Switched Preconditioner Circuit for LED Contrast Ratio
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Solution Overview
Problem
LED display screens face issues with residual current flow and noise pickup when in the OFF state, leading to decreased contrast ratios due to electrical current leakage and switching noise.
Innovation Solution
A switched preconditioner circuit is used to eliminate voltage at the power node when the light source is in the OFF state, employing a preconditioner connected between the power potential and the light source, with a bleed path to shunt power and a control signal that pulses longer than the current control signal, ensuring zero voltage during the OFF state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a current switch is used to control LED arrays in the OFF state, then the light source can be turned off, but residual current still flows through the LEDs due to switch leakage and noise pickup
Solution Approach 1:
The preconditioner circuit is activated before the current switch is turned off to proactively eliminate residual voltage at the power node. By pre-charging or discharging the power node capacitance and establishing a zero-voltage condition before the LED array is supposed to be off, the circuit prevents any residual current flow that would otherwise occur due to switch leakage or noise pickup.
Solution Approach 2:
The preconditioner circuit acts as an intermediary between the power supply and the LED array, specifically targeting the power node. This intermediate circuit actively manages the voltage at the power node independently of the current switch state, ensuring that the voltage is eliminated to prevent unwanted current flow through the LEDs even when the main current switch is in the OFF state.
2Illumination intensity
If the preconditioner circuit eliminates voltage at the power node during OFF state, then residual current is reduced, but the circuit complexity increases
Solution Approach 1:
The preconditioner circuit is designed to perform multiple functions: it eliminates residual voltage at the power node, prevents noise pickup, and works in conjunction with the existing current switch control logic. By integrating this functionality into a single circuit block that can be added to existing LED driver architectures, the patent achieves improved contrast ratio without proportionally increasing overall system complexity.
Data Source
AI summary
A switched preconditioner circuit is provided at the power input end of a light source to effectively drop the voltage of the light source to zero volts whenever the light source is required to be in an OFF state thereby eliminating the problem of unwanted current through the light source. The preconditioner circuit may include a terminal connected to a first power potential, a terminal connected to a power node at the power input end of the light source, and an input to receive a preconditioner control signal to place the preconditioner circuit in one of an ON state and an OFF state. The preconditioner circuit supplies the voltage to the power node in its ON state and effectively eliminates the voltage to the power node in its OFF state. The preconditioner circuit also may include a bleed path connected between the power node and a second or ground potential to shunt all power supplied to the power node when the preconditioner circuit input receives a signal to place the preconditioner circuit in the OFF state.