From schematic to PCB design flow

Establish component parameters — > input network table — > design parameters — > manual layout — > manual wiring — > verification design — > review — >CAM output.


Parameter Settings

The spacing between adjacent conductors must meet the electrical safety requirements and should be as wide as possible for ease of operation and production. The minimum spacing should be at least suitable for the voltage. When the wiring density is low, the spacing of signal lines can be appropriately increased. For signal lines with great disparity between high and low levels, the spacing should be as short as possible and increased.

The distance between the inner hole edge of the welding disc and the edge of the printed board should be more than 1mm, so as to avoid the defect of the welding disc during processing. When the wire connecting with the welding pad is thin, the connection between the welding pad and the wire should be designed in the shape of water drops, which is good because the welding pad is not easy to peel, but the wire and the welding pad are not easy to disconnect.


Component layout

Practice has proved that even if the circuit schematic design is correct and the printed circuit board design is improper, it will have a negative impact on the reliability of electronic equipment. For example, if two thin parallel lines of a printed circuit board are very close together, the delay of the signal waveform will be formed and the reflection noise will be formed at the end of the transmission line. Due to the power supply, ground wire is not considered and caused by the interference, will make the product performance decline, therefore, in the design of printed circuit board, should pay attention to the correct method. Each switching power supply has four current loops:

Power switch ac circuit

Output rectifier ac loop

Input signal source current loop

Output load current loop input loop

An approximate dc current is used to charge the input capacitor. Similarly, the output filter capacitor is used to store high frequency energy from the output rectifier while eliminating the dc energy from the output load loop.

Therefore, the terminals of the input and output filter capacitors are very important. The input and output current loops should be connected to the power supply only from the terminals of the filter capacitors. If the connection between the input/output circuit and the power switch/rectifier circuit is not directly connected to the capacitor terminal, the ac energy will be radiated into the environment by the input or output filter capacitors.

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

1. Place the transformer

2. Design the power switch current loop

3. Design the current loop of the output rectifier

4. Control circuit connected to ac power supply circuit

Design of input current source circuit and input filter design of output load circuit and output filter

First consider the PCB size. When PCB size is too large, the length of printed line will increase, the impedance will increase, the anti-noise ability will decrease, and the cost will also increase. Too small is not good heat dissipation, and adjacent lines are easily disturbed. The optimal shape of the circuit board is a rectangle with a length to width ratio of 3:2 or 4:3. Components located at the edge of the circuit board are generally not less than 2mm from the edge of the circuit board

When placing the device to consider the future of the welding, not too dense

The core component of each functional circuit as the center, around it to layout. Components should be uniformly, neatly and compactly arranged on the PCB to minimize and shorten leads and connections between components, and decoupling capacitors should be as close as possible to the VCC of components

For circuits operating at high frequencies, consider the distribution of parameters between components. In general, the circuit should be arranged in parallel as far as possible. In this way, not only beautiful, and easy welding, easy to mass production

Arrange the position of each functional circuit unit according to the circuit flow, make the layout convenient for signal flow, and make the signal keep consistent direction as far as possible

The first principle of the layout is to ensure the wiring of the distribution rate, mobile devices pay attention to the connection of the flywire, the connection of the devices together

Reduce the area of the loop as much as possible to suppress the radiation interference of the switching power supply



Any printed line on a PCB can act as an antenna. The length and width of the printed line will affect its impedance and inductance, thus affecting the frequency response. Even printed lines that pass through the dc signal can be coupled from adjacent printed lines to the rf signal and cause circuit problems (or even re-radiate interference signals). Therefore, all printed lines for alternating current should be designed to be as short and wide as possible, which means that all components connected to printed lines and to other power lines must be placed close together.



Wiring design is completed, it is necessary to carefully check the wiring design by the designers is in line with the rules, rules at the same time also need to confirm whether accord with the demand of the PCB production process, general inspection line to line, line and element bonding pad, the line and communicating pores, element bonding pad and communicating pores, through hole and the distance between the through hole is reasonable, whether to meet the production requirements. Is the power cord and ground wire width appropriate and is there room in the PCB for the ground wire to be widened? Note: some errors can be ignored, for example, some plugins have a portion of their Outline outside the box, and checking the spacing can be an error; In addition, after each modification of the wire and hole, the copper shall be covered again.