LED Segment Control with Energy Storage for AC Flicker Reduction
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Solution Overview
Problem
Solid-state lighting systems using LEDs face issues with flickering and reduced power factor when driven by rectified AC voltage, leading to increased resistive loss, as LEDs only turn on for part of the AC waveform.
Innovation Solution
A lighting apparatus with serially-connected LED segments and an energy storage circuit that selectively bypasses segments and uses energy storage devices to maintain light output during voltage nulls, charging and discharging them based on the AC waveform, ensuring continuous illumination and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If LEDs are driven by rectified AC voltage, then the system can operate from AC power sources, but the LEDs turn on for only part of the waveform causing visible flickering
Solution Approach 1:
The energy storage capacitor is charged in advance during the peaks of the rectified AC waveform, storing energy before the voltage drops. This preliminary energy storage ensures continuous LED operation during voltage nulls, eliminating flickering while maintaining AC power compatibility
Solution Approach 2:
The patent implements continuous light output by combining the rectified AC voltage with energy stored in the capacitor. The LED driver circuit continuously draws energy from both the AC source and the capacitor, ensuring uninterrupted illumination throughout the entire AC cycle including voltage nulls
2Ease of operation
If LEDs are driven by rectified AC voltage, then AC power sources can be used, but the power factor of the system is lowered
Solution Approach 1:
The LED driver circuit incorporates feedback control that monitors the rectified AC voltage and adjusts the charging current to the energy storage capacitor accordingly. This feedback mechanism optimizes the power factor by regulating energy transfer and reducing reactive power, while maintaining AC power compatibility
3Ease of operation
If LEDs are driven by rectified AC voltage, then AC power sources can be used, but resistive loss in the system increases
Solution Approach 1:
Energy is stored in the capacitor during high-voltage peaks before significant resistive losses occur. By capturing and storing energy at optimal moments, the system reduces the total energy that would otherwise be lost to resistance in the circuit components
Solution Approach 2:
The continuous operation of LEDs powered by the combined AC and capacitor energy reduces the need for repeated voltage transitions and current surges. This continuous energy delivery minimizes resistive heating losses compared to intermittent operation, while maintaining AC power compatibility
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
The solution prevents flickering and reduces resistive losses by maintaining light output during voltage nulls, improving the power factor and efficiency of the lighting system.
Implementation Method 1
a capacitor or other energy storage device may be used to sustain light output during nulls of the waveform of an AC power source
Implementation Method 2
A solid-state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs)
Data Source
AI summary
A lighting apparatus includes a rectifier circuit configured to be coupled to an AC source and to produce a rectified voltage from an AC voltage and a string including at least two serially-connected LED segments and coupled to the rectifier circuit. A segment control circuit is configured to selectively bypass at least one segment of the string responsive to the rectified voltage. An energy storage circuit is coupled to the rectifier circuit and controls current flow between at least one energy storage device and the string. A control circuit controls the segment control circuit and the energy storage circuit. The segment control circuit may support a current from the rectifier circuit through all of the segments in the string circuit at a peak of the rectified voltage and the energy storage circuit may charge the at least one energy storage device to a voltage near the peak of the rectified voltage.