Adaptive Synchronous Rectification Control Circuit for Power Converters
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Solution Overview
Problem
Conventional power converter systems face inefficiencies due to the use of diodes for rectification, especially when output voltages are low, and existing synchronous rectification control methods struggle to optimize control of synchronous rectification transistors (SRTs) in LLC-SRCs, particularly at high frequencies and under discontinuous conduction modes.
Innovation Solution
An adaptive synchronous rectification control circuit and method that samples the source-drain voltage of SRTs when the parasitic capacitor is charging, generating a control signal to minimize charging time and prevent parasitic diode conduction, using a proportional-integral control loop and control pulse generator to optimize SRT control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If diodes are used for rectification in power converters, then the circuit structure is simple, but the efficiency is limited due to positive conducting voltage-drop especially at low output voltages
Solution Approach 1:
The patent changes the operating parameters of the rectification device by using MOSFETs instead of diodes, utilizing the MOSFET's low on-resistance characteristic to reduce conducting voltage-drop and improve rectification efficiency at low output voltages
Solution Approach 2:
The patent replaces the passive diode rectification mechanism with an active MOSFET-based synchronous rectification system that uses control circuits to manage switching timing, thereby substituting a simple passive component with an active controlled system to achieve better performance
2Loss of energy
If synchronous rectification transistors are used instead of diodes, then rectification efficiency is improved, but control complexity increases especially at high frequencies and in discontinuous conduction modes
Solution Approach 1:
The patent employs feedback mechanisms where the control circuit monitors the resonant network state and transformer output to dynamically adjust the MOSFET switching timing, ensuring optimal rectification control under varying operating conditions including high frequencies and discontinuous conduction modes
Solution Approach 2:
The control circuit dynamically adapts the MOSFET gate drive signals based on real-time operating conditions, adjusting switching timing and duration to match the resonant frequency and conduction mode, thereby maintaining optimal efficiency across different operating states
3Reliability
If the resonant frequency is higher than the working frequency, then the SRT can be turned off at the end of resonance to avoid reverse current, but the control precision required increases
Solution Approach 1:
The control circuit is designed to anticipate the end of the resonant cycle by monitoring the resonant frequency relationship with the working frequency, and proactively turns off the MOSFET before reverse current can occur, thereby simplifying the timing precision requirement through predictive control
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
The solution achieves optimized control of SRTs, improving efficiency by minimizing voltage drop across parasitic capacitors and ensuring accurate timing, applicable to both resonant and discontinuous conduction mode converters, with simpler configuration and reduced component requirements.
Implementation Method 1
a first transistor coupled to the secondary side and having a parasitic diode... sampling a source-drain voltage of the synchronous rectification transistor when the parasitic capacitor is charging
Data Source
AI summary
The adaptive synchronous rectification control circuit and its controlling method for a power converter are provided. The proposed control circuit having a transformer with a primary and a secondary sides, a switch coupled to the primary side and a synchronous rectification transistor (SRT) coupled to the secondary side and having a parasitic diode includes a preprocessor receiving a source-drain voltage of the SRT and outputting a first signal, and a control set receiving the first signal, a pre-determined voltage and a pulse signal synchronized to the switch and generating a second signal synchronized to the switch for controlling the SRT, in which a selection of the pre-determined voltage makes the source-drain voltage of the SRT ranged from 0 to a conducting voltage of the parasitic diode of the SRT.