Active EMI Filter Current Source With Unipolar High-Impedance Output
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Solution Overview
Problem
Conventional EMI filters for electric vehicles are either too bulky, expensive, and unsuitable for mass production due to their size, weight, and temperature limitations, and require bipolar power supplies, which are not always economically viable, while passive filters have limitations in attenuating high-frequency wide-bandwidth interferences effectively.
Innovation Solution
A high-frequency current source with a symmetric common-emitter configuration of bipolar transistors, an active bias network, and an analogue control network that maintains a stable DC potential and compensates for temperature variability, allowing for a unipolar power supply and high output impedance, integrated into an active EMI filter with a current sense unit to inject correction currents into the power line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive low-pass LC filters are used to attenuate EMI, then substantial attenuation is achieved, but the filter becomes bulky, heavy, and expensive
Solution Approach 1:
The patent replaces the mechanical/passive LC filter system with an active electronic filter system using operational amplifiers, transistors, and resistors. This substitution eliminates the need for bulky magnetic components while achieving equivalent or superior EMI attenuation through active circuitry that can be implemented on compact printed circuit boards.
Solution Approach 2:
The patent changes the operating parameters of the filter by using active components with high gain and specific frequency response characteristics. The operational amplifiers and transistors are configured to provide frequency-dependent impedance that achieves EMI attenuation without requiring large inductors and capacitors, thus reducing weight and size.
2Object-affected harmful factors
If passive low-pass LC filters are used to attenuate EMI, then substantial attenuation is achieved, but the filter becomes bulky, heavy, and expensive
Solution Approach 1:
The patent replaces temperature-sensitive passive magnetic components with solid-state active components (operational amplifiers, transistors, resistors) that have superior temperature stability. These electronic components maintain consistent performance across wide temperature ranges without the thermal degradation issues that plague passive LC filters.
3Volume of moving object
If conventional active filter architectures are used, then compact size is achieved, but they cannot satisfy the speed and output current requirements of automotive applications
Solution Approach 1:
The patent divides the filter functionality into multiple stages with dedicated operational amplifiers and transistor pairs for different frequency ranges and current levels. This segmentation allows each stage to be optimized for high-speed operation while maintaining compact size, as each segment handles a specific portion of the overall filtering task rather than requiring a single large-signal high-speed component.
Solution Approach 2:
The patent creates a composite active filter architecture combining multiple operational amplifier types, transistor configurations, and feedback networks. This composite structure leverages the high-speed characteristics of certain components for noise cancellation while other components handle DC stabilization and biasing, achieving both speed and compactness simultaneously.
4Volume of moving object
If conventional active filter architectures are used, then compact size is achieved, but they cannot satisfy the speed and output current requirements of automotive applications
Solution Approach 1:
The patent segments the current handling function across multiple transistor stages and operational amplifiers. Each active component operates within its optimal current range, and the stages are cascaded to achieve high total output current capability. This segmentation allows compact implementation because no single component needs to handle the full current load, enabling the use of smaller, lower-power components that maintain high overall power output.
5Device complexity
If bipolar power supply is used for active filters, then adequate input and output impedances are achieved, but bipolar power supplies are not economically available and increase device complexity
Solution Approach 1:
The patent inverts the conventional approach by designing the active filter to operate from a unipolar power supply rather than requiring bipolar supplies. The circuit topology is specifically designed with asymmetric component values and configurations that achieve the necessary input and output impedance characteristics without needing negative voltage rails, thereby simplifying the power supply architecture and reducing overall system complexity.
Data Source
AI summary
A high-frequency current source with a symmetric bipolar output stage piloted by an active bias network with an extended temperature range. The source is configured to provide a high impedance at 1 MHz and above. The invention includes such active EMI filters with such a high-frequency current source, for example in the current-sense current-inject feedback configuration.