PCB Technical - How to make a switching power supply in pcb design

In any switching power supply design, the physical design of the PCB board is the last link. If the design method is improper, the PCB may radiate too much electromagnetic interference and cause the power supply to work unstable. The following are the matters needing attention in each step analyze.

1. From the schematic to the PCB design process

Establish component parameters-"input principle netlist -" design parameter settings-"manual layout-"manual wiring -" verification design-"review -" CAM output.

2. Parameter setting

The distance between adjacent wires must be able to meet electrical safety requirements, and in order to facilitate operation and production, the distance should be as wide as possible. The minimum spacing must be at least suitable to bear

When the PCB wiring density is low, the signal line spacing can be appropriately increased. For signal lines with high and low levels, the spacing should be as short as possible and the spacing should be increased. Generally, the line spacing is set to 8mil. The distance between the edge of the inner hole of the pad and the edge of the printed board should be greater than 1mm, which can avoid the defects of the pad during processing. When the traces connected to the pads are thin, the connection between the pads and the traces should be designed into a drop shape. The advantage of this is that the pads are not easy to peel, but the traces and the pads are not easily disconnected.

3. Component layout

Practice has proved that even

Circuit

The schematic design is correct, and the printed circuit board is not designed properly.

electronic

The reliability of the equipment is adversely affected. For example, if the two thin parallel lines of the printed board are close together, the signal waveform will be delayed and reflected noise will be formed at the terminal of the transmission line. The performance drops, so when designing the printed circuit board, you should pay attention to adopting the correct method. 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 input loop

Pass an approximately DC current to the input

For capacitor charging, the filter capacitor mainly functions as a broadband energy storage; similarly, the output filter capacitor is also used to store high-frequency energy from the output rectifier, and at the same time eliminate the DC energy of the output load loop. Therefore, the terminals of the input and output filter capacitors are very important. The input and output current loops should only be connected to the power supply from the terminals of the filter capacitor respectively; if the connection between the input/output loop and the power switch/rectifier loop cannot be connected to the capacitor The terminal is directly connected, and the AC energy will be radiated into the environment by the input or output filter capacitor.

The AC circuit of the power switch and the AC circuit of the rectifier contain high-amplitude trapezoidal currents. The harmonic components of these currents are very high. The frequency is much greater than the fundamental frequency of the switch. The peak amplitude can be as high as 5 times the amplitude of the continuous input/output DC current. The transition time is usually About 50ns. These two loops are most prone to electromagnetic interference, so these AC loops must be laid out before the other printed lines in the power supply. The three main components of each loop are filter capacitors, power switches or rectifiers,

Inductance transformer

Should be placed next to each other, adjust the position of the components to make the current path between them as short as possible.