Backlight Control Circuit with Parallel Feedback for Open Circuit Protection
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Solution Overview
Problem
Conventional backlight control circuits for LCDs are costly due to the need for multiple transistors and diodes to protect the backlight system from open circuits, especially when a large number of backlight lamps are used.
Innovation Solution
A simplified backlight control circuit design that uses at least two sampling circuits, two feedback circuits, and a PWM IC, where each feedback circuit includes a resistor and a diode in parallel, allowing for efficient detection of open circuits and switching to a protecting state with reduced component requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple transistors and diodes are used to protect the backlight system from open circuits, then the reliability of the backlight system is improved, but the device complexity and cost increase
Solution Approach 1:
The patent combines the protection function and feedback function into a single circuit structure. The feedback resistor and diode are integrated into the sampling circuit, allowing the same components to serve both as feedback elements and protection elements. This merging reduces the need for separate protection transistors and diodes while maintaining open-circuit detection capability.
Solution Approach 2:
The sampling circuit components are designed to perform multiple functions: the feedback resistor provides both feedback current and protection functionality, while the diode serves both as a protection element and a feedback path component. This multi-functionality allows the circuit to detect open circuits and provide feedback without requiring additional dedicated protection components.
2Reliability
If multiple transistors and diodes are used to protect the backlight system from open circuits, then the reliability of the backlight system is improved, but the manufacturing cost increases
Solution Approach 1:
The patent merges protection functionality into existing feedback circuit components, eliminating the need for separate protection transistors and diodes. This reduction in component count directly lowers manufacturing costs while maintaining the protection function through the integrated feedback resistor and diode structure.
Solution Approach 2:
The patent uses standard, inexpensive components (resistors and diodes) in a simplified configuration rather than expensive specialized protection transistors. The feedback resistor and diode are common electronic components that are cheaper than the multiple transistors and diodes required in conventional designs, reducing overall manufacturing cost.
3Illumination intensity
If a large number of backlight lamps are used, then the illumination intensity is improved, but the device complexity and cost increase due to increased protection requirements
Solution Approach 1:
The patent designs a universal protection mechanism where the feedback circuit serves both as a current sensing path and as a protection path for multiple backlight lamps. The same feedback resistor and diode structure protects all lamps in the string, eliminating the need for individual protection circuits for each lamp, thus reducing complexity as the number of lamps increases.
Data Source
AI summary
An exemplary backlight control circuit (20) includes at least two sampling circuits (21), at least two feedback circuits (22), and a PWM IC (23). Each of the sampling circuits includes a sampling output (210) and a backlight lamp (211). The PWM IC includes a current sense pin (230). The at least two feedback circuits correspond to the at least two sampling circuits, respectively. Each of the feedback circuits includes a resistor (222) and a diode (223) electrically coupled in parallel. The sampling output is configured to output a first voltage when the backlight lamp is in a normal working state, and output a second voltage when the backlight lamp has an open circuit. One terminal of the diode is electrically coupled to the sampling output of a corresponding one of the sampling circuits, and an opposite terminal of the diode is electrically coupled to the current sense pin.