Switching power supplies have their specific circuits made up of the following categories:
(1) Buck circuit - a buck chopper whose output average voltage Uo is less than the input voltage Ui with the same polarity.
(2) Boost circuit - a step-up chopper whose output average voltage Uo is greater than the input voltage Ui with the same polarity.
(3) Buck-Boost circuit - Buck or Boost chopper whose output average voltage Uo is greater or less than the input voltage Ui, with opposite polarity and inductive transfer.
(4) Cuk Circuit - Buck or Boost Chopper with an average output voltage Uo greater or less than the input voltage Ui, opposite polarity, and capacitive transfer. Today's soft-switching technology makes a qualitative leap in DC/DC, the United States VICOR company designed and manufactured a variety of ECI soft-switching DC/DC converter, its maximum output power of 300W, 600W, 800W, etc., the corresponding power density of (6, 2, 10, 17) W/cm3, the efficiency of (80-90) per cent. Japan's NemicLambda's latest introduction of a soft-switching technology of high-frequency switching power supply module RM series, its switching frequency (200-300) kHz, power density has reached 27 W/cm3, the use of synchronous rectifiers (MOS-FET instead of Schottky diode), is the entire circuit efficiency increased to 90%.
AC/DC conversion
AC/DC conversion is to convert AC to DC, the power flow can be bidirectional, power flow from the power supply to the load is called 'rectifier', power flow from the load back to the power supply is called 'active inverter'. AC/DC converter input for 50/60Hz AC, because of the 50/60Hz AC input. AC/DC converter input is 50/60Hz alternating current, because it must be rectified, filtered, so the relatively large filter capacitor is essential, and because of the safety standards (such as UL, CCEE, etc.) and EMC directive restrictions (such as IEC, FCC, CSA), the AC input side must be added to the EMC filtering and the use of components that comply with the safety standards, which restricts the miniaturisation of the size of the AC/DC power supply. In addition, due to the internal high-frequency, high-voltage, high-current switching action, making it more difficult to solve the EMC electromagnetic compatibility problem, but also on the internal high-density installation circuit design puts forward high requirements, due to the same reason, high-voltage, high-current switching makes the power supply operating consumption increases, limiting the process of modularity of the AC / DC converter, so it must be used in order to optimise the design of power supply systems in order to make the power system operating efficiency to a certain degree of satisfaction.
AC/DC converter can be divided into half-wave circuit and full-wave circuit according to the wiring of the circuit. According to the number of power supply phases can be divided into single, three-phase, multi-phase. According to the circuit operating quadrant can be divided into one quadrant, two quadrants, three quadrants, four quadrants.
