Classification of switching power supply, detailed explanation of AD/DC and DC/DC power supply.
Classification of switching power supply
People's technical field of switching power supply is to develop related power electronic devices while developing switching frequency conversion technology. The two mutually promote the development of switching power supply in the direction of light, small, thin, low noise, high reliability and anti-interference with an annual growth rate of more than two digits. Switching power supply can be divided into two categories: AC/DC and DC/DC. DC/DC converter has been modularized, and the design technology and production process have been matured and standardized at home and abroad, and have been recognized by users. However, the modularization of AC/DC has encountered more complicated technical and technological manufacturing problems in the process of modularization because of its own characteristics. The structure and characteristics of two types of switching power supplies are described below.
2.1 DC/DC conversion
DC/DC conversion is to convert a fixed DC voltage into a variable DC voltage, also known as DC chopping. Chopper works in two ways, one is that pulse width modulation mode Ts remains unchanged, changing ton (universal), and the other is that frequency modulation mode ton remains unchanged, changing Ts (prone to interference). Its specific circuit 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-boost chopper, whose output average voltage Uo is greater than the input voltage Ui, and the polarity is the same.
(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. Many ECI soft-switching DC/DC converters designed and manufactured by VICOR Company in the United States have * large output powers of 300W, 600W and 800W, and the corresponding power densities are (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%.
2.2 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 AC, so it must be rectified and filtered, so a relatively large filter capacitor is necessary. At the same time, due to the restrictions of 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 conforming to the first standard must be used, which limits the miniaturization of AC/DC power supply. 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.
