Active EMI Filter With Adjustable Shunt Impedance for Low Weight
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Solution Overview
Problem
Existing EMI filters, both passive and active, face challenges in size, weight, and cost due to limitations in capacitor size for safety constraints and magnetic saturation, which are particularly problematic in applications like automotive and aerospace where space and weight are critical.
Innovation Solution
An active electromagnetic interference filter with an adjustable shunt impedance circuit that includes a noise sensing branch and an operational amplifier stage for generating an injection current, allowing for flexible impedance adjustment and reduced size and weight through feedback compensation and optional additional stages for impedance shaping and boosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive EMI filters use larger inductors to provide required LC value for noise reduction, then noise attenuation performance is improved, but size and weight of the filter increase
Solution Approach 1:
The patent replaces the passive mechanical inductor-based filtering system with an active electronic system using operational amplifiers and capacitors. The active filter circuit uses op-amp stages to generate noise cancellation signals that electronically counteract EMI, eliminating the need for large physical inductors while maintaining noise attenuation performance.
Solution Approach 2:
The patent changes the fundamental operating parameters from passive LC filtering to active electronic signal processing. By using operational amplifiers with high gain and precise capacitor values, the system achieves equivalent or superior noise attenuation without the physical constraints of inductor size and weight.
2Object-affected harmful factors
If passive EMI filters use larger capacitors to improve noise attenuation, then noise attenuation performance is improved, but leakage current increases beyond safety constraints
Solution Approach 1:
The patent substitutes the passive capacitor-based shunt filtering approach with an active electronic system. Instead of using large capacitors that shunt noise to ground (causing leakage current), the active filter uses op-amp stages to generate anti-noise signals that cancel EMI without creating harmful leakage currents.
3Object-affected harmful factors
If existing active EMI filters use additional components such as transformers or large capacitors, then noise cancellation capability is improved, but size, weight and cost increase
Solution Approach 1:
The patent extracts and eliminates unnecessary components from existing active EMI filter designs. By removing transformers and large capacitors that were previously required, the invention achieves noise cancellation using only essential operational amplifier stages and small capacitors, thereby reducing size, weight, and complexity.
Solution Approach 2:
The operational amplifier stages in the patent perform multiple functions simultaneously: they sense noise signals, generate cancellation signals, and provide impedance matching, eliminating the need for separate transformer and capacitor components that perform similar functions in traditional designs.
4Volume of stationary object
If existing active EMI filters use only capacitor coupling to reduce size, then size is reduced, but magnetic saturation occurs that degrades filter performance
Solution Approach 1:
The patent replaces capacitor coupling with direct operational amplifier-based signal processing. The op-amp stages directly process and cancel noise signals without relying on capacitor coupling, eliminating magnetic saturation issues while maintaining compact size.
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 active EMI filter design achieves comparable noise attenuation to passive filters while being significantly smaller and lighter, with improved stability and flexibility to meet safety and frequency requirements, reducing overall system size and weight.
Implementation Method 1
an operational amplifier stage configured to generate, at an injection branch, an injection current based on the noise voltage
Data Source
Figure 1~6
AI summary
An active electromagnetic interference filter comprising an adjustable shunt impedance circuit, the adjustable shunt impedance circuit comprising a noise sensing branch that senses input noise and provides a noise voltage representative of the sensed noise, and an operational amplifier stage configured to generate, at an injection branch, an injection current based on the noise voltage.