Switch-mode power supply noise filter with frequency-varying conductance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Switch-mode power supplies for mobile devices, such as those used in charging, face challenges in reducing common-mode noise, particularly at frequencies relevant to touch screen controllers, which can lead to malfunction and inefficiency due to electromagnetic interference (EMI).
Innovation Solution
A switch mode power supply design incorporating an isolation transformer and a noise filter with varying conductance, featuring capacitors and inductors, which boosts conductance in specific frequency ranges to effectively reduce common-mode noise, thereby preventing interference with touch screen controllers during charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional noise filter with fixed conductance is used, then the common-mode noise is reduced across a broad frequency range, but the noise reduction effectiveness is insufficient at specific critical frequencies (e.g., touch screen controller frequencies)
Solution Approach 1:
The patent applies the dynamics principle by making the noise filter conductance variable rather than fixed. The filter conductance changes dynamically with frequency, achieving peak conductance values at specific critical frequencies (such as touch screen controller frequencies) while maintaining lower conductance at other frequencies. This frequency-dependent conductance allows the filter to adaptively target and reduce noise at problematic frequencies without affecting other frequency ranges.
Solution Approach 2:
The patent implements local quality by concentrating the noise reduction effect at specific frequency regions rather than uniformly across the entire frequency spectrum. The filter is designed to provide enhanced common-mode noise reduction specifically at critical frequencies where touch screen controllers operate, while maintaining adequate but not excessive reduction at other frequencies. This localized approach optimizes noise reduction where it is most needed.
2Object-affected harmful factors
If the noise filter conductance is increased across all frequencies, then common-mode noise is reduced more effectively, but the power conversion efficiency decreases due to increased losses
Solution Approach 1:
The patent applies local quality by concentrating the high conductance (and thus high noise reduction) effect only at specific critical frequencies rather than across the entire frequency spectrum. At frequencies where noise reduction is less critical, the filter maintains lower conductance, thereby reducing energy losses and improving overall power conversion efficiency. This selective approach ensures that energy is not wasted on filtering frequencies that do not require aggressive noise suppression.
Solution Approach 2:
The patent uses dynamics by making the filter conductance frequency-dependent rather than uniformly high across all frequencies. The conductance dynamically adjusts to provide peak values only at critical frequencies where noise reduction is essential, while maintaining lower values at other frequencies. This dynamic behavior reduces unnecessary energy dissipation in the filter while maintaining effective noise reduction where required.
3Object-affected harmful factors
If a complex noise filter design is used to achieve frequency-selective noise reduction, then noise reduction effectiveness at critical frequencies is improved, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the conductance parameter of the noise filter as a function of frequency. Rather than using a complex multi-component filter structure, the invention achieves frequency-selective noise reduction by controlling how the filter conductance parameter varies with frequency. This can be accomplished through carefully selected capacitor and inductor values that create the desired frequency-dependent conductance behavior, simplifying the overall filter design while maintaining effectiveness.
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 significantly reduces common-mode noise at critical frequencies, ensuring reliable operation of touch screen devices while charging and allowing for more efficient power conversion by preferentially increasing conductance in specific frequency bands, thus meeting EMI requirements.
Implementation Method 1
The noise filter comprises a capacitor and an inductor. The noise filter further comprises a second capacitor in parallel with a series arrangement of the inductor and the capacitor.
Implementation Method 2
The noise filter comprises a capacitor and an inductor. The noise filter further comprises a second capacitor in parallel with a series arrangement of the inductor and the capacitor.
Implementation Method 3
the noise filter having a conductance value that varies with frequency; wherein the noise filter conductance comprises a peak conductance in a peak conductance frequency region
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A switch mode power supply is described including a primary side for coupling to a mains supply and a secondary side for coupling to a device, an isolation transformer comprising a primary coil and a secondary coil and arranged to isolate the primary side from the secondary side, and a noise filter coupled between a primary ground at the primary side and a secondary ground at the secondary side, the noise filter having a conductance value that varies with frequency. The noise filter conductance comprises a peak conductance in a peak conductance frequency region. The noise filter is operable to reduce the common-mode noise of the switch mode power supply at frequencies occurring in the peak conductance frequency region.