Backlight Control Circuit for LED Brightness Stability
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Solution Overview
Problem
Backlight control circuits in LCDs face significant brightness variations when some LEDs fail, particularly in larger screens requiring higher brightness, as series or parallel connections lead to complete shutdown or severe brightness drops if one LED is inoperative.
Innovation Solution
A backlight control circuit with current matching circuits that maintain a constant total current across multiple LED paths, ensuring that if one path fails, the current and brightness of other paths increase to compensate, using a common node connected to a total current setting circuit, such as a resistor or control current source, to maintain consistent illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If all LEDs are connected in series, then the circuit structure is simple, but if one LED shuts down, all other LEDs are shut down causing complete darkness
Solution Approach 1:
The patent divides the LED array into multiple independent parallel paths (first path, second path, third path, etc.), each containing multiple LEDs. This segmentation allows one path to fail independently without affecting other paths, resolving the contradiction between simple series connection and reliable operation.
2Reliability
If all LEDs are connected in parallel with individual current sources, then each LED path can operate independently, but the overall brightness drops severely when one path fails
Solution Approach 1:
The patent employs an error amplifier circuit that detects the sense voltage from the current source and compares it with a reference voltage. When an LED path fails and current decreases, the error amplifier generates an error signal that adjusts the voltage supply to increase current in remaining paths, compensating for brightness loss and maintaining overall illumination.
3Illumination intensity
If series-parallel connection is used to increase LED quantity for larger screens, then higher backlight brightness is achieved, but if one LED path is inoperative, brightness drops more severely
Solution Approach 1:
The patent divides the LED array into multiple independent parallel paths with multiple LEDs in each path, allowing the system to support larger screens with higher brightness requirements while maintaining reliability through independent path operation.
Solution Approach 2:
The error amplifier circuit continuously monitors current in each path and dynamically adjusts voltage supply to compensate for failures, ensuring that brightness is maintained even when some paths become inoperative in large-scale LED arrays.
4Object-affected harmful factors
If over voltage protection circuit limits output voltage to prevent unlimited increase, then circuit safety is improved, but brightness compensation capability is reduced
Solution Approach 1:
The patent uses a dynamic control approach where the error amplifier continuously adjusts the voltage supply within safe limits defined by the over-voltage protection circuit. This dynamic adjustment enables brightness compensation for failed LEDs while the protection circuit ensures voltage remains within safe operational boundaries, resolving the contradiction between protection and compensation.
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
This solution automatically adjusts the supply current to LEDs, minimizing brightness variations and ensuring uniform screen brightness even if one or more LEDs are inoperative, preventing complete darkness and maintaining optimal display performance.
Implementation Method 1
a voltage supply circuit 11 converting an input voltage Vin to an output voltage Vout which is supplied to a plurality of LEDs L1-LN
Implementation Method 2
a voltage at a node Vsense1 is compared with a reference voltage Vref to check whether a current through the path satisfies a predetermined condition
Implementation Method 3
an over voltage protection circuit 12 is provided in the backlight control circuit 10, which detects the output voltage Vout and sends a signal to stop the voltage supply circuit 11 from increasing the output voltage Vout if the output voltage Vout is excessively high
Implementation Method 4
controls LEDs to illuminate from the back side of an LCD screen
Implementation Method 5
a plurality of light emission device paths; and a common node electrically connected with the plurality of light emission device paths
Data Source
AI summary
The present invention discloses a backlight control circuit, and a method for controlling light emission devices. The method comprises: providing a plurality of light emission device paths connected in parallel; and setting a total current of the paths connected in parallel to a constant.