Liquid Crystal Display Power-Off Residual Image Prevention
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Solution Overview
Problem
Liquid crystal display (LCD) devices exhibit residual images when powered off due to delayed cessation of drive voltage and slow discharge of sub-pixels through thin film transistors.
Innovation Solution
A liquid crystal display device and driving method that involve a power supply unit outputting delayed drive voltages, a voltage detector generating a power-off detect signal, a timing controller increasing the frequency of control signals, and a gate driver rapidly driving gate lines to apply a constant voltage to all sub-pixels, preventing residual image generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power supply unit is turned off, then power consumption is reduced, but residual images are generated due to delayed cessation of drive voltage and slow discharge of sub-pixels
Solution Approach 1:
The patent applies preliminary action by detecting the power-off state in advance and activating a discharge circuit before the main power is completely cut off. The voltage detector monitors the drive voltage and generates a power-off detect signal that triggers the discharge circuit to rapidly discharge the liquid crystal panel, preventing residual image formation before it occurs
Solution Approach 2:
The patent introduces an intermediary discharge circuit with a discharge transistor and discharge capacitor. This intermediary component provides a dedicated discharge path for the liquid crystal panel, separating the discharge function from the normal operation circuitry. The discharge circuit acts as a mediator that rapidly removes residual voltage without requiring full power system activation
2Object-generated harmful factors
If the drive voltage is immediately ceased upon power-off, then residual image is prevented, but the power supply circuit cannot properly discharge due to timing issues
Solution Approach 1:
The patent implements feedback through the voltage detector that continuously monitors the drive voltage level. When the drive voltage falls below a threshold, the power-off detect signal is generated, creating a feedback loop that triggers the discharge circuit at the optimal moment. This feedback mechanism ensures the discharge occurs at the precise timing when it is most effective
Solution Approach 2:
The discharge circuit is activated in advance of complete power shutdown by detecting the decline in drive voltage. This preliminary activation ensures the discharge path is established before residual voltage becomes problematic, preventing residual images while maintaining proper discharge timing
3Loss of energy
If the thin film transistor remains turned off, then power consumption is minimized, but sub-pixels discharge slowly causing residual images
Solution Approach 1:
The discharge transistor is activated in advance of complete power-off based on the power-off detect signal. This preliminary activation prepares the discharge path before the main power is fully cut off, enabling rapid discharge of the liquid crystal panel without requiring the thin film transistor to remain active during normal operation
Solution Approach 2:
The discharge transistor and discharge capacitor form an intermediary discharge circuit that provides a dedicated rapid discharge path. This intermediary circuit bypasses the normal thin film transistor switching mechanism, enabling fast discharge without requiring the main pixel transistors to remain powered
Data Source
AI summary
A liquid crystal display device and a driving method thereof, which are capable of preventing generation of a residual image upon power-off, are disclosed. The liquid crystal display device includes a power supply unit for outputting a plurality of drive voltages after delaying the drive voltages, a voltage detector for monitoring one of the drive voltages, and outputting a power-off detect signal based on the result of the monitoring, a timing controller for increasing a frequency of a control signal in response to the power-off detect signal, and outputting the frequency-increased control signal, a gate driver for outputting a scan signal in response to the frequency-increased control signal, a data driver for outputting a constant voltage in response to another control signal from the timing controller, and a liquid crystal panel for applying the constant voltage to all sub-pixels of the liquid crystal panel in response to the scan signal.