Converter Frequency Fold-Back for Switching Loss Reduction
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Solution Overview
Problem
Power converter circuits, such as PFC circuits and flyback/forward converters, experience significant switching losses, especially under low load conditions, leading to efficiency degradation and increased costs due to large switching losses from transistors and inductors.
Innovation Solution
A power factor controller is introduced, comprising a regulator stage, control stage, and output stage, which operates in critical conduction mode for high input currents and frequency fold-back mode for low input currents, synchronizing the gate drive signal with the drain-to-source voltage valley to reduce switching losses, and optionally enters a skip mode at line zero crossing for very small input currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional switching operation is used in power converter circuits, then the converter can operate under various load conditions, but switching losses increase significantly under low load conditions leading to efficiency degradation
Solution Approach 1:
The patent implements dynamic switching frequency adjustment based on load conditions. The control circuit monitors the operating state and automatically adapts the switching frequency: operating at high frequency under full load conditions and reducing to low frequency under light load conditions. This dynamic adaptation resolves the contradiction by making the switching frequency a variable parameter rather than a fixed value, thereby maintaining efficiency across different load conditions while preserving operational versatility
Solution Approach 2:
The patent changes the switching frequency parameter in response to varying load conditions. By detecting light load conditions and reducing the switching frequency, the system modifies a key operating parameter to minimize switching losses. This parameter change approach allows the converter to maintain adaptability across different loads while significantly reducing energy losses during low-load operation
2Loss of energy
If switching frequency is reduced to mitigate switching losses, then efficiency improves under low load conditions, but the converter's ability to respond to load changes and maintain regulation may be compromised
Solution Approach 1:
The control circuit dynamically adjusts switching frequency based on real-time load detection. When light load conditions are detected, the frequency is reduced to minimize losses; when load increases, the frequency automatically increases to maintain proper regulation. This dynamic response ensures that regulation performance is maintained across varying load conditions while achieving efficiency improvements during low-load operation
Solution Approach 2:
The patent employs feedback mechanisms where the control circuit continuously monitors operating conditions and adjusts switching frequency accordingly. This feedback loop ensures that when load changes occur, the switching frequency is appropriately modified to maintain stable output voltage and current regulation, thereby preserving reliability while enabling loss reduction during light load conditions
3Reliability
If conventional PFC circuits are used, then power factor correction is achieved, but efficiency is degraded under light or low load conditions due to large switching losses from switching transistor and inductor
Solution Approach 1:
The PFC circuit incorporates dynamic switching frequency control that automatically adapts to load conditions. During light load operation, the switching frequency is reduced to minimize losses from the switching transistor and inductor, while during full load conditions, the frequency increases to maintain proper power factor correction. This dynamic approach preserves the essential PFC function across all operating conditions while significantly reducing energy losses during low-load operation
Data Source
AI summary
In accordance with an embodiment, a converter includes a power factor controller that varies the switching frequency of a switching transistor in accordance with a signal representative of power at the input of the converter.