LED switching power supply SMI LED PCB design
The development speed of LED PCB switching power supplies has seen a major technological leap in recent years, and the speed of new product replacement has also accelerated. As a final design step, the design of the PCB is also very important, because once there is a problem with 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 also has an adverse effect. So, is the PCB design correct?
Through the component layout research and market practice results of LED power sources 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, the reliability will be adversely affected. Electronic equipment. This effect, such as interference due to poor consideration of power and ground, will degrade product performance. Therefore, the correct method is required when designing a PCB.
In the input and input loops of LED switching power supplies, each loop consists of three main components: a filter capacitor, a power switch or rectifier, an inductor or a transformer. These three important components should be placed next to each other to adjust the position of the components 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: 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 the input filter.
The setting and connection of the input and output loops is very important for the entire printed circuit board, and its rationality 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 is not directly connected to the terminals of the capacitor, the AC energy will be radiated into the environment through the input or output filter capacitors. The AC circuit of the power switch AC circuit and the rectifier includes a high amplitude ladder current. The harmonic content of these currents is very high and its frequency is much greater than the fundamental frequency of the switch. The peak amplitude can be as much as five times the amplitude of the continuous input and output DC current. The transition time is usually around 50 ns. These two loops are most susceptible to electromagnetic interference, so these AC loops must be routed before other traces in the power supply.
In a PCB board commonly used for switching power supplies, typically each switching power supply has four current loops, which are an input signal source current loop, a power switch AC loop, an output rectified AC loop, and an output load current loop. The input loop charges the input capacitor by approximating the DC current. Filter capacitors are mainly used for broadband energy storage. 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 important. The input and output current loops should only be connected to the power supply through the terminals of the filter capacitor.
