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Ten points of attention in the development of switching power supply technology

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  • Time of issue:2017-03-14 09:27
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(Summary description)In the 1960s, the advent of switching power supplies gradually replaced linear stabilized power supplies and SCR phase-controlled power supplies. Over the past 40 years, switching power supply technology has developed and changed rapidly, and has experienced three development stages of power semiconductor devices, high frequency and soft switching technology, and integration technology of switching power supply systems.

Ten points of attention in the development of switching power supply technology

(Summary description)In the 1960s, the advent of switching power supplies gradually replaced linear stabilized power supplies and SCR phase-controlled power supplies. Over the past 40 years, switching power supply technology has developed and changed rapidly, and has experienced three development stages of power semiconductor devices, high frequency and soft switching technology, and integration technology of switching power supply systems.

  • Categories:Industry news
  • Author:
  • Origin:
  • Time of issue:2017-03-14 09:27
  • Views:
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   In the 1960s, the advent of switching power supplies gradually replaced linear stabilized power supplies and SCR phase-controlled power supplies. Over the past 40 years, switching power supply technology has developed and changed rapidly, and has experienced three development stages of power semiconductor devices, high frequency and soft switching technology, and integration technology of switching power supply systems.  


Power semiconductor devices have evolved from bipolar devices (BPT, SCR, GTO) to MOS devices (power MOSFET, IGBT, IGCT, etc.), making it possible for power electronic systems to achieve high frequency and greatly reduce conduction losses. It is also simpler.


   Since the 1980s, the development and research of high-frequency and soft-switching technologies have enabled power converters to have better performance, lighter weight, and smaller size. High-frequency and soft-switching technologies have been one of the hotspots in the international power electronics industry in the past 20 years.


   In the mid-1990s, integrated power electronic system and integrated power electronic module (IPEM) technology began to develop. It is one of the new problems that need to be solved urgently in the international power electronics industry today.


Focus 1: Power semiconductor device performance

   In 1998, Infineon introduced a cold MOS tube, which uses a "Super-Junction" (Super-Junction) structure, so it is also called a super-junction power MOSFET. The working voltage is 600V~800V, the on-state resistance is almost reduced by an order of magnitude, and the switching speed is still maintained. It is a promising high-frequency power semiconductor device.   When the IGBT first appeared, the voltage and current ratings were only 600V and 25A. For a long period of time, the withstand voltage level was limited to 1200V~1700V. After a long period of research and improvement, the voltage and current ratings of the IGBT have reached 3300V/1200A and 4500V/1800A respectively, and the single-chip withstand voltage of the high-voltage IGBT has reached At 6500V, the upper limit of the working frequency of general IGBT is 20kHz~40kHz. The IGBT manufactured with new technology based on punch-through (PT) structure can work at 150kHz (hard switching) and 300kHz (soft switching).  The technological progress of IGBT is actually a compromise between on-state voltage drop, fast switching and high withstand voltage capability. With the difference in technology and structure, IGBT has the following types in the 20-year historical development process: punch-through (PT) type, non-punch-through (NPT) type, soft punch-through (SPT) type, trench type and electric field cut-off (FS) type. Silicon carbide SiC is an ideal material for power semiconductor device wafers. Its advantages are: forbidden bandwidth, high operating temperature (up to 600°C), good thermal stability, low on-state resistance, good thermal conductivity, extremely small leakage current, and PN junction High withstand voltage is conducive to the manufacture of high-frequency and high-power semiconductor devices with high temperature resistance.  It is foreseeable that silicon carbide will be the most likely material for new power semiconductor devices to be successfully applied in the 21st century.


Focus Two: Switching Power Supply Power Density

   Increasing the power density of the switching power supply, making it smaller and lighter, is the goal that people are constantly striving to pursue. The high frequency of power supply is one of the research hotspots in the international power electronics industry. Miniaturization and weight reduction of power supplies are particularly important for portable electronic devices (such as mobile phones, digital cameras, etc.). The specific methods to miniaturize the switching power supply are:   


One is high frequency. In order to achieve high power density of the power supply, the operating frequency of the PWM converter must be increased, thereby reducing the volume and weight of the energy storage element in the circuit. 


