Anode Line Switching Circuit to Prevent LED Backlight Ghost Lighting
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Solution Overview
Problem
Passive driving in LED backlight systems for liquid crystal display devices can lead to abnormal lighting issues, where an LED intended to be turned off may be faintly turned on due to changes in the voltage of an anode line, resulting in erroneous lighting.
Innovation Solution
A light-emitting device configuration that includes a switching circuit with power supply line control circuits, each containing a first and second switching element, resistors, and control signals to manage the electrical connection state of anode lines, ensuring that LEDs are properly turned off by suppressing charge flow due to voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If passive driving (time division driving) is used to drive LEDs in blocks, then the number of area divisions can be increased, but abnormal lighting occurs where LEDs intended to be turned off are faintly turned on due to voltage changes in anode lines
Solution Approach 1:
The patent extracts the problematic voltage change effect from the anode line by introducing a dedicated discharge path with a discharge control circuit. This separates the power supply function from the voltage stabilization function, allowing the anode line to be quickly discharged when blocks are switched, thereby preventing abnormal lighting while maintaining the ability to drive large numbers of LED areas.
Solution Approach 2:
The patent introduces a discharge control circuit as an intermediary component between the power supply line and ground. This intermediary actively manages the voltage state of anode lines by providing a controlled discharge path, mediating between the power supply switching and the LED blocks to prevent erroneous lighting during block transitions.
2Use of energy by moving object
If the luminance of each LED is controlled based on input gray scale values for local dimming, then power consumption is reduced, but the complexity of the drive circuit increases
Solution Approach 1:
The patent segments the LED backlight into multiple independently controllable blocks, with each block having its own power supply line control. This segmentation allows local dimming to be implemented by controlling specific blocks based on gray scale values from different areas of the display, reducing overall power consumption while distributing circuit complexity across multiple simple, identical control units.
Data Source
AI summary
An anode line control circuit provided corresponding to each of anode lines includes a first resistor connected to a control terminal of a first switching element, which controls the supply of a power supply voltage to the anode line, and a second switching element connected to a second resistor connected to one end of the anode line. When the first switching element changes from an OFF state to an ON state, the second switching elements corresponding to the anode lines other than the anode line connected to the first switching element are maintained in the OFF state.