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　　Reliability Research on Switching Power Supply Design

　　There are two indispensable properties for the quality of electronic products - technology and reliability. As a successful electronic product is launched, the comprehensive level of two aspects affects product quality. As an important component in an electronic system, the reliability of power supply determines the safety performance of the entire system. Switching power supply is widely used in various fields due to its small size and high efficiency. However, how to improve the reliability of switching power supply is a matter of power electronics technology. An important turning point for a great leap forward.

　　1. Electromagnetic compatibility (EMC) design technology

　　Switching power supplies mostly use pulse width modulation (PWM) technology. The pulse waveform is rectangular, and its rising and falling edges contain a large number of harmonic components. In addition, the reverse recovery of the output rectifier will also produce electromagnetic interference (EMI), which has an impact Disadvantages to reliability, which makes electromagnetic compatibility of the system an important issue. There are three necessary conditions for the generation of electromagnetic interference: interference source, transmission medium, and sensitive receiving unit. EMC design is to destroy one of these three conditions.

　　For switching power supplies, the main purpose is to suppress interference sources, which are concentrated in the switching circuit and the output rectifier circuit. The technologies used include filtering technology, layout and wiring technology, shielding technology, grounding technology, sealing technology and other technologies.

　　2. Switching power supply electrical reliability engineering design technology

　　For power factor correction technology, it specifically refers to the fact that the harmonic current of the switching power supply pollutes the power grid and interferes with other common network equipment, which may cause the neutral line current of the three-phase four-wire system to be too large and cause an accident. The generally chosen solution is to use Switching power supply with power factor correction technology.

　　In terms of protection circuits, in order to enable the power supply to work reliably in various harsh environments, a variety of protection circuits should be added to the design, such as protection circuit measures against surge impact, over-under voltage, overload, short circuit, overheating, etc.

　　Regarding the choice of control strategy, it can be traced back to the fact that current-mode PWM control is a widely used method in small and medium-power power supplies. In DC-DC converters, the output ripple can be controlled at 10mV, which is superior to conventional power supplies with voltage-type control. Due to the limitation of switching losses in hard switching technology, the switching frequency is generally below 350kHz; soft switching technology enables switching devices to switch at zero voltage or zero current to achieve zero switching loss, thereby increasing the switching frequency to the megahertz level. This technology is mainly used in high-power systems and is less common in low-power systems.

　　For power supply methods, they are generally divided into centralized power supply systems and distributed power supply. Modern power electronic systems generally adopt distributed power supply systems to meet the requirements of high-reliability equipment.

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