Switching power supply EMI technology suppression
(1) Reduce dv/dt and di/dt (reduce its peak value and slow down its slope)
(2) Reasonable application of varistors to reduce surge voltage
(3) Damping network suppresses overshoot
(4) Diodes with soft recovery characteristics are used to reduce high-frequency EMI
(5) Active power factor correction, and other harmonic correction techniques
(6) Use a reasonably designed power line filter
(7) Reasonable grounding treatment
(8) Effective shielding measures
(9) Reasonable PCB design
EMI Technology Interference Source of Switching Power Supply
(1) Power switch tube
The power switch tube works in the state of On-Off rapid cycle switching, and the dv/dt and di/dt are changing rapidly. Therefore, the power switch tube 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 the high-frequency transformer is concentrated in the di/dt rapid cycle transformation corresponding to the leakage inductance, so the high-frequency transformer is an important interference source of magnetic field coupling.
(3) Rectifier diode
The EMI source of the rectifier diode is mainly reflected in the reverse recovery characteristics. The discontinuous point of the reverse recovery current will generate high dv/dt in the inductance (lead inductance, stray inductance, etc.), resulting in 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 suppression of the above-mentioned EMI sources.
Control of Leakage Inductance of High Frequency Transformer
The leakage inductance of the high-frequency transformer is one of the important reasons for the turn-off peak voltage of the power switch tube. Therefore, controlling the leakage inductance becomes the primary problem to solve the EMI caused by the high-frequency transformer.
There are two entry points for reducing the leakage inductance of high-frequency transformers: electrical design and process design!
(1) Choose a suitable magnetic core to reduce leakage inductance. The leakage inductance is proportional to the square of the number of turns on the primary side, reducing the number of turns will significantly reduce the leakage inductance.
(2) Reduce the insulating layer between the windings. Now there is an insulating layer called "gold 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.
