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How to do PCB circuit design for LED switching power supply ?

                                              How to do PCB circuit design for LED switching power supply ?

    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 power supply will also be adversely affected. So, how to do the PCB design 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. For example, the interference caused by improper consideration of power supply and ground wire will degrade the performance of the product. Therefore, when designing PCB, the correct method should be adopted.

    In a commonly used switching power supply of PCB, each switching power supply usually has four current loops, which are an input signal source current loop, a power switch AC loop, an output rectifying 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. The output filter capacitor is also used to store the 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 PCB, and its reasonableness will directly affect the size of the electromagnetic interference. If the connection between the input/output loop and the power switch/rectifier loop cannot be directly connected to the capacitor terminal, the AC energy will be radiated by the input or output filter capacitor to the PCB operating environment. The AC circuit of power switch and rectifier contains high trapezoidal current, the harmonic content of these currents is very high, the frequency is much larger than the fundamental frequency of the switch, the peak amplitude can be up to 5 times the continuous input/output DC current, and the transition time is usually about 50 ns. These two loops are the most susceptible to electromagnetic interference, so these AC loops must be designed before other circuits in the power supply.

    In the input/output loop of the LED switching power supply, each loop is composed of three main components: a filter capacitor, a power switch rectifier and an inductor transformer. These three important components should be placed adjacent to each other, and the components positions should be adjusted 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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