Synchronous Rectifier LLC Resonant Converter Noise Control
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Solution Overview
Problem
Existing synchronous rectifiers face challenges in precisely controlling the on/off time of the secondary coil switch due to low voltage noise and parasitic components, limiting efficiency improvement beyond general LLC resonant converters, and additional components like photocouplers or transformers are required for precise control, increasing production costs and potentially reducing efficiency.
Innovation Solution
A synchronous rectifier design incorporating a square wave generator, resonator, and output unit with switching controllers that maintain switches in specific on states based on voltage reductions, allowing precise control of switches SR1 and SR2 without additional components like photocouplers or transformers, thereby enhancing efficiency and reducing production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage sensing method is used to control secondary coil switch, then simplicity is maintained, but measurement precision deteriorates due to low voltage noise and parasitic components
Solution Approach 1:
The patent introduces an intermediary transformation process: instead of directly sensing the low voltage at the secondary coil terminals, the system transforms the control signal through a resonant circuit that converts it into a high-voltage square wave. This high-voltage signal serves as an intermediary that is much more resistant to noise and parasitic effects, enabling precise timing control without direct low-voltage sensing.
Solution Approach 2:
The patent replaces the electrical voltage sensing method with a resonant oscillation-based control method. By using the natural resonance of the LC circuit, the system determines switch timing through oscillation cycles rather than direct voltage measurement, thereby avoiding the noise and parasitic component issues inherent in voltage sensing.
2Measurement precision
If additional components like photocoupler or transformer are added for precise control, then switching control precision is improved, but device complexity and production cost increase
Solution Approach 1:
The patent makes the resonant circuit serve multiple functions: it transforms the control signal, provides precise timing reference through resonance, and eliminates the need for separate isolation components. By making the resonant circuit multi-functional, the system achieves precise switching control without adding photocouplers or transformers.
Solution Approach 2:
The system uses its own resonant characteristics to generate the timing reference signal needed for precise switching control. The resonant circuit self-generates the square wave signal that provides the control timing, eliminating the need for external precision timing components or additional control circuits.
3Ease of operation
If switching frequency is reduced below resonance frequency, then ease of operation is improved, but productivity deteriorates due to premature resonance termination and reverse current flow
Solution Approach 1:
The patent implements feedback through the resonant circuit that continuously monitors the oscillation state and automatically adjusts the switching timing. The resonant oscillation provides real-time feedback about the energy transfer status, ensuring that switching occurs at the optimal moment regardless of the absolute frequency, thus preventing premature termination and reverse current flow.
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 design enables precise control of the on/off states of the switches, improving efficiency and reducing production costs by eliminating the need for additional components, while maintaining a stable and cost-effective synchronous rectifier.
Implementation Method 1
a resonator including a first coil of a primary coil of a transformer, and generating a resonance waveform corresponding to the square wave
Implementation Method 2
A current is induced by the primary coil in the secondary coil of the transformer
Data Source
AI summary
This invention relates to a synchronous rectifier for LLC resonant converter. This method allows simple drive method for the synchronous rectifier MOSFETS by using the transformer secondary winding voltage and one-shot vibrator. The synchronous rectifier MOSFETs are turned on by being triggered to the transformer secondary side winding voltage and turned off after predetermined time set by one shot vibrator. The predetermined time is set by the resonant period of the resonant network.