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The electric energy obviously is not used in the form in which it was produced or distributed. All electronic systems require some form of energy conversion, which can be accomplished by different methods.
Power supply unit (PSU) refers to a device that transfers electric energy from a source to a load by using electronic circuits. Of course, a PSU does not really
supply power, it just converts it from one form to another, so "converter" would be a more accurate term for such a device.
A typical application of a power supply is to convert utility AC voltage into a set of regulated DC voltages required for electronic equipment. There are different types of PSU depending on their mode of operation. Back in the 70's, most PSE were linear, efficiency was around 50%, power density was less than one watt per cubic inch, and power factor was 0.5-0.7. Nowadays most PSUs are of SMPS type with efficiency over 90%, power density of tens of watts per cubic inch, and power factor up to 0.99. This type is the main subject of this site.
WHAT IS IT?
SMPS stands for switched mode power supply. It is an electronic device in which energy conversion and regulation is provided by power semiconductors that are continuously switching with high frequency between "on" and "off" states. An output parameter (usually output voltage) is controlled by varying duty cycle, frequency or a phase shift of these transitions.
HOW DOES IT WORK?
. The energy flow in any PSU is controlled by power semiconductors. However, in different systems they operate in different modes. In legacy systems they worked in
linear mode, and excessive power dissipated in a series transistor. When a semiconductor operates in
switching mode, it can control energy flow with low losses: when a switch is "on", it has low voltage drop and will pass any current imposed on it; when it is "off", it blocks the flow of current. As the result, in such an electronic device the power dissipation which is the product of voltage and current, can be relatively low in both states. That's why switch mode PSUs offer greater efficiency compared with linear ones. Such units are also smaller in size and lighter in weight due to the reduced size of passive components and lower heat generation. Higher efficiency and smaller size coupled with advancements in semiconductor technology and various energy efficiency regulations have made "switcher" the dominant type of PSU across practically the full spectrum of applications. Most PSU manufactured today for AC input applications also include another conversion stage- a power factor correcting (PFC) front end. There is a huge variety of complete
off-the-shelf power supplies and DC-DC modules on the market to meet most practical requirements and safety standards.
Nevertheless, custom designs are still being done when there is a need for special characteristics or an unusual form-factor, particularly for harsh environment military applications or avionics.
In general, power converters can be classified into four types according to the form of input and output voltages: AC to DC (also called off-line DC power supply), DC to DC (voltage or current converter), AC to AC (frequency changer or cycloconverter), and DC to AC (
inverter). In addition to the main DC-DC converter, most PSU manufactured today for AC input applications also include another switching regulator- power factor correction (PFC) front end, and may include additional PCB-mounted regulators for auxiliary outputs.
The field of engineering that deals with the design and analysis of power conversion circuits and devices is called
power electronics, although power supply design is a true cross-disciplinary task. It involves the circuit, magnetics, thermal management, control and compliance issues. This site is SMPS/power electronics information guide. Here you will find a tutorial, tools, reviews, schematics, and other free online resources on all aspects of switching power supply design and selection, information on other energy conversion devices, as well as basic
electrical engineering reference and
electronic formulas.