Switching power modules have always been a very popular technology in the electronics industry, and their development trends are issues that everyone must always pay attention to, otherwise they will not be able to keep up with the pace of technological development if they are not careful. Let’s briefly talk about several key points in the development of switching power supply module technology.
Point 1: Power semiconductor device performance
For example, in 1998, Infineon launched a cold mos tube, which uses a super-junction structure, also known as a super-junction power MOSFET. The operating voltage is 600V to 800V, the on-state resistance is almost reduced by an order of magnitude, and the switching speed is still fast. It is a promising high-frequency power semiconductor electronic device.
When IGBT first appeared, the voltage and current ratings were only 600V and 25Ah. For a long time, the withstand voltage level was limited to 1200V~1700V. After a long period of exploration, research and improvement, the voltage and current ratings of IGBT have now reached 3300V/1200A and 4500V/1800A respectively, and the single-chip withstand voltage of high-voltage IGBT has reached 6500V. Generally, the upper limit of the IGBT is 20kHz to 40kHz. IGBTs manufactured based on the IGBTs using new technologies based on the through-through (PT) structure can operate at 150kHz (hard switch) and 300kHz (soft switch). The technological progress of IGBT is actually a compromise between on-state voltage drop, fast switching and high voltage resistance. With the different processes and structural forms, IGBT has several types in its 20-year historical development process, including throughput (PT), non-through (NPT), soft-through (SPT), ditch type and electric field cutoff (FS) type.
SiC SiC is an ideal material for power semiconductor device chips. Its advantages are bandwidth barrier, high working temperature (up to 600℃), good thermal stability, small on-state resistance, good thermal conductivity, extremely small leakage current, high PN junction withstand voltage, etc., which is conducive to the manufacture of high-frequency and high power semiconductor electronic components that are resistant to high temperatures.
Point 2: Power density of switching power supply module
Improving the power density of switching power modules to make them smaller and lighter is the goal that people are constantly striving to pursue. Miniaturization of power supplies and weight reduction are particularly important for portable electronic devices. The specific method to miniaturize the switching power supply module is to increase the frequency. In order to achieve high power density of the power supply, the operating frequency of the PWM converter must be increased to reduce the volume weight of the energy storage element in the circuit.
Or use piezoelectric transformers, which can enable high-frequency power converters to achieve light, small, thin and high power density. Piezoelectric transformers use the voltage-vibration, conversion and vibration-voltage unique to piezoelectric ceramic materials. The conversion properties transmit energy. The equivalent circuit is like a series-parallel resonant circuit, which is one of the research hotspots in the field of power conversion.
In order to reduce the volume and weight of power electronic equipment, it is necessary to try to improve the performance of capacitors, improve the energy density, and study and develop new capacitors suitable for power electronics and module power systems, requiring large capacitance, small equivalent series resistance ESR, small volume, etc.
Point 3: High-frequency magnetic and synchronous rectification technology
A large number of magnetic components are used in power systems. The materials, structure and performance of high-frequency magnetic components are different from those of power frequency magnetic components, and there are many problems that need to be studied. There are requirements for low loss, good heat dissipation and superior magnetic properties for high-frequency magnetic components. Magnetic materials suitable for megahertz-level frequencies are of concern, and nanocrystalline soft magnetic materials have also been developed and used. After high frequency, in order to improve the efficiency of switching power supply modules, soft switching technology must be developed and applied. For soft switch converters with low voltage and high current output, the measure to further improve their efficiency is to try to reduce the on-state loss of the switch. For example, synchronous rectification SR technology, that is, the reverse connection of the power MOS tube is used as a rectification switch diode instead of the SBD, which can reduce the tube voltage drop and improve circuit efficiency.
Point 4: Distribute the power supply structure
The distributed power supply system is suitable for use as a power supply for large workstations composed of ultra-high-speed integrated circuits, large digital electronic switching systems, etc. Its advantage is that it can realize the modularization of DC-DC converter components, easily achieve N+1 power redundancy, easily amplify load capacity, and reduce the current and voltage drop on the 48V bus. It is easy to achieve uniform heat distribution, easy to dissipate heat, design, good transient response, and can replace failure modules online. There are now two types of distributed power systems and three-level structures.
Point 5: PFC converter
Since the input end of the AC-DC conversion circuit has rectifier components and filter capacitors, when the sine voltage is input, the power factor of the electronic equipment powered by a single-phase rectifier power supply is only 0.6~0.65 on the grid side (AC input end). Using PFC (Power Factor Correction) converter, the power factor on the grid side can be increased to 0.95~0.99, and the input current THD is less than 10%. It not only cures harmonic pollution in 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 is developed earlier at home and abroad, and the technology is more mature. Although there are many topology types and control strategies for three-phase APFC, they still need to be studied and developed.
