Synchronous Rectifier Controller Blanking Time Optimization
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Solution Overview
Problem
Increasing the blanking time beyond 700ns in switched mode power supplies leads to energy loss as energy is transferred back to the input converter, reducing efficiency.
Innovation Solution
A controller that senses the output of the synchronous rectification switch at the end of the blanking time and generates a control signal to disable the synchronous rectifier if its conduction time is shorter than the blanking time, preventing energy loss and maintaining high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the blanking time is increased beyond 700ns to cover ringing caused by primary switch turn-off, then the system becomes less susceptible to false triggering, but energy loss increases as energy is transferred back to the input converter
Solution Approach 1:
The patent implements dynamic adjustment of the blanking time period based on operating conditions. The controller adapts the blanking time to be sufficient for ringing suppression under normal conditions, but reduces or disables it when synchronous rectification conduction time is insufficient, thereby dynamically optimizing the trade-off between reliability and energy efficiency
Solution Approach 2:
The patent changes the blanking time parameter adaptively based on the conduction time of the synchronous rectification switch. When the conduction time is determined to be less than the blanking time period, the controller modifies the blanking time configuration to prevent energy loss while still maintaining adequate ringing suppression when needed
2Loss of energy
If the synchronous rectifier is kept active during transient conditions with short conduction times, then energy transfer efficiency is maintained, but false triggering occurs due to ringing noise on the Inhibit pin
Solution Approach 1:
The patent employs feedback mechanisms where the controller monitors the conduction time of the synchronous rectification switch and uses this information to determine whether to enable or disable synchronous rectification. This feedback loop ensures that synchronous rectification is only disabled when truly necessary, maintaining energy efficiency while preventing false triggering
Solution Approach 2:
The system dynamically determines whether to enable synchronous rectification based on real-time conduction time measurements. During transient conditions with insufficient conduction time, synchronous rectification is disabled to prevent false triggering, while under normal conditions it remains active to maintain energy efficiency
Data Source
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AI summary
In a controller (CC2) for controlling a synchronous rectification switch (S2), the controller (CC2) comprises a sensing circuit (SRL) for sensing an output (D2) of the synchronous rectification switch (S2) at an end of a blanking time to obtain a sense signal (Q), and a control signal generating circuit (ANDl) for generating a control signal (G2) for the synchronous rectification switch (S2) in dependence on the sense signal (Q).