The research and development speed of LED switching power supplies has made a significant technological leap in recent years, and the speed of new product upgrades has also accelerated a lot. As the last design link, PCB design is also particularly important, because once a problem occurs in this link, it is likely to cause more electromagnetic interference to the entire LED switching power supply system, which will affect the stability and safety of the power supply. also
will cause adverse effects. So, what is the correct way to design PCB?
Through component layout research and market practice results of LED power supplies in recent years, it has been proven that even if the circuit schematic diagram designed in the early stage of research and development is very correct, once there is a problem with the PCB design, it will have adverse effects on the reliability of the electronic equipment. Influences, such as interference caused by insufficient consideration of power supply and ground wires, will degrade the performance of the product. Therefore, when designing the PCB board, it is necessary to adopt the correct method.
In a PCB board commonly used in switching power supplies, each switching power supply usually has four current loops, which are the input signal source current loop, the power switch AC loop, the output rectifier AC loop, and the output load current loop. The input loop charges the input capacitor through an approximately DC current, and the filter capacitor mainly plays a broadband energy storage role. Similarly, the output filter capacitor is also used to store high-frequency energy from the output rectifier while eliminating DC energy from 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 respectively.
The setting and connection of the input and output loops are very important for the entire printed circuit board. Whether it is reasonable or not will be directly related to the magnitude of electromagnetic interference. If the connection between the input and output circuits, the power switch, and the rectifier circuit cannot be directly connected to the terminals of the capacitor, the AC energy will be radiated to the environment by the input or output filter capacitor. The AC circuit of the power switch and the AC circuit of the rectifier contain high-amplitude trapezoidal currents. The harmonic components of these currents are very high. Their frequencies are much greater than the fundamental frequency of the switch. The peak amplitude can be as high as 5 times the continuous input and output DC current amplitude. The transition time is usually About 50ns. These two loops are most likely to produce electromagnetic interference, so these AC loops must be laid out before other printed lines in the power supply are routed.
In the input and output circuits of LED switching power supplies, each circuit is composed of three main components. These three components are filter capacitors, power switches or rectifiers, and inductors or transformers. These three important components should be placed adjacent to each other, positioning the components so that the current path between them is as short as possible. The best way to build a switching power supply layout is similar to its electrical design. The best design process is as follows: Place the transformer → Design the power switch current loop → Design the output rectifier current loop → Connect the control circuit to the AC power circuit → Design the input current source loop and input filter.