Switching Power Converter with Dynamic Peak Current Thresholds
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Solution Overview
Problem
Single-stage AC-DC power converters face challenges in maintaining high power factor while preventing triac flicker and thermal stress due to triac resetting, especially when using a triac for dimming in solid state lighting applications, where conventional peak current control methods either worsen the power factor or increase the risk of triac resetting.
Innovation Solution
A switching power converter that dynamically adjusts the peak magnetizing current by using two thresholds: a low threshold as the rectified input voltage approaches zero crossing and a high threshold as it rises, ensuring a high power factor and sufficient triac holding current to prevent triac resetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If peak current control methodology is used to achieve high power factor, then power factor is improved, but triac holding current becomes insufficient causing triac reset and flicker
Solution Approach 1:
The patent applies dynamics by making the peak current threshold dynamic rather than fixed. The controller adjusts the peak current threshold based on the operating mode: using a first (lower) threshold in dimming mode and a second (higher) threshold in no-dimming mode. This dynamic adjustment allows the system to maintain high power factor in dimming mode while ensuring sufficient triac holding current in no-dimming mode, thereby resolving the contradiction between power factor improvement and triac operation stability.
Solution Approach 2:
The patent changes the parameter of peak current threshold based on operating conditions. By detecting whether the system is in dimming or no-dimming mode and accordingly selecting different threshold values, the system optimizes both power factor and triac holding current. This parameter change strategy enables the system to achieve high power factor correction when needed while preventing triac reset and flicker when triac holding current is critical.
2Reliability
If minimum peak current threshold is increased to prevent triac reset, then triac holding current is sufficient, but power factor deteriorates
Solution Approach 1:
The patent resolves this contradiction by making the peak current threshold dynamic. In dimming mode, the controller uses a first peak current threshold that allows the magnetizing current to follow the rectified input voltage profile closely, achieving high power factor. In no-dimming mode, the controller switches to a second, higher peak current threshold that ensures sufficient triac holding current. This dynamic switching eliminates the need to permanently increase the threshold, thus preventing power factor deterioration while ensuring triac reliability when needed.
Solution Approach 2:
The patent changes the peak current threshold parameter based on the detected operating mode. When dimming is detected, a lower threshold is applied to maintain high power factor. When no-dimming is detected, a higher threshold is applied to ensure adequate triac holding current. This conditional parameter change allows the system to optimize for power factor when dimming is active and for triac stability when dimming is inactive, resolving the contradiction between these two objectives.
3Adaptability or versatility
If triac is used for dimming control, then dimming functionality is achieved, but multi-firing causes flicker and thermal stress
Solution Approach 1:
The patent applies dynamics by implementing mode detection and dynamic threshold adjustment. The controller detects whether the system is in dimming or no-dimming mode and dynamically adjusts the peak current threshold accordingly. In dimming mode, the lower threshold allows proper triac holding current while maintaining power factor. In no-dimming mode, the higher threshold prevents triac reset and multi-firing. This dynamic adaptation eliminates flicker and thermal stress while preserving dimming functionality.
Solution Approach 2:
The patent uses feedback by detecting the operating mode (dimming or no-dimming) and using this information to adjust the peak current threshold. The mode detection circuit provides feedback to the controller, which then selects the appropriate threshold. This feedback mechanism ensures that the system automatically prevents triac multi-firing and associated harmful effects like flicker and thermal stress, while maintaining dimming capability when required.
Data Source
AI summary
A switching power converter is provided that uses at least two peak current thresholds. In particular, the switching power converter clamps a desired peak current to not fall below a low peak current threshold value while a rectified input voltage is decreasing and to not fall below a high peak current threshold value subsequent to zero crossing times for an AC input voltage.