Synchronous Rectification Control Circuit for Conduction Loss Reduction
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Solution Overview
Problem
Synchronous rectification control circuits face inefficiencies due to parasitic diode conduction losses during rectification periods, as the MOSFET is turned off while rectification current flows, leading to increased conduction loss and reduced efficiency.
Innovation Solution
A synchronous rectification control circuit with a first drive unit controlling the on/off of the MOSFET, a second drive unit maintaining the voltage between the MOSFET's terminals at a threshold voltage during rectification, and a drive switching unit selectively supplying outputs from both units to minimize parasitic diode conduction and maintain the MOSFET in an on-state during most of the rectification period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the MOSFET is turned off during rectification period, then the circuit structure is simple, but conduction loss increases due to parasitic diode
Solution Approach 1:
The control circuit is segmented into two independent drive units: a first drive unit that provides basic on/off control based on rectification current detection, and a second drive unit that provides voltage clamping control to maintain MOSFET on-state. This segmentation allows each unit to perform a specific function, reducing overall conduction loss while keeping individual unit complexity manageable.
Solution Approach 2:
The control circuit dynamically switches between two control modes by selectively connecting the output of the first drive unit or the second drive unit to the MOSFET gate. The switching is controlled by a switching signal that activates the appropriate drive unit based on operating conditions, enabling adaptive optimization of conduction loss reduction.
2Loss of energy
If the MOSFET remains on during rectification period, then conduction loss is reduced, but control precision requirements increase
Solution Approach 1:
The second drive unit implements voltage feedback control by detecting the voltage between the drain and source of the MOSFET and comparing it with a reference voltage. When the detected voltage exceeds the reference voltage, the second drive unit activates to clamp the voltage, ensuring the MOSFET remains in the on-state with precise voltage control.
Solution Approach 2:
The control circuit changes the control parameter from simple on/off switching to voltage-level control. By maintaining the voltage between drain and source below a predetermined threshold, the circuit ensures the MOSFET operates in the desired on-state region, reducing conduction loss while maintaining controllable operation.
3Productivity
If dual drive units are used, then rectification efficiency improves, but circuit complexity increases
Solution Approach 1:
The control circuit merges the functions of two drive units into a unified control architecture. The first drive unit handles basic rectification current-based switching, while the second drive unit handles voltage-based on-state maintenance. Their outputs are combined through a switching mechanism that selects the appropriate drive unit based on operational needs, achieving synergistic improvement in rectification efficiency.
Solution Approach 2:
The control circuit is designed with multi-functionality by enabling the same control circuit to perform both basic switching control (first drive unit) and voltage clamping control (second drive unit). The switching signal allows the circuit to adaptively select which function to execute based on real-time operating conditions, maximizing rectification efficiency across different scenarios.
Data Source
AI summary
A synchronous rectification control circuit includes a first drive unit that outputs a signal for controlling turning on/off of a synchronous rectification element disposed on a secondary side, a second drive unit that performs control to make a voltage between both ends of the synchronous rectification element equal to a predetermined threshold voltage during a predetermined period during which a rectification current flows on the secondary side, and a drive switching unit that selectively supplies an output from the first drive unit and an output from the second drive unit to the synchronous rectification element.