AC LED Driving Circuit with PTF Unit for Harmonic Reduction
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Solution Overview
Problem
Light emitting diodes (LEDs) connected in series and operated with an AC voltage source experience issues such as power factor decrease, total harmonic distortion, and excessive flickering due to sudden current flow when the voltage exceeds the sum of forward threshold voltages, leading to a short operating region and inefficient operation.
Innovation Solution
A light emitting device and driving circuit configuration that includes a first and second light emitting unit connected in series, with a PTF unit in parallel with the second unit, allowing it to operate before the first unit when an AC voltage is applied, thereby extending the operating period and reducing sudden current flow, harmonic distortion, and flickering. This configuration involves various elements like resistors, capacitors, and inductors to manage the AC voltage source effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple AC LEDs are connected in series to increase light emitting region, then the light emitting region is increased, but total harmonic distortion and flickering become severe
Solution Approach 1:
The patent divides the series-connected AC LEDs into multiple groups, with each group containing LEDs connected in series. Parallel connection of these groups allows current to be distributed across multiple paths, reducing the severity of harmonic distortion and flickering while maintaining an extended light emitting region. This segmentation approach resolves the contradiction by distributing the load across parallel branches rather than having all LEDs in a single series chain.
Solution Approach 2:
The patent introduces a specific circuit configuration involving resistors and capacitors as intermediary elements between the AC power source and the LED groups. These intermediary components regulate current flow, filter harmonics, and reduce flickering effects, thereby enabling series-connected LED groups to operate with reduced total harmonic distortion and flickering while maintaining expanded light emitting coverage.
2Device complexity
If AC voltage source is applied directly to series-connected LEDs, then the circuit is simple, but sudden current flow occurs when voltage exceeds forward threshold voltages
Solution Approach 1:
The patent incorporates preliminary current limiting resistors and capacitive elements in the circuit configuration that activate before the LEDs reach their forward threshold voltage. These components pre-regulate the current flow and prevent sudden current surges from occurring when the AC voltage exceeds the LED forward voltage thresholds, thereby improving current control stability without significantly increasing circuit complexity.
3Productivity
If LEDs are operated in short operating region, then the circuit configuration is simple, but optical efficiency deteriorates due to severe flickering
Solution Approach 1:
The patent employs parallel connection of LED groups with carefully designed circuit elements that ensure continuous and stable current flow through the LEDs throughout the AC cycle. This continuity of useful action eliminates the short operating region problem and severe flickering, thereby improving optical efficiency. The circuit configuration maintains LED operation during both positive and negative half-cycles of the AC input, ensuring sustained light emission without interruption.
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 total harmonic distortion, and minimizes flickering by ensuring a wider operating region and controlled current flow, enhancing the optical efficiency and reliability of the light emitting device.
Implementation Method 1
Light emitting diodes (LEDs) also exhibit common characteristics of diodes that are turned on upon application of a forward threshold voltage or more thereto
Data Source
AI summary
A light emitting device comprises a first light emitting unit and a second light emitting unit connected in series with each other, and a PTF unit connected in parallel with the first light emitting unit and in series with the second light emitting unit. Each of the first light emitting unit and second light emitting unit comprises at least one LED. The PTF unit allows the second light emitting unit to be operated before operation of the first light emitting unit upon application of an AC voltage source. The light emitting device reduces total harmonic distortion and flickering, and improves power factor and optical efficiency. A driving circuit of the light emitting device is also disclosed.