LED String Short Circuit Detection via Control Pin Extraction
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Solution Overview
Problem
Existing LED drive systems face challenges in detecting short circuits and matching among LED strings due to high-voltage MOSFET drain pins and varying voltage drops across LED strings, leading to incorrect results and increased pin count on control chips.
Innovation Solution
A system comprising current and voltage obtaining units, calculating, comparing, and determining units to identify short circuits and mismatches by comparing current and voltage differences across LED strings, reducing the need for high-voltage pin detection and optimizing chip area and pin count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage detection is performed on MOSFET drain pin to detect LED short circuit, then short circuit detection capability is achieved, but chip area is substantially expanded and pin count increases
Solution Approach 1:
The patent extracts the voltage detection function from the high-voltage MOSFET drain pin and relocates it to the low-voltage control pin. By detecting the voltage on the control pin (which is logically inverted relative to the drain pin), the system achieves LED short circuit detection without requiring high-voltage tolerance components, thereby reducing chip area and pin count requirements
Solution Approach 2:
The control pin serves as an intermediary that provides indirect access to the LED string status. Instead of directly measuring the high-voltage drain pin, the system uses the control pin voltage as a mediator to infer the LED string condition, enabling safe and area-efficient detection
2Reliability
If voltage detection is performed on MOSFET drain pin to detect LED short circuit, then short circuit detection capability is achieved, but pin count of control chip increases
Solution Approach 1:
The patent extracts the detection function from a dedicated high-voltage pin and implements it using the existing low-voltage control pin. This eliminates the need for additional high-voltage pins while maintaining detection capability, thereby reducing pin count and simplifying device complexity
Solution Approach 2:
The control pin is given multi-functionality by using it both for switching control and for LED short circuit detection. This dual usage eliminates the need for separate detection pins, reducing overall pin count and simplifying the device interface
3Adaptability or versatility
If LED strings with different voltage drops are used, then manufacturing flexibility is improved, but detection accuracy deteriorates due to incorrect short circuit detection results
Solution Approach 1:
The patent introduces a preliminary matching detection process before normal operation. By comparing the voltage drops of different LED strings in advance and identifying those with excessive differences, the system prevents inaccurate short circuit detection in mismatched strings, thereby maintaining detection accuracy across diverse LED configurations
Solution Approach 2:
The system uses feedback from voltage drop measurements to identify mismatched LED strings. By monitoring the voltage characteristics and comparing them against expected ranges, the system can detect and flag LED strings with excessive voltage drop variations, preventing false short circuit detection results
Data Source
AI summary
This specification relates to a method and a system for detecting light emitting diode (LED) short circuit in a plurality of LED strings or detecting matching among the plurality of LED strings, wherein one end of each of the plurality of LED strings is connected to a same output end of a power supply, and the other end is respectively connected to a corresponding switch. According to the present invention, first current of each of LED strings is obtained when the output end of the power supply outputs a first voltage; differences between the minimum of the first currents of LED strings and other first currents are calculated; the differences are compared with a comparing threshold; it is determined that the LED strings corresponding to the other currents for which differences are larger than the comparing threshold include short circuit or mismatch with the LED string corresponding to the minimum current. Accordingly, it is possible to reduce the number of pins and area of a control chip.