The specific circuit of switching power supply consists of the following categories:
(1) Buck circuit-step-down chopper, whose output average voltage Uo is less than the input voltage Ui and has the same polarity.
(2) Boost circuit-step-up chopper, whose output average voltage Uo is greater than the input voltage Ui and has the same polarity.
(3) Buck-Boost circuit-buck or boost chopper, whose output average voltage Uo is greater than or less than the input voltage Ui, with opposite polarity and inductive transmission.
(4) Cuk circuit-step-down or step-up chopper, whose output average voltage Uo is greater than or less than the input voltage UI, with opposite polarity and capacitive transmission. Nowadays, soft-switching technology has made a qualitative leap in DC/DC. The maximum output power of various ECI soft-switching DC/DC converters designed and manufactured by American VICOR Company is 300W, 600W and 800W, and the corresponding power density is (6, 2, 10, 17)W/cm3, and the efficiency is (80-90)%. A high-frequency switching power supply module RM series with soft-switching technology recently introduced by NemicLambda Company of Japan has a switching frequency of (200~300)kHz and a power density of 27 W/cm3. The synchronous rectifier (MOS-FET instead of Schottky diode) is adopted, which improves the efficiency of the whole circuit to 90%.
AC/DC conversion
AC/DC conversion converts AC to DC, and its power flow direction can be bidirectional. The power flow from power supply to load is called "rectification", and the power flow from load to power supply is called "active inverter". The input of AC/DC converter is 50/60Hz alternating current, so it must be rectified and filtered, so a relatively large filter capacitor is necessary. At the same time, due to the restrictions of safety standards (such as UL, CCEE, etc.) and EMC instructions (such as IEC, FCC, CSA), EMC filter must be added to the AC input side and components meeting safety standards must be used, which limits the miniaturization of AC/DC power supply. In addition, Because of the internal high frequency, high voltage and high current switch action, it is more difficult to solve the EMC electromagnetic compatibility problem, which also puts forward high requirements for the internal high-density installation circuit design. For the same reason, the high voltage and high current switch increases the power consumption and limits the modularization process of AC/DC converter. Therefore, the optimization design method of power system must be adopted to achieve a certain degree of satisfaction.
AC/DC conversion can be divided into half-wave circuit and full-wave circuit according to the wiring mode of the circuit. According to the number of power phases, it can be divided into single, three-phase and multi-phase. According to the working quadrant of the circuit, it can be divided into one quadrant, two quadrant, three quadrant and four quadrant.
