LED Driver Circuit Deep Dimming Flicker Control
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Solution Overview
Problem
Current LED driver control systems experience undesirable visible flickering as they enter burst mode during deep dimming, failing to maintain dimmed LED output current levels effectively without flickering.
Innovation Solution
A driver control circuit that switches between closed loop and open loop control using pulse width modulation signals, with calibration to determine transfer functions for accurate current regulation, preventing burst mode operation and maintaining preset output current levels during deep dimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If PWM dimming is used to control LED output current, then brightness control is achieved, but visible flickering occurs during deep dimming due to burst mode operation
Solution Approach 1:
The patent applies dynamics by switching between two distinct control modes (closed-loop and open-loop PWM) based on the dimming level. The system dynamically transitions from closed-loop control at higher brightness levels to open-loop control at deep dimming levels, optimizing performance for each operating condition and eliminating flickering during deep dimming operations.
Solution Approach 2:
The patent changes the control parameter approach by using different PWM control strategies depending on the operating conditions. At deep dimming levels, the system changes from feedback-based closed-loop control to feedforward-based open-loop control with pre-calculated PWM values, thereby maintaining stable operation without visible flickering while achieving accurate dimming control.
2Measurement precision
If closed loop control is used for current regulation, then accurate current control is achieved, but system complexity increases
Solution Approach 1:
The patent segments the control operation into two distinct modes: closed-loop control for normal operating conditions and open-loop control for deep dimming conditions. This segmentation allows the system to use the simpler open-loop mode (with pre-calculated PWM values from calibration) during deep dimming, avoiding the complexity of continuous closed-loop control while maintaining accuracy where needed.
Solution Approach 2:
The patent applies preliminary action by performing calibration during manufacturing to pre-calculate and store PWM values for various dimming levels. This preliminary calibration creates lookup tables or lookup curves that enable the system to use simple open-loop control during deep dimming operations, eliminating the need for complex real-time closed-loop control and reducing system complexity during critical deep dimming operations.
Data Source
AI summary
Provided is a deep dimming control method and a driver control circuit for controlling brightness to a plurality of LEDs, that includes a controller which generates a first pulse width modulation signal, and a second pulse width modulation signal is used to switch between closed loop control and open loop control of the light intensity of the LEDs, and at least one comparator configured to receive the first PWM signal or the second PWM signal from the controller. The comparator compares the first PWM signal to a measured output current signal and regulates the output current to the LEDS in the closed loop control until a predetermined output dimming level is reached. Upon reaching the predetermined output dimming level, the controller generates the second PWM signal to another comparator, and the output current is maintained at a preset value determined by calibration during the closed loop control.