Synchronous Rectification Control Circuit for Flyback Converter Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In isolated type switching circuits, controlling synchronous rectification transistors is challenging due to difficulties in obtaining the switching signal of the main switching tube, leading to inefficient system operation and potential simultaneous turn-on of synchronous rectification transistors and main switching tubes, resulting in low system efficiency.
Innovation Solution
A synchronous rectification control circuit that includes a drive circuit, a threshold comparison circuit, and a voltage regulation control circuit to dynamically regulate the drive signal of the synchronous rectification transistor, ensuring it turns off from a low voltage value, preventing direct connection with the main switching tube and improving system reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification transistor is used to replace diode to improve conversion efficiency, then system efficiency is improved, but it is difficult to obtain the switching signal of the main switching tube in isolated type switching circuit, causing simultaneous turn-on or partial turn-on, resulting in reduced system efficiency
Solution Approach 1:
The patent introduces an auxiliary winding on the transformer and an auxiliary switching tube to create an intermediary control path. The auxiliary switching tube, controlled by a separate oscillating signal, generates a control signal for the synchronous rectification transistor through the auxiliary winding, eliminating the need to directly obtain the main switching tube's signal while preventing simultaneous turn-on
Solution Approach 2:
The control system is segmented into independent components: the main switching tube circuit, the auxiliary switching tube circuit with its own oscillating signal, and the synchronous rectification control circuit. This segmentation allows each part to operate independently while maintaining proper coordination, solving the signal acquisition problem in isolated circuits
2Loss of energy
If synchronous rectification transistor turns on quickly to improve efficiency, then conversion efficiency is improved, but turn-off speed is slow, causing direct connection with main switching tube and reducing system reliability
Solution Approach 1:
The patent applies preliminary action by using the auxiliary switching tube to preemptively control the synchronous rectification transistor's turn-off. Before the main switching tube turns off and causes voltage spike, the auxiliary circuit already initiates the turn-off sequence by controlling the synchronous rectification transistor through the auxiliary winding, preventing direct connection and improving reliability
Solution Approach 2:
The patent implements feedback through the auxiliary winding that senses the voltage state and feeds it back to control the synchronous rectification transistor. The voltage regulation control circuit monitors the voltage and adjusts the drive signal accordingly, creating a closed-loop control system that accelerates turn-off when needed while maintaining efficiency
Data Source
AI summary
The present invention provides a synchronous rectification control circuit, a method and a flyback switching circuit. A drive circuit outputs a drive signal to control the turn-on and turn-off of a synchronous rectification transistor; a threshold comparison circuit controls the drive circuit to output a pull-up drive signal to turn on the synchronous rectification transistor when a drain-source voltage is lower than a preset low threshold voltage and controls the drive circuit to output a pull-down drive signal to turn off the synchronous rectification transistor when the drain-source voltage is higher than or equal to a preset high threshold voltage; a voltage regulation control circuit controls the drive circuit to output a drive signal for pulling up a voltage of the drive signal to a preset pull-up voltage high value when the drain-source voltage is lower than a preset voltage regulation reference value.