The second is the application of piezoelectric transformers. The application of piezoelectric transformers can enable high-frequency power converters to achieve lightness, smallness, thinness and high power density. Piezoelectric transformers use the unique characteristics of piezoelectric ceramic materials of "voltage-vibration" transformation and "vibration-voltage" transformation to transfer energy, and its equivalent circuit is like a series-parallel resonance circuit, which is a research hotspot in the field of power conversion. one.  


The third is to use new capacitors. In order to reduce the size and weight of power electronic equipment, we must try to improve the performance of capacitors, increase energy density, and research and develop new types of capacitors suitable for power electronics and power supply systems, requiring large capacitance, small equivalent series resistance ESR, and volume Wait a minute.
 

Focus 3: High-frequency magnetic and synchronous rectification technology

   A large number of magnetic components are used in the power supply system. The materials, structure and performance of high-frequency magnetic components are different from those of power frequency magnetic components. There are many problems that need to be studied. The magnetic materials used in high-frequency magnetic components have the following requirements: low loss, good heat dissipation performance, and superior magnetic performance. Magnetic materials suitable for megahertz frequencies have attracted people's attention, and nanocrystalline soft magnetic materials have also been developed and applied.   After the high frequency, in order to improve the efficiency of the switching power supply, it is necessary to develop and apply soft switching technology. It has been a research hotspot in the international power supply industry in the past few decades.   For the soft switching converter with low voltage and large current output, the measure to further improve its efficiency is to try to reduce the on-state loss of the switch. For example, the synchronous rectification SR technology, which uses the reverse connection of the power MOS tube as the switching diode for rectification, instead of the Schottky diode (SBD), can reduce the tube voltage drop and improve the circuit efficiency.


Focus 4: Distributed power structure

  Distributed power supply system is suitable for use as a power supply for large workstations (such as image processing stations) and large digital electronic switching systems composed of ultra-high-speed integrated circuits. Its advantages are: DC/DC converter components can be modularized; easy Realize N+1 power redundancy, improve system reliability; easy to expand load capacity; can reduce the current and voltage drop on the 48V bus; easy to achieve uniform heat distribution and easy heat dissipation design; good transient response; can be replaced online Failed modules, etc. There are two types of distributed power systems, one is a two-level structure, and the other is a three-level structure.
 

Focus 5: PFC converter

   Because there are rectifier elements and filter capacitors at the input end of the AC/DC conversion circuit, when sinusoidal voltage is input, the power factor of the single-phase rectifier power supply for electronic equipment is only 0.6 to 0.65 on the grid side (AC input end). Using PFC (power factor correction) converters, the grid-side power factor can be increased to 0.95 to 0.99, and the input current THD is less than 10%. It not only controls the harmonic pollution of the power grid, but also improves the overall efficiency of the power supply. This technology is called Active Power Factor Correction APFC. Single-phase APFC has been developed earlier at home and abroad, and the technology is relatively mature; although there are many types of topology and control strategies for three-phase APFC, they still need to be researched and developed.   Generally, high power factor AC/DC switching power supplies are composed of two-level topology. For low-power AC/DC switching power supplies, the two-level topology is generally low in efficiency and high in cost. If the requirements for the input power factor are not particularly high, combine the PFC converter and the downstream DC/DC converter into a topology to form a single-stage high-power-factor AC/DC switching power supply. Only one main switch tube can be used. The power factor is corrected to above 0.8 and the output DC voltage is adjustable. This topology is called a single-tube single-stage or S4PFC converter.
 

Focus 6: Voltage Regulator Module VRM

   voltage regulator module is a type of low-voltage, high-current output DC-DC converter module that provides power to the microprocessor. Now that the speed and efficiency of data processing systems are increasing day by day, in order to reduce the electric field intensity and power consumption of the microprocessor IC, the logic voltage must be reduced. The logic voltage of the new generation of microprocessors has been reduced to 1V, and the current is as high as 50A-100A. Therefore, the requirements for VRM are: low output voltage, large output current, high current change rate, fast response, etc.


