Generation mechanism and Countermeasures of switching power supply EMC

Classification and standard of EMC:
EMC (Compatibility Electromagnetic) is an electromagnetic compatibility, which includes EMI (electromagnetic disturbance) and EMS (electromagnetic anti harassment). EMC is defined as the ability of a device or system to work properly in its electromagnetic environment and not to constitute an electromagnetic disturbance that is not capable of any device in the environment. EMC the entire call is electromagnetic compatibility. EMP is an electromagnetic pulse.
EMC = EMI + EMI EMS: electromagnetic interference EMS: electromagnetic compatibility (immunity)
EMI can be divided into two parts, which are Conduction and Radiation. The Conduction specification can be divided into: Part 15J Class B CISPR; FCC 22 (EN61000-3-2, EN61000-3-3, EN55022) B Class; IT (GB17625, GB13837) and AV (GB17625, GB9254). FCC test frequency in 450K-30MHz, CISPR 22 test frequency in 150K–30MHz, Conduction can use the spectrum analyzer test, Radiation will have to go to a special laboratory testing.
EN55022 is Test Conduction & Test Radiation (conduction & radiation testing); EN61000-3-2 is Test Harmonic (power supply harmonic test); EN61000-3-3 is Test Flicker (voltage fluctuation test).
CISPR22 (Special des Purturbations Radioelectrique Comite) is applied to the information technology. It is suitable for European and Asian regions; EN55022 is the European standard, Part FCC 15 (Communications Commission Federal) is applied to the United States, EN30220 European EMI testing standards, power radiation testing standards are EN55013 frequency in 30MHZ-300MHz.
EN55011 radiation testing standards are: some of the high frequency requirements, some of the low frequency requirements. Conduction (150KHZ-30MHZ) to the LISN mainly is the differential current mode and the common mode impedance for a 100 ohm (50 + 50); LISN is mainly the common mode current and the total circuit impedance for 25 ohms (50 / 50).
4 line 60dB/uV 150KHZ-2MHZ start 9KHZ AV
5 line 100dB/uV 150KHZ-3MHZ PEAK
6 line 100dB/uV 2MHZ-30MHZ PEAK
7 line 70dB/uV 150KHZ-500KHZ QP
Radiated (30MHZ-1GHZ): 4N7/250V Y CAP 90dB/uV 30MHZ-300MHZ ADD
EMI is an electromagnetic interference, EMI is a part of the EMC, EMI (Magnetic Interference Electronic) electromagnetic interference, EMI including conduction, radiation, current harmonics, voltage flicker, etc.. The electromagnetic interference is caused by the interference source, coupling path and the receiver is composed of three parts of the three elements, usually called interference. EMI linear proportional to the current, the current loop area and the square of the frequency: K*I*S*F2 = EMI. I is a current, S is the circuit area, F is the frequency, K is a constant with the circuit board material and other factors.
EMI refers to the external electromagnetic interference. Generally divided into two levels of A Class & B Class. A Class for industrial grade, B Class for the civilian level. Civil to be more stringent than the industry, because of the industrial use of the allowable radiation a little big. Requirements products also products in the EMI test radiation test, in 30-230MHz class B radiation value cannot be more than 40dbm and class a request can not be more than 50dbm (to three meters anechoic chamber, for example) relative to loose the limits, generally class A is that the EMI test conditions under, without intervention from the operator, equipment can according to expected to continue normal work, not allowed to appear below specified levels of performance performance degradation or loss of functionality.
EMI is a normal operation of the equipment to measure its radiation and conduction. At the time of testing, EMI’s radiation and conduction in the receiver has two caps, representing the A Class and B Class, if the observed waveform is more than B line but below the A line, then the product is a class A. EMS is used to test equipment for product interference, observe whether the product can work normally, if the normal work or does not appear to exceed the performance of the standard, for a class. Can automatically restart and restart does not exceed the performance of the standard provisions of the decline in performance for the B class. No need to restart automatically restart C, hang D. The national standard of D level, EN only A, C, B. EMI at work frequency of the odd number is the most difficult.
EMS (Suseeptibilkr Electmmagnetic) is commonly known as the electromagnetic sensitivity of electromagnetic immunity, is the ability to resist external disturbance of the device, EMI is the device’s external harassment.
EMS levels are: A Class, the test is completed after the device is still in normal work; B Class, the test is completed or the test needs to be restarted after the normal work; C Class, the need for human adjustment can be normal to restart and normal work; D Class, the device has been damaged, no matter how the adjustment can not be started. Strictly EMI is B>A, EMS is A>B>C>D.

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