EMI technology transfer channel for switching power supplies
Switching Power Supply EMI Technology Transmission Channel
(I). Conducted interference transmission channel
(1) Capacitive coupling
(2) Inductive coupling
(3) Resistive coupling
a. Resistive conductive coupling generated by the internal resistance of the public power supply
b. Resistive conductive coupling generated by public ground impedance
c. Resistive conductive coupling generated by the common line impedance
Switching power supply EMI technology suppression
(1) Reduce dv/dt and di/dt (reduce its peak value, slow down its slope)
(2) The rational application of varistors to reduce the surge voltage
(3) damping network to suppress overshoot
(4) the use of soft recovery characteristics of the diode to reduce high-frequency band EMI
(5) active power factor correction, and other harmonic correction techniques
(6) the use of reasonably designed power line filters
(7) Reasonable grounding
(8) Effective shielding measures
(9) Reasonable pCB design
Switching power supply EMI technology sources of interference
(1) Power switching tube
Power switching tube works in the On-Off rapid cycle conversion state, dv/dt and di/dt are in the rapid transformation, therefore, the power switching tube is both the main source of electric field coupling interference, but also the main source of magnetic field coupling interference.
(2)
The EMI source of high-frequency transformer is concentrated in the rapid cyclic transformation of di/dt 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 rectifier diode is concentrated in the reverse recovery characteristics, and the intermittent point of reverse recovery current will produce high dv/dt in the inductance (lead inductance, stray inductance, etc.), which leads to strong electromagnetic interference.
(4) pCB
To be precise, pCB is the coupling channel of the above interference sources, and the advantages and disadvantages of pCB directly correspond to the good or bad suppression of the above EMI sources.
