The switching power supply module will produce strong harmonic interference and peak interference because of the high operating frequency of the switching power supply and the rapid internal current and voltage changes, that is, the dv/dt and di/dt, cause the switching power supply module to produce strong harmonic interference and peak interference, and affect the normal operation of its own circuit and other electronic systems through coupling channels such as conduction, radiation and crosstalk. of course, it itself will also be affected by the electromagnetic interference of other electronic devices. This is the electromagnetic compatibility problem discussed, and the design of electromagnetic disturbance EMD and electromagnetic sensitivity EMS switching power supply electromagnetic compatibility.


　　Importance of EMC

　　As early as the early 1980s, the infant mortality rate was quite high in area of a hospital in New Jersey was quite high. Late at night, the warning lights on the baby monitor always go out for no reason. The nurses were annoyed, so they turned off the monitors and went back and forth.

　　After some preliminary investigation, the professor found out the truth of the matter, and the transmitter of a nearby television station had been authorized by the American Communications Commission to increase its output power considerably after about midnight, but had to return to its original level o'clock in the morning, or at other specified times. The connecting cable between the nurse station and the monitor of each baby resonates at these interference frequencies, and the induced voltage extinguishes the monitor warning lamp. Before the hospital discovered the problem, almost six children had died.

　　For enterprises, different EMC design concepts will lead to different costs and time waste.


　　EMC content

　　● basic concepts:

　　★EMC( EMC): Electromagnetic Compatibility)

　　★EMI( EMI): Electromagnetic Interference)

　　★EMS( electromagnetic immunity): Electromagnetic Susceptibility

　　★ESD( Electrostatic): Electrostatic Discharges)

　　★RS( radiation anti-interference): Radiated Susceptibility)

　　★EFT( fast transient pulse group): Electronic fast transients

　　★SURGE( Lightning Surge)

　　★CS( conduction interference): Conducted Susceptibility)

　　●EMC =EMI +EMS

　　★EMI = Conduction（ Harmonic） +Radiation

　　Discussion on EMI of Switching Power Supply

　　●EMI causes:

　　★ first, the biggest disadvantage of switching power supply is that the noise voltage generated by switching action (TURN-ON or TURN OFF) is its noise source. Because the waveform of switching action is square wave, square wave contains many high order harmonics. (dv/dt)

　　★ second, due to the nonlinear characteristics of switched transistors and the reverse recovery of diodes, the current changes rapidly and nonlinearly, which causes noise. (di/dt)


　　●EMI modes and means of communication:

　　★EMI interference signals can be divided into common mode signals (COMMON MODE) and differential mode signals (DIFFERENTIAL MODE).

　　★ common mode signal: the current direction of the interference signal current on the wire of the two circuits is the same signal relative to the earth, called common mode signal, see the lower left figure;

　　★ differential mode signal: the direction of the current on the wire of the two circuits that interferes with the signal current is the opposite signal, called the differential mode signal, see the lower right.

　　Please contact RenhotecIC if you want to know more about switching power supply EMC, our engineer will give you a special detailed explanation, please click https://www.renhotecic.com/ URL to buy products.