PCB Technical - Introduction to PCB single point grounding and multi-point grounding

In the pcb single point grounding,the grounding is to prevent electric shock or to protect the safety of the equipment. Connect the metal chassis or shell of power and telecommunications equipment to the ground wire;use the earth as the current loop ground wire.In the power system, a good electrical connection between the neutral point of the equipment and the electrical device,the shell or the support and the conductor of the grounding device is called grounding. In addition to introducing some useless current or noise interference into the ground, the function of grounding is to protect users from electric shock. In terms of UPS,some UPSs will mark the voltage between the neutral wire and the ground wire to ensure that the product does not It will cause electric shock to the human body.

1.PCB single point grounding

Low operating frequency (<1MHz) adopts single-point grounding (that is, a structural point in the entire circuit system is regarded as a ground reference point, all ground connections are connected to this point, and a safety ground bolt is set), Prevent two-point grounding to produce circuit coupling of common ground impedance. The single-point grounding of multiple circuits is divided into series and parallel. Because series grounding produces circuit coupling of common ground impedance, it is better to use parallel single-point grounding for low-frequency circuits.

To prevent power frequency and other stray currents from interfering with the signal ground wire, the signal ground wire should be insulated from the power ground wire and the chassis ground wire. And only connect to the power ground wire, chassis ground wire and the safety ground bolt of the ground wire connected to the earth (except for the floating type).

2.PCB multi-point grounding

The high working frequency (>30MHz) adopts the multi-point grounding type (that is, in the circuit system, a grounding plate is used to replace the respective ground loops in each part of the circuit). Because the inductance of the ground lead is proportional to the frequency and length, the common ground impedance will increase when the operating frequency is high, which will increase the electromagnetic interference generated by the common ground impedance, so the length of the ground wire is required to be as short as possible. When using multi-point grounding, try to find the nearest low-resistance ground plane to ground.

3.PCB mixed grounding

The circuit with operating frequency between 1～30MHz adopts mixed grounding type. When the length of the ground wire is less than 1/20 of the wavelength of the working signal, the single-point grounding type is adopted, otherwise, the multi-point grounding type is adopted.

The above is an introduction to the difference between PCB single-point and multi-point grounding. I hope that designers who are beginners to PCB can master the skills of PCB single-point and multi-point grounding.