Adaptive Valley Mode Switching for EMI Reduction
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Solution Overview
Problem
Conventional valley mode switching techniques in switching power converters result in high electromagnetic interference (EMI) peak amplitudes, which can invade adjacent frequency bands, posing issues for applications requiring low noise emissions, such as capacitive sensing in touch screens.
Innovation Solution
An adaptive valley mode switching scheme that randomly varies the switch-on time within the valley period, determined by a controller, to lower EMI amplitudes while keeping noise confined to specific frequency bands, using a valley threshold voltage and frequency dithering within the valley period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional valley mode switching is used to reduce switching losses and EMI, then switching efficiency is improved, but peak EMI amplitudes increase and invade adjacent frequency bands
Solution Approach 1:
The patent applies dynamics by making the switching timing flexible rather than fixed. The controller randomly selects switch-on times within the valley period based on a probability distribution function, creating dynamic switching behavior that reduces peak EMI amplitudes while maintaining the benefits of valley mode switching for reducing switching losses.
Solution Approach 2:
The patent changes the parameter of switching timing from a fixed valley minimum point to a randomly varied time within the valley period. By modifying the timing parameter according to a probability distribution function, the system reduces peak EMI amplitudes while still operating during the low-voltage valley period to maintain efficiency.
2Loss of energy
If the controller switches on the power switch at a fixed valley minimum, then switching losses are minimized, but EMI noise is concentrated at the switching frequency and harmonics
Solution Approach 1:
The patent transforms the fixed switching timing into a dynamic, randomly varied timing within the valley period. This dynamic approach maintains the energy efficiency of valley mode switching while dispersing EMI noise across a broader frequency range, preventing concentration at specific switching frequencies and harmonics.
Solution Approach 2:
The patent converts the harmful concentration of EMI noise at specific frequencies into a benefit by using random dithering within the valley period. The randomness transforms the concentrated EMI peaks into a more distributed noise profile, while the valley period constraint ensures switching losses remain minimized.
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 adaptive valley mode switching effectively reduces peak EMI noise amplitudes without spreading noise into adjacent frequency bands, maintaining low noise levels in critical frequency regions.
Implementation Method 1
the resonant voltage ringing that occurs across the power switch transistor when it is cycled off. The resonant voltage ringing causes the switch voltage to cycle through local minimums that are denoted as voltage valleys
Implementation Method 2
A switching scheme that switches on the power switch at these local minimums is thus denoted as a valley-mode switching scheme. The resulting voltage waveforms for an example switching power converter configured to implement valley-mode switching
Data Source
AI summary
An adaptive valley mode switching power converter is provided that switches on a power switch within valley periods of a resonant voltage oscillation for the power switch. Each valley period is determined with regard to a valley threshold voltage.