AC-Driven LED Lighting with Switched Segments
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Solution Overview
Problem
Solid state lighting devices face challenges in achieving high color rendering index (CRI) and efficiency when driven by alternating current (AC) power, as existing solutions often result in flickering, increased resistive loss, and higher costs due to the need for power converters to convert AC to direct current (DC).
Innovation Solution
A circuit for a light emitting apparatus that includes a comparator to compare a rectified AC input signal with a reference voltage, a voltage-controlled current source to supply current proportional to the AC signal, and a switch to shunt current away from light emitting devices when the AC signal is below a threshold, allowing for efficient AC-driven operation without the need for additional power converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power converter is used to convert AC power to DC power for driving solid state lighting devices, then the lighting source can be driven with DC power as required, but the cost of the lighting source and overall installation increases and additional efficiency losses are introduced
Solution Approach 1:
The invention extracts and eliminates the power converter component from the LED lighting system by directly driving the LEDs with rectified AC power. The circuit removes the unnecessary AC-to-DC conversion stage while maintaining proper LED operation through selective segment switching based on instantaneous voltage comparison.
Solution Approach 2:
The LED string is divided into multiple segments that can be independently controlled. The circuit automatically selects which segments to activate based on the instantaneous rectified AC voltage level, allowing the system to self-regulate without external power conversion equipment.
2Adaptability or versatility
If LEDs are driven using a rectified AC waveform, then AC power can be used directly, but the LEDs may turn on for only a part of the rectified AC waveform which may result in visible flickering and may undesirably lower the power factor
Solution Approach 1:
The LED string is divided into multiple segments with different forward voltage requirements. The circuit compares the instantaneous rectified AC voltage with reference voltages to determine which segments can be activated, ensuring smooth transitions and eliminating flickering while maintaining high power factor.
Solution Approach 2:
The circuit dynamically adjusts which LED segments are activated based on the instantaneous voltage level of the rectified AC waveform. This dynamic segmentation allows full utilization of the AC waveform without flickering or power factor penalties.
3Adaptability or versatility
If LEDs are placed in an anti-parallel configuration to be driven on each half-cycle of AC waveform, then AC power can be utilized, but twice as many LEDs are required to produce the same luminous flux
Solution Approach 1:
The circuit utilizes the periodic nature of the AC waveform by rectifying it to create a continuously positive voltage. LED segments are activated during different portions of the AC cycle based on voltage thresholds, allowing efficient use of both half-cycles without requiring anti-parallel configurations or doubling the LED count.
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 improves the power factor, reduces visible flicker, and enhances efficiency by fully utilizing the AC waveform, while maintaining high CRI and luminous efficacy, thus addressing the limitations of existing AC-driven solid state lighting systems.
Implementation Method 1
a comparator configured to receive a rectified AC input signal and a reference voltage and to generate a control signal in response to comparison of the rectified AC input signal with the reference voltage
Implementation Method 2
a voltage controlled current source configured to supply a current to the plurality of light emitting diodes that is proportional to the rectified AC input signal
Data Source
Figure 1A~1C
Figure 2
Figure 3A~3B
AI summary
A diode selection circuit for a light emitting apparatus according to some embodiments includes a plurality of light emitting devices coupled in series. The diode selection circuit includes a comparator configured to receive a rectified AC input signal and a reference voltage and to generate a control signal in response to comparison of the rectified AC input signal with the reference voltage, a voltage controlled current source configured to supply a current to the plurality of light emitting diodes that is proportional to the rectified AC input signal, and a switch configured to receive the control signal and to shunt current away from at least one of the plurality of light emitting devices in response to the control signal.