LED Switching Power Supply PCB Circuit Board Design(I)
Seven steps of LED switching power supply PCB circuit board design.
In the switching power supply design, if the PCB board design is incorrect will lead to too much electromagnetic interference.There are seven PCB design steps will great stable power supply.Through the various steps in the need to pay attention to analyze,step by step on the board to do a good job PCB board design.
1.From schematic to PCB design flow
Create component parameters—> Input principle netlist—>Design parameter setting—>Manual layout—> Manual wiring—>Verify design—>Review—>CAM output
Adjacent wire spacing must meet electrical safety requirements, and for ease of operation and production,the spacing should be as wide as possible.The minimum spacing at least able to withstand the voltage,the signal line spacing can be appropriately increase when the wiring density is low, the high and low disparity of the signal line should be as short as possible and increase the spacing. In generally, the distance should be more than 1mm between the edge of hole to printed circuit board edge avoid pad defect in the processing.when the traces are thin connected to the pads,the pad should design to droplet-like.the advantage is that the pads will not peeling and the traces are not be easily broken.
Practice has proved although circuit schematic design is correct, if printed circuit board design is improper also impact the reliability of electronic equipment.For example,if two parallel lines of printed circuit board are close,will formed a delay signal waveform and reflection noise at the terminal of the transmission line.it will decline the performance of product due to power and ground considerations are not thoughtful.so should use the correct method in the design of printed circuit board.Each switching power supply has four current loops:
- ) Power switch AC circuit
- ) Output rectifier AC circuit
- ) Input signal source current loop
- ) Output load current loop
The input loop charge the input capacitor through an approximately DC current and filter capacitor acts primarily as a broadband energy storage.Similarly,the output filter capacitor is used to store the high frequency energy from the output rectifier and eliminating the DC energy from the output load loop.Therefore, the input and output filter capacitor terminals are very important,input and output current loop should be only from the filter capacitor terminals connected to the power supply.If the connection between the input/output circuit and the power switch/rectifier circuit can not be directly connected to the terminal of the capacitor,the AC energy will be filtered by the input or output filter and radiated into the environment.
Power switch AC circuit and rectifier AC circuit contains high trapezoidal current,these currents in high harmonic component,the frequency is much larger than the switching base frequency,the peak amplitude can be up to 5 times of continuous input/output DC current, the transition time is usually about 50ns.These two circuits are most susceptible to electromagnetic interference and must be routed before other wiring lines in the power supply.The three main components of each circuit filter capacitor,power switch or rectifier, inductor or transformer should be connected to each other adjacent to place, adjust the position of the components so that the current path between them as short as possible.
The best way to build 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 supply circuit
- Design input current source circuit and input filter design Output load circuit and output filter according to the functional unit of the circuit,all the components of the circuit layout,to meet the following principles:
(1.)First consider the size of the PCB. PCB size is too large, the printed line is too long will increase impedance and decrease anti-noise ability,then increase the cost. If the printed circuit board is too small will lead to bad heat dissipation,and adjacent lines are vulnerable to interference. The best shape of the board is rectangular,with an aspect ratio of 3:2 or 4:3.
(2.) Consider the subsequent welding when place the components,the better not too density.
(3.)With the core components of each functional circuit as center,layout around it.Components should be uniform,neat and compactly arranged on the PCB,minimizing and shortening the lead and connection between the components,decoupling capacitors as close as possible to the device.
(4.) In the high frequency of the circuit, to consider the distribution of components between the parameters.In generally should arrange the components as parallel as possible.This is not only beautiful,but easy to assembly and mass production.
(5.)According to the circuit process to arrange the location of the various functional circuit unit,so that the layout flow, and make the signal as much as possible to maintain a consistent direction.
(6.) The first principle of the layout is ensure that the wiring rate,pay attention the fly line connection of mobile devices,put the connection devices together.
(7.)As far as possible to reduce the loop area to suppress the switching power supply radiation interference.