Switching Power Supply EMI Filter Using Ferrite Bead-Capacitor Network
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Solution Overview
Problem
Switching power supplies using wide-bandgap semiconductor devices experience high electromagnetic interference (EMI) radiation due to higher switching frequencies and power densities, which conventional ferrite beads cannot adequately attenuate, leading to operational limits being exceeded.
Innovation Solution
Incorporating a capacitor network in parallel with a ferrite bead to customize its EMI suppressive ability, thereby reducing radiated EMI by fine-tuning impedance characteristics to specific frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If wide-bandgap semiconductor devices are used to increase switching frequency and power density, then power conversion efficiency is improved, but radiated electromagnetic interference increases
Solution Approach 1:
The patent changes the electrical parameters of the EMI filtering circuit by introducing a capacitor network in parallel with the ferrite bead. This modifies the impedance characteristics across different frequency ranges, enabling the circuit to maintain low EMI attenuation at high frequencies while preserving the high switching frequency operation enabled by wide-bandgap devices.
Solution Approach 2:
The patent creates a composite EMI filtering structure by combining the ferrite bead (with its high-frequency attenuation properties) and the capacitor network (with its frequency-dependent impedance characteristics). This composite approach allows selective EMI suppression that preserves the benefits of wide-bandgap device operation.
2Object-generated harmful factors
If conventional ferrite beads are used to attenuate EMI, then some EMI reduction is achieved, but EMI limits are still exceeded at high switching frequencies
Solution Approach 1:
The patent modifies the frequency response parameters of the EMI filtering circuit by adding the capacitor network. This changes the impedance characteristics to create a more effective attenuation profile that maintains compliance with EMI limits across the extended frequency range generated by high-frequency switching.
Solution Approach 2:
The capacitor network acts as an intermediary element that works in conjunction with the ferrite bead to provide enhanced EMI suppression. The capacitor network specifically targets and attenuates the high-frequency EMI components that the ferrite bead alone cannot sufficiently suppress.
3Productivity
If switching frequency is increased to improve power density, then power conversion efficiency is improved, but EMI radiation increases
Solution Approach 1:
The patent changes the electrical parameters of the filtering circuit to accommodate higher switching frequencies. The capacitor network introduces new poles and zeros in the transfer function that enhance attenuation at the higher frequency ranges, allowing the system to operate at higher frequencies for improved power density without excessive EMI radiation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces radiated EMI to acceptable levels, enabling wide-bandgap based power supplies to operate within EMI limits without disturbing adjacent devices.
Implementation Method 1
a ferrite bead coupled between the first primary terminal and the first drain terminal
Implementation Method 2
a capacitor network coupled in parallel with the ferrite bead and arranged to reduce radiated electromagnetic interference of the converter circuit
Data Source
AI summary
Systems and methods for improving radiated electromagnetic interference (EMI) in switching power supplies are disclosed. In one aspect, a converter circuit includes a transformer having a primary winding and a secondary winding, the primary winding extending from a first primary terminal to a second primary terminal, a first switch having a first gate terminal, a first source terminal and a first drain terminal, wherein the first drain terminal is coupled to the first primary terminal, and the first source terminal is coupled to a power source, and a capacitor having a first capacitor terminal and second capacitor terminal, wherein the first capacitor terminal is coupled to the power source. A ferrite bead is coupled between the first primary terminal and the first drain terminal, and a capacitor network is coupled in parallel with the ferrite bead and arranged to reduce radiated electromagnetic interference of the converter circuit.