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Switching Noise - EMC

Basics of EMC

What is EMC?

Under a title “switching Noise – EMC”, we will provide commentary on the EMC related to switching power supplies and its countermeasures. First, let us review basics of the EMC and then discuss noise countermeasures.

The first session entitled “What is the EMC?” devotes itself to the verification of terms related to the EMC which is the starting line of the discussion. There are a number of English abbreviations, including EMC, with an array of similar alphabet letters. Each term must be understood and used correctly to avoid a situation where intended meaning is not conveyed or discussions end up off the mark.

What is EMC?

EMC stands for Electromagnetic Compatibility. This term conveys the meaning “Without causing electromagnetic interference to other devices, the ability to maintain the inherent performance even subjected to electromagnetic interference from other devices”. Because of the need to sustain both of the capabilities, the term “electromagnetic compatibility” is used.

”Without causing electromagnetic interference to other devices“ means that without this proviso devices could give an electromagnetic interference to other devices. EMI stands for Electromagnetic Interference. Since generating electromagnetic waves can be linked to interference, the term EMI is often used in pair with the expression ”Emission“. In terms of switching power supplies, the action of switching generates switching noise.

Conversely, the term related to ”subject to electromagnetic interference from other devices“ is EMS (Electromagnetic Susceptibility). Used in pair with EMS is ”Immunity“. What is needed in a device is the immunity that do not cause errors, such as a malfunction, when subjected to an EMI.

Among the types of EMI are conducted emission and radiated emission. Conductive emission is propagated through wires and PCB wiring. Radiated emission is a type of noise that is emitted (radiated) through the air. With respect to these emissions, in EMS there are immunity required of the devices. The relationship between EMC, EMI and EMS is given below:

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In short, in EMC, the question is whether EMI and EMS satisfy specifications and regulations. The above explanation is summarized in the table below:

Term Meaning Notes
EMC:Electromagnetic Compatibility Without creating electromagnetic interference, the ability to maintain the device’s inherent performance even if subjected to electromagnetic interference from another device. Because of a need to ensure both EMI and EMS, the term “electromagnetic compatibility” is used.
EMI:Electromagnetic Interference Interference with other devices by emission of electromagnetic waves. From the standpoint of EMC, the requirement is not to produce/minimize EMI.
EMS:Electromagnetic Susceptibility Immunity with respect to EMI. From the standpoint of EMC, the requirement is a tolerance that do not produce errors even if subjected to EMI.
Conducted Emission Noise that is propagated via wires and PCB wiring.  
Radiated Emission Noise that is emitted (radiated) through the air.  

Next time, we will explain “The Basics of Spectrum”.

Key Points:

・EMC (electromagnetic compatibility) means supporting both EMI (electromagnetic interference) and EMS (electromagnetic susceptibility) capabilities.

・EMI means the interference due to the emission of electromagnetic waves.

・EMS means an immunity to EMI.


Power Supply Design Technical Materials Free Download

Power Supply Design Technical Materials Free Download

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