Analysis and introduction of practical rectification strategies for EMI in switching power supplies
Classification and standards of EMC:
EMC (Electromagnetic Compatibility) is electromagnetic compatibility, which includes EMI (Electromagnetic Disturbance) and EMS (Electromagnetic Immunity). EMC is defined as the ability of a device or system to function properly in its electromagnetic environment without causing any unacceptable electromagnetic interference to any device or object in that environment. The term EMC refers to electromagnetic compatibility. EMP refers to electromagnetic pulses.
EMC = EMI + EMS EMI： Electromagnetic interference EMS: Electromagnetic compatibility (immunity)
EMI can be divided into two parts: conduction and radiation,
The FCC testing frequency is between 450K-30MHz, and the CISPR 22 testing frequency is between 150K-30MHz. Conduct can be tested using a spectrum analyzer, while Radiation must be tested in a specialized laboratory.
EMI is electromagnetic interference, which is a part of EMC. EMI (Electronic Magnetic Interference) is electromagnetic interference, EMI includes conduction, radiation, current harmonics, voltage flicker, and so on. Electromagnetic interference is composed of three parts: interference source, coupling channel, and receiver, commonly referred to as the three elements of interference. EMI is linearly proportional to current, the current loop area, and the square of frequency EMI = K*I*S*F2. I is the current, S is the loop area, F is the frequency, and K is a constant related to the circuit board material and other factors.
Radiation interference (30MHz-1GHz) propagates through space with the characteristics and laws of electromagnetic waves. But not all devices can emit electromagnetic waves.
Conducted interference (150K-30MHz) is interference that propagates along a conductor. So the propagation of conducted interference requires a complete circuit connection between the interference source and the receiver.
EMI refers to the external electromagnetic interference of a product. Generally, it is divided into two levels: Class A and Class B. Class A is industrial grade, and Class B is civilian grade. Civilian use is stricter than industrial use because industrial use allows for slightly higher levels of radiation. In terms of EMI radiation testing for the same product, at 30-230MHz, Class B requires that the radiation limit of the product should not exceed 40dBm, while Class A requires that it should not exceed 50dBm (measured in a three meter anechoic chamber as an example), which is relatively more relaxed. Generally speaking, CLASSA refers to the ability of the equipment to continue to operate normally as expected under EMI testing conditions without the need for operator intervention, and does not allow performance degradation or functional loss below the specified performance level.
