Power-Off Discharge Circuit for LCD Source Drivers
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Solution Overview
Problem
Liquid crystal display (LCD) devices experience vertical stripe ghost images due to residual electric charges when entering a power-off state, as the source driver circuit disconnects from the load circuit, causing the load circuit to enter a floating state with unsupplied power voltage.
Innovation Solution
A power-off discharge circuit is introduced, comprising a power voltage detection unit and a discharge unit that generates a discharge control signal to rapidly discharge the load circuit when the power voltage is blocked, preventing ghost images by coupling the load circuit to ground voltage during power-off and maintaining normal operation during power-on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the source driver circuit disconnects from the load circuit using a switching element during power-off state, then power consumption is reduced, but the load circuit enters a floating state causing vertical stripe ghost images
Solution Approach 1:
A discharge control signal is introduced as an intermediary control mechanism that activates a discharge path for the load circuit during power-off state. This mediator enables the switching element to disconnect the source driver circuit while simultaneously providing a controlled discharge path through the load circuit to ground, preventing the floating state that causes ghost images without requiring continuous power supply
Solution Approach 2:
The discharge control signal dynamically changes the state of the load circuit based on the power voltage status. During power-on state, the load circuit operates normally; during power-off state, the discharge control signal activates to create a discharge path, allowing the system to adapt its behavior according to power conditions and prevent ghost images only when necessary
2Object-affected harmful factors
If the load circuit is continuously discharged to prevent ghost images, then display quality is improved, but normal display operation is interfered with during power-on state
Solution Approach 1:
The discharge control signal operates periodically based on power state transitions rather than continuously. It activates to discharge the load circuit only during power-off state when ghost images would occur, and deactivates during power-on state to allow normal display operation, creating a rhythmic on-demand discharge pattern that prevents interference with normal functionality
Solution Approach 2:
The discharge control signal functions as a feedback mechanism that responds to the power voltage status. When power voltage is detected as blocked (power-off state), the discharge control signal activates to discharge the load circuit; when power voltage is present (power-on state), the discharge control signal deactivates. This feedback-based control ensures discharge occurs only when ghost images would form, preserving normal display operation
Data Source
AI summary
A power-off discharge circuit comprises a power voltage detection unit that detects whether a first power voltage for driving a source driver circuit is blocked and generates a discharge control signal, and a discharge unit that discharges a load circuit in a display panel based on the discharge control signal.