Synchronous Rectification Controller for LLC Converters
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Solution Overview
Problem
The existence of parasitic inductors in LLC converters causes premature turning off of synchronous rectification transistors, leading to efficiency reduction and increased efficiency loss as load increases, due to the influence of induced voltages on drain voltage thresholds.
Innovation Solution
An isolated synchronous rectifying DC/DC converter with a synchronous rectification controller that includes comparators, a flip-flop, and a threshold adjusting part to dynamically adjust the second threshold voltage based on drain voltage, using a sample hold circuit, V/I conversion, current mirror circuits, and a delay circuit to optimize switching control and mitigate the effects of parasitic inductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed threshold voltage is used for turn-off detection, then circuit simplicity is maintained, but premature turning off occurs due to parasitic inductor induced voltages
Solution Approach 1:
The patent introduces an intermediary component (the threshold adjusting part) between the drain voltage detection and the turn-off decision. This intermediary dynamically adjusts the threshold based on the actual drain voltage, mediating between the simple fixed-threshold approach and the need for accurate turn-off detection in the presence of parasitic inductors.
2Speed
If synchronous rectification transistor is turned off early due to parasitic inductor effects, then turn-off detection speed is improved, but conduction time is reduced leading to efficiency loss
Solution Approach 1:
By dynamically changing the threshold voltage parameter based on drain voltage levels, the system maintains accurate turn-off detection timing. This prevents premature turn-off while still enabling timely detection, thus preserving both detection speed and adequate conduction time for efficient operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively suppresses efficiency reduction by adjusting the threshold voltage according to load conditions and parasitic inductor effects, ensuring proper timing for turning off synchronous rectification transistors and maintaining converter efficiency.
Implementation Method 1
a first comparator configured to compare a drain voltage of the drain terminal with a first threshold voltage; a second comparator configured to compare the drain voltage of the drain terminal with a second threshold voltage
Implementation Method 2
using a sample hold circuit, V/I conversion, current mirror circuits, and a delay circuit to optimize switching control
Implementation Method 3
The existence of parasitic inductors in LLC converters causes premature turning off of synchronous rectification transistors, leading to efficiency reduction and increased efficiency loss as load increases, due to the influence of induced voltages on drain voltage thresholds
Data Source
AI summary
A synchronous rectification controller includes: a drain terminal connected to a drain of a synchronous rectification transistor; a first comparator configured to compare a drain voltage of the drain terminal with a first threshold voltage; a second comparator configured to compare the drain voltage of the drain terminal with a second threshold voltage; a flip-flop to which an ON signal output from the first comparator and an OFF signal output from the second comparator are input; a driver configured to output a gate signal to the synchronous rectification transistor based on an output signal of the flip-flop; and a threshold adjusting part configured to adjust the second threshold voltage based on the drain voltage.