LLC Resonant Converter Primary-Side Load Detection
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Solution Overview
Problem
Conventional LED converters require complex and costly circuitry to detect loads on the secondary side and adjust operations accordingly, often necessitating measurements across the SELV barrier, which increases installation space and costs while lacking efficient energy transfer and adaptive operation.
Innovation Solution
An LLC resonant converter with a primary-side clocked half-bridge that detects load changes based on measured variables on the primary side, allowing for load-independent output voltage control without secondary-side measurements or active circuit breaker control, using a control device to adjust switching frequencies and compensate for load-dependent voltage shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If load detection is performed on the secondary side using conventional methods (isolators or circuit breakers), then accurate load information is obtained, but device complexity and installation space increase
Solution Approach 1:
The patent inverts the conventional load detection approach by performing load detection on the primary side instead of the secondary side. The control device determines load information by measuring primary side quantities (such as primary current or voltage) and inferring the secondary load condition, thereby eliminating the need for isolators or circuit breakers on the secondary side while maintaining detection accuracy
Solution Approach 2:
The patent uses the transformer coupling as an intermediary to transfer load information from the secondary side to the primary side. The magnetic coupling in the transformer allows the control device to detect secondary load conditions through primary side measurements without direct electrical connection, thus avoiding complex isolation components
2Measurement precision
If conventional load detection methods are used with isolators, then load information is obtained, but installation space and costs increase
Solution Approach 1:
The patent extracts the load detection function from the secondary side and relocates it to the primary side. By removing the isolator and circuit breaker components from the secondary side, the installation space requirements are significantly reduced while the load detection capability is preserved through primary side measurements
3Reliability
If the converter is optimized for a specific LED configuration, then performance is improved, but adaptability to different loads decreases
Solution Approach 1:
The patent implements dynamic adaptation by enabling the converter to automatically detect the actual LED load configuration through primary side measurements and adjust its operating parameters accordingly. The control device modifies switching frequency, duty cycle, or other control variables to optimize performance for the detected load, transforming the converter from a static, fixed-configuration device to a dynamic, adaptive system
Solution Approach 2:
The patent changes operating parameters (such as switching frequency, duty cycle, or resonant frequency) based on the detected load conditions. By adjusting these parameters in response to the actual LED configuration, the converter maintains optimal performance across different load scenarios without requiring manual reconfiguration or optimization for a specific setup
4Measurement precision
If secondary-side measurements are implemented, then precise load control is achieved, but electromagnetic interference increases
Solution Approach 1:
The patent inverts the measurement location from the secondary side to the primary side, where electromagnetic interference is inherently lower. By measuring primary side quantities (current, voltage, power) instead of secondary side quantities, the system achieves precise load control while minimizing exposure to electromagnetic interference generated by the LED load and switching operations
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 the complexity and cost of load detection, enables efficient energy transfer, and maintains a stable output voltage across varying loads without the need for secondary-side measurements, enhancing operational adaptability and reducing electromagnetic interference.
Implementation Method 1
A galvanically decoupled energy transfer can be achieved by using a transformer or other transmitter
Implementation Method 2
Resonant converters that include an LLC resonant circuit with two inductances and one capacitance can be controlled in a resonant or quasi-resonant manner on the primary side
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
An LLC resonant transformer (19) for a lamp (5) comprises a primary circuit (19) and a secondary side (30) galvanically isolated therefrom. During operation of the LLC resonant transformer (19), a first switch (21) and a second switch (22) of a half-bridge to which an LLC resonant circuit (25-27) of the primary circuit (19) is connected are actuated in a clocked fashion. A load (5) to which an output (35) on the secondary side (30) supplies energy is detected on the basis of a measured variable (iavg) acquired in the primary circuit (20). The half-bridge (21, 22) is variably controlled on the basis of the measured variable (iavg) that is acquired in the primary circuit (20) and indicates the load (5).