Switching mode power supply EMI technology interference source
(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.
Control of leakage inductance in high-frequency transformers
The leakage inductance of high-frequency transformers is one of the important reasons for the generation of power switch off peak voltage. Therefore, controlling leakage inductance has become the primary problem to solve the EMI caused by high-frequency transformers.
Two entry points for reducing leakage inductance in high-frequency transformers: electrical design and process design!
(1) Choose the appropriate magnetic core to reduce leakage inductance. The leakage inductance is directly proportional to the square of the original side turns, and reducing the number of turns will significantly reduce the leakage inductance.
(2) Reduce the insulation layer between windings. There is now an insulation layer called "golden thin film" with a thickness of 20-100um and a pulse breakdown voltage of several thousand volts.
(3) Increase the coupling between windings and reduce leakage inductance.
