Flyback Converter Auxiliary Switch Control for Variable Output Voltage
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Solution Overview
Problem
Conventional flyback converter control schemes with constant turn-on time and dead time are not suitable for applications with variable output voltages, such as USB PD, leading to inefficiencies and complexity, especially at higher switch frequencies where transmission delay and parameter tolerance become significant obstacles.
Innovation Solution
A method and apparatus that dynamically control the turn-on time of the auxiliary switch and dead time based on input and output voltage signals, using control signals to generate a magnetizing current and ensure zero-voltage-switching (ZVS) of the main switch, by determining the turn-on time of the auxiliary switch and dead time through specific voltage and impedance relationships.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If constant turn-on time and dead time are used in conventional control scheme, then device complexity is reduced, but efficiency optimization fails for variable output voltage applications
Solution Approach 1:
The patent applies parameter changes by making the turn-on time of the auxiliary switch and the dead time variable rather than constant. These parameters are dynamically adjusted based on the input voltage and output voltage to optimize efficiency across different operating conditions. The controller calculates appropriate timing parameters based on voltage measurements, allowing the system to adapt to variable output voltage applications while maintaining manageable complexity through systematic calculation methods.
2Productivity
If switch frequency is increased, then productivity is improved, but transmission delay and parameter tolerance become significant obstacles
Solution Approach 1:
The patent applies preliminary action by calculating and setting the turn-on time of the auxiliary switch in advance based on the measured input and output voltages. This pre-calculation approach allows the controller to compensate for transmission delays and parameter tolerances before they become critical issues. By determining the appropriate timing parameters beforehand, the system can operate at higher switching frequencies while maintaining accurate control despite the inherent delays in signal transmission and parameter variations.
3Loss of energy
If variable turn-on time and dead time are implemented, then efficiency is optimized for USB PD applications, but device complexity increases
Solution Approach 1:
The patent applies feedback by continuously measuring the input voltage and output voltage and using these measurements to dynamically adjust the turn-on time of the auxiliary switch and the dead time. This closed-loop control approach optimizes conversion efficiency for USB PD applications with variable output voltages. The controller receives feedback from voltage sensors and automatically adjusts timing parameters to maintain optimal efficiency across different operating conditions, managing complexity through systematic feedback-based adjustment rather than requiring complex manual tuning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for optimized efficiency and ZVS of the main switch across a range of loads and output voltages, providing a constant dead time and improved design efficiency for flyback converters, particularly in high-frequency applications.
Implementation Method 1
generating a third control signal SI3 and turning on the auxiliary switch according to the third control signal SI3, so as to generate a magnetizing current
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
A method and an apparatus for controlling a flyback converter, the flyback converter including a main switch (S1), a transformer (T) and an auxiliary switch (S2). The method includes: obtaining a first voltage signal and a second voltage signal, the first voltage signal representing an input voltage of the flyback converter, and the second voltage signal representing an output voltage of the flyback converter (S201); controlling turn-on of the auxiliary switch, wherein the turn-on time period of the auxiliary switch is determined according to the first voltage signal and the second voltage signal (S202); and turning on the main switch at ZVS condition, wherein the main switch is turned on at the time delayed for a duration of a dead time after turning off of the auxiliary switch (S203).