A computer power supply typically is designed to convert 120 V or 240 V AC power from
the electrical company to usable power for the internal components of the computer. The most
common computer power supply is 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 wattages range from 200 W to 500 W, although some new personal computers with high energy requirements may draw as much as 1000 W (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. The connector for the motherboard is typically 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, ranging from diodes to capacitors to transformers. Also, many power supplies have metal heatsinks and fans to dissipate large amounts of heat produced. It is dangerous to open a power supply while it is connected to an electrical outlet as high voltages may be present even while the unit is switched off.
In desktop computers, the power supply is a small (PSU) 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. If only a small voltage is needed, the mains power needs to be transformed to a suitable level in order for the component to work.
In portable computers there is usually an external power supply that produces low voltage DC power from a mains electrical supply (typically a standard AC wall outlet). Circuitry inside the portable computer uses this transformed power to charge the battery as needed, in addition to providing the various voltages required by the other components of the portable computer.
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, 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 thousands to millions of times per second. 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.
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 from the power produced by the 400 Hz, three-phase AC generators attached to the shafts 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 the voltage peaks where the input voltage is higher than the 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 is done by using a switching power supply technique called "power factor correction" which creates a balanced current draw over the entire AC waveform.
Computer power supplies are rated for certain wattages based on their maximum output power. Typical wattages range from 200 W to 500 W, although some new personal computers with high energy requirements may draw as much as 1000 W (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. The connector for the motherboard is typically 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, ranging from diodes to capacitors to transformers. Also, many power supplies have metal heatsinks and fans to dissipate large amounts of heat produced. It is dangerous to open a power supply while it is connected to an electrical outlet as high voltages may be present even while the unit is switched off.
In desktop computers, the power supply is a small (PSU) 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. If only a small voltage is needed, the mains power needs to be transformed to a suitable level in order for the component to work.
In portable computers there is usually an external power supply that produces low voltage DC power from a mains electrical supply (typically a standard AC wall outlet). Circuitry inside the portable computer uses this transformed power to charge the battery as needed, in addition to providing the various voltages required by the other components of the portable computer.
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, 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 thousands to millions of times per second. 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.
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 from the power produced by the 400 Hz, three-phase AC generators attached to the shafts 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 the voltage peaks where the input voltage is higher than the 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 is done by using a switching power supply technique called "power factor correction" which creates a balanced current draw over the entire AC waveform.
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