Power supply has always been a very popular technology in the electronics industry, and its development trend is a problem that everyone must always pay attention to, otherwise it will not keep up with the pace of technological development. The author made a focus survey on the development of switching power supply technology, and came to the following ten popular concerns.
Focus One: Performance of Power Semiconductor Devices
In 1998, Infineon launched a cold mos tube, which uses a "super-junction" (Super-Junction) structure, so it is also known as super junction power MOSFET. The operating voltage is 600V ~ 800V, the on-state resistance is reduced by almost an order of magnitude, and the switching speed is still maintained The fast feature is a promising high-frequency power semiconductor electronic device.
When the IGBT first appeared, the voltage and current ratings were only 600V and 25A. For a long time, the withstand voltage level was limited to 1200V ~ 1700V. After a long period of research and improvement, the IGBT voltage and current ratings have reached 3300V, respectively / 1200A and 4500V / 1800A, the high-voltage IGBT monolithic withstand voltage has reached 6500V, the upper limit of the general IGBT operating frequency is 20kHz ~ 40kHz, based on the punch-through (PT) type structure using new technology IGBT manufacturing, can work at 150kHz (hard switching) And 300kHz (soft switching).
The technical progress of IGBT is actually a compromise between on-state voltage drop, fast switching and high withstand voltage capability. With the different processes and structural forms, in the 20-year history of IGBT development, there are the following types: 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, small on-state resistance, good thermal conductivity, very small leakage current, PN junction High withstand voltage, etc., is conducive to the production of high-frequency high-frequency high-power semiconductor electronic components.
It is foreseeable that silicon carbide will be a new type of power semiconductor device material that may be successfully applied in the 21st century.
Concern 2: Power density of switching power supply
Increasing the power density of switching power supplies to make them smaller and lighter is the goal that people are constantly striving for. The high frequency of power supply is one of the research hotspots in the international power electronics community. The miniaturization and weight reduction of power supplies are particularly important for portable electronic devices (such as mobile phones, digital cameras, etc.). Specific methods for miniaturizing 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 make high-frequency power converters light, small, thin and high power density. Piezoelectric transformers use the unique "voltage-vibration" transformation and "vibration-voltage" transformation properties of piezoelectric ceramic materials to transfer energy. Their equivalent circuit is like a series-parallel resonant circuit, which is one of the research hotspots in the field of power conversion.
The third is the use of new capacitors. In order to reduce the volume and weight of power electronic equipment, we must try to improve the performance of capacitors, increase energy density, and research and develop new capacitors suitable for power electronics and power supply systems. They require large capacitance, small ESR, and small volume. Wait a minute.
Concern 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.
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, and the current is as high as 50A-100A. So the requirements for VRM are: low output voltage, large output current, high current change rate, fast response, etc.
Focus 7: Full digital control
The control of the power supply has been controlled by analog, mixed analog and digital control, and entered the stage of full digital control. Full digital control is a new development trend and has been applied in many power conversion devices.
But in the past digital control has been used less in DC / DC converters. In the past two years, high-performance full-digital control chips for power supplies have been developed, and the cost has been reduced to a reasonable level. Several companies in Europe and America have developed and manufactured digital control chips and software for switching converters.
The advantages of full digital control are: the digital signal can be calibrated with a smaller amount than the mixed analog signal, and the chip price is lower; the digital correction of the current detection error can be performed, and the voltage detection is also more; fast and flexible Control design.
Concern 8: 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 switching tube during the switching process cause powerful conducted electromagnetic interference and harmonic interference. In some cases, it also causes strong electromagnetic field (usually near-field) radiation. Not only does it severely pollute the surrounding electromagnetic environment and cause electromagnetic interference to nearby electrical equipment, it may also endanger the safety of nearby operators. At the same time, the control circuit inside the power electronic circuit (such as a switching converter) must also be able to withstand the interference of EMI generated by the switching action and electromagnetic noise at the application site. The above-mentioned particularity, coupled with the specific difficulties in EMI measurement, in the field of electromagnetic compatibility of power electronics, there are many cutting-edge topics that need to be studied by people. 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 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, 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 supply system, we must first 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. 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. Using the expert system based on simulation to carry out the CAD of the power system can make the designed system performance superior, reduce design and manufacturing costs, and can do manufacturability analysis. It is one of the development directions of simulation and CAD technology in the 21st century. In addition, the development, research and application of power system thermal testing, EMI testing and other technologies should also be vigorously developed.
Focus ten: system integration technology
The manufacturing characteristics of power supply equipment are: many non-standard parts, large labor intensity, long design cycle, high cost, low reliability, etc., and users require the power supply products produced by the manufacturer to be more practical, more reliable, and lighter. , Lower cost. These circumstances have put power supply manufacturers under tremendous pressure, and there is an urgent need to carry out research and development of integrated power modules, so that the goals of standardization, modularization, manufacturability, scale production, and cost reduction of power supply products can be achieved. In fact, in the development process of power supply integration technology, it has experienced the development stages of power semiconductor device modularization, power and control circuit integration, and integration of passive components (including magnetic integration technology). In recent years, the development direction is to integrate a low-power power supply system on one chip, which can make the power supply product more compact and smaller, and also reduce the length of the lead, thereby reducing the parasitic parameters. On this basis, integration can be achieved, all components and control protection are integrated into a module.
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