire is +12 V.
Inside the computer power supply is a complex arrangement of electrical components, including diodes, capacitors and transformers. Also, computer power supplies have metal heatsinks and fans to dissipate the heat produced. It is dangerous to open a power supply while it is connected to an electrical outlet as high voltages may be present. These may remain even while the unit is switched off, as there can be charge stored in the capacitors. However, for most PSU’s this can be fixed by unplugging the PSU and then pressing the on button, which will drain the capacitors. Still, care should be taken as some PSU’s require a load on the output in order to discharge the capacitors fully. Even when the PC is turned off, a PSU will draw power from the wall.
In desktop computers, the power supply is a box inside the computer; it is an important part of the computer because it provides electrical power in a form that is suitable for every other component inside or attached to the computer in order for it to work. In portable computers there is usually an external power brick which converts AC power to one DC voltage (most commonly 19v), and further DC-DC conversion occurs within the laptop to supply the various DC voltages required by the other components of the portable computer.
The original ATX main connector is a 20-pin connector. Most newer boards have a 24-pin connector; however many will function perfectly with only the original 20 pins connected. Similarly, most PSUs split the connector into 20+4, so that it will be compatible with both past and future motherboards.
Domestic mains adaptors
A power supply (or in some cases just a transformer) that is built into the top of a plug is known as a wall wart, power brick, plug-in adapter or just power adapter.
Linear power supply
A simple AC powered linear power supply uses a transformer to convert the voltage from the wall outlet to a lower voltage. A diode circuit (generally either a single diode or an array of diodes called a diode bridge but other configurations are possible) then rectifies the AC voltage to pulsating DC. A capacitor smooths out most of the pulsating of the rectified waveform to give a DC voltage with some ripple. Finally depending on the requirements of the load a linear regulator may be used to reduce the voltage to the desired output voltage and remove the majority of the remaining ripple. It may also provide other features such as current limiting.
Switched-mode power supply
In a switched-mode power supply the incoming power is passed through a transistor and transformer network that switches on and off at typical rates of 10kHz to 1 MHz. This means that a smaller, less expensive, lighter transformer can be used, because the voltage is being made to alternate faster, and thus a smaller magnetic core can be used. The switch mode PSU is also significantly more efficient than the linear design. Typically 80 - 90% compared to 50 - 60%. The downside to this design is that the switching on and off at high speeds introduces electrical noise into the system which can cause interference with the power supply load or other connected systems.
Switching power supplies can be used as DC to DC converters. In this application, the power supply is designed to accept a limited range DC input and then output a different DC voltage. This is particularly useful in portable devices, as well as power distribution in large electronic equipment. A transformerless switching power supply that outputs a voltage higher than its input voltage is typically called a boost converter. A transformerless switching power supply that outputs a voltage lower than its input voltage is typically called a buck converter. These transformerless switching power supplies use an inductor as the primary circuit element in converting the voltage. Circuitry is used to pass current through the inductor to store a certain amount of electrical energy as a magnetic field. The current flow is then stopped, and the magnetic field collapses causing the stored energy to be released as current again. This is done rapidly (up to millions of times per second). By carefully metering the amount of energy stored in the inductor, the current released by the inductor can be regulated thus allowing the output voltage to be tightly regulated. A switching power supply incorporating a transformer can provide many output voltages simultaneously, and is typically called a flyback converter. Switching power supplies are typically very efficient if well designed, and therefore waste very little power as heat. Because of these efficiencies, they are typically much smaller and lighter than an equivalently rated linear supply.
Power conversion
The term “power supply” is sometimes restricted to those devices that convert some other form of energy into electricity (such as solar power and fuel cells and generators). A more accurate term for devices that convert one form of electric power into another form of electric power (such as transformers and linear regulators) is power converter.
Uses in aviation
The most exotic power supplies are used in aviation to enable reliable restarting of stalled engines.
In jet transports, an engine is restarted using power produced by 400 Hz three-phase AC generator(s) attached to the shaft(s) of the other engine(s). Most of the starting torque generated by the engine’s motor/generator is provided by the current at the peaks of the AC waveform.
If the aircraft electronics used simple rectifying power supplies, they would use current only from these peaks, since the diodes conduct only during voltage peaks where input voltage is higher than output voltage. This could prevent the pilot from restarting an engine in an emergency.
Therefore, aircraft power supplies take energy evenly from all parts of the AC waveform. This uses a switching power supply technique called “power factor correction,” which creates a balanced current draw over the entire AC waveform.
