Briefly describe the type and performance of the ground wire

The ground technology has been widely and deeply applied in the field of modern electronics. The line between the same ground points is called the ground line.

The "ground" of an electronic device usually has two meanings: one is "earth" (safely), and the other is "system reference ground" (signal ground). Grounding is the establishment of a low-resistance conductive path between the system and a potential reference plane.

"Connecting to the earth" is based on the earth's potential, and uses the earth as the zero potential to connect the metal casing of the electronic device and the circuit reference point to the earth. Since the capacitance of the earth is very large, it is generally assumed that the potential of the earth is zero. At the beginning, the grounding technology was mainly applied to the power system. Later, the grounding technology was extended to the weak current system. Grounding in a weak current system is generally not a grounding that is connected to the Earth in the true sense. For power electronic equipment, the grounding wire is directly connected to the ground or connected to a conductor as a reference potential. When a current passes through the reference potential, the grounding point is a common reference point in the circuit, and the voltage at this point is 0V, the circuit The voltage level of other points in the middle is based on this reference point. Generally, the voltage data of each point marked in the circuit diagram is the relative grounding size, which can greatly facilitate the voltage measurement in the repair.

Connecting the ground plane to the earth is often due to the following considerations: improving the stability of the equipment circuit system, static discharge, and providing security for the staff. The purpose of grounding: safety considerations, that is, protective grounding. Provides a stable zero potential reference point (signal ground or system ground) shielding protection for the signal voltage.

First, the type of grounding and the different functions of the circuit have different grounding methods. The common grounding methods in electronic power equipment are as follows:

1. Safety grounding

The safety ground is connected to the earth's casing of the high-voltage equipment. One is to prevent the accumulation of electric charge on the casing, causing electrostatic discharge and endangering equipment and personal safety. For example, the grounding of the computer case, the tail of the tanker dragged on the ground, is to release the accumulated charge and prevent accidents. Second, when the equipment is damaged and the casing is charged, the power supply is protected and the power is cut off to protect the safety of the staff, such as the refrigerator and the rice cooker. The third is to shield the huge electric field of the equipment and protect it, such as the protective rail of the civilian transformer.

2, lightning protection grounding

When power electronic equipment encounters lightning strikes, whether it is direct lightning strike or induced lightning strike, if there is no corresponding protection, the power electronic equipment will be greatly damaged or even scrapped. In order to prevent lightning strikes, we usually set lightning rods on the ground (such as the roof and the top of the chimney) to connect with the earth to prevent the safety of equipment and staff when lightning strikes. Both safety grounding and lightning protection grounding are designed to provide electrical protection to electronic equipment or personnel to protect the safety of equipment and personnel.

3, work ground

The working ground is a reference potential provided for the normal operation of the circuit. This reference potential is typically set to zero. The reference potential can be set to a certain point, a certain section or a block in the circuit system. When the reference potential is not connected to the ground, it is regarded as a relative zero potential. However, this relative zero potential is unstable, and it will change with the change of the external electromagnetic field, causing the parameters of the system to change, resulting in unstable operation of the circuit system. When the reference potential is connected to the ground, the reference potential is regarded as the zero potential of the earth, and does not change with the change of the external electromagnetic field. But unfair working grounding will increase circuit interference. For example, the interference caused by the incorrect grounding point, the interference generated by the common end of the electronic device is not properly connected. In order to effectively control the circuit to produce various interferences in the work, so that it can comply with the principle of electromagnetic compatibility. When designing a circuit, depending on the nature of the circuit, the working ground can be divided into different types, such as DC ground, AC ground, digital ground, analog ground, signal ground, power ground, power ground, and the like. Different groundings should be set separately. Do not mix them together in a circuit. For example, digital ground and analog ground cannot share a ground line. Otherwise, the two circuits will generate very strong interference and make the circuit sink!

4, the signal

The signal ground is a common reference ground for the zero potential of various physical quantity signal sources. Since the signal is generally weak and susceptible to interference, the grounding of the injustice will cause interference to the circuit, so the signal ground is highly demanded.

5, analog ground

The analog ground is the common reference ground of the analog circuit zero potential. There are small signal amplifying circuits, multi-stage amplification, rectifier circuits, voltage regulator circuits, etc. in the analog circuit. Unsuitable grounding can cause interference and affect the normal operation of the circuit. The grounding in the analog circuit has great significance for the whole circuit, and it is one of the foundations for the normal operation of the whole circuit. Therefore, the effect of the fair grounding in the analog circuit on the entire circuit cannot be ignored.

6, digitally

The digital ground is the common reference ground for the zero potential of the digital circuit. Since the digital circuit operates in a pulse state, especially when the front and rear edges of the pulse are steep or the frequency is high, a large number of electromagnetic wave interference circuits are generated. If the grounding is unfair, the interference will be intensified, so the grounding point selection of the digital ground and the laying of the grounding wire should also be fully considered.

7, power ground

The power ground is the common reference ground of the zero potential of the load circuit or power drive circuit. Since the current of the load circuit or the power drive circuit is strong and the voltage is high, if the grounding resistance of the ground is large, a significant voltage drop will occur and a large interference will occur, so the interference on the power ground is large. Therefore, the power ground must be set separately from other weak current grounds to ensure stable and reliable operation of the entire system.

Shielding and grounding should be used together to achieve good shielding. Mainly to consider electromagnetic compatibility, the typical two types of shielding are electrostatic shielding and alternating electric field shielding.

Electrostatic Shielding: When a complete metal shield is used to enclose the live conductor, an electric charge of the same kind as the charged conductor is induced on the inside of the shield, and the same kind of charge as the charged conductor appears on the outside, so there is an electric field on the outside. exist. If the metal shield is grounded, the external charge will flow into the earth, and there will be no electric field outside the metal shell, which is equivalent to the electric field of the charged body in the shell being shielded.

8, power ground

The power ground is the common reference ground of the power supply zero potential. Since the power supply is often supplied to each unit in the system at the same time, and the power supply characteristics and parameters required by each unit may be greatly different, it is necessary to ensure stable and reliable operation of the power supply, and to ensure stable and reliable operation of other units. The power ground is generally the negative pole of the power supply.

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