CLLC Converter Synchronous Rectification Without Extra Current Sensors
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Solution Overview
Problem
Existing methods for determining synchronous rectification on-time in CLLC converters require additional hardware or laborious pre-measurements, increasing costs and complexity.
Innovation Solution
A method for determining synchronous rectification on-time in CLLC converters that does not require additional hardware, using simulation and linear interpolation to calculate diode on-time based on transformer turns ratio, resonant frequency, and current measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current sensor and zero-crossing comparator circuit are added to detect diode current and generate synchronous rectification trigger signals, then synchronous rectification can be achieved, but system cost increases
Solution Approach 1:
The patent extracts the essential information needed for synchronous rectification control from the existing circuit operations. Instead of adding external current sensors and zero-crossing comparators, the solution utilizes the transformer primary current waveform that already exists in the CLLC converter circuit. The microcontroller analyzes this existing waveform to detect zero-crossing points and determine diode conduction intervals, thereby achieving synchronous rectification control without extracting or adding separate sensing components.
Solution Approach 2:
The patent makes the existing primary current sensing circuit serve multiple functions. The same current sensor and ADC that are used for general control and protection functions are also utilized to capture the transformer primary current waveform for synchronous rectification timing detection. This multi-functional use of existing components eliminates the need for dedicated synchronous rectification sensing circuits, reducing overall system complexity and cost.
2Ease of operation
If a lookup table with pre-measured diode on-time data is created under different operating conditions, then synchronous rectification on-time can be determined, but laborious pre-measurements are required
Solution Approach 1:
The patent implements a self-calibrating system where the microcontroller automatically performs the measurements and calculations needed to determine synchronous rectification timing. During normal operation, the system continuously monitors the transformer primary current waveform, automatically detects zero-crossing points, and calculates the appropriate diode conduction interval based on the detected operating conditions. This self-service approach eliminates the need for external laboratories to perform laborious pre-measurements under various operating conditions to create lookup tables.
Solution Approach 2:
Instead of using static pre-measured lookup tables, the patent implements a dynamic calculation approach where the synchronous rectification on-time is determined in real-time based on actual operating conditions. The microcontroller continuously adapts the diode conduction interval detection to the current operating point by analyzing the actual primary current waveform characteristics, allowing the system to automatically adjust to any operating condition without relying on pre-characterization data.
3Speed
If high-speed current sensors and additional zero-crossing comparator circuits are used, then synchronous rectification trigger signals can be generated, but hardware cost increases
Solution Approach 1:
The patent creates a digital copy of the zero-crossing detection function through software processing of the primary current waveform. Instead of using hardware zero-crossing comparator circuits that generate trigger signals, the microcontroller samples the primary current waveform using its built-in ADC and digitally identifies zero-crossing points through software algorithms. This digital copying approach achieves the same functional result as hardware comparators while utilizing the microcontroller's existing processing capabilities, thereby eliminating the need for additional hardware components.
Data Source
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AI summary
The present disclosure relates to a method for determining the synchronous rectification on-time of a CLLC converter. The CLLC converter operates in an under-resonant operation mode. The method comprises: determining a transformer turns ratio and resonant frequency of a converter; using a simulation method to determine the peak current and output current of a secondary side diode as well as a data set of excitation current when the secondary side diode is turned off and when a primary side driving signal is turned off; measuring a current operating frequency and current output current of the converter; determining a first coefficient and a second coefficient by means of a linear interpolation method according to the operating frequency and the output current; measuring a resonant current initial value of a primary resonant inductor; and calculating a diode on-time according to the transformer turns ratio, the resonant frequency, the resonant current initial value, the current output current, the first coefficient, and the second coefficient.