Other definitions and resources for information about power supplies
The type of battery a unit requires. Most devices require either 2 AA batteries or one 3V Lithium CR123 battery.
www.nightvisionplanet.com/index.asp
A sub-component found in most computers and switches, which converts 120 Volts AC (alternating current) to the DC (direct current) voltages required by the unit to operate. Note that some computers or switches are designed to connect directly to DC power, in which case an external DC power source is needed.
www.answerstat.com/articles/glossary.html
A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system.
www.flw.com/define_p.htm
Generally this comes with the case. It can have an AT or ATX power connector and it is measured in its rated output. It converts power from your outlets into a steady stream of power the computer can use. A 235 or 250 Watt power supply is generally sufficient for home users, but power users may need a 300 or 400 Watt power supply if they have a lot of hard drives or other components. …
www.basichardware.com/glossary.html
A source for the power needed for active electronic circuitry. Can consist of one or more batteries, or an electronic circuit which converts AC line voltage to the type of power required by a particular device.
www.kareoke.com/glossary/microphone_glossary_of_terms.htm
A term that refers to a device that is powered by an AC source, but produces DC output voltages.
www.elpac.com/resources/glossary.html
The box inside your computer that supplies it with the electricity that it needs. The Power Supply converts the house AC current to voltages the computer can use, 3.3, 5, and 12 volts DC.
www.pccomputernotes.com/pcterms/glossaryp.htm
plugs into line power and changes the electrical signal to the high frequency, high voltage needed to drive the ultrasonic system.
www.sonobondultrasonics.com/glossary.asp
A part of the computer that converts the power from a wall outlet into the lower voltages, typically 5 to 12 volts DC, required internally in the computer. PC power supplies are usually rated in watts, ranging from 90 watts at the low end to 300 watts at the high end. If the power supply in your computer fails, nothing works, not even the fan.
www.angelfire.com/ny3/diGi8tech/PGlossary.html
A standard power supply usually has one wire lead which can be connected to the electrode or workpiece and through which the total power available can be channeled. With a multilead power supply, it is possible to divide the total power available into small units, each capable of being channeled through separate wire leads connected to multiple electrodes or workpieces for production work. Or, all power can be put through a single wire lead by connecting all the individual leads into one.
www.mmsonline.com/edm/glossary/am.html
The unit which provides power to a machine.
www.euromat.org/dictionnary/machines_terminology/p.htm
The module which outputs power required for printer operations. Printers contain three power modules (or those functions within one or more circuits): AC, DC, and high voltages power supplies.
www.depot-america.com/tr_glossary.asp
The device within a computer that converts external AC power to internal DC voltage.r
www.onesixsigma.com/tools_resources/glossary/glossary_p.php
The power supply takes the current from your wall electrical socket and coverts it into the various voltages your computer needs. The size of a power supply is measured in watts, and a general rule of thumb is the more peripherals the more powerful the supply. Generally speaking, however, a 200 watt power supply will work for most systems. The fan is a great collector of dust, so it’s a good idea to blow it out with canned air every once in a while, just to keep the air flowing.
www.startech.com/glossary/glossary.cfm
Supplies the motherboard with 5v and the other devices with 12v. It powers the computer.
www.scotsmist.co.uk/glossary_p.html
the device used to convert, regulate, and transmit external power for use by the components housed inside the computer chassis Additional Terms Applicable to Motherboard.
www.pcbargainhunter.com/computers/computer-glossary.html
A device, such as a generator or a transformer-rectifier-filter arrangement, that produces the power needed to operate on electronic equipment.
www.noahtec.com/power-glossary-terms.htm
This device converts the normal AC power at 120 or 240 volts to the different voltages and frequencies of AC and DC power that are required to operate the equipment.
www.satellite-tv-hq.com/telecom-glossary-p.htm
The unit in a computer which changes the AC mains electricity input into the lower DC voltages that the computer requires.
www.msun.edu/infotech/its/how/glossary/p.htm
Electrical equipment used to deliver either AC or DC voltage.
www.sciencelobby.com/dictionary/p.html
A power supply changes the alternating current (AC) that comes from an outlet to the direct current (DC) that a computer can use. The capacity of a power supply is measured in watts.
www.knm.co.za/Other/KMGlossay.htm
Converts AC voltage to low-voltage DC. The output is tightly regulated to keep noise pulses and voltage variations from upsetting the computer’s circuits.
www.cs.trinity.edu/~thicks/Tutorials/Hardware/Hardware.html
A power supply unit (sometimes abbreviated power supply or PSU) is a device that supplies electrical power to a device or group of devices. The term is most commonly applied to units that are integrated with the devices they supply, such as computers and household electronics, and never to devices supplying, conditioning or otherwise supporting an electric utility grid. (For large-scale power supplies, see electricity generation.)
http://en.wikipedia.org/wiki/Power_supply
Other related phrases
Power supplies (PSU)
Uninterruptible power supply
DC power supply
Ferroresonant power supply
Regulated power supply
Switching power supply