Flyback Converter Control Device for Variable Output ZVS
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Solution Overview
Problem
Soft switching flyback converters face efficiency degradation and loss of zero voltage switching (ZVS) in wide range output applications due to excessive circulation current, particularly in variable output voltage scenarios like USB-PD adapters, where fixed on-time control methods fail to maintain optimal magnetizing current amplitude.
Innovation Solution
A control device and method for a flyback converter that integrates output voltage to determine the amplitude of the negative magnetizing current and compares it with a reference value, adjusting the auxiliary switch accordingly to achieve ZVS across varying output voltages, using an output voltage integrator and comparator controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed on-time control method is used, then the control is simple, but zero voltage switching is lost and efficiency degrades in wide range output applications
Solution Approach 1:
The patent implements dynamic control by making the on-time of the auxiliary switch variable rather than fixed. The control device dynamically adjusts the on-time based on real-time detection of magnetizing current amplitude and comparison with reference values, allowing the system to adapt to varying output voltage conditions and maintain optimal efficiency across wide output ranges.
Solution Approach 2:
The patent employs feedback control mechanisms where the control device continuously detects the amplitude of magnetizing current, compares it with predetermined reference values, and adjusts the auxiliary switch on-time accordingly. This closed-loop feedback ensures zero voltage switching is maintained while optimizing efficiency for different output conditions.
2Reliability
If auxiliary switch on-time is extended to maintain magnetizing current amplitude, then zero voltage switching is achieved, but excessive circulation current increases loss
Solution Approach 1:
The patent applies partial action by using multiple reference values (first reference value and second reference value) instead of a single threshold. The control device compares the magnetizing current amplitude against these staged reference values to determine the appropriate on-time, ensuring sufficient current amplitude for zero voltage switching while avoiding excessive circulation current and associated losses.
3Loss of energy
If auxiliary switch on-time is reduced to decrease circulation current, then loss is reduced, but magnetizing current amplitude becomes insufficient and ZVS is lost
Solution Approach 1:
The system performs self-adjustment by automatically detecting the actual magnetizing current amplitude and comparing it with reference values, then autonomously adjusting the auxiliary switch on-time to achieve optimal performance. This self-service mechanism ensures zero voltage switching is maintained without requiring external intervention or 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 ensures zero voltage switching of the primary-side power switch across different outputs and input voltages, optimizing efficiency by dynamically setting the reference value based on input and output voltages, thus addressing the inefficiencies in existing technologies.
Implementation Method 1
an output voltage integrator, configured to integrate an output voltage of the flyback converter to obtain an amplitude of a negative magnetizing current of the flyback converter
Implementation Method 2
a comparator controller, configured to compare the obtained amplitude of the negative magnetizing current with a reference value, and turn off the auxiliary switch according to a comparison result
Implementation Method 3
turning off the auxiliary switch according to a comparison result to achieve zero voltage switching of a primary-side power switch of the flyback converter
Data Source
AI summary
A control device applied to a flyback converter including an auxiliary switch includes: an output voltage integrator, configured to integrate an output voltage of the flyback converter to obtain an amplitude of a negative magnetizing current of the flyback converter; and a comparator controller, configured to compare the obtained amplitude of the negative magnetizing current with a reference value, and turn off the auxiliary switch according to a comparison result. According to the present disclosure, it is able to achieve zero voltage switching of a primary-side switch of the flyback converter with variable outputs.