LED Short Circuit Detection via Feedback Terminal and Rectifier
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Solution Overview
Problem
Existing light-emitting diode power supplies for liquid crystal panels cannot accurately identify which series of light-emitting diodes is experiencing a short circuit, leading to unnecessary shutdown of all diodes and high costs due to the need for expensive high voltage switches.
Innovation Solution
A short circuit detection circuit with a feedback terminal, constant current source, and rectifier that compares feedback current with a reference current to trigger protection and independently detect short circuits in each series of light-emitting diodes, eliminating the need for high voltage components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a maximum voltage terminal MAX and high voltage switch are used to detect short circuits, then short circuit detection capability is improved, but device complexity and cost increase due to expensive high voltage components
Solution Approach 1:
The patent introduces an intermediary detection terminal SD that is electrically isolated from the high voltage environment. This terminal receives detection signals through a high voltage switch, allowing the control circuit to indirectly monitor cathode voltages without being directly exposed to high voltages. This resolves the contradiction by enabling short circuit detection while protecting the control circuit from high voltage damage, thus maintaining reliability without requiring the entire control circuit to be high-voltage rated.
Solution Approach 2:
The detection system is segmented into a high voltage side (cathode terminals D1-DN) and a low voltage side (detection terminal SD and control circuit). The high voltage switch acts as a boundary between these segments, allowing voltage monitoring to be performed without transferring high voltage to the control circuit. This segmentation enables reliable detection while keeping the control circuit simple and low-cost.
2Reliability
If voltage VMAX at maximum voltage terminal MAX is monitored to detect short circuits, then short circuit detection is enabled, but loss of information occurs because the control circuit cannot determine which specific series of light-emitting diodes has a short circuit
Solution Approach 1:
The patent segments the detection function by providing individual detection paths for each series of light-emitting diodes. Each cathode terminal D1-DN has its own detection circuit path leading to the detection terminal SD. When a short circuit occurs in a specific series, the corresponding detection path detects the voltage anomaly, allowing the control circuit to identify which specific series has the short circuit based on which detection signal triggers the protection response.
Solution Approach 2:
The detection terminal SD provides feedback information to the control circuit about the status of each series of light-emitting diodes. By monitoring the detection signals from different cathode terminals and comparing them against reference values, the control circuit receives feedback that enables it to determine which specific series has a short circuit condition, thus preventing loss of diagnostic information.
3Reliability
If all series of light-emitting diodes L1-LN are turned off when a short circuit is detected, then protection from damage is improved, but productivity decreases due to unnecessary shutdown of healthy diodes
Solution Approach 1:
The patent implements local quality by enabling independent control of each series of light-emitting diodes based on local detection results. When a short circuit is detected in one series, only that specific series is turned off through its dedicated control signal, while other series continue to operate normally. This localized response maintains system reliability by isolating the fault, while preserving productivity by keeping healthy components operational.
Solution Approach 2:
The control system is segmented to provide independent control over each series of light-emitting diodes. Each series has its own control signal path from the controller to the switching element. This segmentation allows the controller to selectively shut down only the affected series when a short circuit is detected, rather than forcing a complete system shutdown, thus maintaining operational efficiency while providing adequate protection.
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
Enables accurate detection and isolation of short circuits in individual series of light-emitting diodes, reducing unnecessary shutdowns and lowering costs by eliminating the need for high voltage components, while maintaining efficient operation of the backlight controller.
Implementation Method 1
the rectifier is coupled between a feedback terminal and a constant current source. When a feedback voltage of the feedback terminal exceeds a short circuit reference voltage, the rectifier make the setting current sink the feedback terminal
Implementation Method 2
providing a stable reference current; comparing feedback current with the reference current
Data Source
AI summary
A short circuit detection circuit for detecting short circuit of a series of light-emitting diodes includes a constant current source, a rectifier, and a detector. The constant circuit source provides a setting current. The rectifier is coupled between a feedback node and the constant current source. The feedback node is coupled to a terminal of the series of light-emitting diodes. When a feedback voltage of the feedback node exceeds a short reference voltage, the rectifier allows the setting current sinks the feedback node. The detector detects the feedback voltage of the feedback node. When the feedback voltage exceeds a predetermined value, short-circuit protection is triggered to make the series of light-emitting diodes be turned off.