Power supply
From Wikipedia, the free encyclopedia
A power supply (sometimes known as a power supply unit or PSU) is a device or system that supplies electrical or other types of energy to an output load or group of loads. The term is most commonly applied to electrical energy supplies.
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[edit] General description
The complete range of power supplies is very broad, and could be considered to include all forms of energy conversion from one form into another. Conventionally though, the term is usually confined to electrical or mechanical energy supplies. Constraints that commonly affect power supplies are the amount of power they can supply, how long they can supply it for without needing some kind of refueling or recharging, how stable their output voltage or current is under varying load conditions, and whether they provide continuous power or pulses.
The 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. This kind of regulation is commonly categorised as a Stabilized power supply.
[edit] 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.
[edit] Computer power supply
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 to the ATX form factor.
[edit] Domestic mains adaptor
A linear or switchmode 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", "adaptor block", "AC adaptor" or just "power adapter". Because they consume Standby power, they are sometimes known as "electricity vampires". Expensive switchmode power supplies can cutoff leaky electrolyte-capacitors, use powerless MOSFETs, and reduce their working frequency to get a gulp of energy once in a while to power for example a clock, which would otherwise need a battery.
This type of power supply is popular among manufacturers of low cost electrical items because
- Devices sold in the global marketplace don't need to be individually configured for 120 volt or 230 volt operation. Just sold with the appropriate AC adapter.
- The device itself doesn't need to be tested for compliance with electrical safety regulations. Only the adaptor needs to be tested.
[edit] Linear power supply
A simple AC powered linear power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, usually a lower voltage. If it is used to produce DC a rectifier circuit is employed either as a single chip, an array of diodes sometimes called a diode bridge or Bridge Rectifier, both for fullwave rectification or a single diode yielding a half wave (pulsating) output. More elaborate configurations rectify the AC voltage at first to pulsating DC. Then a capacitor smooths out part of the pulses giving a type of DC voltage. The smaller pulses remaining are known as ripple. Because of a fullwave rectification they occur at twice the mains frequency (in USA then at 120 Hz). Finally, depending on the requirements of the load, a linear regulator may be used to reduce the ripple sometimes also allowing for adjustment of the output to the desired but a lower voltage. More elaborate versions used by circuit designers are adjustable up to 30 volts and up to 5 amperes output. These often employ current limiting. Some can be driven by an external signal, for example, for applications requiring a pulsed output.
In the simplest case a single diode is connected directly to the mains and uses a resistor in series with a more or less fixed load to recharge a battery. This circuit is common in rechargeable flashlights.
[edit] 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.
[edit] Mechanical power supplies
- Flywheels coupled to electrical generators or alternators
- Compulsators
- Explosively pumped flux compression generators
[edit] Terminology
- SCP
- Short circuit protection
- OPP
- Overpower (overload) protection
- OCP
- Overcurrent protection
- OTP
- Overtemperature protection
- OVP
- Overvoltage protection
- UVP
- Undervoltage protection
- UPS
- Uninterruptible Power System
