Backlight Unit Ripple Suppression via Capacitor Pre-Charging
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Solution Overview
Problem
Existing backlight units using light emitting diodes (LEDs) face challenges in maintaining brightness and color uniformity across the display area due to ripple effects in the supply voltage caused by dimming operations, leading to non-uniform image brightness.
Innovation Solution
A backlight unit design that includes a power converter, a light emitting element, and a controller with a ripple prevention mechanism, utilizing a comparator and transistors to regulate current flow and suppress voltage ripples, ensuring stable voltage supply to LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If dimming method is used to adjust power on/off time to control brightness, then brightness adjustment is achieved, but voltage ripple occurs causing non-uniform image brightness
Solution Approach 1:
The capacitor is pre-charged to a specific voltage level before the LED turns on, and the controller predicts when the voltage will drop to a threshold level, enabling proactive switching decisions that prevent voltage ripple before it occurs
Solution Approach 2:
The controller continuously monitors the capacitor voltage and uses feedback signals to adjust the switching timing, ensuring that the LED receives stable current by turning on/off based on real-time voltage conditions rather than fixed timing
2Stability of the object's composition
If LED current is momentarily controlled to combine colors, then color uniformity is improved, but brightness uniformity deteriorates due to voltage ripple
Solution Approach 1:
The capacitor is pre-charged to compensate for upcoming voltage drops, and the controller anticipates ripple conditions to adjust switching timing, preventing brightness non-uniformity before it occurs during color transition periods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively minimizes voltage ripples, maintaining consistent brightness and improving image quality by controlling current flow through the LEDs, thereby enhancing display uniformity.
Implementation Method 1
a light emitting element connected between the first node and the second node
Implementation Method 2
a light emitting element configured to receive the light source power voltage
Data Source
AI summary
A backlight unit of a display apparatus includes a power converter generating a light source power voltage in response to a power control signal, a first node, a second node, a light emitting element connected between the first node and the second node, and a controller connected to the second node. The light emitting element is configured to receive the light source power voltage through the first node, and the controller is configured to output the power control signal for controlling current flowing through the light emitting element in response to a dimming signal. When the dimming signal has a first level, the controller outputs the power control signal to turn off the power converter.