Switching power supply electromagnetic compatibility technical terms
(1) Electromagnetic compatibility
Electromagnetic compatibility refers to the ability of a device or system to operate normally in its electromagnetic environment without causing intolerable electromagnetic disturbance to anything in the environment.
(2) Electromagnetic harassment
Electromagnetic disturbance refers to any electromagnetic phenomenon that may cause the performance of equipment, equipment or systems to degrade or cause damage to living or inanimate substances. Electromagnetic disturbance can cause degradation of equipment, transmission channels or system performance. Its main elements include natural and man-made disturbance sources, coupling through public ground impedance/internal resistance, electromagnetic disturbance and radiated interference conducted along power lines, etc. The paths for interference in electronic systems are: through the power supply, through signal lines or control cables, field penetration, and directly through the antenna; through cable coupling, conduction interference from other equipment; internal field coupling in the electronic system; radiation interference from other equipment; Electronic equipment externally coupled to internal fields; broadband transmitter antenna systems; external environmental fields, etc.
(3) Electromagnetic environment
The electromagnetic environment is a time-varying electromagnetic phenomenon that apparently does not transmit information and may be superimposed or combined with useful signals.
(4) Electromagnetic radiation
Electromagnetic radiation refers to the phenomenon of electromagnetic waves emitted from a source into space. The meaning of the term "electromagnetic radiation" can sometimes be extended to include the phenomenon of electromagnetic induction. RFI/EMI can be radiated through openings, vents, inlets and outlets, cables, measuring holes, door frames, hatches, drawers and panels of any equipment case, as well as non-ideal connection surfaces of the case. RFI/EMI can also be radiated by wires and cables entering sensitive equipment, and any good radiator of electromagnetic energy can also serve as a good receiver.
(5) Pulse
A pulse refers to a physical quantity that mutates 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 power lines: common mode interference and differential mode interference. Common mode interference exists between any one of the power supply and the ground or between the wire and the ground. Common mode interference is sometimes also called 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 the power supply phase line and the neutral line and between the phase line and the phase line. Differential mode interference is also called normal mode interference, transverse mode interference or symmetrical interference. This is interference between current-carrying conductors. Common mode interference indicates that the interference is coupled into the circuit by radiation or crosstalk, while differential mode interference indicates that the interference originates from the same power circuit. Usually these two interferences exist at the same time. Due to the imbalance of line impedance, the two interferences will transform into each other during transmission, so the situation is very complicated. After the interference is transmitted over a long distance, the attenuation of the differential mode component is greater than that of the common mode. This is because the line-to-line impedance is different from the line-to-ground impedance. For the same reason, common mode interference will also radiate to adjacent space during line transmission, but differential mode will not, so common mode interference is more likely to cause electromagnetic interference than differential mode. Different interference methods require different interference suppression methods to be effective. An easy way to determine the interference method is to use a current probe. The current probe first surrounds each wire individually to obtain the induction value of the single wire, and then surrounds two wires (one of which is the ground wire) to detect its induction. If the induction value increases, the interference current in the line is common mode; otherwise, it is differential mode.
(7) Immunity level and sensitivity level
Immunity level refers to the maximum disturbance level when a given electromagnetic disturbance is applied to a device, equipment or system and it can still operate normally and maintain the required performance level. That is, the device, equipment, or system will experience performance degradation above this level. The sensitivity level is the level at which performance degradation just begins to occur. Therefore, for a certain device, equipment or system, the immunity level and the sensitivity level are the same value.
(8) Immunity margin
The immunity margin refers to the interpolation between the immunity level limit and the electromagnetic compatibility level of the equipment, equipment or system.
