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Selection of switching power supply Switching power supply in the input anti-interference performance, due to its own circuit structure characteristics (multi-level series connection), general input interference such as surge voltage is difficult to pass, in the output voltage stability this technical index compared with linear power supply has a greater advantage, its output voltage stability can reach (0.5 ~ 1)%. As a power electronic integrated device, switching power supply module should pay attention to the following points in the selection:

3.1 Selection of output current Because the switching power supply has high work efficiency, generally can reach more than 80%, so in the selection of its output current, should accurately measure or calculate the maximum absorption current of the electrical equipment, so that the selected switching power supply has a high performance-price ratio, usually the output calculation formula is: Is=KIf, in the formula: Is—the rated output current of the switching power supply; If—the maximum absorbed current of the electrical equipment; K—margin coefficient, generally 1.5~1.8;

3.2 Grounding Switching power supply will produce more interference than linear power supply, common mode interference sensitive electrical equipment, should take grounding and shielding measures, according to ICE1000.EN61000.FCC and other EMC restrictions, shape switching power supply are EMC electromagnetic compatibility measures, so switching power supply should generally have EMC filter. For example, the HA series switching power supply of Leadhuafu Technology can connect its FG terminal to the earth or to the user's chassis to meet the above electromagnetic compatibility requirements.

3.3 Protection circuit The switching power supply must have over-current, overheating, short circuit and other protection functions in the design, so the switching power supply module with complete protection function should be preferred in the design, and the technical parameters of the protection circuit should match the working characteristics of the electrical equipment to avoid damage to the electrical equipment or switching power supply. Switching power supply is a voltage conversion circuit, the main work content is to boost and step-down, widely used in modern electronic products. Because the switching transistor always works in the "on" and "off" state, it is called a switching power supply.

Switching power supply is essentially an oscillation circuit, this way of converting electric energy, not only used in power supply circuits, but also in other circuit applications are also common, such as LCD backlight circuits, fluorescent lamps, etc. Compared with transformers, switching sources have the advantages of high efficiency, good stability and small size, but the disadvantage is that the power is relatively small, and it will cause high-frequency interference to the circuit, and the circuit is complex and difficult to maintain.