The power module is a power supply that can be directly mounted on the printed circuit board. Its feature is that it can provide power for application specific integrated circuit (ASIC), digital signal processor (DSP), microprocessor, memory, field programmable gate array (FPGA) and other digital or analog loads. In general, such modules are called point of load (POL) power supply system or point of use power supply system (pups). Due to the advantages of modular structure, modular power supply is widely used in switching equipment, access equipment, mobile communication, microwave communication, optical transmission, routers and other communication fields, as well as automotive electronics, aerospace and so on.
Generally speaking, such modules are called point of load (POL) power supply system or point of use power supply system (pups). Due to the advantages of modular structure, modular power supply is widely used in switching equipment, access equipment, mobile communication, microwave communication, optical transmission, routers and other communication fields, as well as automotive electronics, aerospace and so on.
Especially in recent years, due to the rapid development of data services and the continuous promotion of distributed power supply system, the increase of module power supply has exceeded that of primary power supply. The module power supply has isolation function, strong anti-interference ability, and its own protection function is convenient for integration. With the extensive use of semiconductor technology, packaging technology and high-frequency soft switches, the power density of module power supply is getting larger and larger, the conversion efficiency is getting higher and higher, and the application is becoming simpler and simpler.
In the field of switching power supply technology, people develop relevant power electronic devices while developing switching frequency conversion technology. The two promote each other and promote the development of switching power supply towards light, small, thin, low noise, high reliability and anti-interference with a growth rate of more than two digits every year. Switching power supply can be divided into ac/dc and dc/dc. Dc/dc converter has realized modularization, and the design technology and production process have been mature and standardized at home and abroad, and have been recognized by users. However, the modularization of ac/dc, due to its own characteristics, has encountered more complex technical and process manufacturing problems in the process of modularization. The following describes the structure and characteristics of the two types of switching power supplies
dc chopping 
Dc/dc conversion is to convert variable DC voltage into fixed DC voltage, also known as DC chopping. There are two working modes of the chopper, one is that the pulse width modulation mode TS remains unchanged and the ton (general) is changed, and the other is frequency modulation（
(1) Buck circuit - step-down chopper, whose output average voltage U0 is less than input voltage UI, with the same polarity.
(2) Boost circuit - boost chopper, whose output average voltage U0 is greater than input voltage UI, with the same polarity.
(3) Buck boost circuit - step-down or step-up chopper, whose output average voltage U0 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 U0 is greater than or less than input voltage UI, with opposite polarity and capacitive transmission. There are also SEPIC and zeta circuits.
The above is a non isolated DC-DC converter circuit. The isolated DC-DC converter includes forward circuit, flyback circuit, half bridge circuit, full bridge circuit and push-pull circuit.
Today's soft switching technology has made a qualitative leap in dc/dc. Various ECI soft switching dc/dc converters designed and manufactured by VICOR company in the United States have maximum output power of 300W, 600W, 800W, etc., corresponding power density of (6.2, 10, 17) w/cm3 and efficiency of (80 ~ 90)%. A new high-frequency switching power supply module RM series with soft switching technology introduced by TDK lambda company of Japan has a switching frequency of (200 ~ 300) kHz and a power density of 27w/cm3. A synchronous rectifier (MOSFET instead of Schottky diode) is used to improve the efficiency of the whole circuit to 90%.
Transformation
Ac/dc conversion is to convert AC to DC. The 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, which must be rectified and filtered, so a relatively large filter capacitor is essential. At the same time, due to the limitations of safety standards (such as UL, CCEE, etc.) and EMC directives (such as IEC, FCC, CSA), EMC filtering and components meeting safety standards must be added to the AC input side, which limits the miniaturization of ac/dc power supply volume. In addition, due to the internal high frequency, high voltage The high current switch action makes it more difficult to solve the EMC problem, which also puts forward high requirements for the design of internal high-density installation circuit. For the same reason, the high voltage and high current switch increases the power loss and limits the modularization process of ac/dc converter. Therefore, the power system optimization design method 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. It can be divided into single-phase, three-phase and multi-phase according to the number of power phases. According to the working quadrant of the circuit, it can be divided into one quadrant, two quadrants, three quadrants and four quadrants.
Selection of switching power supply
As for the input anti-interference performance of switching power supply, due to the characteristics of its own circuit structure (multi-level series connection), it is difficult for general input interference such as surge voltage to pass through. Compared with linear power supply, switching power supply has greater advantages in the technical index of output voltage stability, and its output voltage stability can reach (0.5 ~ 1)%. As a power electronic integrated device, switching power supply module shall pay attention to the following points in selection:
Current selection
Since the switching power supply has high working efficiency, which can generally reach more than 80%, the maximum absorption current of the electrical equipment shall be accurately measured or calculated in the selection of its output current, so that the selected switching power supply has a high performance price ratio. The general output calculation formula is:
Is=KIf
Where: is - rated output current of switching power supply;
If - maximum absorption current of electric equipment;
K - margin coefficient, generally 1.5 ~ 1.8;
protection circuit 
The switching power supply must have the protection functions of overcurrent, overheating, short circuit, etc. in the design, the switching power supply module with complete protection functions shall be preferred, and the technical parameters of its protection circuit shall match the working characteristics of the electrical equipment to avoid damaging the electrical equipment or switching power supply.
Several major indicators
Power p=ui is the product of output voltage and output current.
Input voltage is divided into AC input and DC input.
The output voltage is usually DC output, but AC output is also available.
working temperature 
Isolation voltage: isolation is the separation of output and input circuits. It has the following functions:
1、 Current conversion;
2、 To prevent mutual interference between input and output;
3、 The signal characteristics of input and output circuits are too different, such as equipment that uses weak signals to control strong current
Package sizes are pin, patch, and screw.
The output includes single channel output, double channel output and multi-channel output. The power module is a power supply that can be directly mounted on the printed circuit board. Its feature is that it can provide power for application specific integrated circuit (ASIC), digital signal processor (DSP), microprocessor, memory, field programmable gate array (FPGA) and other digital or analog loads. In general, such modules are called point of load (POL) power supply system or point of use power supply system (pups). Due to the advantages of modular structure, modular power supply is widely used in switching equipment, access equipment, mobile communication, microwave communication, optical transmission, routers and other communication fields, as well as automotive electronics, aerospace and so on.