| abstract | - Switched-mode power supplies have applications in various areas. Switched-mode PSUs in domestic products such as personal computers often have universal inputs, meaning that they can accept power from most mains electricity throughout the world, with rated frequencies in the 50 - 60 Hz range and a voltage range between 100 - 240 V AC (although a manual voltage range switch may be required). In practice they will operate from a much wider frequency range and often from a DC supply as well. In 2006, at an Intel Developers Forum, Google engineers proposed the use of a single 12 V supply inside PCs, due to the high efficiency of switch mode supplies directly on the PCB. The efficiency went from ordinary 60 - 70% to 90 % with Voltage regulator modules on the motherboard instead of providing the different voltages from the PSU directly. Most modern desktop and laptop computers also have a voltage regulator module which is a DC-DC converter on the motherboard that step down the voltage from the power supply or the battery to the CPU core voltage, which may need to be as low as 0.8 V for a low voltage CPU to 1.2 - 1.5 V for a desktop CPU as of 2007. Some motherboards have a setting in the BIOS that allows overclockers to set a new CPU core voltage; other motherboards support dynamic voltage scaling which constantly adjust the CPU core voltage. Most laptop computers also have a DC-AC converter to step up the voltage from the battery to drive the cold cathode backlight in the flat-screen monitor, which typically requires around 1000 VRMS. Due to their high volumes mobile phone chargers have always been particularly cost sensitive. The first chargers were linear power supplies but they quickly moved to the cost effective ringing choke converter (RCC) SMPS topology, when new levels of efficiency were required. Recently the demand for even lower no load power requirements in the application has meant that flyback topology is being used more widely; primary side sensing flyback controllers are also helping to cut the bill of materials (BOM) by removing secondary-side sensing components such as optocouplers. Where integration of capacitors for stabilization and batteries as a energy storage or AC hum and other interference needs to be avoided in the power distribution, SMPS may be essential for efficient conversion of electric DC energy. For AC applications where frequency and voltage can't be produced by the primary source an SMPS may be essential as well. Applications may be found in the automobile industry where ordinary trucks uses nominal 24 V DC but may need 12 V DC. Ordinary cars use nominal 12 V DC and may need to convert this to drive equipment. In industrial settings, DC supply is sometimes chosen to avoid hum and interference and ease the integration of capacitors and batteries used to buffer the voltage that makes SMPS essential. Most small aircraft use 28 V DC. Larger aircraft that still need to avoid heavy transformers use a frequency higher than the usual mains frequency, like the Boeing-747 often use 3-phase 200 V AC 400 Hz at current up to 90 kVA, though they often have a DC bus as well. Fighter planes such as the F-16 also use 400 Hz distribution power. The MD-81 airplane has an 115/200 V 400 Hz AC and 28 V DC power system generated by three 40 kVA AC generators. Helicopters also use the 28 V DC system. Some submarines like the Soviet Alfa class submarine uses two synchronous generators providing a variable three-phase current, 2×1500 kW, 400 V, 400 Hz. The space shuttle uses three fuel cells generating 30 - 36 V DC. Some is converted into 400 Hz AC power and 28 V DC power. The International Space Station uses 120 V DC power. Larger trucks use 24 V DC. More on aircraft electric power: Avionics, Airplane ground support In the case of TV sets, for example, an excellent regulation of the power supply can be shown by using a variac. For example, in some TV-models made by Philips, the power supply starts when the voltage reaches around 90 V. From there, one can change the voltage with the variac, and go as low as 40 V and as high as 260 V (a peak voltage of 260× ≈ 360 Vp-p), and the image will show absolutely no alterations. The electrical power system on the International Space Station (ISS) uses 8 solar panels that generate a maximum system voltage of 160 V DC and with a maximum total power capacity of 262.4 kW that charges NiH2 batteries such that they can provide for 35 minutes with 6.6 kW during earth eclipse. A system voltage of 160 V DC is used for the main power distribution throughout the station. The European and American part (USOS) uses 124 V DC as the end user voltage while the Russian part (ROS) and the space shuttle uses 28 V DC. Powering of LED circuits is accomplished with switched-mode power supply setup as an constant current source where efficiency is important.
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