Synchronous Rectification Latch-Off for Light Load Efficiency
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Solution Overview
Problem
Conventional synchronous rectification in flyback converters experiences inefficiency during light load conditions due to frequent switching between synchronous and non-synchronous rectification modes, leading to unreliable operation and power loss, especially when the load is at a 'border' condition, and the rectifier tends to be turned off too late with reverse current.
Innovation Solution
A real-time synchronous rectification method where the gate voltage of the rectifier continuously changes to regulate the drain-source voltage, and a light load control method that selectively latches off synchronous rectification based on the input voltage level, using a control circuit with comparators and latching circuits to determine load conditions and switch between rectification modes, ensuring efficient power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification is used during light load conditions, then power loss is reduced, but the driver power consumption increases and efficiency decreases
Solution Approach 1:
The patent changes the operational parameters of the synchronous rectifier by detecting light load conditions through voltage threshold comparison and subsequently latching the rectifier in an off state. This parameter change transitions the system from active synchronous rectification to a latched-off state, eliminating driver power consumption during light load conditions while maintaining efficient rectification through the body diode.
2Loss of energy
If the rectifier is turned off late during light load condition, then reverse current occurs, but turning it off early may cause incomplete rectification
Solution Approach 1:
The patent applies preliminary action by detecting light load conditions in advance through voltage threshold comparison before the rectifier current becomes negative. The latching circuit is triggered proactively to turn off the synchronous rectifier switch before reverse current can occur, ensuring complete and reliable rectification while preventing energy loss from reverse current.
3Adaptability or versatility
If synchronous rectification switching is frequent at border load conditions, then system adaptability is improved, but system stability and efficiency decrease
Solution Approach 1:
The patent implements feedback through voltage threshold comparison to detect light load conditions. The feedback mechanism monitors the voltage across the synchronous rectifier and triggers the latching circuit when the voltage exceeds the threshold, providing stable and reliable load condition detection that prevents frequent switching at border load conditions while maintaining system adaptability.
4Use of energy by moving object
If synchronous rectification is latched off during light load, then driver loss is reduced, but the rectifier cannot respond quickly to load increases
Solution Approach 1:
The patent uses feedback through continuous voltage monitoring to detect when load conditions change. When the voltage across the latched-off rectifier drops below the threshold, indicating a load increase, the system automatically transitions from latched-off mode to active synchronous rectification, ensuring quick response to load changes while maintaining driver loss reduction during sustained light load conditions.
Data Source
Figure 1A~1B
Figure 1C~2
Figure 3~4
AI summary
The present invention discloses a light load control circuit and the method accordingly where the synchronous rectification is latched off selectively according to the gate voltage of the synchronous rectifier.