Abstract: High-frequency switching power supplies are the future trend. High-frequency switching enables miniaturization and allows them to enter a wider range of applications, especially in high-tech fields, driving the miniaturization and portability of high-tech products. Furthermore, the development and application of switching power supplies are of great significance in energy conservation, resource conservation, and environmental protection . Keywords: Switching power supply, high frequency, miniaturization 1 Introduction With the rapid development of power electronics technology, power electronic equipment is increasingly intertwined with people's work and life. Reliable power supplies are indispensable for electronic equipment. In the 1980s, computer power supplies were fully converted to switching power supplies, leading the way in power supply replacement for computers. In the 1990s, switching power supplies entered various electronic and electrical equipment fields. Program-controlled exchanges, communication equipment, electronic testing equipment power supplies, and control equipment power supplies have all widely adopted switching power supplies, further promoting the rapid development of switching power supply technology. A switching power supply utilizes modern power electronics technology to control the on and off time ratio of switching transistors to maintain a stable output voltage. Switching power supplies are generally composed of a pulse width modulation (PWM) control IC and MOSFETs. Compared to linear power supplies, the cost of both increases with increasing output power, but the rates of increase differ. At a certain output power point, the cost of linear power supplies is actually higher than that of switching power supplies—this cost reversal point. With the development and innovation of power electronics technology, switching power supply technology is constantly innovating, and this cost reversal point is increasingly shifting towards lower output power levels, providing a wide range of development opportunities for switching power supplies. High-frequency switching is the development direction of switching power supplies. Higher frequencies enable miniaturization and allow switching power supplies to enter a wider range of applications, especially in high-tech fields, driving the miniaturization and portability of high-tech products. Furthermore, the development and application of switching power supplies are of great significance in energy conservation, resource conservation, and environmental protection. 2. Classification of Switching Power Supplies The field of switching power supply technology involves the simultaneous development of related power electronic devices and switching frequency conversion technology. These two aspects mutually promote each other, driving the development of switching power supplies at a double-digit annual growth rate towards lighter, smaller, thinner, lower-noise, higher-reliability, and more interference-resistant designs. Switching power supplies can be divided into two main categories: AC/DC and DC/DC. DC/DC converters have now achieved modularization, and their design technology and manufacturing processes are mature and standardized both domestically and internationally, and have been recognized by users. However, the modularization of AC/DC converters, due to their own characteristics, has encountered more complex technical and manufacturing problems in the process of modularization. The structure and characteristics of the two types of switching power supplies are described below. 2.1 DC/DC conversion DC/DC conversion is the conversion of a fixed DC voltage into a variable DC voltage, also known as DC chopper. There are two working modes of choppers: one is pulse width modulation mode where Ts remains unchanged and ton is changed (general), and the other is frequency modulation mode where ton remains unchanged and Ts is changed (easily generates interference). The specific circuits are as follows: (1) Buck circuit - buck chopper, whose average output voltage Uo is less than the input voltage Ui, and the polarity is the same. (2) Boost circuit - boost chopper, whose average output voltage Uo is greater than the input voltage Ui, and the polarity is the same. (3) Buck-Boost circuit – a buck or boost chopper whose average output voltage Uo is greater than or less than the input voltage Ui, with opposite polarities and inductive transmission. (4) Cuk circuit – a buck or boost chopper whose average output voltage Uo is greater than or less than the input voltage UI, with opposite polarities and capacitive transmission. Today, soft-switching technology has brought about a qualitative leap in DC/DC converters. Various ECI soft-switching DC/DC converters designed and manufactured by VICOR in the United States have maximum output powers of 300W, 600W, and 800W, with corresponding power densities of (6, 2, 10, 17) W/cm³ and efficiencies of (80-90)%. Nemic Lambda in Japan recently launched the RM series of high-frequency switching power supply modules using soft-switching technology. Its switching frequency is (200-300) kHz, and its power density has reached 27 W/cm³. Using a synchronous rectifier (MOS-FET instead of Schottky diode), the overall circuit efficiency is increased to 90%. 