Jittering Switching Frequency Power Controller EMI Reduction
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Solution Overview
Problem
Switching-mode power supplies in quasi-resonance mode can cause switching frequencies to stabilize at a single frequency or toggle between two frequencies, potentially inducing electromagnetic interference (EMI) issues.
Innovation Solution
A power controller that generates a PWM signal to control a power switch, jittering the maximum switching frequency within a variation range centered at an average switching frequency, while maintaining a constant variation ratio, to spread radiation energy and reduce EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If valley switching is implemented in quasi-resonance mode to reduce switching loss, then conversion efficiency is improved, but switching frequency stabilizes at a single frequency or toggles between two frequencies, causing electromagnetic interference
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. A jittering mechanism is introduced that dynamically varies the switching frequency around a nominal value, preventing the frequency from stabilizing at a single point or toggling between two fixed frequencies. This dynamic frequency variation spreads the electromagnetic radiation energy across a frequency range, reducing EMI while maintaining the efficiency benefits of valley switching in quasi-resonance mode
Solution Approach 2:
The patent changes the frequency parameter from a fixed value to a varying value within a specified range. By introducing frequency jitter that varies the switching frequency around a nominal frequency, the system maintains average frequency performance while preventing harmful frequency stabilization. This parameter change resolves the contradiction by allowing efficient switching while reducing electromagnetic interference through frequency distribution
2Object-affected harmful factors
If switching frequency is jittered to spread radiation energy and reduce EMI, then electromagnetic interference is reduced, but switching frequency varies which may affect conversion efficiency
Solution Approach 1:
The patent applies partial action by introducing small, controlled frequency variations (jitter) rather than large frequency changes. The jittering mechanism varies the switching frequency within a limited range around the nominal frequency, providing enough variation to spread electromagnetic radiation energy and reduce EMI, while keeping the variations small enough to maintain conversion efficiency. This partial action resolves the contradiction by achieving EMI reduction without excessive frequency deviation that would harm efficiency
Data Source
AI summary
A power controller provides a PWM signal to a power switch in response to a compensation signal to control the power switch, the compensation signal generated in response to an output voltage of a power converter. The power controller is configured to provide a maximum switching frequency limiting a switching frequency of the PWM signal. The power controller jitters the maximum switching frequency, making the maximum switching frequency have a first average switching frequency and a first variation ratio when the compensation signal is a first compensation value, and have a second average switching frequency and a second variation ratio when the compensation signal is a second compensation value. The first average switching frequency is higher than the second average switching frequency, and the second variation ratio is larger than the first variation ratio.