LED Converter PFC Modulation for Low-Load Flicker Suppression
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Solution Overview
Problem
Existing LED converter systems experience visible light flicker under low-load conditions due to low-frequency modulation of the switch operation, leading to noticeable quantization of light output.
Innovation Solution
The implementation of a closed-loop voltage control system for the PFC converter, which modulates the control signal with a modulation term based on the electrical power consumption parameter of the LED load, increasing regulation activity and spreading quantization noise over a wider frequency range to suppress flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the DC/DC converter operates under low-load conditions, then power consumption is reduced, but visible light flicker occurs due to low-frequency modulation of switch operation
Solution Approach 1:
The patent introduces a periodic dither signal to the control voltage of the DC/DC converter, which modulates the switch operation frequency. This periodic action ensures that even under low-load conditions, the converter maintains sufficient switching activity to prevent visible light flicker while keeping power consumption low. The dither signal creates small, continuous variations in the control voltage that keep the converter operating in a more stable regime.
Solution Approach 2:
The patent dynamically changes the operating parameters of the DC/DC converter by adding a dither component to the control voltage. This parameter change allows the converter to maintain optimal performance across different load conditions, particularly preventing the low-frequency modulation that causes flicker at low loads while maintaining energy efficiency.
2Stability of the object's composition
If the feedback control operates continuously to regulate LED current, then current stability is maintained, but light output quantization becomes noticeable due to variation in LED current
Solution Approach 1:
The patent applies periodic dithering to the control voltage, which prevents the feedback control from settling into a pattern that causes quantization of light output. The continuous small variations introduced by the dither signal keep the LED current modulation below the threshold of human perception, thereby maintaining both current stability and smooth light output.
Solution Approach 2:
The patent employs feedback control that incorporates a dither signal to regulate the LED current. This feedback mechanism continuously adjusts the control voltage based on the actual LED current while superimposing a small periodic signal that prevents quantization effects, thereby achieving both stability and smooth illumination.
3Device complexity
If the PFC converter provides a constant output voltage, then regulation is simplified, but ripple on the supply voltage increases under low-load conditions
Solution Approach 1:
The patent introduces periodic dithering to the PFC converter control, which prevents the converter from operating in a mode that generates excessive voltage ripple under low-load conditions. The dither signal maintains sufficient switching activity in the PFC stage, ensuring stable output voltage without increasing regulation complexity.
Solution Approach 2:
The patent dynamically adjusts the control parameters of the PFC converter by superimposing a dither signal on the control voltage. This parameter change allows the PFC converter to maintain low output voltage ripple across different load conditions without complicating the regulation mechanism.
Data Source
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AI summary
An LED converter (1) is provided, which comprises a power factor correction, PFC, converter (11) providing a feedback-controlled output voltage (12), and a switched DC/DC converter (13) supplied by the output voltage (12) of the PFC converter (11) and providing a feedback-controlled output current (14) to output terminals of the LED converter (1). The output terminals are designed for supplying an LED load (15). The PFC converter (11) further comprises a feedback control unit (21) configured to provide a control signal (22) for operating a switch of the PFC converter (11) such that the output voltage (12) is feedback-controlled to a preset nominal value (20), and a modulation unit (23) configured to modulate the control signal (22) with a modulation term (24) prior to supplying it to the switch, resulting in a modulated output voltage (12) of the PFC converter (11). A modulation amplitude of the modulation term (24) depends on an electrical power consumption parameter of the LED load (15) fed to the modulation unit (23). The modulation unit (23) is further configured to selectively apply the modulation only when the value of the electrical power consumption parameter of the LED load (15) is below a preset threshold value, or apply a higher modulation amplitude at lower values of the electrical power consumption parameter of the LED load (15) compared to the modulation amplitude at higher values thereof. A resulting more frequent variation of the output/LED current (14) may suppress visible light flicker.