Flyback Converter Secondary Control Adaptive Power Selection
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Solution Overview
Problem
The existing flyback power converters face inefficiency due to high conduction resistance of the synchronous rectifier switch when the output voltage is low, preventing full conductivity and reducing power conversion efficiency.
Innovation Solution
A secondary side control circuit that adaptively selects between a first power related to the output voltage and a second power related to a secondary phase signal to generate a synchronous rectifier switch signal, ensuring the synchronous rectifier switch is fully conductive by converting the secondary phase signal into a suitable power supply, thereby reducing conduction resistance and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the synchronous rectifier switch is controlled using only the first power related to the output voltage, then the control circuit is simple, but when the output voltage is low the conduction resistance increases dramatically and the switch cannot be fully conductive
Solution Approach 1:
The control circuit dynamically switches between two power sources (first power from output voltage and second power from secondary phase signal) based on operating conditions. When output voltage is high, the first power is used; when output voltage is low, the second power is used to ensure the synchronous rectifier switch achieves full conductivity and low conduction resistance, thereby resolving the contradiction between circuit simplicity and power conversion efficiency.
Solution Approach 2:
The invention changes the power supply parameter (voltage level) adaptively based on the output voltage condition. By selecting different power sources, the gate-source voltage of the synchronous rectifier switch is optimized for different operating ranges, ensuring low conduction resistance across the full operating range while maintaining reasonable circuit complexity.
2Use of energy by moving object
If the output voltage is low, then the power consumption is reduced, but the conduction resistance of the synchronous rectifier switch increases dramatically
Solution Approach 1:
The second power source (secondary phase signal) acts as an intermediary that provides the necessary voltage boost when the first power source (output voltage) is insufficient. This intermediary power source ensures the synchronous rectifier switch can achieve full conductivity even when the output voltage is low, maintaining reliable switch operation across all operating conditions.
3Ease of operation
If a fixed power source is used for the synchronous rectifier switch, then the control is simple, but it cannot adapt to different output voltage conditions
Solution Approach 1:
The control circuit is designed with multi-functionality by incorporating two power sources and a selection mechanism. It can universally handle both high output voltage conditions (using first power) and low output voltage conditions (using second power), making the control system adaptable to different voltage conditions while maintaining relatively simple operation through automated selection.
Data Source
AI summary
A flyback power converter includes: a transformer, a power switch, a switch control unit, a synchronous rectifier switch and a secondary side control circuit. The secondary side control circuit includes: a switch signal generation circuit and a first power conversion circuit. The secondary side control circuit is coupled to the synchronous rectifier switch and the secondary winding of the transformer. The switch signal generation circuit generates the synchronous rectifier switch signal selectively according to a first power or a second power, to control the synchronous rectifier switch. The first power is related to the output voltage. The first power conversion circuit generates the second power according to a secondary phase signal on a phase node between the secondary winding of the transformer and the synchronous rectifier switch.