CLLLC Synchronous Rectification Using Duty Cycle Symmetry Control
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Solution Overview
Problem
Sensing the current in the transformer of a CLLLC topology DC-DC converter is challenging due to its bidirectional nature, making synchronous rectification difficult to achieve, and the reference voltage offset often drifts, requiring recalibration.
Innovation Solution
A controller is positioned on the primary side of the CLLLC converter to measure the duty cycle of secondary current signals, compare pulse widths, and adjust the reference voltage based on the difference to maintain symmetry and compensate for drift without direct measurement, using a Hall effect sensor and digital signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification is implemented in CLLLC topology, then conversion efficiency is improved, but current sensing becomes difficult due to bidirectional nature
Solution Approach 1:
The patent uses the transformer's voltage signal as an intermediary to indirectly sense the secondary current. Instead of directly sensing the bidirectional current which is difficult, the system measures the voltage across the transformer winding during rectification intervals, which correlates with the current flow. This intermediary measurement approach resolves the sensing difficulty while enabling synchronous rectification control.
Solution Approach 2:
The patent replaces direct current sensing with voltage-based detection and digital signal processing. By using voltage measurements and duty cycle analysis instead of direct current sensors, the system avoids the complexity of bidirectional current sensing while achieving the same control objective for synchronous rectification.
2Device complexity
If reference voltage offset is used for duty cycle control, then control simplicity is improved, but voltage drift occurs requiring recalibration
Solution Approach 1:
The patent implements feedback by monitoring the duty cycle symmetry and using it to adjust the reference voltage offset. The system continuously compares the positive and negative half-cycle duty cycles and dynamically adjusts the reference voltage to maintain symmetry, eliminating drift without requiring shutdown for recalibration.
Solution Approach 2:
The patent transforms the static reference voltage offset into a dynamic parameter that automatically adjusts based on operating conditions. The reference voltage is no longer fixed but varies with duty cycle measurements, allowing the system to adapt to voltage drift and maintain optimal rectification without manual intervention.
3Loss of energy
If duty cycle symmetry is maintained through reference voltage adjustment, then synchronous rectification performance is improved, but control complexity increases
Solution Approach 1:
The patent changes the control parameter from direct current sensing to duty cycle measurement and reference voltage adjustment. By measuring duty cycle symmetry and adjusting the reference voltage offset accordingly, the system maintains optimal rectification performance while using simpler, more reliable voltage-based measurements instead of complex current sensing.
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 effective synchronous rectification by maintaining duty cycle symmetry and compensating for reference voltage drift, ensuring continuous operation of the converter without shutdown for recalibration.
Implementation Method 1
The signal indicative of the current is sensed by a current sensor, the current sensor being a Hall effect sensor
Data Source
AI summary
The disclosure provides a method for enabling synchronous rectification in a converter, such as, but not limited to a CLLLC circuit. The converter includes a primary side circuit, a transformer, and a secondary side circuit. The method includes receiving a signal indicative of a current from the transformer to the secondary side circuit and measuring a duty cycle of the signal. The duty cycle includes a first pulse width being above a reference voltage and a second pulse width being below the reference voltage. The method also includes determining a difference between the first pulse width and the second pulse width and adjusting the reference voltage based on the determined difference.