Terminology of electromagnetic compatibility technology for switching power supplies
(1) Electromagnetic compatibility
Electromagnetic compatibility refers to the ability of a device or system to operate normally in its electromagnetic environment without causing unbearable electromagnetic interference to anything in that environment.
(2) Electromagnetic disturbance
Electromagnetic disturbance refers to any electromagnetic phenomenon that may cause a decrease in the performance of equipment, equipment, or systems or cause damage to living or inanimate substances. Electromagnetic interference can cause a decrease in the performance of equipment, transmission channels, or systems. Its main elements include natural and human disturbance sources, coupling of impedance/internal resistance through common ground wires, electromagnetic disturbances conducted along power lines, and radiation disturbances. The path of electronic system interference is: through the power supply, through signal lines or control cables, through field penetration, and directly into the antenna; Conducted interference from other devices through cable coupling; Internal field coupling in electronic systems; Radiation interference from other equipment; External coupling of electronic devices to internal fields; Broadband transmitter antenna system; External environmental fields, etc.
(3) Electromagnetic environment
The electromagnetic environment is a time-varying electromagnetic phenomenon that clearly does not transmit information, which may be superimposed or combined with useful signals.
(4) Electromagnetic radiation
Electromagnetic radiation refers to the phenomenon of electromagnetic waves being emitted from a source into space. The meaning of the term "electromagnetic radiation" can sometimes be extended to include electromagnetic induction phenomena. RFI/EMI can radiate through openings, ventilation holes, entrances and exits, cables, measurement holes, door frames, hatch covers, drawers and panels, as well as non ideal connection surfaces of any type of equipment casing. RFI/EMI can also be radiated by wires and cables entering sensitive equipment, and any good electromagnetic energy emitter can also serve as a good receiver.
(5) Pulse
Pulse refers to a physical quantity that undergoes a sudden change in a short period of time and then quickly returns to its initial value.
(6) Common mode interference and differential mode interference
There are two types of interference on the power line: common mode interference and differential mode interference. Common mode interference exists between any phase of the power supply and the ground or between wires and the ground. Common mode interference is sometimes also known as longitudinal mode interference, asymmetric interference, or ground interference. This is the interference between the current carrying conductor and the earth. Differential mode interference exists between power supply phase lines and neutral lines, as well as between phase lines and phase lines. Differential mode interference is also known as normal mode interference, transverse mode interference, or symmetric interference. This is the interference between current carrying conductors. Common mode interference indicates that interference is coupled into the circuit by radiation or crosstalk, while differential mode interference indicates that interference originates from the same power circuit. Usually, these two types of interference coexist, and due to the imbalance of line impedance, the two types of interference will also transform into each other during transmission, making the situation very complex. After long-distance transmission of interference, the attenuation of the differential mode component is greater than that of the common mode component, because the impedance between lines is different from that between lines and ground. For the same reason, common mode interference also radiates into adjacent spaces during line transmission, while differential mode interference does not. Therefore, common mode interference is more likely to cause electromagnetic interference than differential mode interference. Different interference methods require different interference suppression methods to be effective. A simple way to determine interference methods is to use a current probe. The current probe first wraps around each wire separately to obtain the induction value of a single wire, and then wraps around two wires (one of which is the ground wire) to detect their induction situation. If the induction value increases, the interference current in the circuit is common mode; On the contrary, it is differential mode.
(7) Immunity level and sensitivity level
Immunity level refers to the maximum disturbance level at which a given electromagnetic disturbance is applied to a device, equipment, or system, while still functioning normally and maintaining the required performance level. That is to say, beyond this level, the device, equipment, or system will experience performance degradation. Sensitivity level refers to the level at which performance degradation is just beginning to occur. So, for a certain device, equipment, or system, the immunity level and sensitivity level are the same value.
(8) Immunity margin
Immunity margin refers to the interpolation between the immunity level limit of equipment, equipment, or system and the electromagnetic compatibility level.
