LED Light Source Asymmetric Forward Voltage AC Utilization
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Solution Overview
Problem
Existing LED light sources connected to low frequency AC voltage have low LED utilization due to different LED loads carrying current for varying durations, leading to inefficient use of LED packages, as all packages are designed for the highest current load, resulting in over-engineering and higher costs.
Innovation Solution
A LED light source design where the forward voltage of the first LED load is at least 50% higher than the others, allowing it to start conducting at a higher amplitude and stop earlier, optimizing current distribution and reducing the number of LED loads, with control means managing the current flow through switchable current sources and capacitive elements to enhance efficiency and reduce components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all LED loads are designed to meet worst case requirements (highest current load), then reliability is improved, but LED utilization deteriorates because most LED packages are not used at full capacity
Solution Approach 1:
The patent applies local quality by differentiating the forward voltage characteristics of LED loads based on their position in the series arrangement. The first LED load has a higher forward voltage than subsequent loads, creating localized differences in conduction behavior. This allows each LED load to operate at appropriate current levels matched to its specific role, improving overall utilization while maintaining reliability through proper current distribution.
2Device complexity
If LED loads are arranged in series with equal forward voltages, then device complexity is reduced, but LED utilization deteriorates due to varying conduction durations
Solution Approach 1:
The patent introduces asymmetry by setting the forward voltage of the first LED load to be at least 50% higher than that of subsequent LED loads. This asymmetric design creates a systematic difference in conduction timing, where the first LED load conducts during a specific subset of the AC cycle. The asymmetry is deliberately engineered to optimize current distribution patterns, improving LED utilization without requiring complex control circuitry.
3Productivity
If the first LED load has a higher forward voltage, then LED utilization is improved by optimizing current distribution, but the number of LED loads that can be used is reduced
Solution Approach 1:
The patent changes the forward voltage parameter of the first LED load relative to subsequent loads, setting it at least 50% higher. This parameter change fundamentally alters the conduction characteristics, causing the first LED load to conduct only when the AC voltage amplitude is sufficiently high. By optimizing this parameter relationship, the patent improves LED utilization efficiency while managing the trade-off on the total number of loads that can be effectively integrated.
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
This design increases LED utilization, reduces the severity of worst-case conditions for LED packages, lowers costs by using less expensive components, and allows for a reduction in the number of LED loads, while maintaining or improving light output and reducing flicker and harmonic distortion.
Implementation Method 1
a rectifier coupled to the input terminals for rectifying the low frequency AC supply voltage
Implementation Method 2
N LED loads that are directly connectable to a supply source supplying a low frequency AC voltage
Data Source
AI summary
A series arrangement of LED loads (LP1-LP4) is coupled between output terminals of a rectifier having its input terminals coupled to a mains supply supplying a low frequency AC voltage. Control means render the LED loads conductive one by one, when the amplitude of the supply voltage increases, and non-conductive one by one when the amplitude of the supply voltage decreases. The first LED load (LP1, LP2) has a forward voltage that is substantially higher than that of the other LED loads. As a consequence, the LED utilization is comparatively high, thus allowing the LED loads used in the series arrangement to be comparatively cheap.