Synchronous Rectifying Controller Double Turn-On Prevention
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Solution Overview
Problem
In insulating synchronous rectifying DC/DC converters, the synchronous rectifying transistor M2 is prone to turning on twice due to variations in its ON resistance, leading to increased switching losses and efficiency degradation, especially in light load states.
Innovation Solution
A synchronous rectifying controller is designed with additional comparators and control circuits to prevent the synchronous rectifying transistor from being turned on twice by using a third comparator for a release signal and a forcible OFF circuit to manage the control pulse, ensuring the transistor remains off after transitioning to an OFF level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If additional comparators and control circuits are added to prevent double turn-on, then switching losses are reduced, but device complexity increases
Solution Approach 1:
The control circuit is designed to perform multiple functions: it monitors drain voltage, detects turn-on completion, prevents double turn-on, and drives the gate of the synchronous rectifying transistor. By making the control circuit multi-functional, the patent reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall device complexity.
Data Source
AI summary
A synchronous rectifying controller on secondary side of insulating synchronous rectifying converter to control synchronous rectifying transistor, comprising: first comparator to compare drain voltage of the transistor with first negative threshold voltage, and assert set signal based on the comparison of them; second comparator to compare drain voltage with second negative threshold voltage, and assert reset signal based on the comparison of them; third comparator to compare drain voltage with third positive threshold voltage, and assert release signal based on the comparison of them; control circuit set in response to the assertion of the set signal and to adjust control pulse to have ON level, and reset in response to the assertion of the reset signal and to adjust the control pulse to have OFF level; and driver to drive the transistor, wherein set operation of the control circuit is inhibited until the release signal is asserted.