Switching mode power supply EMI technology transmission channel
(1) Transmission channels for conducting interference
(1) Capacitive coupling
(2) Sensory coupling
(3) Resistance coupling
a. Resistance conduction coupling generated by internal resistance of public power sources
b. Resistance conduction coupling generated by impedance of common ground wire
c. Resistance conduction coupling generated by impedance of public lines
EMI suppression technology for switch mode power supply
(1) Reduce dv/dt and di/dt (reduce their peak and slope)
(2) Reasonable application of varistors to reduce surge voltage
(3) Damping network suppresses overshoot
(4) Diodes with soft recovery characteristics to reduce high-frequency EMI
(5) Active power factor correction and other harmonic correction techniques
(6) Using a reasonably designed power line filter
(7) Reasonable grounding treatment
(8) Effective shielding measures
(9) Reasonable pCB design
Switching mode power supply EMI technology interference source
(1) Power switch tube
The power switch operates in an On Off fast cycle transition state, with both dv/dt and di/dt rapidly changing. Therefore, the power switch is not only the main interference source of electric field coupling, but also the main interference source of magnetic field coupling.
(2)
The EMI source of high-frequency transformers is mainly reflected in the di/dt fast cycle transformation corresponding to leakage inductance, so high-frequency transformers are an important interference source for magnetic field coupling.
(3) Rectifier diode
The EMI source of rectifier diodes is mainly reflected in the reverse recovery characteristics. The intermittent point of reverse recovery current will generate high dv/dt in inductance (lead inductance, stray inductance, etc.), leading to strong electromagnetic interference.
(4)pCB
To be precise, pCB is the coupling channel of the above-mentioned interference sources, and the quality of pCB directly corresponds to the quality of EMI source suppression mentioned above.
