Bridgeless Flyback Converter Circuit for AC Adapter Miniaturization
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Solution Overview
Problem
Conventional AC adapters for portable devices face limitations in power density due to significant physical size consumption and power losses in the input stage, particularly the bulk capacitor and diode bridge rectifier, which restricts the miniaturization of AC adapters and chargers.
Innovation Solution
The implementation of a bridgeless flyback converter system that eliminates the diode bridge rectifier and moves AC line frequency filtering to the secondary side, utilizing a transformer for electromagnetic coupling and a compensation stage with a storage capacitor to regulate voltage, thereby reducing the size and losses associated with the bulk capacitor and diode bridge rectifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional input stage with bulk capacitor and diode bridge rectifier is used, then AC line frequency filtering is achieved, but physical size and power losses increase significantly
Solution Approach 1:
The patent extracts the AC line frequency filtering function from the primary side input stage and relocates it to the secondary side. This is achieved by removing the bulk capacitor and diode bridge rectifier from the primary side and implementing a compensation stage with filtering capacitors on the secondary side, thereby eliminating the volume-consuming input stage components while maintaining ripple filtering performance.
Solution Approach 2:
The patent inverts the conventional architecture by placing the filtering function on the secondary side instead of the primary side. Traditionally, filtering components are located on the input side, but this patent reverses that arrangement by using a compensation stage on the output side to filter AC mains frequency ripple, thus avoiding the need for large bulk capacitors on the primary side.
2Object-affected harmful factors
If a conventional input stage with bulk capacitor and diode bridge rectifier is used, then AC line frequency filtering is achieved, but power losses increase significantly
Solution Approach 1:
The patent extracts the filtering function from the lossy primary side components and relocates it to the secondary side compensation stage. By removing the bulk capacitor and diode bridge rectifier from the primary side, the patent eliminates the significant power losses associated with these components while maintaining effective AC mains frequency ripple filtering through the secondary side compensation circuitry.
3Loss of energy
If the primary side is devoid of a diode bridge rectifier, then power losses are reduced, but voltage regulation becomes more complex
Solution Approach 1:
The patent merges the voltage regulation and filtering functions into a single compensation stage on the secondary side. By combining these functions in one stage with carefully selected capacitor values, the patent simplifies the overall control architecture while eliminating the need for a diode bridge rectifier on the primary side, thus reducing power losses without significantly increasing complexity.
4Volume of stationary object
If switching frequency is increased, then EMI filter size can be reduced, but electromagnetic interference may increase
Solution Approach 1:
The patent converts the potential harmful effect of increased switching frequency (EMI) into a benefit by using the higher frequency to reduce EMI filter size. The bridgeless flyback topology with optimized switching frequency allows the EMI filter to be smaller while the secondary side compensation stage ensures that electromagnetic interference is managed effectively, transforming what would normally be a trade-off into a mutually beneficial solution.
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 significantly reduces the physical size and power losses of AC adapters, enabling higher power density and compliance with regulatory requirements for PFC and THDi, while allowing for smaller and more efficient EMI filters through increased switching frequencies.
Implementation Method 1
a primary side electromagnetically coupled to a secondary side by a transformer
Implementation Method 2
The input capacitor has a capacitance such that the compensation stage filters the AC mains frequency ripple of the AC input from the secondary side
Data Source
AI summary
A circuit includes a bridgeless flyback converter having a primary side electromagnetically coupled to a secondary side by a transformer, the primary side being devoid of a diode bridge rectifier, an input capacitor coupled to the primary side of the bridgeless flyback converter, an output capacitor coupled to the secondary side of the bridgeless flyback converter, an EMI (electromagnetic interference) filter coupled between an AC input and the input capacitor, and a compensation stage coupled in parallel with the output capacitor and including a storage capacitor. The input capacitor has a capacitance such that the compensation stage filters the AC mains frequency ripple of the AC input from the secondary side. The compensation stage is configured to store energy in the storage capacitor and regulate the voltage across the output capacitor. The bridgeless flyback converter is configured to regulate the voltage across the storage capacitor.