LLC Resonant Converter Burst-Mode Controller for Light Load Efficiency
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Solution Overview
Problem
LLC resonant converters experience significant switching losses and reduced power conversion efficiency when operating at light or no loads due to increased switching frequency, which degrades their performance.
Innovation Solution
The implementation of a burst-mode operation in LLC resonant converters, where high-side and low-side switches alternate between ON and OFF periods (work time and break time) to form a constant burst cycle time, independent of the load, reducing switching losses and maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency of an LLC resonant converter is increased to handle light or no loads, then the converter can maintain power delivery capability, but switching losses increase significantly degrading power conversion efficiency
Solution Approach 1:
The patent implements burst-mode operation where the converter operates in periodic bursts rather than continuous switching. During light or no-load conditions, the converter performs short bursts of switching activity followed by idle periods, maintaining power delivery capability while significantly reducing average switching losses. The controller enables burst-mode operation by detecting light-load conditions and adjusting the switching pattern accordingly.
2Loss of energy
If conventional continuous switching operation is used in LLC resonant converter, then power conversion efficiency is maintained at moderate loads, but switching losses become significant at light or no loads
Solution Approach 1:
The patent dynamically adjusts the switching operation mode based on load conditions. The controller monitors load status and transitions between continuous switching mode (for moderate loads) and burst-mode operation (for light or no loads). This dynamic adaptation optimizes power conversion efficiency across the full load range by selecting the appropriate operating mode for each condition.
3Device complexity
If the LLC resonant converter operates without special light-load mode, then the control system remains simple, but audible noise is generated and efficiency degrades
Solution Approach 1:
The burst-mode operation inherently reduces audible noise by limiting switching activity to periodic bursts rather than continuous operation. The reduced switching frequency and duty cycle during light loads minimize the generation of audible electromagnetic noise while maintaining necessary power delivery. The controller implements this with minimal additional complexity by monitoring load conditions and enabling burst-mode operation.
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 reduces switching losses and improves power conversion efficiency by maintaining a constant burst cycle time, even at light or no loads, thereby enhancing the converter's performance and preventing audible noise.
Implementation Method 1
transformer TF, capacitors CIN, CVCC, CL, and COUT, diodes D1, D2H, and D2L, error amplifier ER, and photo coupler OPT. Inside transformer TF, there are primary winding LP, auxiliary winding LA, secondary windings LSH and LSL, inductively coupled to each other. LLC resonant tank that is driven to resonate and transfer power from the primary side to the secondary side
Implementation Method 2
an LLC resonant converter can operate its two main power switches, high-side and low-side switches, to perform zero voltage switching (ZVS), a technology that a power switch is turned ON around the moment when the voltage drop across the conduction channel of the power switch is about zero
Data Source
AI summary
A power controller for an LLC resonant converter controls a high-side switch and a low-side switch. An ON-time generator in the power controller determines a high-side ON time of the high-side switch and a low-side ON time of the low-side switch in response to the bigger one between a feedback voltage and a burst voltage, where the feedback voltage is generated in response to an output voltage of the LLC resonant converter. A burst-mode controller in the power controller has a triangular-wave generator providing a triangular-wave signal with an amplitude in association with the burst voltage. A comparator comparing the triangular-wave signal and the feedback voltage to determine a break time when both the high-side and low-side switches are turned OFF. The LLC resonant converter operates in a burst mode when the break time is introduced.