Backlight Unit Current Balancing for CCFL Brightness Uniformity
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Solution Overview
Problem
In direct-illumination type backlight units, the uneven temperature distribution leads to uneven current flow through light sources due to the negative resistance characteristic of cold cathode fluorescent lamps, resulting in brightness differences across a liquid crystal display.
Innovation Solution
A backlight unit design incorporating a boost circuit, balance circuits with capacitors, and resistors to stabilize current distribution among light sources, including variable resistors to account for temperature and usage effects, thereby reducing current deflection and brightness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If light sources are arranged in parallel in a direct-illumination type backlight unit, then the structure is simple and easy to manufacture, but uneven current flow occurs due to temperature differences causing brightness non-uniformity
Solution Approach 1:
The patent applies local quality by introducing individual balance circuits with capacitors and resistors to each light source branch. These balance circuits are selectively configured with different capacitance values and resistance values according to the specific temperature characteristics and impedance of each light source position, thereby achieving localized current balancing without changing the overall parallel structure
Solution Approach 2:
The patent changes electrical parameters by introducing capacitors with specific capacitance values and resistors with specific resistance values into each light source branch. The capacitance and resistance parameters are carefully selected to compensate for the negative resistance characteristic of cold cathode fluorescent lamps at different temperatures, transforming the current distribution pattern from uneven to uniform
2Adaptability or versatility
If cold cathode fluorescent lamps are used as light sources, then the backlight unit can be manufactured with existing technology, but the negative resistance characteristic causes current deflection and brightness differences
Solution Approach 1:
The patent introduces balance circuits with capacitors and resistors as intermediary elements between the power supply and each cold cathode fluorescent lamp. These intermediary components act as buffering and stabilizing elements that decouple the negative resistance characteristic of the lamps from the power supply, thereby stabilizing current distribution while maintaining compatibility with existing light source technology
Solution Approach 2:
The patent applies beforehand cushioning by pre-configuring balance circuits with appropriate capacitance and resistance values to compensate for the anticipated temperature-induced impedance changes in cold cathode fluorescent lamps. This preventive measure stabilizes current distribution before temperature variations cause significant current deflection
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 solution ensures stable driving of the backlight unit and reduces brightness differences among light sources, enhancing the display quality by uniformly distributing current and maintaining consistent illumination across the display.
Implementation Method 1
The boost circuit boosts an input alternating current voltage and applies a driving alternating current voltage to the light sources
Implementation Method 2
Each of the balance circuits is connected between an output terminal of the boost circuit and a corresponding light source of the light sources and includes a first capacitor
Implementation Method 3
For each light source, a first resistor is connected between two balance circuits of the balance circuits
Implementation Method 4
The cold cathode fluorescent lamp used as the light source of the backlight unit has a negative resistance characteristic with respect to a temperature
Data Source
AI summary
A backlight unit includes a plurality of light sources, a boost circuit, a plurality of balance circuits, and a plurality of first resistors. The boost circuit boosts an input alternating current voltage and applies a driving alternating current voltage to the light sources. Each of the balance circuits includes a first capacitor and is disposed between an output terminal of the boost circuit and the light sources. Each of the first resistors connects two balance circuits among the balance circuits.