Backlight Unit Boost Converter Variable Frequency Control
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Solution Overview
Problem
The existing backlight unit driving systems for liquid crystal displays experience flickering due to the slow rising rate of the output voltage from the DC-DC boost converter, which affects image quality.
Innovation Solution
A method and system that utilize a comparator circuit and frequency modulation circuit to generate different frequencies, controlling the boost converter's voltage rising rate, allowing the output voltage to reach the desired value quickly and preventing flickering by using a first higher frequency when the soft start voltage is lower than the predetermined voltage and a second lower frequency when it is higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a DC-DC boost converter is used to drive LEDs in series, then the system can provide sufficient brightness and uniform light source, but the output voltage rises too slowly causing flickering
Solution Approach 1:
The patent applies dynamics by making the switching frequency of the boost converter variable rather than fixed. The controller adjusts the switching frequency dynamically based on the current voltage level during startup: using a first (higher) frequency when voltage is below a threshold and a second (lower) frequency when above it. This dynamic adjustment resolves the contradiction by enabling fast voltage rise (high frequency) when needed while preventing excessive frequency operation at steady state.
Solution Approach 2:
The patent changes the operating parameter (switching frequency) of the boost converter to resolve the contradiction. By transitioning from a fixed frequency design to a variable frequency design where the switching frequency changes based on voltage conditions, the system achieves both fast voltage rising rate during startup and stable operation during normal driving, eliminating flickering while maintaining brightness.
2Ease of operation
If a fixed switching frequency is used in the boost converter, then the circuit operation is simple, but the voltage rises too slowly causing visible flickering
Solution Approach 1:
The patent transitions from a static fixed-frequency operation to a dynamic variable-frequency operation. The controller monitors the voltage level and automatically adjusts the switching frequency between two values, simplifying the overall control logic while dramatically reducing voltage rising time and eliminating flickering without adding excessive complexity.
Solution Approach 2:
The patent uses periodic switching action with two distinct frequency periods: a first periodic switching at higher frequency during the voltage buildup phase to quickly reach the target voltage, and a second periodic switching at lower frequency during the maintenance phase. This periodic action with variable frequency resolves the contradiction between simple operation and fast voltage rise.
3Object-affected harmful factors
If the output voltage rises quickly to the desired value, then flickering is prevented, but the control system becomes more complex
Solution Approach 1:
The patent implements a dynamic control system that adjusts switching frequency based on voltage feedback. This relatively simple dynamic control mechanism (comparing voltage to a threshold and selecting between two frequencies) effectively eliminates flickering without requiring complex control algorithms or additional hardware components.
Solution Approach 2:
The patent employs feedback control where the controller monitors the output voltage level and uses this information to adjust the switching frequency. This feedback mechanism enables the system to automatically prevent flickering by maintaining appropriate voltage rising rate, achieving the goal with minimal added complexity through a straightforward feedback loop.
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 approach effectively prevents screen flickering by ensuring the output voltage of the boost converter reaches the required level swiftly, thereby enhancing image quality by controlling the voltage rising rate with two distinct frequencies.
Implementation Method 1
comparing the strength of a soft start signal with a predetermined signal through a comparator circuit
Implementation Method 2
outputting a first frequency from a frequency modulation circuit according to the first comparison signal
Implementation Method 3
increasing the rising rate of the output voltage of a boost converter according to the first frequency
Data Source
AI summary
A method for driving the backlight unit of the liquid crystal display includes: comparing the strength of a soft start signal with a predetermined signal through a comparator circuit, and generating a first comparison signal or a second comparison signal according to the comparison result; outputting a first frequency from a frequency modulation circuit according to the first comparison signal; and increasing the rising rate of the output voltage of a boost converter according to the first frequency. Therefore, the rising rate of the output voltage is increased, thereby solving the screen-flickering problem.