LLC Resonant Converter Capacitive Mode Exit Control
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Solution Overview
Problem
LLC resonant converters face challenges in quickly returning to the inductive mode from the capacitive mode, which can lead to switch damage and inefficiencies due to slow response times in adjusting switching frequency.
Innovation Solution
A control method and circuit that utilize a setting capacitor with N up and low thresholds to dynamically adjust the switching frequency by comparing the setting voltage signal with these thresholds, allowing for quicker transitions between operational modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LLC resonant converter operates in capacitive mode, then the converter can handle certain load conditions, but the switching frequency adjustment is slow which can lead to switch damage
Solution Approach 1:
The patent implements dynamic threshold adjustment where the first threshold is initially set to a first value and changes to a second value after detecting capacitive mode operation. This dynamic adaptation allows the control circuit to respond more quickly to mode transitions while maintaining reliable operation, directly resolving the contradiction between switch safety and adjustment speed
Solution Approach 2:
The control circuit continuously monitors the operating mode and uses feedback to adjust the threshold values. When capacitive mode is detected, the threshold changes to accelerate frequency adjustment, creating a feedback loop that prioritizes rapid response when needed while maintaining safety through continuous monitoring
2Reliability
If the switching frequency is adjusted quickly to exit capacitive mode, then switch damage is prevented, but the control complexity increases
Solution Approach 1:
The control method is segmented into distinct operational phases: normal operation with standard threshold comparison, and capacitive mode detection with threshold adjustment. This segmentation allows the complex protective function to be implemented as a separate, manageable control routine rather than complicating the entire control system
Solution Approach 2:
The patent changes the threshold parameter dynamically based on operating conditions. By modifying only the threshold value rather than the entire control algorithm, the system achieves rapid protective response with minimal increase in control complexity
3Device complexity
If the resonant converter uses traditional frequency control, then the circuit is simple, but the response time to exit capacitive mode is slow
Solution Approach 1:
The control circuit performs preliminary detection of capacitive mode operation and proactively adjusts the threshold before the situation becomes critical. This preliminary action enables faster mode transition without requiring complex real-time adjustments, maintaining circuit simplicity while reducing transition time
Data Source
AI summary
A control circuit used for controlling a resonant converter. The control circuit has a setting capacitor, N up thresholds and N low thresholds. If the resonant converter operates in the inductive mode, a setting voltage signal across the setting capacitor is respectively compared with the largest one of the N up thresholds and the smallest one of the N low thresholds in each operation cycle to generate a high-side control signal and a low-side control signal for controlling a high-side switch and a low-side switch of the resonant converter. If the resonant converter enters into the capacitive mode, the setting voltage signal is respectively compared with each of the N up thresholds and each of the N low thresholds operation cycle by operation cycle to generate the high-side control signal and the low-side control signal.