Fractional Valley Switching Controller for EMI Reduction
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Solution Overview
Problem
Conventional switch-mode power supplies face challenges in reducing peak electromagnetic interference (EMI) while maintaining high power processing efficiency, as wide frequency variations can lead to efficiency deterioration and audible tone generation.
Innovation Solution
The implementation of fractional valley switching, where the average off-time of the main switch is modulated to correspond to a series of intermediate valley numbers, spreading EMI across a wide frequency range without significant efficiency reduction, and disabling audible tones by selecting modulation frequencies less sensitive to human hearing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the switching frequency of the main switch is varied widely to spread EMI across a wide frequency range, then peak conducted EMI is reduced, but power processing efficiency deteriorates significantly
Solution Approach 1:
The patent applies dynamics by modulating the average off-time of the main switch dynamically across multiple intermediate valley numbers rather than using a fixed off-time. This dynamic adjustment allows the switching frequency to vary and spread EMI across multiple frequency bands while maintaining optimal operating points that preserve power processing efficiency. The controller continuously adapts the off-time based on the resonant waveform valleys, enabling flexible frequency distribution without settling at suboptimal fixed frequencies.
2Object-generated harmful factors
If the switching frequency is varied quickly and abruptly between fixed frequencies to spread EMI, then EMI reduction is achieved, but audible tones are introduced
Solution Approach 1:
The patent applies periodic action by modulating the average off-time across multiple intermediate valley numbers in a structured, periodic manner. Instead of abrupt frequency changes, the controller cycles through a sequence of intermediate valley numbers (e.g., 1st, 2nd, 3rd, 4th valleys) in a repeating pattern. This periodic modulation spreads EMI effectively while avoiding sudden transitions that would generate audible tones, as the changes occur in a controlled, rhythmic fashion that pushes noise energy into less sensitive frequency ranges.
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
This approach effectively minimizes peak conducted EMI across multiple frequency bands without compromising power processing efficiency, while ensuring the generated tones are within a frequency range that is less bothersome to humans, thus meeting optimized operating criteria.
Implementation Method 1
Quasi-resonant control methods induce a resonant waveform having sinusoidal voltage oscillations at the drains of one or more semiconductor switches of the power converter
Data Source
AI summary
A method involves controlling, for a duration of a first modulation period, a first average off-time of a main switch of a power converter such that the first average off-time of the main switch corresponds to a first intermediate valley number of multiple intermediate valley numbers, an average of the intermediate valley numbers corresponding to a target number of valleys of a resonant waveform at a drain node of the main switch. A second intermediate valley number of the intermediate valley numbers is selected upon expiration of the first modulation period. A difference of the second intermediate valley number and the first intermediate valley number is equal to a fractional valley number offset. A second average off-time of the main switch is controlled for a duration of a second modulation period such that the second average off-time of the main switch corresponds to the second intermediate valley number.