Analysis of New Switching Power Supply Technology

　　Switching power supply has always been a very popular technology in the electronics industry. Although its performance cannot bring about earth-shaking changes in our daily lives, its development trend is one of the issues that electronic product designers and merchants are concerned about. New products will inevitably drive more merchant orders and customer consumption. According to the current situation and development of switching power supplies in the market, five major design performance focus points are summarized, which are analyzed one by one below.

　　Focus 1: Innovation of high-frequency magnetic and synchronous rectification technology

　　In the power supply system, we will use a large number of magnetic components. The materials, structures and performances of high-frequency magnetic components are different from those of industrial frequency magnetic components, and there are many issues that need to be studied. We have certain requirements for the performance of magnetic materials used in high-frequency magnetic components, among which low loss and good heat dissipation performance are basic requirements. Only by meeting such standards can we optimize the product and have superior magnetic properties. Magnetic materials suitable for megahertz frequencies are a major concern of users, and nanocrystalline soft magnetic materials have also been developed and applied.

　　After having high-frequency technology, improving the efficiency of switching power supplies is another technical challenge, which requires our technical designers to develop and apply soft switching technology. The research on this soft switching technology has become a scientific research hotspot in the industry for many years and has attracted the attention of more and more designers.

　　We have seen such technologies, such as synchronous rectification SR technology, which uses a reverse-connected power MOS tube as a switching diode for rectification, replacing a Schottky diode (SBD). This design can reduce the tube voltage drop, thereby improving circuit efficiency. This is what we do for low-voltage, high-current output soft-switching converters. We try every means to reduce the on-state loss of the switch and further improve its efficiency.

　　Focus 2: Improvement of power density of switching power supplies

　　Improving the power density of switching power supplies and making them smaller and lighter is one of the concerns of designers. Miniaturization and weight reduction of power supplies are particularly important for portable electronic devices (such as mobile phones, digital cameras, etc.). Designers will use three solutions to reduce the power density of switching power supplies.

　　The first solution is to achieve 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 components in the circuit.

　　The second solution is to use new capacitors. To reduce the size and weight of power electronic equipment, it is necessary to 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 should have large capacitance, small equivalent series resistance (ESR), and small size, so as to reduce the size of new capacitors.

　　The third solution is to improve 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" and "vibration-voltage" conversion properties of piezoelectric ceramic materials to transmit energy. Its equivalent circuit is like a series-parallel resonant circuit, and improvements are made to the application of piezoelectric transformers.

　　Focus 3: Power semiconductor device performance

　　As early as the end of the last century, Infineon launched the cold MOS tube, which adopts the "super junction" (Super-Junction) structure, also known as super junction power MOSFET. The operating voltage is 600V ~ 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 the promising high-frequency power semiconductor electronic device 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 exploration, research and improvement, the voltage and current ratings of IGBT have reached 3300V/1200A and 4500V/1800A respectively. The withstand voltage of high-voltage IGBT has reached 6500V. The upper limit of the operating frequency of general IGBT is 20kHz~40kHz. The IGBT manufactured by the new technology based on the punch-through (PT) structure can work at 150kHz (hard switching) and 300kHz (soft switching), which greatly improves the application performance.

　　The IGBT technology progress we see is actually a compromise between on-state voltage drop, fast switching and high withstand voltage capability. With different processes and structural forms, IGBT has been developed into punch-through (PT), non-punch-through (NPT), soft punch-through (SPT), trench and field stop (FS) types in the 20-year history.

　　Silicon carbide SiC is an ideal material for power semiconductor device wafers. Its advantages are: wide bandgap, high operating temperature (up to 600°C), good thermal stability, small on-resistance, good thermal conductivity, extremely small leakage current, high PN junction withstand voltage, etc., which is conducive to the manufacture of high-frequency, high-power semiconductor electronic components that are resistant to high temperatures. It is not difficult to see that silicon carbide will be the most likely new power semiconductor device material to be successfully applied in the 21st century, and its appearance will greatly improve the performance of our original product design.

　　Focus 4: Distributed power structure

　　Before talking about the distributed power structure, let's talk about the distributed power system. There are two types of distributed power systems: two-level structure and three-level structure. The distributed power system is suitable for use as a power supply for large workstations (such as image processing stations) composed of ultra-high-speed integrated circuits, large digital electronic switching systems, etc. It has the advantages of realizing modularization of DC/DC converter components, easy to achieve N+1 power redundancy, easy to expand load capacity, can reduce the current and voltage drop on the 48V bus, easy to achieve uniform heat distribution, convenient heat dissipation design, good transient response, and online replacement of failed modules.

　　Focus 5: PFC converter

　　Since there are rectifier elements and filter capacitors at the input end of the AC/DC conversion circuit, when the sinusoidal voltage is input, the power factor of the electronic equipment powered by the single-phase rectifier power supply on the grid side (AC input end) is only 0.6 to 0.65. With the PFC (power factor correction) converter, 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 was developed earlier at home and abroad, and the technology is relatively mature; although there are many types of topology types and control strategies for three-phase APFC, there is still room for further research and development.

　　Generally, a high power factor AC/DC switching power supply is composed of a two-stage topology. For a low-power AC/DC switching power supply, the overall efficiency is low and the cost is high when a two-stage topology is used.

　　If the input power factor requirement is not particularly high, the PFC converter and the subsequent DC/DC converter can be combined into a topology to form a single-stage high power factor AC/DC switching power supply. Only one main switch tube is used to correct the power factor to above 0.8 and make the output DC voltage adjustable. The adjusted DC voltage promotes the application performance of the PFC converter, ultimately achieving overall efficiency improvement and cost reduction.