Flyback Converter Control with Single-Isolation Drive Interlocking
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Solution Overview
Problem
Existing flyback converters face efficiency losses due to the need to reduce drive voltage in continuous current mode, which can be mitigated by adding an additional isolation device, but this increases cost and size.
Innovation Solution
A flyback converter design that uses a single isolation device to achieve lossless equivalent peak current control and driving interlocking between primary and secondary sides, preventing drive shoot-through without reducing drive voltage, thus improving efficiency and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an additional isolation device is added to interlock drive signals, then shoot-through problem is solved and efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the functions of multiple isolation devices into a single isolation device by implementing a control mechanism where the synchronous rectifier controller receives both the drive signal and shoot-through prevention signal through the same isolation device. This consolidation reduces the number of isolation devices from two to one, thereby reducing device complexity and cost while maintaining the shoot-through prevention functionality that improves system efficiency.
Solution Approach 2:
The single isolation device is designed to handle multiple functions: transmitting the primary-side drive signal to the synchronous rectifier controller and simultaneously transmitting the shoot-through prevention signal. This multi-functional design eliminates the need for separate isolation devices for different signal types, reducing overall device complexity while preserving efficiency improvements.
2Reliability
If drive voltage is reduced to prevent shoot-through, then shoot-through problem is solved, but system efficiency decreases
Solution Approach 1:
The patent implements preliminary action by generating a shoot-through prevention signal before the actual shoot-through condition occurs. The synchronous rectifier controller receives this prevention signal in advance and adjusts the drive signal timing accordingly, allowing the controller to maintain full drive voltage while preventing shoot-through through proactive timing control rather than reactive voltage reduction.
Solution Approach 2:
Instead of changing the drive voltage parameter to prevent shoot-through, the patent changes the timing parameter of the drive signal. The shoot-through prevention signal modifies the temporal characteristics of the drive waveform, creating appropriate dead-time between switching events while maintaining the amplitude (voltage level) at its optimal value for efficiency.
3Device complexity
If a single isolation device is used, then device complexity is reduced, but achieving both peak current control and drive interlocking becomes more difficult
Solution Approach 1:
The patent segments the control functions within the synchronous rectifier controller to handle multiple tasks through a single isolation device. The controller is divided into distinct functional blocks: one for processing the drive signal, another for generating the shoot-through prevention signal, and a third for implementing peak current control. This functional segmentation allows complex control to be achieved systematically without requiring multiple physical isolation devices.
Solution Approach 2:
The single isolation device acts as an intermediary that transmits multiple types of control signals from the primary side to the synchronous rectifier controller. The controller uses this intermediary connection to receive both drive and protection signals, and internally generates the necessary control logic to coordinate peak current control and drive interlocking functions through this single communication channel.
Data Source
AI summary
Disclosed is a flyback converter and a control method thereof. The flyback converter comprises: a transformer; a power switch; a driver; a synchronous rectifier; and a feedback control module, wherein the feedback control module is configured to output a primary-side turn-on signal when a new switching cycle is started; in each switching cycle, the feedback control module is configured to turn off a primary-side power switch according to a voltage across the synchronous rectifier and an output voltage of the flyback converter. The flyback converter only needs a single isolation device to achieve lossless equivalent peak current control and driving interlocking of primary side and the secondary side, and the synchronous rectifier can effectively prevent driving shoot-through of the primary side and the secondary side in terms of control without reducing a drive voltage, which further improves system efficiency and reliability.