Flyback Synchronous Rectification With Demagnetization Timing Check
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Solution Overview
Problem
Synchronous rectification in flyback switching power supply systems increases complexity and adversely affects reliability and stability due to mis-triggering during resonance, leading to inefficiencies and operational disorders.
Innovation Solution
A system and method for synchronous rectification that determines if the input voltage becomes lower than a predetermined threshold, checking if this occurs during or not during a demagnetization process, and generates a drive signal to turn off the transistor if it does not happen during demagnetization, preventing mis-triggering during resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification is implemented in flyback switching power supply systems, then power conversion efficiency is improved and heat generation is reduced, but system complexity increases and reliability deteriorates due to mis-triggering during resonance
Solution Approach 1:
The control circuit detects the voltage across the secondary winding and determines whether it is during a demagnetization process before generating the drive signal. This preliminary detection and timing check prevents mis-triggering during resonance by ensuring the transistor is only activated at the appropriate time, thus maintaining reliability while preserving the efficiency benefits of synchronous rectification.
2Difficulty of detecting and measuring
If synchronous rectification control circuit directly detects voltage at secondary winding, then detection simplicity is maintained, but mis-triggering occurs during resonance causing operational disorders
Solution Approach 1:
Before using the detected voltage to generate the drive signal, the control circuit performs a preliminary check to determine whether the voltage detection is during a demagnetization process. This additional timing verification step prevents mis-triggering during resonance while still using the simple direct voltage detection method, thus maintaining detection simplicity while improving operational stability.
3Speed
If synchronous rectification transistor is activated based on voltage threshold alone, then response speed is improved, but unnecessary activation during resonance causes inefficiencies
Solution Approach 1:
The control circuit performs a preliminary determination of whether voltage threshold crossing is during a demagnetization process before activating the transistor. This timing check ensures that the fast response capability is only utilized when appropriate, preventing unnecessary activation during resonance and maintaining both response speed and power efficiency.
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 approach enhances the reliability and efficiency of flyback switching power supply systems by preventing unnecessary transistor activation during resonance, thus improving power efficiency and system stability.
Implementation Method 1
a transformer (102) including a primary winding (104) and a secondary winding (106)
Implementation Method 2
the body diode of the SR switch (122) from the terminal of the SR switch (122) that is biased to the ground voltage of the secondary side to the terminal of the SR switch (122) that is connected to the secondary winding (106)
Data Source
AI summary
System and method for synchronous rectification of a power converter. For example, the system for synchronous rectification includes: a first system terminal configured to receive an input voltage; and a second system terminal configured to output a drive signal to a first transistor terminal of a transistor, the transistor further including a second transistor terminal and a third transistor terminal, the second transistor terminal being connected to a secondary winding of the power converter, the power converter further including a primary winding coupled to the secondary winding; wherein the system is configured to: determine whether the input voltage becomes lower than a predetermined voltage threshold; and if the input voltage becomes lower than the predetermined voltage threshold, determine whether a time when the input voltage becomes lower than the predetermined voltage threshold is during or not during a demagnetization process of the secondary winding.