How to design EMI for 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: conducted Conducion and radiated RadiaTIon,
Conduction specifications can generally be divided into: FCC Part 15J Class B; CISPR 22(EN55022, EN61000-3-2, EN61000-3-3) Class B;
National standards for IT (GB9254, GB17625) and AV (GB13837, GB17625).
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) electromagnetic interference 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, current loop area, and frequency squared, i.e. 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.
