Backlight Unit Short-Circuit Detection and Protection
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Solution Overview
Problem
Existing backlight units with LED strings face challenges in detecting short circuits, which can lead to overcurrent and damage, due to non-uniform luminance and color distribution across the display area, requiring advanced transient control of LED current for color mixing and high technology for uniformity.
Innovation Solution
A backlight unit is designed with a power converter, an LED string, a short-circuit detector, and a light source controller, including a voltage divider and comparing circuit to generate a reference voltage for detecting short circuits by comparing the detection voltage with predefined voltage levels, enabling a short-circuit signal to interrupt the light-source power voltage when a short circuit is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LED strings are used to provide luminance in backlight units, then power consumption is reduced and eco-friendly usage is achieved, but uniformity of luminance and colors over the whole area becomes difficult to design
Solution Approach 1:
The backlight unit is divided into multiple LED strings, each independently controllable. This segmentation allows for localized adjustment of luminance and color parameters, enabling uniformity across the entire display area while maintaining energy efficiency through selective operation of individual strings based on spatial requirements
2Volume of moving object
If LED strings are used in backlight units, then slimness is achieved, but uniformity of luminance and colors requires high technology for transient control of LED current
Solution Approach 1:
The system implements dynamic control of LED current parameters including pulse width modulation (PWM) for luminance adjustment and current ratio control for color mixing. This dynamic approach enables precise transient control to achieve uniform luminance and color distribution while maintaining the slim form factor through efficient current management circuits
3Device complexity
If LED strings are connected in series to provide luminance, then the backlight unit structure is simplified, but if at least one LED is short-circuited, overcurrent flows causing damage to the backlight unit
Solution Approach 1:
The control circuit continuously monitors the operational status of LEDs in each string and performs preliminary detection of potential short circuit conditions. When a short circuit is detected in any LED, the control circuit proactively interrupts the current path for that specific LED string before overcurrent can propagate and damage other components, thereby protecting the overall backlight unit while maintaining the simplified series connection structure
Data Source
AI summary
A backlight unit includes: a power converter to generate a light-source power voltage according to a voltage control signal; an LED string connected to the light-source power voltage; a short-circuit detector to receive the light-source power voltage and to enable a short-circuit signal; and a light source controller to generate the voltage control signal to interrupt generation of the light-source power voltage when the short-circuit signal is enabled. The short-circuit detector includes: a voltage divider to divide the light-source power voltage to output a detection voltage; and a comparing circuit to generate a reference voltage corresponding to a voltage level of the detection voltage, to compare the reference voltage with the detection voltage, and to enable the short-circuit signal in accordance with a result of the comparison.