Switching Converter Rectifier Control for Body Diode Conduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In LLC resonant converters, the presence of parasitic inductances causes undesired earlier turn-off of transistors, leading to increased residual conduction time of body diodes and reduced efficiency due to higher voltage drops, which existing RC compensation methods can partially address but introduce turn-on delays and depend on external components.
Innovation Solution
A control device for the rectifier that measures the conduction time of body diodes cycle by cycle and adjusts the turn-off timing of transistors by delaying, advancing, or maintaining the off time instant based on threshold values to minimize parasitic inductance effects, thereby optimizing switching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification is implemented to reduce rectifier losses, then conversion efficiency is improved, but parasitic inductances cause earlier transistor turn-off and increased body diode conduction time
Solution Approach 1:
The patent implements a feedback mechanism that measures the actual conduction time of body diodes and uses this information to dynamically adjust the turn-off timing of synchronous rectifier transistors. The control device monitors the conduction time and compares it against reference values, then adjusts the transistor gate drive timing in subsequent cycles to optimize the turn-off moment, thereby minimizing parasitic inductance effects and reducing residual body diode conduction time while maintaining the efficiency benefits of synchronous rectification.
Solution Approach 2:
The patent introduces dynamic adjustment of transistor turn-off timing based on real-time measurement of body diode conduction characteristics. Instead of using fixed timing, the system continuously adapts the transistor gate drive signals to match the actual operating conditions, optimizing the turn-off moment cycle by cycle. This dynamic approach allows the system to compensate for variations in parasitic inductances and operating conditions, maintaining optimal performance across different load and voltage conditions.
2Loss of time
If RC compensation is used to address parasitic inductance effects, then turn-off timing is improved, but turn-on delays are introduced and external components are required
Solution Approach 1:
The patent employs a self-service approach where the control device directly measures the body diode conduction time and uses this self-generated information to adjust its own transistor drive timing. The system serves itself by using its own operational characteristics as the basis for optimization, eliminating the need for external RC compensation networks or additional passive components. The control device extracts the conduction time information from its own circuit operation and applies this knowledge to improve its timing control.
Solution Approach 2:
The patent replaces the passive RC compensation mechanism with an active digital measurement and control system. Instead of using analog RC circuits to indirectly compensate for timing errors, the system directly measures the conduction time using digital timing circuits and uses this precise measurement to control the transistor gate drive. This substitution of mechanical/analog compensation with electronic/digital measurement and control eliminates the need for external passive components while improving timing accuracy.
3Loss of energy
If transistor turn-off is advanced to reduce body diode conduction time, then efficiency is improved, but current inversion may occur causing converter malfunction
Solution Approach 1:
The patent uses feedback control to dynamically adjust transistor turn-off timing based on measured body diode conduction time. The control device measures the actual conduction time and compares it against optimal reference values, then makes incremental adjustments to the turn-off timing in subsequent cycles. This closed-loop approach ensures that the turn-off moment is optimized to minimize power dissipation while maintaining reliable operation, preventing current inversion by avoiding excessive advance turn-off.
Solution Approach 2:
The patent applies partial optimization rather than extreme advance turn-off. Instead of aggressively advancing the turn-off moment to maximize efficiency improvement, the system makes moderate, measured adjustments based on actual conduction time measurements. This partial action approach achieves sufficient efficiency improvement while maintaining a safety margin that prevents current inversion and ensures reliable converter operation under all conditions.
Data Source
AI summary
A control device for a transistor of a switching converter rectifier generates a control signal of the transistor and includes a circuit to measure the conduction time of the body diode of the transistor cycle by cycle. When the conduction time is greater than a first threshold, the off time instant of the transistor is delayed by a first quantity in the next cycles, until the conduction time is less than the first threshold and greater than a second threshold. When the conduction time is between the first and second thresholds, the off time instant is delayed by a fixed second quantity in the next cycles until the conduction time is lower than the second threshold, with the second quantity less than the first quantity. When the conduction time is lower than the second threshold, the off time instant is advanced by the second quantity in the next cycle.