Discussion on Design Scheme of LED Switching Power Supply System for PCB Board
The development speed of LED switching power supplies has made a significant leap in recent years, and the speed of new product replacement has also accelerated. As the last design step, PCB design 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. Will have an adverse effect. So, what is the design of the PCB is correct?
In recent years, the component layout research and market practice results of LED power supply have proved that 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 have an adverse effect on the reliability of the electronic device. For example, due to the inconsistency caused by the consideration of the power supply and the ground wire, the performance of the product is degraded. Therefore, when designing a PCB, you need to use the correct method.
In the PCB board commonly used in switching power supplies, 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 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 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 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. Both the AC circuit of the power switch AC and the AC circuit of the rectifier contain high-amplitude trapezoidal currents with high harmonic content, which is much higher than the fundamental frequency of the switch. The peak amplitude of the loop can be as much as five times the amplitude of the input or output DC current, and the transition time is typically about 50ns. These two loops are the most susceptible to electromagnetic interference, so the AC loop must be placed in the power supply design before other wiring is set.
In the input and input loops of the LED switching power supply, each loop 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, 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:
1, placing the transformer
2, design the power switch current loop
3. Design the output rectifier current loop
4. Control circuit connected to the AC power circuit
5. Design the input current source loop and input filter