Backlight Control Circuit for Isolating Faulted LED Columns
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Solution Overview
Problem
In LED displays with common cathode connections, a shorted or open LED in a column affects the light emission of other LEDs in the same column due to shared cathodes, leading to incorrect dimming signals.
Innovation Solution
A backlight control circuit with LED circuits, an LED driver circuit, first and second switches, and a switch module circuit, which includes error detection mechanisms to isolate shorted or open LED circuits, ensuring other LEDs receive normal dimming signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If common cathode connection is used to reduce device complexity, then the number of connections is reduced, but reliability deteriorates because a shorted or open LED affects other LEDs in the same column
Solution Approach 1:
The patent divides the common cathode connection into segmented zones by inserting switching elements (first switches and third switches) between the LED circuits and the common cathode line. Each dimming zone can be independently controlled and isolated, transforming a single failed LED from affecting the entire column to only affecting its specific zone. This segmentation resolves the contradiction by maintaining the simplified common cathode structure while adding isolation capability to prevent fault propagation.
2Reliability
If error detection and isolation mechanisms are added to improve reliability, then LED column operation is protected, but device complexity increases due to additional switches and control circuits
Solution Approach 1:
The patent merges the error detection function with the existing LED driver circuit by utilizing the same control signals and timing mechanisms already present in the scanning driver chip. The detection of shorted or open LEDs is integrated into the existing row scanning and column data transmission process, eliminating the need for separate detection circuits. This merging approach improves reliability through error detection and isolation while minimizing the increase in device complexity.
3Reliability
If independent control of each LED circuit is implemented to prevent fault propagation, then reliability is improved, but ease of operation deteriorates due to more complex switching control
Solution Approach 1:
The patent implements a self-service mechanism where the system automatically detects LED failures and activates the appropriate isolation switches without requiring manual intervention. The error detection circuit continuously monitors LED status, and upon detecting a shorted or open condition, automatically controls the first switches and third switches to isolate the affected zone. This self-service approach improves reliability through automatic fault isolation while maintaining ease of operation by eliminating the need for manual switching control.
Data Source
AI summary
A backlight control circuit includes LED circuits, a LED driver circuit, first switches and a switch module circuit. Each LED circuit includes a first and a second terminal. The second terminals of the LED circuits are connected. The LED driver circuit provides driving signals and dimming signal in sequence and provides error detection signals when the LED circuit is shorted or opened. The first switches are connected to the first terminals of the LED circuits for switching on or off the LED circuits based on the error detection signals. The switch module circuit includes second switches and third switches for timing provision of dimming signal. When a short or open circuit occurs, the error detection signal turns off corresponding first switch and third switch, so that the first terminal of the shorted/opened LED circuit is floating, and the second terminals can receive the dimming signal in other timing periods.