Self-Oscillating LLC Converter with Threshold Feedback for PFC
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Solution Overview
Problem
Conventional resonant LLC converters face challenges in achieving efficient power factor correction due to high gain ratio requirements and sensitivity to frequency variations, making it difficult to maintain optimal performance across a wide range of input and output conditions.
Innovation Solution
The implementation of a self-oscillating AC/DC PFC converter with a control circuit that uses a threshold-based feedback mechanism to control the switching of the resonant LLC circuit, allowing for adaptive gate drive signal generation and restart mechanisms to ensure continuous operation, particularly during light load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional resonant LLC converters are used for power factor correction, then the converter can operate with relatively low switching losses, but the converter requires high gain ratio and is sensitive to frequency variations making it difficult to maintain optimal performance
Solution Approach 1:
The patent implements dynamic control of the resonant LLC converter by continuously adjusting the switching frequency based on real-time feedback from the electrical feedback parameter. This dynamic adaptation allows the converter to maintain optimal performance across varying load conditions and input voltages, resolving the contradiction between low switching losses and adaptability to wide operating ranges.
Solution Approach 2:
The patent changes the operating parameters of the resonant LLC converter by modulating the switching frequency in response to feedback signals. This parameter adjustment enables the converter to adapt its gain ratio dynamically, maintaining efficient operation across different operating conditions without requiring fixed high gain ratio design.
2Ease of operation
If threshold-based feedback control is used to control switching of the resonant LLC circuit, then adaptive gate drive signal generation is achieved, but the system requires restart mechanisms to ensure continuous operation during light load conditions
Solution Approach 1:
The patent employs threshold-based feedback control where the electrical feedback parameter from the resonant circuit is continuously monitored and compared against predetermined thresholds. This feedback mechanism enables adaptive generation of gate drive signals that automatically adjust switching timing and duration, achieving ease of operation while maintaining reliable continuous operation through proper threshold selection and restart logic.
Solution Approach 2:
The patent implements restart mechanisms that are pre-configured to activate under specific conditions (such as light load detection). These preliminary actions ensure that the converter can reliably restart and maintain continuous operation when load conditions change, preventing operational interruptions while maintaining the simplicity of threshold-based control.
3Measurement precision
If explicit mains current measurement is implemented, then power factor correction can be controlled, but the system complexity increases
Solution Approach 1:
The patent uses the electrical feedback parameter from the resonant LLC circuit as an intermediary that indirectly provides information about mains current conditions without requiring direct current measurement. This feedback parameter serves as a mediator that enables power factor correction control while avoiding the complexity of explicit current sensing and measurement circuits.
Solution Approach 2:
The patent replaces the mechanical/electrical current measurement system with a control approach based on electrical feedback from the resonant circuit. By substituting direct current sensing with feedback-based control of the resonant tank, the system achieves power factor correction functionality while significantly reducing device complexity and eliminating the need for separate current measurement hardware.
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 enables efficient power factor correction and stable operation across varying load conditions without the need for explicit mains current measurement, reducing complexity and improving power factor correction efficiency.
Implementation Method 1
converters which comprise an LLC resonant circuit having two inductances and one capacitance are well-known. Such converters have the advantage that energy-efficient operation with relatively low switching losses is possible.
Data Source
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AI summary
Various improvements are provided to resonant DC/DC and AC/DC converter circuit. The improvements are of particular interest for LLC circuits. Some examples relate to self-oscillating circuit and others relate to converter circuits with frequency control, for example for power factor correction, driven by an oscillator.