Switch Controller for LED Power Supply Duty Distortion
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Solution Overview
Problem
The existing power supply systems using buck converters face issues with power factor deterioration and increased total harmonic distortion (THD) due to minimum on-time, leading to overcurrent and potential damage to LED elements.
Innovation Solution
A switch controller that detects the on-time of a power switch and decreases the switching frequency when the detected on-time is shorter than or equal to the minimum on-time, preventing duty distortion by adjusting the clock signal frequency, thereby maintaining a sine wave LED current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the power switch duty is controlled to be inversely proportional to the input voltage, then the LED current follows the sine wave shape, but when the input voltage exceeds a threshold, the duty is maintained at minimum on-time causing duty distortion and LED current distortion
Solution Approach 1:
The patent dynamically adjusts the switching frequency of the power supply based on the detected on-time of the power switch. When the on-time is shorter than or equal to the minimum on-time, the switching frequency is decreased to extend the on-time, thereby maintaining proper duty cycle and preventing LED current distortion while adapting to varying input voltage conditions
Solution Approach 2:
The patent implements a feedback mechanism where the on-time detector continuously monitors the power switch on-time and provides feedback to the frequency controller. This closed-loop control enables real-time adjustment of switching frequency to maintain optimal duty cycle and prevent distortion across different operating conditions
2Device complexity
If the switching frequency is maintained at a fixed value, then the control is simple, but the on-time cannot be extended when input voltage increases causing duty distortion
Solution Approach 1:
The patent transitions from fixed-frequency control to dynamic frequency adjustment by adding an on-time detector and frequency controller that automatically adjust the switching frequency based on real-time on-time measurements, maintaining duty cycle accuracy without excessive complexity
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on input voltage conditions and measured on-time, allowing the system to adapt to varying operating conditions while maintaining proper duty cycle and preventing distortion
3Manufacturing precision
If the minimum on-time is increased to prevent duty distortion, then the duty cycle accuracy improves, but the switching frequency must be decreased reducing overall productivity
Solution Approach 1:
The patent dynamically adjusts the switching frequency based on actual on-time measurements rather than using a fixed conservative minimum on-time value. This allows the system to maintain high switching frequency when conditions permit while extending on-time only when necessary, optimizing both accuracy and productivity
Solution Approach 2:
The patent changes the switching frequency parameter adaptively based on input voltage and load conditions, allowing frequency to increase or decrease as needed to maintain proper duty cycle, rather than being constrained by a fixed frequency that would limit performance
Data Source
AI summary
The present invention relates to a switch controller, a switch control method, and a power supply including the switch controller. An exemplary embodiment of the present invention detects an on-time of a power switch of the power supply and decreases a frequency of a clock signal according to a period during which the detected on-time is shorter than or equal to the minimum on-time. According to the exemplary embodiment, switching of the power switch is controlled according to a clock signal, and the minimum on-time is an on period of the power switch that cannot be shortened.