The development speed of LED switching power supplies has seen a significant technological leap in recent years, and the speed of new product replacement has also accelerated. As the last design step, the design of the PCB is also very important, because once there is a problem in this link, it is likely to generate more electromagnetic interference to the entire LED switching power supply system, and the stability and safety of the power supply work. It will also have an adverse effect. So, what is the design of the PCB is correct? Through the component layout research and market practice results of LED power supply in recent years, even if the circuit schematic designed in the early stage of development is very correct, once the design of the PCB is problematic, it will also be detrimental to the reliability of electronic equipment. The impact, such as the interference caused by the poor consideration of the power supply and the ground wire, will degrade the performance of the product. Therefore, when designing the PCB board, the correct method is needed. In a PCB board commonly used in a switching power supply, usually every switching power supply has four current loops, which are an input signal source current loop, a power switch AC loop, an output rectification AC loop, and an output load current loop. The input loop charges the input capacitor through an approximately DC current. The filter capacitor acts primarily as a broadband energy storage. Similarly, the output filter capacitor is also used to store high frequency energy from the output rectifier while eliminating the DC energy of the output load loop. Therefore, the terminals of the input and output filter capacitors are very important. The input and output current loops should be connected to the power supply only from the terminals of the filter capacitor. The setting and connection of the input and output loops is very important for the entire printed circuit board, and its reasonableness will directly affect the size of the electromagnetic interference. If the connection between the input and output circuits and the power switch and rectifier circuit cannot be directly connected to the terminals of the capacitor, the AC energy will be radiated into the environment by the input or output filter capacitor. The AC circuit of the power switch AC circuit and rectifier contains high amplitude trapezoidal current. The harmonic content of these currents is very high, and its frequency is much larger than the fundamental frequency of the switch. The peak amplitude can be up to 5 times the amplitude of the continuous input and output DC current. The transition time is usually It is about 50ns. These two loops are the most susceptible to electromagnetic interference, so these AC loops must be routed before other traces in the power supply are routed. In the input and input loops of the LED switching power supply, each loop is composed of three main components: a filter capacitor, a power switch or a rectifier, an inductor or a transformer. These three important components should be placed adjacent to each other, adjusting the component position so that the current path between them is as short as possible. The best way to establish a switching power supply layout is similar to its electrical design. The best design flow is as follows: placing the transformer → designing the power switch current loop → designing the output rectifier current loop → connecting the control circuit to the AC power circuit → designing the input current source loop and input filter.
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