Resonant Flyback Converter Control for Light-Load ZVS Efficiency
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Solution Overview
Problem
Existing resonant flyback power converters suffer from low power efficiency during light load conditions and inability to provide variable output voltage.
Innovation Solution
A resonant flyback power converter with novel power saving control methods, including a switching control circuit that generates adaptive driving signals to manage the transformer and resonant capacitor, ensuring efficient operation across varying load conditions. The circuit includes a magnetizing control circuit and a resonant and ZVS control circuit to manage the on-time of the first driving signal and the pulse width of the second driving signal, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the second driving signal maintains a fixed minimum on-time to discharge the resonant capacitor, then the resonant capacitor can be properly discharged, but high circulated current is generated during light load causing high power loss
Solution Approach 1:
The patent applies dynamics by making the on-time of the second driving signal variable rather than fixed. The control circuit adjusts the on-time duration based on load conditions, extending it during light load to ensure complete resonant capacitor discharge while maintaining it at minimum during heavy load to reduce circulated current and power loss.
Solution Approach 2:
The patent changes the time parameter of the second driving signal adaptively. The on-time duration is modified according to load level, with the control circuit detecting load conditions and adjusting the pulse width accordingly to optimize both power efficiency and capacitor discharge reliability.
2Loss of energy
If the pulse width of the first driving signal is decreased to reduce magnetizing current during light load, then power efficiency is improved, but the transformer may not be properly magnetized
Solution Approach 1:
The patent employs feedback mechanisms where the control circuit monitors transformer magnetization status and load conditions, then adjusts the first driving signal pulse width accordingly. This closed-loop control ensures sufficient magnetization during light load while preventing over-magnetization that would increase power loss.
Solution Approach 2:
The pulse width of the first driving signal is made dynamic rather than fixed, allowing the control circuit to optimize the magnetization duration based on real-time load conditions, thereby balancing power efficiency with adequate transformer magnetization.
3Loss of energy
If the resonant flyback power converter operates in DCM during light load with fixed timing, then the control circuit is simple, but power efficiency is low due to high circulated current
Solution Approach 1:
The patent modifies the timing parameters of the driving signals adaptively based on load conditions. The control circuit adjusts pulse widths and timing intervals of both first and second driving signals to optimize power efficiency during light load while maintaining DCM operation, without requiring complex additional circuitry.
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
The proposed solution significantly improves power efficiency during light load and no-load operations by minimizing power loss through adaptive control of the resonant pulse width and ZVS pulse, while also providing over-current protection.
Implementation Method 1
a transformer and a resonant capacitor which are connected in series and are coupled to the half-bridge circuit
Implementation Method 2
a resonant capacitor which are connected in series and are coupled to the half-bridge circuit; the second driving signal is configured to discharge the resonant capacitor
Implementation Method 3
ZVS (zero voltage switching) for achieving the higher power efficiency. The ZVS can be defined as the transistor is switched on when the voltage across the transistor (e.g. drain-source voltage) is zero or close to zero
Data Source
AI summary
A resonant flyback power converter includes: a first transistor and a second transistor which are configured to switch a transformer and a resonant capacitor for generating an output voltage; and a switching control circuit generating first and second driving signals for controlling the first and the second transistors. The turn-on of the first driving signal magnetizes the transformer. The second driving signal includes a resonant pulse having a resonant pulse width and a ZVS pulse during the DCM operation. The resonant pulse is configured to demagnetize the transformer. The resonant pulse has a first minimum resonant period for a first level of the output load and a second minimum resonant period for a second level of the output load. The first level is higher than the second level and the second minimum resonant period is shorter than the first minimum resonant period.