Quasi-Resonant Flyback Synchronous Rectification Dead-Time Control
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Solution Overview
Problem
In small and medium power flyback converters, the forward conduction loss of traditional rectifier diodes significantly contributes to system losses, exceeding 50% of total power loss when the output voltage is not more than ten times the forward voltage drop, necessitating a more efficient rectification method.
Innovation Solution
A synchronous rectification control system and method for quasi-resonant flyback converters, which involves sampling the output terminal voltage of the switching transistor, determining dead-time based on a preset relationship, and controlling the synchronous rectification transistor accordingly to reduce conduction losses through valley conduction technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional rectifier diode is used, then device complexity is reduced, but conduction loss increases significantly
Solution Approach 1:
The patent changes the key parameter of the rectification device from a passive diode to an active MOSFET with controllable on-resistance. By dynamically adjusting the MOSFET's resistance state through gate voltage control, the system achieves low conduction loss while maintaining simplicity through integrated control logic that adapts to different operating conditions.
Solution Approach 2:
The control system automatically adjusts the synchronous rectification transistor's switching parameters based on real-time detection of transformer leakage inductance and operating conditions. This self-adjusting mechanism eliminates the need for external manual tuning or complex external control circuits, allowing the system to optimize its own performance across different load and voltage conditions.
2Loss of energy
If synchronous rectification transistor is used, then conduction loss is reduced, but device complexity and control difficulty increase
Solution Approach 1:
The control system automatically adjusts the synchronous rectification transistor's switching parameters based on real-time detection of transformer leakage inductance and operating conditions. This self-adjusting mechanism eliminates the need for external manual tuning or complex external control circuits, allowing the system to optimize its own performance across different load and voltage conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the control circuit continuously monitors the switching transistor's output terminal voltage and uses this information to dynamically adjust the synchronous rectification transistor's dead-time and switching timing. This closed-loop control optimizes rectification efficiency while keeping the control circuit relatively simple through intelligent algorithms.
3Productivity
If fixed dead-time is used, then control simplicity is maintained, but rectification efficiency varies under different operating conditions
Solution Approach 1:
The patent transforms the static dead-time parameter into a dynamic one that automatically adapts to different operating conditions. The control system calculates optimal dead-time values based on real-time detection of transformer leakage inductance, switching frequency, and load conditions, then dynamically adjusts the synchronous rectification transistor's timing parameters to maintain peak efficiency across varying operating points.
Solution Approach 2:
The patent changes the key parameter of the rectification device from a passive diode to an active MOSFET with controllable on-resistance. By dynamically adjusting the MOSFET's resistance state through gate voltage control, the system achieves low conduction loss while maintaining simplicity through integrated control logic that adapts to different operating conditions.
Data Source
AI summary
A synchronous rectification control system and method for a quasi-resonant flyback converter are provided. The control system includes a switching transistor voltage sampling circuit configured to sample an output terminal voltage of the switching transistor to obtain a sampled voltage of the switching transistor; a sampling calculation module configured to obtain a dead-time based on the sampled voltage of the switching transistor and a preset relationship, the preset relationship being a correspondence between the duration of the sampled voltage of the switching transistor being below a first preset value and the dead-time during an on-time of a switching cycle of the switching transistor, the dead-time being a time from when the switching transistor is turned off to when the synchronous rectification transistor is turned on; and a control module configured to receive the dead-time and control switching of the synchronous rectification transistor based on the dead-time.