Synchronous Rectifier Control Circuit Adaptive Turn-Off
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Solution Overview
Problem
Synchronous rectifier switches in power converters face efficiency reduction due to lead inductance, leading to negative current turn-off issues when a fixed high turn-off threshold is set, which can be too high and adversely affect the system.
Innovation Solution
A method and control circuit for adjusting the falling amplitude of the drive voltage and shielding time of a synchronous rectifier switch based on its operation state, allowing for dynamic turn-off control by sampling the drain-source voltage and adjusting parameters such as pull-down time and shielding time to optimize turn-off performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed high turn-off threshold is set for the synchronous rectifier switch, then the turn-off timing can be controlled, but the efficiency of synchronous rectification deteriorates due to negative current turn-off
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed turn-off threshold to a dynamic adaptive threshold that changes based on operating conditions. The control circuit continuously monitors the drain-source voltage and adjusts the turn-off threshold in real-time, allowing the system to adapt to varying load conditions and minimize negative current turn-off effects while maintaining reliable control.
Solution Approach 2:
The patent implements parameter changes by modifying the turn-off threshold voltage dynamically rather than using a fixed value. The control circuit adjusts the threshold parameter based on the detected drain-source voltage and operating state, enabling optimal turn-off timing that prevents negative current while maintaining high rectification efficiency across different operating conditions.
2Reliability
If the turn-off threshold is set too high to avoid negative current, then turn-off control is improved, but the applicability and reliability of the system deteriorate
Solution Approach 1:
The patent uses parameter changes to make the turn-off threshold adaptive rather than fixed. By continuously adjusting the threshold based on operating conditions, the system achieves accurate turn-off control while maintaining broad applicability across different load conditions and voltage levels, resolving the contradiction between control accuracy and system versatility.
Solution Approach 2:
The patent implements feedback by continuously monitoring the drain-source voltage and using this information to dynamically adjust the turn-off threshold. This closed-loop control ensures accurate turn-off timing while adapting to various operating conditions, thereby maintaining both high reliability and broad system applicability.
3Loss of energy
If synchronous rectifier switches are used instead of diodes, then rectification efficiency is improved, but lead inductance causes negative current turn-off issues
Solution Approach 1:
The patent applies preliminary action by proactively adjusting the turn-off threshold before negative current occurs. The control circuit detects the drain-source voltage and preemptively sets the appropriate turn-off threshold, preventing the harmful negative current effect before it happens while maintaining the high efficiency benefits of synchronous rectification.
Solution Approach 2:
The patent converts the harmful effect of lead inductance into a beneficial control mechanism. By monitoring the drain-source voltage and using the inductance effect as a signal, the control circuit determines the optimal turn-off moment, transforming the potential harm into useful information for precise control that maintains high efficiency.
Data Source
AI summary
A method of controlling a synchronous rectifier circuit can include: adjusting a falling amplitude of a drive voltage of a synchronous rectifier switch in the synchronous rectifier circuit in a pull-down mode; adjusting a shielding time during which the synchronous rectifier switch is in a turn-off shielding mode and is not to be turned off; turning off the synchronous rectifier switch after a drain-source voltage of the synchronous rectifier switch reaches a turn-off threshold; and where the falling amplitude of the drive voltage in the pull-down mode and the shielding time for a current period are adjusted according to an operation state of the synchronous rectifier switch in a previous period.