There are different grounding methods for the types of grounding and different circuits. The common grounding methods in electronic power equipment are as follows:
1. Safety grounding
The safety ground is to connect the outer casing of the high voltage equipment to the ground. 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 electric charge and prevent accidents. Second, when the insulation of 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 workers, such as the outer casing of the refrigerator and rice cooker. Third, it can 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 a power electronic device encounters a lightning strike, whether it is a direct lightning strike or an 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 generally 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 personnel when lightning strikes. Safety grounding and lightning protection grounding are designed to provide safe protection for electronic power equipment or personnel to protect equipment and personnel.
3, working 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, it will change with the change of the external electromagnetic field, and the parameters of the system will 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. However, unreasonable work grounding will increase circuit interference. For example, interference caused by incorrect grounding points, interference caused by improper connection of the common end of the electronic device. 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 the circuit, according to 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. Don't mix them together in a circuit. For example, digital ground and analog ground can't share a ground line. Otherwise, the two circuits will generate very powerful interference and make the circuit fall into paralysis!
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, unreasonable grounding 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 reasonable grounding in the analog circuit can not be ignored for the whole circuit.
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 unreasonable, 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 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.
8, 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 grounding 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.
Electrostatic shielding: When a complete metal shield is used to enclose the charged conductor, an electric charge of the same kind as the charged conductor will be induced on the inside of the shield, and the same kind of charge as the charged conductor will appear on the outside, so there is an electric field on the outside. presence. If the metal shield is grounded, the outside 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.