9 measures to suppress EMI in switching power supplies
In switch mode power supplies, sudden changes in voltage and current, namely high dv/dt and di/dt, are the main causes of EMI generation. The EMC design technology measures for implementing switch mode power supplies are mainly based on the following two points:
(1) Minimize the interference sources generated by the power supply itself, use methods to suppress interference or use components and circuits that generate less interference, and arrange them reasonably;
(2) Suppress EMI of power supply and improve EMS of power supply through grounding, filtering, shielding and other technologies.
Speaking separately, the 9 major measures are:
(1) Reduce dv/dt and di/dt (decrease their peak and slow down their slope)
(2) Reasonable application of varistors to reduce surge voltage
(3) Damping network suppresses overshoot
(4) Using diodes with soft recovery characteristics to reduce high-frequency EMI
(5) Active power factor correction and other harmonic correction techniques
(6) Adopting a well-designed power line filter
(7) Reasonable grounding treatment
(8) Effective shielding measures
(9) Reasonable PCB design
Shielding of high-frequency transformers
To prevent the leakage magnetic field of high-frequency transformers from interfering with surrounding circuits, shielding tapes can be used to shield the leakage magnetic field of high-frequency transformers. Shielding tape is generally made of copper foil, wrapped around the outside of the transformer and grounded. The shielding tape is a short-circuit loop relative to the leakage magnetic field, thereby suppressing the leakage of a larger range of leakage magnetic field.
High frequency transformers experience relative displacement between the magnetic cores and windings, resulting in noise (whistling, vibration) during operation. To prevent this noise, reinforcement measures need to be taken for the transformer:
(1) Use epoxy resin to bond the three contact surfaces of magnetic cores (such as EE and EI cores) to suppress relative displacement;
(2) Using "Glass beads" adhesive to bond the magnetic core yields better results.
