Primary Side Burst Mode Controller for LLC Converter Light-Load Efficiency
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Solution Overview
Problem
LLC converters are inefficient at light-load due to constant losses, and existing burst mode strategies that monitor load conditions on the secondary side introduce additional complexity and cost by requiring components to transmit information across an isolation barrier to the primary side.
Innovation Solution
Implementing a burst mode controller on the primary side of the LLC converter to measure and control the primary side current, adjusting the off-time of half bridge switches to maintain current within specific thresholds, thereby eliminating the need for secondary side measurements and reducing complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LLC converters are operated at light-load, then the converter continues to operate, but efficiency deteriorates due to constant losses
Solution Approach 1:
The patent implements burst mode operation where the LLC converter alternates between active switching periods and idle periods. During light-load conditions, the converter operates in bursts rather than continuously, allowing the half-bridge switches to remain off for extended periods. This periodic action reduces switching losses and maintains efficiency while ensuring the converter can resume operation when load conditions change.
2Measurement precision
If secondary side load monitoring is implemented, then load conditions can be detected, but device complexity increases due to additional components and isolation barrier requirements
Solution Approach 1:
Instead of monitoring load conditions from the secondary side and transmitting information back to the primary side, the patent inverts the approach by implementing burst mode control directly on the primary side. The controller monitors primary side current and voltage to detect light-load conditions and autonomously adjusts the switching behavior. This eliminates the need for secondary side monitoring components and isolation barrier communication, significantly reducing device complexity while maintaining accurate load condition detection.
Data Source
AI summary
Embodiments include systems, methods, and apparatuses for controlling off-time during a burst mode in an LLC converter. In one embodiment, a circuit comprises an LLC converter having a primary side and a burst mode controller, the burst mode controller configured to monitor, on the primary side of the LLC converter, electrical current, and in response to a determination that the electrical current is below a first threshold, increase an off-time for switches in the LLC converter and in response to a determination that the electrical current is above a second threshold that is higher than the first threshold, decrease the off-time for the switches in the LLC converter.