LED Illuminator Circuit Reduces Harmonic Distortion
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Solution Overview
Problem
Existing LED illuminators with full-wave rectified waveforms suffer from significant total harmonic distortion due to non-sinusoidal current waveforms, leading to harmonic noise and inadequate reduction of total harmonic distortion (THD).
Innovation Solution
The proposed LED illuminator employs a dual LED drive circuit configuration with first and second LED strings, each with multiple partial LED strings connected in series, and switching circuits that adjust the number of serial stages based on the full-wave rectified voltage waveform. The switching timing between these circuits is synchronized differently to produce a total current waveform that approximates a sinusoidal shape, thereby reducing THD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single LED string with bypass circuit is used to control current, then the circuit complexity is reduced, but the total harmonic distortion increases significantly due to non-sinusoidal current waveform
Solution Approach 1:
The patent divides the LED lighting system into multiple independent LED strings (first LED string and second LED string), each with its own switching control. This segmentation allows each string to contribute differently to the total current waveform, enabling the combined current to approximate a sinusoidal shape and reduce harmonic distortion while maintaining manageable circuit complexity within each string.
2Illumination intensity
If the current through LED string is increased to improve luminance, then the luminance improves, but the harmonic noise and total harmonic distortion increase
Solution Approach 1:
The patent employs periodic switching control of the LED strings synchronized with the AC power cycle. By switching the LED strings on and off in a periodic manner that follows the sinusoidal voltage waveform, the current through the LEDs becomes periodic and sinusoidal-shaped, improving luminance while minimizing harmonic noise generation.
Solution Approach 2:
The patent dynamically changes the operating parameters (current magnitude and switching timing) of the LED strings to follow the sinusoidal voltage waveform. This parameter modulation ensures that the LED current waveform matches the sinusoidal shape of the voltage, allowing high luminance output without generating excessive harmonic distortion.
3Illumination intensity
If the number of serial stages in LED string is increased to improve luminance, then the luminance improves, but the flicker increases
Solution Approach 1:
The patent uses multiple LED strings that are switched to maintain continuous light output throughout the AC voltage cycle. By coordinating the switching of different LED strings, the system ensures that at least one string is always conducting current, providing continuous illumination and eliminating flicker while maintaining high luminance through the combined output of multiple strings.
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 configuration effectively reduces total harmonic distortion by smoothing the current waveform, minimizing harmonic noise, and improving luminance by adjusting the current at small steps in response to voltage changes.
Implementation Method 1
a full-wave rectified voltage waveform that is output from a rectifier increases/decreases
Implementation Method 2
an LED illuminator including an LED drive circuit configured to drive an LED
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
An LED illuminator 70 comprises a rectifier 11, a first LED string connected to the rectifier 11 and including a first partial LED string 81a and a second partial LED string 81b connected in series with the first partial LED string 81a, a second LED string connected to the rectifier 11 in parallel to the first LED string and including a third partial LED string 91a and a fourth partial LED string 91b connected in series with the third partial LED string 91a, a first switching circuit 76 configured to switch between a state where only the first partial LED string 81a is connected to the rectifier 11 and a state where the first partial LED string 81a and the second partial LED string 81b connected in series are connected to the rectifier 11 as a full-wave rectified voltage waveform that is output from the rectifier 11 increases/decreases, and a second switching circuit 77 configured to switch between a state where only the third partial LED string 91a is connected to the rectifier 11 and a state where the third partial LED string 91a and the fourth partial LED string 91b connected in series are connected to the rectifier 11 as the full-wave rectified voltage waveform that is output from the rectifier 11 increases/decreases. The switching timing by the first switching circuit 76 and the switching timing by the second switching circuit 77 are set so as to differ from each other. The first switching circuit 76 is configured to detect a voltage of a full-wave rectified voltage waveform that is output from the rectifier 11 and to switch between a state where only the first partial LED string 81a is connected to the rectifier 11 and a state where the first partial LED string 81a and the second partial LED string 81b connected in series are connected to the rectifier 11 in accordance with the detected voltage.