Active EMI Reduction Circuit for Switching Converters
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Solution Overview
Problem
Switched-mode power supply converters face electromagnetic interference (EMI) issues due to inductor loading and unloading, which existing passive low-pass input filters fail to adequately address, being cumbersome and inefficient.
Innovation Solution
An active electromagnetic interference (EMI) reduction circuit using a current source with a variable resistance adjusted by a comparator to regulate voltage and maintain a constant average current, potentially incorporating III/V semiconductor transistors like GaN, to reduce EMI without increasing the power circuit's size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a passive low-pass input filter is used to reduce EMI, then electromagnetic interference is reduced, but the circuit becomes cumbersome and complex
Solution Approach 1:
The patent applies dynamics by using an active EMI reduction circuit with variable resistance that dynamically adjusts based on converter current conditions, replacing the static passive filter structure. The circuit includes a controller that actively modulates the resistance value to maintain constant average current, adapting to changing operating conditions rather than using fixed passive components.
Solution Approach 2:
The patent changes the resistance parameter dynamically through the active circuit, which varies the resistance value based on the converter current. This allows the EMI reduction mechanism to adapt its parameters in real-time, achieving effective EMI filtering without the fixed, cumbersome structure of traditional passive filters.
2Object-affected harmful factors
If passive filtering components are added to reduce EMI, then electromagnetic interference is reduced, but the power circuit size increases
Solution Approach 1:
The active EMI reduction circuit serves multiple functions within a compact structure: it provides EMI reduction, maintains constant average current, and adapts to varying converter conditions. This multi-functionality eliminates the need for separate passive filtering components, reducing overall circuit area while achieving EMI compliance.
Solution Approach 2:
The patent replaces the mechanical/passive filter structure with an active electronic control system. Instead of using physical passive components (inductors, capacitors) that occupy space, the solution uses active electronic elements controlled by a controller, achieving the same EMI reduction effect in a more compact form factor.
3Adaptability or versatility
If the converter current varies with amplitude, then the converter operates flexibly, but electromagnetic interference increases
Solution Approach 1:
The patent implements feedback through the controller that monitors the converter current and adjusts the resistance accordingly. The feedback mechanism maintains a constant average current value while allowing natural amplitude variations, thereby preserving converter flexibility while reducing EMI through active compensation rather than rigid current limiting.
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 EMI by stabilizing the inductor current's average value, minimizing amplitude variations and power losses, thereby meeting regulatory EMI standards without the need for additional filtering components.
Implementation Method 1
Switched-mode power supply converters suffer from electromagnetic interferences (EMI) caused by the loading and unloading of the converter's inductor
Implementation Method 2
the EMI reduction circuit comprises an electronic component having a variable resistance; and an adjuster adapted to adjust the variable resistance based on the converter current
Data Source
AI summary
A method and apparatus for limiting or preventing electromagnetic interferences in a switching converter are presented. In particular, a power circuit provided with an active electromagnetic interference filter is presented. There is an electromagnetic interference EMI reduction circuit for use with a switching converter. This EMI reduction circuit has a current source and is adapted to regulate a voltage across the current source to provide a current having a constant average value. The switching converter is adapted to provide a converter current, and the current source constant average value may be substantially equal to an average value of the converter current. The circuit has a variable resistance; and an adjuster adapted to adjust the variable resistance based on the converter current. The adjuster may have a comparator, which is adapted to compare a voltage value at a terminal of a transistor switch, and a reference value.