Switching Power Supply EMI Technology Transfer Channel
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 the 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 electric field coupling of the main source of interference, but also the magnetic field coupling of the main source of interference.
(2)
The EMI source of the 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 merit of pCB directly corresponds to the good or bad suppression of the above EMI sources.
Control of leakage inductance of high frequency transformer
The leakage inductance of high-frequency transformer is one of the important reasons for the generation of power switching off spike voltage, therefore, controlling the leakage inductance has become the first problem to be faced in solving the EMI brought by high-frequency transformer.
Reduce the leakage inductance of high frequency transformer two entry points: electrical design, process design!
(1) choose the right core, reduce leakage inductance. Leakage inductance is proportional to the square of the number of turns on the original side, reduce the number of turns will significantly reduce the leakage inductance.
(2) Reduce the insulation layer between the windings. Now there is a kind of insulating layer called "gold film", the thickness of 20 ~ 100um, pulse breakdown voltage up to several thousand volts.
(3) increase the coupling between the windings, reduce leakage inductance.
