What are the key measures for the EMS design of the input-to-system system?
EMS in switching power supply systems:
Transient Interference (EMS) will pose a threat to the electronic products or equipment of the switching power supply system, and there will be problems with product function and performance, and the injection test of differential mode interference & common mode interference in the system is as follows:
(Common Mode Interference (Common Mode Current): The current that travels between the L and N lines (or signal lines) and the ground wire in the same phase)
(Differential Mode Interference (Differential Mode Current): A current that travels between L and N lines (or between signal lines and return lines) and is opposite in amplitude and phase)
1. Common mode current and differential mode current can exist in a pair of wires at the same time:
UDM is the differential mode voltage, IDM is the differential mode current, the IDM is the same size, the direction is opposite, and the simple understanding is wire-to-line loop interference.
How differential mode interference affects equipment: Differential mode interference directly acts on both ends of the product equipment, directly affects the work of the equipment, and even damages the product equipment. (manifested as a spike noise voltage, which can paralyze the operation of the circuit system), and at the same time, the disturbance source inside the system will cause the problem of electromagnetic compatibility EMI.
2. Effect of spike noise voltage of differential mode interference (EMS):
ICM2 is approximately equal to ICM1, while Z1 may not be equal to Z2
UP=ICM2*ZCM2; UQ=ICM1*ZCM1: So UP is not equal to UQ, which is converted to differential mode voltage UPQ!
3. The peak noise voltage of common mode interference (EMS) will not directly threaten electronic products & equipment, but indirectly affect the equipment by converting it into differential mode voltage, because the system needs to use AC power supply, and at the same time requires limited volume and efficiency, so electronic products & equipment in terms of switching power supply system (except input filter), its shortcomings are as follows:
-The essence of pulse cluster interference is high-frequency common-mode interference, and the suppression effect of switching power supply lines on pulse cluster interference is very low
-The filter capacitors in the switching power supply circuit are all set to suppress low-frequency differential mode interference, and the electrolytic capacitors have a weak ripple suppression effect on the switching power supply itself, and the suppression effect on pulse group interference with harmonic components above 60MHz is even more minimal
-When observing the burst waveforms at the input and output of a switching power supply with an oscilloscope, the interference attenuation effect is low
In order to effectively suppress the pulse cluster interference and noise suppressed by the switching power supply, we need to add an EMI low-pass filter to the input front end of the switching power supply system of the Internet of Things and smart products & devices.