1, safety grounding
Safety grounding is the shell of high-voltage equipment connected to the earth. First, to prevent the accumulation of charge on the casing, resulting in electrostatic discharge and endanger the equipment and personal safety, such as computer chassis grounding, tanker trucks that dragged on the ground tail, are designed to make the accumulation of charge release, to prevent accidents; the second is that when the insulation of the equipment is damaged to make the casing charged, prompting the power supply to cut off the power supply protection action, in order to protect the staff's safety, for example, refrigerator, rice cooker Shell. Third, the equipment can be shielded from the huge electric field, play a protective role, such as civilian transformer guardrail.
2, lightning grounding
When the power electronic equipment in the event of a lightning strike, whether it is a direct lightning strike or induction lightning strike, if the lack of appropriate protection, power electronic equipment will be greatly damaged or even scrapped. In order to prevent lightning strikes, we generally set up lightning rods in high places (such as roofs, chimneys, tops) connected to the earth, in order to prevent lightning strikes endangering the safety of equipment and personnel. Safety grounding and lightning grounding are designed to provide safe protective measures for electronic and electrical equipment or personnel, used to protect equipment and personnel safety.
3, working ground
Working ground is for the normal operation of the circuit to provide a reference potential. This reference potential is generally set to zero. The reference potential can be set to a point in the circuit system, a section or a piece. When the reference potential is not connected to the earth, it is regarded as a relative zero potential. But this relative zero potential is not stable, it will change with the changes in the external electromagnetic field, so that the system parameters change, resulting in unstable circuit system. When the reference potential is connected to the earth, the reference potential is regarded as the zero potential of the earth, and will not change with the change of the external electromagnetic field. But unreasonable working grounding will instead increase the interference of the circuit. For example, the interference caused by incorrect grounding, electronic equipment **** the same end is not properly connected to the interference generated. In order to effectively control the circuit in the work of producing a variety of interference, so that it can comply with the principle of electromagnetic compatibility. When we design circuits, according to the nature of the circuit, the working ground can be divided into the following different types, such as DC ground, AC ground, digital ground, analog ground, signal ground, power ground, power ground and so on. Different grounds should be set up separately. Do not mix them together inside a circuit, for example, digital ground and analog ground can not **** a ground, otherwise the two circuits will produce very powerful interference, paralyzing the circuit!
4, signal
Signal ground is a variety of physical quantities of signal source zero potential of the public **** reference ground. Because the signal is generally weak, vulnerable to interference, unreasonable grounding will cause the circuit to produce interference, so the signal ground requirements are higher.
5, analog ground
Analog ground is the analog circuit zero potential of the public **** reference ground. Analog circuits have a small signal amplification circuit, multi-stage amplification, rectifier circuits, voltage regulator circuits, etc., improper grounding will cause interference, affecting the normal operation of the circuit. The grounding of analog circuits has a great significance for the whole circuit, it is one of the basis for the normal operation of the whole circuit. So the role of reasonable grounding in analog circuits on the whole circuit can not be ignored.
6, digital ground
Digital ground is the digital circuit zero potential of the public **** reference ground. As digital circuits work in the pulse state, especially when the front and rear edges of the pulse is steeper or higher frequency, it will produce a large number of electromagnetic wave interference circuit. If the grounding is not reasonable, it will aggravate the interference, so the choice of the grounding point of the digital ground and the laying of the grounding wire should also be fully considered.
7, power supply ground
Power supply ground is the power supply zero potential of the public **** reference ground. As the power supply is often simultaneously supplied to the various units of the system, and the various units require the nature of the power supply and parameters may be very different, so both to ensure that the power supply is stable and reliable, but also to ensure that other units are stable and reliable work. Power supply ground is generally the negative pole of the power supply.
8, power ground
Power ground is the zero potential of the load circuit or power drive circuit of the public **** reference ground. As the load circuit or power drive circuit of the current is stronger, higher voltage, if the grounding of the ground resistance is larger, it will produce a significant voltage drop and produce greater interference, so the power ground on the interference is greater. Therefore, the power ground must be set separately from other weak ground to ensure the stable and reliable operation of the whole system.
Shielding and grounding should be used in conjunction with each other to provide good shielding. Mainly for the consideration of electromagnetic compatibility, the typical two shielding is electrostatic shielding and alternating electric field shielding, the following are introduced:
Electrostatic shielding: when the complete metal shielding will be surrounded by a charged conductor, in the shielding body on the inner side will be induced with the same amount of charged conductor heterogeneous charge, the outer side of the same kind of charge with an equal amount of charged conductor, so the outer side of the field is still present. If the metal shield is grounded, the outer charge will flow into the earth, the metal shell will not exist on the outside of the electric field, equivalent to the shell of the charged body of the electric field is shielded up.