LED String Overvoltage Protection Circuit with Differential IC Triggering
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Solution Overview
Problem
In large-size LCD TVs, the overvoltage protection circuit for LED strings is unstable due to differing triggering voltage values between main and secondary ICs, leading to incomplete protection of LED strings when open circuits occur, causing the output voltage to remain high and destabilizing the entire circuit.
Innovation Solution
An overvoltage protection circuit is designed with separate triggering circuits for the main and secondary ICs, where the secondary IC's triggering voltage is set lower than the main IC's, using adjustable resistor ratios to ensure the secondary IC triggers protection earlier, and control modules to adjust output voltage and detect abnormal conditions in LED strings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overvoltage protection triggering voltage of the main IC is set lower than that of the secondary IC, then the main IC can trigger protection first when voltage rises, but the secondary IC cannot trigger its own protection when LED strings open circuit, resulting in unstable high voltage state
Solution Approach 1:
The patent inverts the conventional approach by setting the secondary IC's triggering voltage lower than the main IC's. This ensures that when LED strings open circuit, the secondary IC triggers protection first, preventing the main IC from entering an unstable high voltage state. The inversion resolves the contradiction by making the secondary IC the primary protector in open-circuit scenarios.
Solution Approach 2:
The patent applies different triggering voltage characteristics to different ICs based on their specific functions. The secondary IC uses a lower triggering voltage optimized for detecting LED string open circuits, while the main IC uses a higher voltage suitable for normal overvoltage protection. This local differentiation allows each IC to excel at its specific protection scenario.
2Device complexity
If multiple ICs are coupled in main-secondary mode with same overvoltage protection settings, then the circuit structure is simple, but resistance accuracy and IC individual differences cause inconsistent triggering voltages, leading to protection failures
Solution Approach 1:
The patent changes the key parameter of triggering voltage from being uniform across all ICs to being differentiated, with secondary ICs having lower triggering voltages. This parameter change compensates for resistance accuracy variations and IC individual differences, ensuring reliable protection triggering regardless of manufacturing tolerances.
Solution Approach 2:
The patent implements preliminary action by configuring the secondary IC's lower triggering voltage in advance, so that when LED strings open circuit, the secondary IC is already primed to trigger protection before the main IC can enter an unstable state. This pre-configured difference ensures protection reliability without requiring complex real-time adjustments.
Data Source
AI summary
The present invention provides an overvoltage protection circuit, an overvoltage protection method and a panel driving circuit, wherein, the overvoltage protection circuit adjusts drive output voltage of LED strings coupled with a main IC and a secondary IC and includes a main IC overvoltage triggering circuit and a secondary IC overvoltage triggering circuit, wherein, the main IC overvoltage triggering circuit connected respectively in series with said main IC and several LED strings, said secondary IC overvoltage triggering circuit connected respectively in series with the secondary IC and several LED strings, overvoltage protection triggering points are set respectively in the main IC and the secondary IC, and the voltage value of the overvoltage protection's triggering point of the secondary IC is less than that of the main IC.