For switching power supply system EMI conduction of efficient design is to optimize the design of EMI filters;
Switching power supply EMC advanced optimization design; for products and control systems with switching power supply; its input EMI low-pass filter placed at the input side of the EMI-conduction of the system Even the design of EMS is also very critical!
Transient interference (EMS) to the switching power supply system of electronic products or equipment will produce a threat to product function and performance problems!
This transient EMS is tested by injecting differential mode interference & common mode interference into the system;
Common Mode Interference (Common Mode Current): A current that travels in the same phase to and from the L and N lines (or signal lines) to ground;
Differential Mode Interference (Differential Mode Current): A current that travels between the L and N lines (or between the signal line and the return line) with opposite amplitude and phase;
Common mode currents and differential mode currents can exist in a pair of wires at the same time; the following theoretical analysis is performed:
Differential mode interference (EMS) with its spike noise voltages can be a direct threat to electronic products & equipment, resulting in product functionality and performance problems!
Common mode interference (EMS) with its spike noise voltage does not pose a direct threat to electronic products & equipment; common mode interference does not directly affect the equipment, but rather affects the equipment by converting it to differential mode voltage! The use of switching power supplies is essential as the system is powered by AC power and requires small size and efficiency!
Note: Electronic products & equipment in terms of switching power supply systems! If you leave out the input filter of the switching power supply
1. Switching power supply line itself on the pulse group interference suppression is very low, the reason for this, mainly due to the nature of the pulse group interference is a high-frequency common-mode interference.
2. The filter capacitors in the switching power supply line are all set up for suppressing low-frequency differential mode interference, in which the electrolytic capacitors are not enough for suppressing the ripple of the switching power supply itself, not to mention the harmonic components of the pulse group of more than 60 MHz of the interference suppression effect.
3. In the oscilloscope to observe the switching power supply input and output pulse group waveforms, do not see any obvious interference attenuation effect.
Thus, it seems that the input filter of the switching power supply system for IoT and smart products & devices is an important measure in terms of suppressing the pulse group interference to which the switching power supply is subjected.
EMS issues note to focus on PCB design issues!
1. Switching power supply system line in the high-frequency transformer design is good or bad, for pulse group interference has a certain inhibition effect;
2. Switching power supply system between the primary circuit and the secondary circuit across the capacitance, can be from the primary circuit into the secondary circuit of the common-mode interference return to the primary circuit to provide a path, so for the pulse group interference also has a certain inhibition effect;
3. Switching power supply system output common-mode filter circuit settings, can have a certain inhibition of pulse group interference.
4. The switching power supply system line itself has no inhibition effect on the pulse group interference, but if the switching power supply line layout is not good, it can aggravate the invasion of pulse group interference on the switching power supply.
In particular, the nature of the pulse group interference is a composite of conducted and radiated interference, even if the input filter is used to suppress the conducted interference component, but the radiated interference that exists around the transmission line still exists, and can still pass through the poor layout of the switching power supply.
(A "big loop antenna" is formed when the distance between the primary and secondary circuits of a switching power supply is too long).
The radiated component of pulse group interference can be induced, thus affecting the anti-jamming performance of the whole equipment.
