New method for designing LED switching power supply PCB board

In the design of the switching power supply, the physical design of the PCB is the last link. If the design method is improper, the PCB may radiate too much electromagnetic interference, causing the power supply to be unstable. The following points should be analyzed for the matters needing attention in each step:

First, from the schematic diagram to the PCB design process to establish component parameters -> input principle netlist -> design parameter settings -> manual layout -> manual wiring -> verification design -> review -> CAM output.

Second, the parameters set adjacent conductor spacing must be able to meet electrical safety requirements, and for ease of operation and production, the spacing should be as wide as possible. The minimum spacing should be at least suitable for the voltage to withstand. When the wiring density is low, the spacing of the signal lines can be appropriately increased. The signal lines with high and low levels should be as short as possible and the spacing should be increased. Under normal circumstances Set the trace spacing to 8 mils.

The distance from the edge of the pad to the edge of the board is greater than 1mm, which avoids pad defects during processing. When the traces connected to the pads are thinner, the connection between the pads and the traces is designed to be water droplets. This has the advantage that the pads are not easy to peel, but the traces are not easily disconnected from the pads.

Third, the component layout practice proves that even if the circuit schematic design is correct and the printed circuit board is not properly designed, it will adversely affect the reliability of the electronic equipment. For example, if the two thin parallel lines of the printed board are close together, the delay of the signal waveform will be formed, and the reflection noise will be formed at the end of the transmission line; the interference caused by the inconsistency of the power supply and the ground line will cause the product to be Performance is degraded, so when designing a printed circuit board, care should be taken to use the correct method. Each switching power supply has four current loops:

(1). Power switch AC circuit (2). Output rectifier AC circuit (3). Input signal source current loop

(4). Output load current loop The input loop charges the input capacitor through an approximately DC current. The filter capacitor mainly acts as a broadband energy storage; similarly, the output filter capacitor is also used to store the high frequency energy from the output rectifier. At the same time, the DC energy of the output load loop is eliminated. Therefore, the terminals of the input and output filter capacitors are very important. The input and output current loops should be connected only from the terminals of the filter capacitor to the power supply; if the connection between the input/output loop and the power switch/rectifier loop cannot be connected to the capacitor The terminals are directly connected and the AC energy is radiated from the input or output filter capacitors to the environment. The AC circuit of the power switch AC loop and rectifier contains high amplitude trapezoidal currents. The harmonic components of these currents are very high. The frequency is much higher than the fundamental frequency of the switch. The peak amplitude can be up to 5 times the amplitude of the continuous input/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 placed before other traces in the power supply. The three main components of each loop are filter capacitors, power switches or rectifiers, inductors or transformers. Place them adjacent to each other and adjust the position of the components so that the current path between them is as short as possible.

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