Line-Powered LED Driver Calibration for Stable Peak Inductor Current
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Solution Overview
Problem
Existing LED systems face inefficiencies due to variations in switching performance and power losses caused by factors like aging and temperature drift, which affect the peak inductor current.
Innovation Solution
The on-time of a power transistor in a power converter circuit is periodically calibrated to maintain a desired peak inductor current, using control logic to adjust the on-time duration and keep it constant until the next calibration cycle, employing techniques like valley and peak detection to ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the on-time of the power transistor is fixed, then the system operation is simple, but the peak inductor current drifts due to aging and temperature variations
Solution Approach 1:
The patent implements periodic calibration of the power transistor on-time parameter. A calibration routine is executed at predetermined intervals (e.g., every N switching cycles or at specific AC line voltage peaks) to remeasure and update the on-time value, ensuring the peak inductor current returns to its target level while maintaining simplicity between calibration events.
Solution Approach 2:
The patent employs feedback mechanisms to monitor the peak inductor current and use this information to adjust the power transistor on-time. Current sensing circuits measure the actual peak current, and this measurement feeds back to the control logic which modifies the on-time parameter to maintain the desired current level despite environmental variations.
2Measurement precision
If the on-time is frequently calibrated, then the peak inductor current accuracy is maintained, but the system efficiency decreases due to additional calibration overhead
Solution Approach 1:
The calibration process is performed periodically rather than continuously, at predetermined intervals such as every N switching cycles or at specific points in the AC line voltage cycle. This approach maintains current accuracy while minimizing the overhead and energy consumption associated with calibration operations.
Solution Approach 2:
The system performs calibration at predetermined optimal moments, such as at the peak of the rectified AC line voltage or at specific switching cycle intervals. This preliminary positioning of calibration events ensures accurate measurements are taken under known conditions while minimizing disruption to normal operation and reducing overall calibration overhead.
Data Source
AI summary
A line-powered LED lighting system includes rectifier circuit to provide a rectified AC voltage on a voltage node. A power transistor is coupled to a control signal having an on-time and an off-time. An inductor is coupled between the rectified voltage node and a drain of the power transistor. Series coupled LEDs are coupled between the rectified voltage node and the drain of the power transistor in parallel with the inductor. Control logic periodically calibrates the on-time of the power transistor to achieve a predetermined peak inductor current. The control logic maintains the calibrated on-time constant for a plurality of switching cycles of the power transistor until a next calibration event. The on-time is calibrated at least once every N cycles of the rectified AC voltage, where N is an integer greater than or equal to 1.