PCB design points and component layout of switching power supply

1、 Design flow from schematic diagram to PCB

Create component parameters ->Input principle netlist ->Design parameter settings ->Manual layout ->Manual routing ->Verify design ->Review ->CAM output.

2、 Parameter setting

The spacing between adjacent conductors must meet the electrical safety requirements, and in order to facilitate operation and production, the spacing should also be as wide as possible. The minimum spacing shall at least be suitable for the voltage. When the wiring density is low, the spacing of signal lines can be appropriately increased. The signal lines with high and low level differences shall be as short as possible and the spacing shall be increased. Generally, the wiring spacing is set to 8mil. The distance from the edge of the inner hole of the pad to the edge of the printed board shall be greater than 1mm, so as to avoid pad defects during processing. When the wiring connected with the pad is thin, the connection between the pad and the wiring should be designed as a water drop. This has the advantage that the pad is not easy to peel, but the wiring and the pad are not easy to disconnect.

3、 Layout of components

Practice has proved that even if the circuit schematic is correctly designed and theprinted circuit board is improperly designed, the reliability of electronic equipment will be adversely affected. For example, if two thin parallel lines of the printed board are close together, the delay of the signal waveform will be formed and the reflected noise will be formed at the end of the transmission line; The interference caused by improper consideration of power supply and ground wire will degrade the performance of the product. Therefore, correct methods should be used when designing printed circuit boards. Each switching power supply has four current circuits:

(1) AC circuit of power switch

(2) Output rectifier AC circuit

(3) Input signal source current loop

(4) Output load current loop The input loop charges the input capacitor with an approximate DC current

The best way to establish the switching power supply layout is similar to its electrical design. The best design process is as follows:

1. Place the transformer

2. Design switching power supply current circuit

3. Design current circuit of output rectifier

4. Control circuit connected to AC power circuit

Design input current source circuit and input filter Design output load circuit and output filter According to the functional unit of the circuit, the layout of all components of the circuit shall comply with the following principles:

(1) First, consider PCB size. When the PCB size is too large, the printed line is long, the impedance increases, the noise resistance decreases, and the cost increases; If it is too small, the heat dissipation is poor, and adjacent lines are vulnerable to interference. The optimal shape of the circuit board is rectangular, with a length to width ratio of 3:2 or 4:3. The distance between the components located at the edge of the circuit board and the edge of the circuit board is generally not less than 2mm.

(2) When placing the device, it is necessary to consider the future welding, not too intensive.

(3) Take the core components of each functional circuit as the center, and arrange around it. The components and parts shall be evenly, orderly and compactly arranged on the PCB to minimize and shorten the lead and connection between components and parts, and the decoupling capacitor shall be close to the VCC of components as much as possible.

(4) For circuits operating at high frequencies, the distribution parameters between components should be considered. For general circuits, components shall be arranged in parallel as far as possible. In this way, it is not only beautiful, but also easy to assemble and weld, and easy to mass produce.

(5) Arrange the position of each functional circuit unit according to the circuit flow, so that the layout is convenient for signal flow and the signal is kept in the same direction as far as possible.

(6) The primary principle of layout is to ensure the distribution rate of wiring, pay attention to the connection of flying wires when moving components, and put the components with wiring relationship together.

(7) Reduce the loop area as much as possible to suppress the radiated interference of switching power supply.