2.2 AC/DC Conversion AC/DC conversion transforms alternating current (AC) into direct current (DC). The power flow can be bidirectional; power flowing from the power source to the load is called "rectification," and power flowing back from the load to the power source is called "active inversion." AC/DC converters accept 50/60Hz AC input. Because rectification and filtering are necessary, relatively large filter capacitors are essential. Furthermore, due to safety standards (such as UL and CCEE) and EMC directives (such as IEC, FCC, and CSA), EMC filtering and the use of safety-compliant components are required on the AC input side. This limits the miniaturization of AC/DC power supplies. Additionally, the high-frequency, high-voltage, and high-current switching operations increase the difficulty of resolving EMC issues, placing high demands on the internal high-density circuit design. For the same reason, high-voltage and high-current switching increases power consumption, limiting the modularization of AC/DC converters. Therefore, power system optimization design methods must be employed to achieve satisfactory efficiency. AC/DC converters can be classified according to their circuit wiring method into half-wave circuits and full-wave circuits. They can also be classified according to the number of power phases into single-phase, three-phase, and multi-phase. Furthermore, they can be classified according to the circuit's operating quadrant into one-quadrant, two-quadrant, three-quadrant, and four-quadrant circuits. 3. Selection of Switching Power Supplies Due to their unique circuit structure (multi-stage series connection), switching power supplies are less susceptible to input interference such as surge voltages. They also offer a significant advantage over linear power supplies in terms of output voltage stability, which can reach (0.5~1)%. As a power electronic integrated device, switching power supply modules should be selected with attention to the following points: 3.1 Output Current Selection Because switching power supplies have high efficiency, generally exceeding 80%, the maximum current absorbed by the equipment should be accurately measured or calculated when selecting their output current. This ensures the selected switching power supply has a high performance-price ratio. The typical output current calculation formula is: Is = KIf Where: Is—rated output current of the switching power supply; If—maximum current absorbed by the equipment; K—margin coefficient, generally taken as 1.5 to 1.8. 3.2 Grounding Switching power supplies generate more interference than linear power supplies. For equipment sensitive to common-mode interference, grounding and shielding measures should be taken. According to EMC restrictions such as ICE1000, EN61000, and FCC, all form-factor switching power supplies must adopt EMC electromagnetic compatibility measures. Therefore, switching power supplies should generally have an EMC electromagnetic compatibility filter. For example, the HA series switching power supplies from Leadway Technology require connecting their FG terminals to earth or the user's chassis to meet the above electromagnetic compatibility requirements. 3.3 Protection Circuit Switching power supplies must have overcurrent, overheat, and short-circuit protection functions in their design. Therefore, switching power supply modules with comprehensive protection functions should be prioritized during the design process. Furthermore, the technical parameters of their protection circuits should match the operating characteristics of the electrical equipment to avoid damage to the equipment or the switching power supply. 4. Development Trends of Switching Power Supply Technology The development direction of switching power supplies is high frequency, high reliability, low power consumption, low noise, anti-interference, and modularity. Since high frequency is a key technology for making switching power supplies lightweight, small, and thin, major international switching power supply manufacturers are committed to simultaneously developing new, highly intelligent components, especially improving the losses of secondary rectifier devices, and increasing technological innovation in power ferrite (Mn-Zn) materials to improve magnetic performance at high frequencies and high magnetic flux densities (Bs). Capacitor miniaturization is also a key technology. The application of SMT technology has enabled significant progress in switching power supplies, allowing components to be arranged on both sides of the circuit board to ensure the switching power supply is lightweight, small, and thin. The increasing frequency of switching power supplies necessitates innovation in traditional PWM switching technology. Soft-switching technologies such as ZVS and ZCS have become mainstream in switching power supplies, significantly improving their efficiency. Regarding high reliability, US switching power supply manufacturers have reduced stress on components by lowering operating current and junction temperature, greatly enhancing product reliability. Modularization is the overall trend in switching power supply development. Modular power supplies can be used to form distributed power systems, designed as N+1 redundant power systems, and their capacity can be expanded through parallel connections. Addressing the issue of high operating noise in switching power supplies, simply pursuing higher frequencies will inevitably increase noise. Theoretically, partial resonant converter technology can achieve both higher frequencies and lower noise. However, practical applications of partial resonant converter technology still face technical challenges, requiring further research to make this technology practical. Continuous innovation in power electronics technology gives the switching power supply industry broad development prospects. To accelerate the development of my country's switching power supply industry, it is essential to pursue technological innovation and forge a unique path of industry-academia-research collaboration, contributing to the rapid development of my country's national economy.