LED Driver Circuitry Parasitic Capacitance Ghosting
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Solution Overview
Problem
Light emitting diodes (LEDs) in displays and illumination systems often experience ghosting due to parasitic capacitances in the circuitry, which store energy and cause faint illumination when LEDs are turned off.
Innovation Solution
The proposed solution involves a circuit with a discharge circuit and a pre-charge circuit designed to manage parasitic capacitances. The discharge circuit discharges stored energy from LED line terminals when a line switch is turned off, while the pre-charge circuit applies a pre-charge voltage to channel output terminals when channels are turned off to prevent ghosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If parasitic capacitances are present in the circuitry, then energy storage occurs which can be utilized, but faint illumination or ghosting occurs when LEDs are turned off
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitance (ghosting) into a beneficial effect by intentionally charging the parasitic capacitances during a pre-charge interval before the LED is supposed to turn off. This pre-charging eliminates the voltage difference that would otherwise cause ghosting, while the stored energy is then safely discharged through the discharge circuit after the LED turns off, preventing both ghosting and energy waste.
2Object-affected harmful factors
If a discharge circuit is added to eliminate ghosting, then ghosting is reduced, but device complexity increases
Solution Approach 1:
The patent implements a multi-functional control circuit that performs multiple functions: it controls the main LED switching, manages pre-charging of parasitic capacitances, and handles discharge of stored energy. By integrating these functions into a single control mechanism that operates during specific time intervals, the patent reduces the need for separate dedicated circuits for each function, thereby managing device complexity while achieving ghosting elimination.
Solution Approach 2:
The patent applies preliminary action by pre-charging the parasitic capacitances before the LED is supposed to turn off. This pre-charge operation prepares the circuit in advance to prevent ghosting, and the subsequent discharge operation is timed to occur after the LED turns off but before the next LED activation. This timing-based approach allows the same circuit elements to serve multiple purposes without requiring additional dedicated components.
Data Source
AI summary
In a described example, a circuit includes a plurality of line switches, each having a line input terminal, a line terminal and a line control terminal. Each of the line input terminals is coupled to a light emitting diode (LED) voltage terminal and each line terminal is coupled to a respective LED line terminal of a plurality of LED line terminals. A discharge circuit has a plurality of discharge inputs, in which each discharge input is a coupled to a respective line terminal. The discharge circuit includes a plurality of discharge switches, each having a discharge input terminal, a discharge output terminal and a discharge control terminal, in which each discharge input terminal is coupled to a respective LED line terminal. The discharge circuit also includes a current sink circuit coupled between each discharge output terminal and a ground terminal.