Design points and electrical requirements of switch power supply PCB
Time:2023-04-28
Views:970
In any switching power supply design, the physical design of the PCB board is the last step. If the design method is not appropriate, the PCB may radiate too much electromagnetic interference, causing unstable power supply operation. The following is an analysis of the precautions required in each step:
1、 Design process from schematic to PCB
Establish component parameters ->Input principle network table ->Design parameter settings ->Manual layout ->Manual wiring ->Verify design ->Review ->CAM output.
2、 Parameter settings
The spacing between adjacent conductors must meet the requirements of Electrical safety, and in order to facilitate operation and production, the spacing should also be as wide as possible. The minimum spacing should be at least suitable for the voltage it can withstand. When the wiring density is low, the spacing between signal lines can be appropriately increased. For signal lines with high and low level differences, the spacing should be as short and increased as possible. Generally, the wire spacing should be set to 8mil. The distance from the edge of the inner hole of the solder pad to the edge of the printed board should be greater than 1mm, which can avoid causing solder pad defects during processing. When the wiring connected to the pad is thin, the connection between the pad and the wiring should be designed as a water droplet shape. This has the advantage that the pad is not easy to peel, and the wiring is not easily disconnected from the pad.
3、 Component layout
Practice has proven that even if the circuit schematic design is correct and the printed circuit board design is inappropriate, it can have adverse effects on the reliability of electronic equipment. For example, if two thin parallel lines of a printed circuit board are close together, it will cause a delay in the signal waveform and generate reflected noise at the end of the transmission line; The interference caused by inadequate consideration of power and ground wires can lead to a decrease in product performance. Therefore, when designing printed circuit boards, attention should be paid to using the correct methods. Each switching power supply has four current circuits:
(1) Power switch AC circuit
(2) Output rectifier AC circuit
(3) Input signal source current circuit
(4) The input circuit of the output load current circuit charges the input capacitor through an approximate DC current
The best method to establish a switch power supply layout is similar to its electrical design, and the optimal design process is as follows:
1. Place the transformer
2. Design the current circuit of the switching power supply
3. Design the output rectifier current circuit
4. Control circuit connected to AC power circuit
Design the input current source circuit and input Filter design Design the output load circuit and output filter According to the functional unit of the circuit, the layout of all components of the circuit should comply with the following principles:
(1) First, consider the size of the PCB. When the PCB size is too large, the printed lines are long, the impedance increases, the noise resistance decreases, and the cost also increases; If it is too small, the heat dissipation is poor, and adjacent lines are easily disturbed. The optimal shape of a circuit board is a rectangular shape with a aspect ratio of 3:2 or 4:3. Components located at the edge of the circuit board are generally not less than 2mm away from the edge of the circuit board.
(2) When placing the device, it is important to consider future welding and avoid being too dense.
(3) Layout around the core components of each functional circuit as the center. The components shall be evenly, orderly and compactly arranged on the PCB to minimize and shorten the lead wires and connections between the components, and the decoupling capacitor shall be as close to the VCC of the components as possible.
(4) For circuits operating at high frequencies, consideration should be given to the distribution parameters between components. The general circuit should arrange the components in parallel as much as possible. In this way, not only is it aesthetically pleasing, but it is also easy to assemble and weld, making it easy for mass production.
(5) Arrange the positions of each functional circuit unit according to the circuit flow, making the layout convenient for signal flow and keeping the signal in the same direction as much as possible.
(6) The primary principle of layout is to ensure the routing rate of the wiring, pay attention to the connection of flying wires when moving devices, and place devices with wiring relationships together.
(7) Minimize the loop area as much as possible to suppress radiation interference from the switching power supply.
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