PCB LED switching power supply design
Switching power supply design in the physical design of PCB board is the last link, if the improper design, PCB can radiate excessive electromagnetic interference, resulting in unstable power supply, the following steps for each analysis required attention:
First, theLED PCB from the schematic design process to establish device parameters -> Enter the principle of network table -> design parameter settings -> manual layout -> hand-wiring -> verify the design -> Review -> CAM output.
Second, the parameter setting adjacent wire spacing must be able to meet the electrical safety requirements, and in order to facilitate the operation and production, spacing should be as wide as possible more. Minimum distance at least be suitable to withstand the voltage, the wiring density is low, the distance between the signal line may be appropriate to increase, the high, low disparity signal line should be as short as possible and increase the distance, under normal circumstances will take the line spacing is set to 8mil.
PCB pad side of the hole edge to the distance is greater than 1mm, pad lead to avoid processing defects. When connected with the alignment of smaller pads, the pads and traces to the connection between the design into a teardrop-shaped, so that the benefits are not easy to pad from the skin, but not easy to go off line and the pad.
Third, the component layout proved correct even if the circuit schematic design, printed circuit board design properly, the reliability of electronic equipment will also adversely affected. For example, if the boards of two thin parallel lines are very close, it will delay the formation of the signal waveform, the formation of the transmission line terminal reflection noise; the power, ground and thoughtful consideration is not caused by interference, the product will performance degradation, therefore, in the design of printed circuit board, they should note that with the right approach. Each switching power supply has four current loop:
(1.) AC power switch circuit
(2.) AC output rectifier circuit
(3). Current loop input signal source
(4). Output load current loop input circuit via a DC approximation of the input capacitor current, filter capacitor play a major role in broadband energy storage; Similarly, the output filter capacitor is also used to store high-frequency energy from the output rectifier while eliminating the DC output load circuit energy. Therefore, the input and output filter capacitor terminal is very important input and output current loop should be the only difference from the filter capacitor connected to the power terminals; if the input / output circuit and power switch / rectifier circuit connected between the capacitor can not The terminal is directly connected to AC power will be input or output filter capacitor and radiation into the environment. AC power switch and the rectifier circuit loop includes the exchange of high-amplitude trapezoidal current, high harmonic components of these currents, the switching frequency is much larger than the base frequency, peak amplitude of up to continuous input / output DC current range of 5 times, the transition time is usually about 50ns. The two loops most prone to electromagnetic interference, it must be printed in the power line wiring in the other before the exchange of good cloth loop, each loop filter capacitor three main components, the power switch or rectifier, inductor or transformer to be with each other be placed adjacent to adjust the element position to the current path between them as short as possible. Establish the best way switching power supply layout similar to their electrical design, best design process is as follows:
Place the transformer
Power switch current loop design
Output rectifier current loop design
Circuit connected to AC power control circuit