Focus 7: Fully digital control   The control of the power supply has been controlled by analog control, analog-digital mixed control, and has entered the fully digital control stage. Full digital control is a new development trend, which has been applied in many power conversion equipment.   But in the past, digital control was less used in DC/DC converters. In the past two years, high-performance all-digital control chips for power supplies have been developed, and the cost has been reduced to a reasonable level. Many companies in Europe and the United States have developed and manufactured digital control chips and software for switching converters. The advantages of all-digital control are: digital signals can be calibrated in smaller quantities compared with mixed analog-digital signals, and the chip price is lower; accurate digital correction of current detection errors can be carried out, and voltage detection can be more accurate; it can be realized quickly, Flexible control design.
 

Focus Eight: Electromagnetic Compatibility

   The EMC problem of high frequency switching power supply has its particularity. The di/dt and dv/dt generated by the power semiconductor switch tube during the switching process cause strong conduction electromagnetic interference and harmonic interference. Some conditions will also cause strong electromagnetic field (usually near field) radiation. Not only seriously pollutes the surrounding electromagnetic environment, but also causes electromagnetic interference to nearby electrical equipment, and may also endanger the safety of nearby operators. At the same time, the internal control circuit of the power electronic circuit (such as the switching converter) must also be able to withstand the EMI generated by the switching action and the interference of the electromagnetic noise of the application site. The above-mentioned peculiarities, coupled with the specific difficulties in EMI measurement, in the field of electromagnetic compatibility of power electronics, there are many frontier topics of cross-border science to be studied. Many universities at home and abroad have carried out research on electromagnetic interference and electromagnetic compatibility of power electronic circuits, and have achieved many gratifying results. Research results in recent years have shown that the source of electromagnetic noise in switching converters mainly comes from the voltage and current changes caused by the switching action of the main switching device. The faster the change rate, the greater the electromagnetic noise.
 

Focus 9: Design and Test Technology

  Modeling, simulation and CAD are a new design tool. In order to simulate the power system, a simulation model must first be established, including power electronic devices, converter circuits, digital and analog control circuits, and magnetic components and magnetic field distribution models. The thermal model, reliability model and EMC model of the switch tube must also be considered. . Various models are very different, and the development direction of modeling is: digital-analog hybrid modeling, hybrid hierarchical modeling, and combining various models into a unified multi-level model. The CAD of the power supply system includes main circuit and control circuit design, device selection, parameter optimization, magnetic design, thermal design, EMI design and printed circuit board design, reliability estimation, computer-aided synthesis and optimization design, etc. The use of simulation-based expert system for power system CAD can optimize the performance of the designed system, reduce design and manufacturing costs, and perform manufacturability analysis. This is one of the development directions of simulation and CAD technology in the 21st century. In addition, the development, research and application of thermal testing, EMI testing, and reliability testing of power systems should also be vigorously developed.
 

Focus ten: system integration technology

The manufacturing characteristics of    power equipment are: many non-standard parts, high labor intensity, long design cycle, high cost, low reliability, etc., while users require the power products produced by the manufacturer to be more practical and more reliable, Lighter, smaller, and lower cost. These conditions have put power supply manufacturers under tremendous pressure and urgently need to carry out research and development of integrated power modules, so that the goals of standardization, modularization, manufacturability, mass production, and cost reduction of power supply products can be achieved. In fact, in the development process of power integration technology, it has gone through the development stages of modularization of power semiconductor devices, integration of power and control circuits, and integration of passive components (including magnetic integration technology). In recent years, the development direction is to integrate low-power power systems on a chip, which can make power products more compact, smaller in size, and reduce lead lengths, thereby reducing parasitic parameters. On this basis, integration can be achieved, with all components and control and protection integrated in one module.

   In the 1990s, with the development of large-scale distributed power systems, integrated design concepts were promoted to the integration of larger capacity and higher voltage power systems, which increased the level of integration, and integrated power electronic modules ( IPEM). IPEM integrates and encapsulates power devices with circuit, control, detection, and execution components to obtain standard and manufacturable modules, which can be used for standard designs, as well as special and special designs. The advantage is that it can provide users with products quickly and efficiently, significantly reduce costs and improve reliability.   In short, power system integration is one of the new problems that need to be solved urgently in the international power electronics industry today.

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