LED Driver Circuit for Open and Short Circuit Failure Detection
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Solution Overview
Problem
Existing light-emitting diode (LED) driving technologies cannot detect short-circuit failures when LEDs are driven by pulse width modulation (PWM), in addition to open-circuit failures.
Innovation Solution
A light-emitting diode driving apparatus that includes a signal processing circuit capable of detecting open-circuit and short-circuit failures in LEDs and switching transistors by analyzing the output state of the PWM signal and the combination of voltage levels from multiple voltage sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If pulse width modulation (PWM) is used to drive the light-emitting diode, then the light emission can be controlled efficiently, but the ability to detect short-circuit failures is lost
Solution Approach 1:
The patent segments the detection function by separating it from the PWM driving function. A dedicated detection circuit with detection transistor is introduced that operates independently from the PWM control circuit, allowing failure detection without interrupting the PWM-driven light emission. This segmentation enables simultaneous achievement of energy-efficient PWM driving and reliable failure detection.
Solution Approach 2:
The patent introduces a detection transistor as an intermediary component between the power supply and the LED array. This detection transistor acts as a mediator that monitors current flow through the LED array during PWM operation, enabling indirect detection of both open-circuit and short-circuit failures without disrupting the primary PWM driving function.
2Device complexity
If a simple current detection method is used, then the detection circuit is simple, but only open-circuit failures can be detected while short-circuit failures remain undetected
Solution Approach 1:
The patent employs dynamic detection by utilizing the PWM signal's on/off states to perform different detection functions. During the on-state, the detection circuit monitors for short-circuit conditions, while during the off-state, it detects open-circuit conditions. This dynamic approach allows a single detection circuit to identify both types of failures without requiring separate static detection paths for each failure mode.
Solution Approach 2:
The patent changes the detection parameter based on the PWM signal state. When the PWM signal is high, the detection circuit measures current to detect short-circuits; when the PWM signal is low, it measures voltage to detect open-circuits. By dynamically changing the detection parameter (current vs. voltage measurement) according to the PWM state, the system achieves comprehensive failure detection with a unified circuit design.
Data Source
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AI summary
Provided is a light-emitting diode driving apparatus, including: a switching transistor which becomes an on-state or an off-state in response to a pulse width modulation signal; a light-emitting diode electrically connected with a second terminal of the switching transistor; a first comparison circuit which outputs a first voltage depending on a comparison result between a first input voltage corresponding to a voltage applied to the light-emitting diode and a first threshold voltage; a second comparison circuit which outputs a second voltage depending on a comparison result between a second input voltage corresponding to a voltage applied to the light-emitting diode and a second threshold voltage; and a signal processing circuit which detects a failure in the light-emitting diode on the basis of an output state of the pulse width modulation signal, the first voltage, the second voltage and a third voltage on the second terminal side of the switching transistor.