EMC classification and standards
EMC (Electromagnetic Compatibility) is electromagnetic compatibility, which includes EMI (electromagnetic disturbance) and EMS (electromagnetic anti-harassment). EMC is defined as the ability of a device or system to function properly in its electromagnetic environment without posing unacceptable electromagnetic disturbances to anything in any device in the environment. EMC's overall name is 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 conduction and radiation Radiation.
The Conduction specification can generally be divided into: FCC Part 15J Class B; CISPR 22 (EN55022, EN61000-3-2, EN61000-3-3) Class B;
National standard IT class (GB9254, GB17625) and AV class (GB13837, GB17625).
The FCC test frequency is 450K-30MHz, the CISPR 22 test frequency is 150K-30MHz, the Conduction can be tested with the spectrum analyzer, and the Radiation must be tested in a special laboratory.
EMI is electromagnetic interference, EMI is part of EMC, EMI (Electronic Magnetic Interference) electromagnetic interference, EMI includes conduction, radiation, current harmonics, voltage flashing and so on. Electromagnetic interference is composed of three sources: interference source, coupling channel and receiver. It is usually called the three elements of interference. The EMI linearity is proportional to the current, the current loop area and the square of the 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 board material and other factors.
Radiated interference (30MHz - 1GHz) is transmitted through space and in the characteristics and laws of electromagnetic waves. But not any device can radiate electromagnetic waves.
Conducted interference (150K--30MHz) is the interference that propagates along the conductor. Therefore, the propagation of conducted interference requires a complete circuit connection between the interferer and the receiver.
EMI refers to the external electromagnetic interference of the product. In general, it is divided into Class A & Class B. Class A is an industrial grade and Class B is a civil grade. Civilian use is stricter than industry, because industrial use allows radiation to be slightly larger. For the radiation test of the same product in the test EMI, at 30-230MHz, the radiation limit of the Class B required product should not exceed 40dBm and the Class A requirement should not exceed 50dBm (for example, the measurement of the three-meter anechoic chamber) is relatively loose. In general, CLASSA means that under EMI test conditions, without operator intervention, the equipment can continue to work as expected, and performance degradation or loss of function below the specified performance level is not allowed.
EMI is the measurement of radiation and conduction when the device is in normal operation. At the time of testing, EMI radiation and conduction have two upper limits on the receiver, representing Class A and Class B. If the observed waveform exceeds the B line but is below the A line, then the product is Class A. EMS is to interfere with the product with the test equipment, and observe whether the product can work normally under the interference. If it works normally or does not exceed the performance degradation specified by the standard, it is Class A. It can be automatically restarted and does not appear to exceed the performance degradation specified in the standard after the restart, which is Class B. Can not automatically restart the need to manually restart to level C, hang up to level D. The national standard has a D-level regulation, and EN has only A, B, and C. The odd multiple of EMI at the operating frequency is the worst.
EMS (Electmmagnetic Suseeptibilkr) Electromagnetic sensitivity is commonly known as "electromagnetic immunity", which is the ability of equipment to resist external disturbances. EMI is the external disturbance of equipment.
The level in EMS refers to: Class A, the device is still working normally after the test is completed; Class B, it can work normally after the test is completed or tested, and Class C needs to be manually adjusted to restart and work normally; Class D The device is damaged and cannot be started anyway. Strict EMI is B > A, and EMS is A > B > C > D.
EMI circuit:
The role of the X capacitor:
Suppress differential mode noise, the larger the capacitance, the better the low frequency noise suppression effect.
The role of Y capacitor:
Suppress common mode noise, the larger the capacitance, the better the low frequency noise suppression effect. The Y capacitor provides a low-impedance loop from the secondary to the primary ground, causing the current flowing back through the LISN to be directly short-circuited. Since the Y capacitor is not completely ideal, there is also impedance between the secondary sections, so it is impossible to return all of them. There is still a part that flows to the ground. The Y capacitor must be connected directly to the primary and secondary cold ground with as short a straight line as possible. If the dv/dt of the MOS is greater than the dv/dt at turn-off, the Y capacitor is connected to the primary ground; otherwise it is connected to V+.
The role of common mode inductance:
Suppress common mode noise, the greater the inductance, the better the low frequency noise suppression effect. Increase the impedance of the common mode current section to reduce the common mode current.
The role of differential mode inductance:
Suppress differential mode noise, the greater the inductance, the better the low frequency noise suppression effect.
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