Generally, high-power factor AC-DC switching power supply modules are composed of two-stage topology. For low-power AC-DC switching power supply modules, the two-stage topology is generally inefficient and cost-effective. If the power factor requirements for the input end are not particularly high, the PFC converter and the later DC-DC converter are combined into one topology to form a single-stage high-power factor AC-DC switching power supply module. Only one main switch tube can correct the power factor to above 0.8 and make the output DC voltage adjustable. This topology is called a single-tube single-stage S4PFC converter.
Point 6: Voltage Regulator Module VRM
The voltage regulator module is a type of low-voltage, high-current output DC-DC converter module that provides power to the microprocessor. Now the speed and efficiency of data processing systems are increasing day by day. In order to reduce the electric field strength and power consumption of microprocessor ICs, the logic voltage must be reduced. The logic voltage of the new generation of microprocessors has been reduced to 1V, while the current is as high as 50A~100A, so there are requirements for VRM, such as very low output voltage, large output current, high current change rate, and fast response.
Point 7: Full digital control
The power supply control has been controlled by analog and analog-digital hybrid control, and has entered the full digital control stage. Full digital control is a new development trend and has been used in many power conversion devices, but digital control has been used less in DC-DC converters in the past. In recent years, high-performance fully digital control chips for power supply have been developed, and the cost has been reduced to a relatively reasonable level. Many companies in Europe and the United States have developed and manufactured digital control chips and software for switch converters. The advantage of full digital control is that digital signals can be calibrated in smaller quantities compared to hybrid analog signals, and the chip price is also cheaper. The current detection error can be accurately digitally corrected, and the voltage detection is more accurate, which can achieve a fast and flexible control design.
Point 8: Electromagnetic compatibility
The electromagnetic compatibility EMC problem of high-frequency switching power supply modules has its own characteristics. The di/dt and dv/dt generated by the power semiconductor switch tube during the switching process cause powerful conductive electromagnetic interference and harmonic interference. Some situations can also cause strong electromagnetic field (usually near field) radiation, which not only seriously pollutes the surrounding electromagnetic environment, causes electromagnetic interference to nearby electrical equipment, but may also endanger the safety of nearby operators. At the same time, the control circuits inside power electronic circuits (such as switch converters) must also be able to withstand the interference of EMI generated by switching operations and electromagnetic noise on the application site. The above special features, coupled with the specific difficulties in EMI measurement, there are many scientific cutting-edge topics in the field of electromagnetic compatibility of power electronics that need to be studied. Research results in recent years have shown that the electromagnetic noise source in the switching converter mainly comes from the voltage and current changes generated by the switching action of the main switching device. The faster the change speed, the greater the electromagnetic noise.
Point 9: Design and Testing Technology
Modeling, simulation and CAD are new design tools. To simulate a power supply system, first of all, we must establish a simulation model, including power electronic devices, converter circuits, digital and analog control circuits, magnetic components and magnetic field distribution models, etc., and also consider the thermal model of the switch tube, EMC model, etc. Various models vary greatly, and the development direction of modeling is digital-analog hybrid modeling, hybrid hierarchical modeling, and the formation of various models into a unified multi-level model.
The CAD of the module power supply system includes main circuit and control circuit design, component selection, parameter optimization, magnetic design, thermal design, EMI design and printed circuit board design, estimation, computer-aided synthesis and optimization design, etc. Using simulation-based systems to perform CAD of power systems can optimize the designed system performance, reduce design and manufacturing costs, and perform manufacturability analysis. It is one of the development directions of simulation and CAD technology. In addition, the development, research and application of thermal testing, EMI testing and other technologies of power supply systems should also be vigorously developed.
Point 10: System Integration Technology
The manufacturing characteristics of power supply equipment are many non-standard parts, high labor intensity, long design cycle, high cost, etc., while users require power supply products produced by power supply manufacturers to be more practical, lighter, and lower cost. These situations have put the module power supply manufacturers under tremendous pressure, and it is urgent to carry out research and development of high-integrated power supply modules, so that the goals of standardization, modularization, manufacturability, large-scale production, and cost reduction of power supply products can be achieved. In fact, in the development of power integration technology, it has gone through the development stages of modularization of power semiconductor devices, integration of power and control circuits, and integrated passive components (including magnetic integration technology). The development direction in recent years is to integrate a small power supply system on one chip, which can make the power supply product more compact, smaller in size, and reduce the lead length, thereby reducing parasitic parameters. On this basis, integration can be achieved, and all components and control protection can be integrated in one module.