LLC Resonant Converter Primary-Side Current Feedback
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Solution Overview
Problem
Conventional LLC resonant converters face inefficiencies in regulating switching frequency due to power loss from sensing output voltage, especially when generating multiple DC output voltages, as they require complex voltage feedback loops that become impractical.
Innovation Solution
Implementing a primary-side current feedback scheme that senses current at the transformer primary winding using AC coupling, allowing for lossless current sensing and regulation of switching frequency without individual output voltage sensing, applicable to both half-bridge and full-bridge LLC resonant converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If voltage feedback loop is used to sense output voltage for regulating switching frequency, then the switching frequency can be regulated, but power loss occurs due to the sensing process
Solution Approach 1:
The patent introduces an auxiliary winding on the transformer as an intermediary element to sense the primary current indirectly. This auxiliary winding generates a voltage proportional to the primary current, which is then rectified and filtered to create a feedback signal. This intermediary approach allows current sensing without directly measuring the main power current, thereby reducing power loss while maintaining effective switching frequency regulation
Solution Approach 2:
The patent replaces the conventional voltage feedback mechanism with a current feedback mechanism based on electromagnetic induction. Instead of sensing output voltage through high-impedance voltage dividers or optocouplers, the system uses the auxiliary winding to convert current information into a usable voltage signal through electromagnetic coupling, substituting one sensing paradigm with another that is more efficient
2Measurement precision
If individual output voltage sensing is implemented for multiple DC outputs, then each output can be regulated accurately, but the feedback loop becomes complex and impractical
Solution Approach 1:
The patent merges multiple output regulation functions into a single unified feedback loop. By sensing the primary current through the auxiliary winding and using it to control the switching frequency, the system simultaneously regulates all secondary outputs without requiring separate sensing circuits for each output. This consolidation maintains regulation accuracy while dramatically simplifying the feedback architecture
Solution Approach 2:
The auxiliary winding serves multiple functions: it senses the primary current, provides isolation between primary and secondary sides, and enables regulation for multiple outputs simultaneously. This single component performs what would traditionally require multiple separate sensing and feedback circuits, achieving multi-functionality that reduces overall system complexity
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
Enables efficient regulation of multiple DC output voltages with reduced power loss and simplified feedback loops, maintaining efficiency and accuracy across various output levels.
Implementation Method 1
an auxiliary winding is provided on the transformer. The auxiliary winding is coupled to a rectifier circuit and a filter circuit
Data Source
AI summary
An LLC resonant converter implements a primary-side current feedback scheme. The LLC resonant converter includes an isolation transformer having a primary winding and at least one secondary winding and is controlled by a control circuit to operate at a switching frequency. The LLC resonant converter includes a first capacitor connected to the primary winding through AC coupling to sense a first voltage indicative of a current flowing through the primary winding of the isolation transformer, and a current sense circuit configured to receive the first voltage and to generate a feedback signal. The feedback signal is coupled to the control circuit to regulate the switching frequency in response to the current at the primary winding. In another embodiment, the current sense circuit is a current and voltage sense circuit configured to sense a voltage at the primary winding.