Active EMI Filtering for Switch-Mode Power Supplies
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Solution Overview
Problem
Switch-mode power supplies (SMPS) generate common-mode electromagnetic interference (EMI) due to parasitic capacitance, which existing passive filtering methods address inadequately, affecting cost, size, and efficiency.
Innovation Solution
An active EMI filtering system comprising a sensor, controller, and amplifier that injects compensation pulses into the chassis ground to reduce noise, with the controller determining pulse magnitude and timing based on sensed chassis voltage and switching transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive filtering using chokes is used to reduce common-mode EMI, then common-mode noise is reduced, but cost, size and efficiency of the SMPS are adversely affected
Solution Approach 1:
The patent replaces passive mechanical filtering components (chokes and capacitors) with an active electronic filtering system comprising a sensor, controller, and amplifier. The sensor detects chassis voltage, the controller processes the signal and determines compensation parameters, and the amplifier generates compensation pulses that are injected into the chassis ground to cancel common-mode noise, thereby eliminating the need for large passive filters
Solution Approach 2:
The patent introduces an intermediary active filtering system between the SMPS and the chassis ground. This intermediary system senses the noise through parasitic capacitance, processes the signal through a controller, and injects compensation pulses through an amplifier to cancel the common-mode EMI, serving as a mediating solution that avoids direct use of large passive components
2Object-affected harmful factors
If passive filtering using chokes is used to reduce common-mode EMI, then common-mode noise is reduced, but efficiency of the SMPS is adversely affected
Solution Approach 1:
The patent replaces energy-lossy passive choke components with an active electronic system that uses minimal power. The sensor, controller, and amplifier consume significantly less energy than large passive filters, thereby improving SMPS efficiency while maintaining EMI reduction performance
Solution Approach 2:
The patent changes the filtering approach from passive component-based to active signal-based filtering. By using electronic signal processing and compensation pulse injection, the system achieves EMI reduction with much lower energy loss compared to traditional passive filters
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 effectively reduces common-mode noise, allowing for smaller passive filters and lower costs, while maintaining or improving noise reduction performance compared to traditional designs.
Implementation Method 1
The amplifier is configured to provide compensation pulses at the amplifier output having magnitude and timing to reduce common-mode noise on the chassis
Implementation Method 2
The switch node can be coupled to a chassis ground through parasitic capacitance, such that the pulsating voltage can inject noise into the chassis ground
Data Source
AI summary
In a described example, a circuit includes a sensor, a controller and an amplifier. The sensor has a sensor input and a sensor output. The sensor input is adapted to be coupled to a chassis of a switch-mode power supply (SMPS). The controller has an input, a timing output and a level output. The input of the control circuit is coupled to the sensor output. The amplifier has a timing control input, a level control input and an amplifier output. The level control input is coupled to the level output of the controller. The timing control input is coupled to the timing output, and the amplifier output is coupled to the sensor input. The amplifier is configured to provide compensation pulses at the amplifier output having magnitude and timing to reduce common-mode noise on the chassis.