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PCB circuit design for LED switching power supply

writer: G December 26, 2017

Even in the early stages of the design of the circuit schematic is very correct, once the PCB design problems, on the reliability of electronic equipment adverse. For example, due to the power supply, ground wire interference caused by inattentive, it will make the product performance degradation, so in the design of PCB board, you need to use the right approach.

Commonly used in a switching power supply PCB board, usually each switching power supply has four current loops, which are the input signal source current loop, the power switch AC loop, the output rectifier AC loop, the output load current loop. The input circuit charges the input capacitor with an approximately dc current, which acts primarily as a broadband tank. Similarly, the output filter capacitor is also used to store the high frequency energy from the output rectifier while eliminating the DC energy from the output load circuit. Therefore, the input and output filter capacitor terminals is very important, the input and output current loop should be connected only from the filter capacitor terminals to the power supply.

Input and output circuit settings and connections for the entire printed circuit board is very important, its reasonable or not will be directly related to the size of electromagnetic interference. If the input and output circuits and the power switch, the connection between the rectifier circuit and the capacitor can not be directly connected to the terminal, the exchange of energy from the input or output filter capacitor and the radiation to the environment. The AC circuit of the power switch AC circuit and rectifier contains high-amplitude 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 and output DC current amplitude, transition time is usually About 50ns. These two loops are most prone to electromagnetic interference, so these AC loops must be laid out before routing other traces in the power supply.

In the LED switching power supply input, the input circuit, each loop consists of three main components, these three components are filter capacitors, power switches or rectifiers, inductors or transformers. The three important elements should be placed next to each other, with the components positioned so that the current path between them is as short as possible. The best way to create a switching power supply layout is similar to that of its electrical design. The best design flow is as follows: Place Transformer → Design Power Switch Current Loop → Design Output Rectifier Current Loop → Connect to AC Power Circuit Control Circuit → Design Input Current Source Loop and Input filter.

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