LED String Dimming Control via Voltage Repositioning
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Solution Overview
Problem
Existing LED dimming systems face challenges in accurately controlling multiple LED strings with different forward voltages, leading to issues like color shift, increased heating, and reduced lifespan due to current overshoots and tail currents, especially when switching between strings with large voltage differences.
Innovation Solution
A controller system that utilizes precise timing and synchronization to regulate output voltage and current, implementing hardware-based timing and asynchronous/synchronous switching to manage voltage repositioning and current regulation, preventing overshoots and tail currents, and providing over-voltage protection through a closed-loop switch mode power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple LED strings with different forward voltages are driven from a single power train using PWM, then the system can illuminate multiple LED regions, but current overshoots and tail currents occur when switching between strings with large voltage differences
Solution Approach 1:
The patent applies preliminary action by pre-positioning the power train output voltage to match the forward voltage of the LED string that is about to be activated. Before switching between LED strings with different forward voltages, the controller adjusts the output voltage in advance, ensuring smooth transitions without current overshoots or tail currents. This proactive voltage adjustment resolves the contradiction by maintaining current control accuracy while driving multiple LED strings.
2Speed
If fast switching between LED strings is implemented, then dimming response time is improved, but voltage repositioning delays and timing synchronization issues arise
Solution Approach 1:
The patent implements continuity of useful action by using hardware-based timing circuits that continuously monitor and control the power train operation. The hardware timing mechanism ensures uninterrupted voltage repositioning and switching operations, eliminating delays that would occur with software-based timing. This continuous hardware control maintains fast switching speeds while preventing timing synchronization issues between multiple LED strings.
3Manufacturing precision
If hardware-based timing is used for precise LED string switching, then current transition accuracy is improved, but device complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a dedicated hardware timing circuit that acts as a mediator between the controller and the power train switching operations. This separate hardware timing module provides precise timing signals without complicating the main control architecture. The intermediary timing circuit ensures accurate current transitions while maintaining clear separation of functions, thus managing device complexity effectively.
4Stability of the object's composition
If output voltage is repositioned quickly between LED strings, then color shift is prevented, but overheating and increased stress on components occur
Solution Approach 1:
The patent applies dynamics by making the voltage repositioning process adaptive rather than fixed. The controller dynamically adjusts the voltage transition rate based on real-time conditions, including the forward voltage difference between LED strings and thermal state of components. This dynamic control ensures fast enough voltage repositioning to prevent color shift while preventing excessive speed that would cause overheating or component stress.
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 system ensures smooth current transitions and prevents color shift and overheating by synchronizing voltage and current regulation across multiple LED strings, enhancing LED lifespan and performance.
Implementation Method 1
the SMPS output capacitor can be discharged very quickly to provide a fast turn off of the LED's
Implementation Method 2
Driving multiple strings of LEDs may be performed from a single output power train. In such cases, the strings may be driven through pulse width modulation (PWM)
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An integrated circuit device is configured to drive multiple LED strings. The device includes a switch mode power supply control circuit configured to generate primary and secondary power transistor control signals and receive at least one current sense signal and an output voltage sense signal. The device also includes an output compare circuit configured to generate a plurality of pulse width modulated signals and a logic circuit configured to generate signals for selecting a reference voltage and for activating an absorber mode. The signal for activating an absorber mode is to be shared with the secondary power transistor control signal. The logic circuit is to be synchronized with the output compare module.