Direct Conduction Control for Power Factor Correction
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Solution Overview
Problem
Reduced bulk capacitance in power factor correction circuits leads to increased output ripple voltage, potentially causing direct conduction conditions and stability issues, especially under high line input voltage conditions, which can result in audible noise and distortions.
Innovation Solution
A direct conduction avoidance circuit and notch filter are implemented to monitor and adjust the power demand signal based on output voltage thresholds, combined with an override circuit to disable the direct conduction avoidance circuit under nominal voltage conditions, and an error amplifier with a filter to mitigate ripple frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If film capacitors are used to replace aluminum electrolytic capacitors, then reliability is improved, but volume efficiency deteriorates
Solution Approach 1:
The patent changes the capacitance value parameter by reducing bulk capacitance from typical values (0.5 uF/W) to lower values (100 nF/W), enabling the use of film capacitors while maintaining system performance through controlled ripple voltage and direct conduction prevention
2Volume of moving object
If bulk capacitance is reduced, then capacitor volume is reduced, but output ripple voltage increases
Solution Approach 1:
The patent implements a feedback control mechanism using a direct conduction avoidance circuit that monitors output voltage and provides feedback signals to adjust the power demand, thereby controlling ripple voltage and preventing direct conduction conditions despite reduced bulk capacitance
3Reliability
If output voltage set point is increased to avoid direct conduction, then direct conduction is prevented, but system complexity increases
Solution Approach 1:
The patent introduces an intermediary direct conduction avoidance circuit that acts as a mediator between the output voltage and the power demand control, using threshold voltage comparisons and signal combining to prevent direct conduction without requiring complex control algorithms or high output voltage set points
Data Source
AI summary
A system includes a switching power supply that includes switch devices configured to provide a regulated output voltage based on an input voltage. A controller is configured to control the switch devices based on a power demand signal. A direct conduction avoidance circuit is configured to provide a direct conduction avoidance signal based on the regulated output voltage exceeding a direct conduction threshold voltage. The direct conduction avoidance signal is combined with a compensation signal to provide the power demand signal to the controller. An override circuit is configured to disable the direct conduction avoidance circuit based on the input voltage of the switching power supply being below an override threshold voltage.