Switched-Mode Power Supply Spread-Spectrum EMI Reduction
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Solution Overview
Problem
Switched-mode power supplies generate high-amplitude, high-frequency switching currents that cause electromagnetic interference (EMI), complicating the design of electronic devices and making it difficult to meet EMI regulatory requirements, especially in portable devices where size constraints are stringent.
Innovation Solution
A switched-mode power supply with a control circuit that provides a control signal, a modulation circuit that frequency modulates the signal using a spread-spectrum modulation signal to spread spectral content over a bandwidth, reducing switching noise and EMI through continuous frequency modulation techniques such as triangle waveforms or multiple-step discrete approximations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If switched-mode power supply uses high-frequency switching to achieve high power-conversion efficiency and smaller transformer size, then power efficiency and device size are improved, but electromagnetic interference (EMI) and switching noise increase
Solution Approach 1:
The patent applies dynamics by continuously varying the switching frequency of the power supply circuit according to a spread-spectrum modulation signal. Instead of using a fixed high-frequency switching signal, the frequency is dynamically adjusted across a range of frequencies, which spreads the spectral content of the switching noise and reduces peak EMI while maintaining the high efficiency benefits of switched-mode operation
Solution Approach 2:
The patent changes the frequency parameter of the switching signal by modulating it with a spread-spectrum signal. This parameter change spreads the concentrated high-frequency spectral content across a broader frequency range, reducing the amplitude of EMI at any single frequency while preserving the overall power conversion efficiency
2Productivity
If switched-mode power supply operates at fixed high frequency, then power conversion efficiency is maintained, but EMI regulatory requirements become difficult to meet
Solution Approach 1:
The system dynamically adjusts the switching frequency using spread-spectrum modulation, allowing the power supply to maintain high conversion efficiency while meeting EMI regulations by distributing spectral energy across a wider frequency range, thus achieving both productivity and reliability goals
3Object-affected harmful factors
If traditional low-pass filtering is used to block switching noise, then EMI is reduced, but device complexity and size increase
Solution Approach 1:
The patent applies preliminary action by spreading the spectral content of the switching noise across a wide frequency range before it can cause EMI problems. This preemptive frequency modulation reduces peak noise levels at any given frequency, eliminating or reducing the need for complex low-pass filtering circuits
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 switching noise and EMI by spreading spectral content over a wide bandwidth, achieving a 10 dB reduction in switching noise compared to 4-step spread-spectrum modulation and an average of 17 dB reduction compared to unmodulated switching noise, while being practical for implementation in portable electronic devices.
Implementation Method 1
a modulation circuit that provides a modulated switching signal by frequency modulating the control signal over a bandwidth using a spread-spectrum modulation signal
Data Source
AI summary
A switched-mode power supply with reduced electromagnetic interference (EMI) is described. This switched-mode power supply includes a modulation circuit that continuously frequency modulates a control signal over a bandwidth associated with a spread-spectrum modulation signal. By frequency modulating the control signal in the switched-mode power supply, spectral content associated with a modulated switching signal is spread evenly over the bandwidth, thereby reducing the EMI.