LLC Resonant AC-DC Converter with Secondary Boost Stage
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Solution Overview
Problem
Conventional AC-DC switching converters face challenges in achieving high efficiency and wide input voltage range while maintaining power factor correction and minimizing component utilization and size, particularly when designing isolated resonant stages for universal power supplies.
Innovation Solution
The proposed solution involves a front-ended LLC resonant isolated stage directly switching the AC mains, followed by a boost converter on the secondary side for power factor correction, allowing for dual or multi-band operation and reduced component requirements through the use of low-Q resonant circuits and high-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an isolated flyback converter is used, then power factor is improved, but device complexity and voltage stress increase
Solution Approach 1:
The power conversion process is divided into two independent stages: a resonant isolated stage for AC-DC conversion and a boost stage for power factor correction. This segmentation allows each stage to be optimized for its specific function, reducing overall complexity while maintaining high power factor performance.
Solution Approach 2:
A resonant isolated stage is introduced as an intermediary between the AC input and the boost stage. This intermediary circuit provides galvanic isolation and enables soft-switching operation, reducing voltage stress on components while maintaining power factor correction capability through the subsequent boost stage.
2Loss of energy
If a boost converter followed by LLC converter is used, then efficiency is improved, but gain range is reduced
Solution Approach 1:
The resonant isolated stage operates dynamically with variable switching frequency to maintain optimal efficiency across a wide input voltage range. The controller adjusts the switching frequency to track the resonant frequency, enabling the circuit to adapt to different operating conditions while maintaining high efficiency and extended gain range.
Solution Approach 2:
The circuit parameters including switching frequency, inductance values, and capacitance values are optimized to enable operation across an extended gain range. The resonant frequency is designed to be可调 (adjustable) through frequency modulation, allowing the converter to maintain high efficiency while adapting to wide input voltage variations from 90V to 264V.
3Adaptability or versatility
If LLC converter operates over wide voltage range, then adaptability is improved, but Q factor must be increased
Solution Approach 1:
The resonant isolated stage uses dynamic frequency adjustment to operate over a wide voltage range without requiring high Q factor. By modulating the switching frequency to track the resonant frequency under varying conditions, the circuit maintains adaptability while avoiding the energy losses associated with high Q factor designs.
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 enhances efficiency and power density, reduces the need for high-voltage electrolytic capacitors, and provides improved surge immunity and smaller magnetics, while maintaining compliance with power factor requirements and minimizing inrush current.
Implementation Method 1
a first LLC resonant circuit comprising the primary winding of a first transformer
Implementation Method 2
a first transformer
Data Source
AI summary
A class of switching power supplies that use a resonant isolation stage (typically LLC) fed directly or via a diode bridge from the line. Extension of the range of available gain values over frequency without material loss of efficiency is facilitated by usage of additional resonant elements. This capability allows the devices to provide narrow-range inputs to secondary-processing circuits, with the ability to achieve power factor correction if required. The conversion architecture is also compatible with optimal usage of energy storage elements suitable for use with switching power supplies.