The power module is a power supply that can be directly mounted on the printed circuit board. Its characteristics are that it can be an application-specific integrated circuit (ASIC), digital signal processor (DSP), microprocessor, memory, field programmable gate array (FPGA) ) And other digital or analog loads to provide power. Generally speaking, this type of module is called a point-of-load (POL) power supply system or a point-of-use power supply system (PUPS). Due to the many advantages of the modular structure, modular power supplies are widely used in switching equipment, access equipment, mobile communications, microwave communications, optical transmission, routers and other communications 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 systems, the increase in module power supplies has exceeded that of primary power supplies. With the extensive use of semiconductor technology, packaging technology, and high-frequency soft switching, the power density of module power supplies is increasing, the conversion efficiency is getting higher and higher, and the application is getting easier and simpler.
In the field of switching power supply technology, people develop related power electronic devices while developing switching frequency conversion technology. The two promote each other to promote the switching power supply to light, small, thin, low noise, high reliability, with a growth rate of more than two digits every year. The direction of anti-interference development. Switching power supplies can be divided into two categories: AC/DC and DC/DC. DC/DC converters have been modularized, and the design technology and production process have been mature and standardized at home and abroad, and have been recognized by users, but The modularization of AC/DC, due to its own characteristics, makes it encounter more complicated technical and process manufacturing problems in the process of modularization. The structure and characteristics of the two types of switching power supplies are described below.
DC/DC conversion is to convert a fixed DC voltage into a variable DC voltage, also known as DC chopping. There are two working modes of the chopper, one is the pulse width modulation method Ts unchanged, changing ton (universal), and the other is frequency modulation (1) Buck circuit-step-down chopper, its output average voltage
U0 is less than the input voltage Ui and has the same polarity.
(2) Boost circuit-boost chopper, its output average voltage
U0 is greater than the input voltage Ui and has the same polarity.
(3) Buck-Boost circuit-Buck or boost chopper, its
The average output voltage U0 is greater than or less than the input voltage Ui, the polarity is opposite, and the inductance transmission.
(4) Cuk circuit-buck or boost chopper, its output average power
The voltage U0 is greater than or less than the input voltage Ui, the polarity is opposite, and the capacitance is transmitted.
There are Sepic and Zeta circuits.
The above is a non-isolated circuit, and the isolated circuit includes a forward circuit, a flyback circuit, a half-bridge circuit, a full-bridge circuit, and a push-pull circuit.
Today's soft-switching technology makes DC/DC a qualitative leap. A variety of ECI soft-switching DC/DC converters designed and manufactured by the American VICOR company have maximum output power of 300W, 600W, 800W, etc., and the corresponding power density is (6.2 , 10, 17) W/cm3, the efficiency is (80～90)%. Japan’s NemicLambda company’s latest high-frequency switching power supply module RM series adopts soft-switching technology. Its switching frequency is (200～300)kHz, and the power density has reached 27W/cm3. It adopts synchronous rectifier (MOS-FET instead of Schott Base diode), so that the efficiency of the entire circuit is increased to 90%.
2.2 AC/DC conversion
AC/DC conversion converts AC to DC, and its power flow can be bidirectional. The power flow from the power source to the load is called "rectification", and the power flow from the load back to the power source is called "active inverter". AC/DC converter input is 50/60Hz alternating current, because it must be rectified and filtered, so relatively large filter capacitor is indispensable. At the same time, it meets safety standards (such as UL, CCEE, etc.) and EMC directives. (Such as IEC, FCC, CSA), the AC input side must add EMC filtering and use components that meet safety standards, which limits the miniaturization of the AC/DC power supply. In addition, due to the internal high-frequency, high-voltage, and large The current switching action makes it more difficult to solve the EMC problem, which also puts forward high requirements on the design of internal high-density mounting circuits. For the same reason, high-voltage and high-current switching makes the power supply loss increase, which limits The process of modularization of AC/DC converters requires the use of power system optimization design methods to achieve a certain degree of satisfaction with its work efficiency.
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-phase, three-phase, and multi-phase. 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
In terms of input anti-interference performance, switching power supply has its own circuit structure (multi-stage series connection), and it is difficult for general input interference such as surge voltage to pass. Compared with linear power supply, the technical index of output voltage stability Great advantage, its output voltage stability can reach (0.5～1)%. As a power electronic integrated device, switching power supply module should pay attention to the following points in the selection:
3.1 Selection of output current
Due to the high efficiency of the switching power supply, which can generally reach more than 80%, in the selection of its output current, the maximum absorption current of the electrical equipment should be accurately measured or calculated, so that the selected switching power supply has a high cost performance. Usually the output calculation formula is:
Is = KIf
Where: Is—the rated output current of the switching power supply;
If—the maximum absorption current of the electrical equipment;
K—Margin coefficient, generally 1.5～1.8;
3.3 Protection circuit
The switching power supply must have protection functions such as overcurrent, overheating, and short circuit in the design. Therefore, the switching power supply module with complete protection functions should be preferred in the design, and the technical parameters of the protection circuit should match the working characteristics of the electrical equipment. Avoid damaging electrical equipment or switching power supply.
Several indicators of power supply
Power P=UI, which is the product of output voltage and output current.
There are two types of input voltage: AC input and DC input.
The output voltage is generally DC output, but there are also AC outputs.
Isolation voltage: Isolation is to separate the output from the input circuit. It has the following functions:
1. Current conversion;
Second, in order to prevent mutual interference between input and output;
Third, the signal characteristics of the input and output circuits are too different, such as using weak signals to control strong current equipment
The package sizes are pin, patch, and spiral.
There are single output, dual output and multiple output. The power module is a power supply that can be directly mounted on the printed circuit board. Its characteristics are that it can be an application-specific integrated circuit (ASIC), digital signal processor (DSP), microprocessor, memory, field programmable gate array (FPGA) ) And other digital or analog loads to provide power. Generally speaking, this type of module is called a point-of-load (POL) power supply system or a point-of-use power supply system (PUPS). Due to the many advantages of the modular structure, modular power supplies are widely used in switching equipment, access equipment, mobile communications, microwave communications, optical transmission, routers and other communications fields, as well as automotive electronics, aerospace, and so on.