Switch Control Circuit for Resonant Converter Frequency Limiting
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Solution Overview
Problem
Resonant converters face sub-harmonic oscillations due to input voltage variations and rapid output voltage changes, making signal detection for synchronous rectification difficult, especially when switching frequency varies from low to high frequencies.
Innovation Solution
A switch control circuit that includes a frequency limit controller to differently control the switching frequency limit ratios of first and second switches by limiting the frequency variation ratio of a clock signal based on input voltage and load variations, using a half cycle signal generator and frequency limit controller to generate frequency limit signals and adjust the enable period of the clock signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If switching frequency is varied rapidly from low to high frequency due to output voltage changes, then responsiveness to load variation is improved, but sub-harmonic oscillation occurs and signal detection for synchronous rectification becomes difficult
Solution Approach 1:
The patent implements dynamic frequency limitation where the frequency limit ratio is adjusted based on operating conditions. The controller dynamically selects between a first frequency limit ratio (when on-time < target on-time) and a second frequency limit ratio (when on-time ≥ target on-time), allowing the system to respond rapidly to load changes while preventing sub-harmonic oscillation through adaptive frequency control.
Solution Approach 2:
The patent changes the frequency limitation parameter based on the relationship between actual on-time and target on-time. By monitoring the on-time of switches and comparing it with the target on-time, the system adjusts the frequency limit ratio parameter to maintain stability while allowing rapid frequency variation when needed for load response.
2Adaptability or versatility
If frequency variation ratio is not limited, then adaptability to load changes is improved, but sub-harmonic oscillation is caused due to input voltage variation
Solution Approach 1:
The system dynamically adjusts the frequency limit ratio based on real-time operating conditions. When the converter operates in continuous conduction mode (on-time < target on-time), a more permissive first frequency limit ratio is applied. When operating in discontinuous conduction mode (on-time ≥ target on-time), a more restrictive second frequency limit ratio is applied, preventing sub-harmonic oscillation while maintaining adaptability.
Solution Approach 2:
The patent implements parameter-based frequency limitation where the frequency variation ratio parameter is changed based on the conduction mode detected through on-time comparison. This allows the system to adapt to different load conditions while preventing harmful sub-harmonic oscillation through appropriate parameter selection.
Data Source
AI summary
A resonant converter includes a primary-side winding electrically coupled to an input voltage, a secondary-side winding electrically coupled to a load, first and second switches coupled to one end of the primary-side winding, and a switch control circuit configured to differently control switching frequency limit ratios of the first and second switches by differently limiting a frequency variation ratio of a first clock signal that determines switching frequencies of the first and second switches according to variation of one of the input voltage and the load.