Light-emitting element drive device startup ground fault detection
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Solution Overview
Problem
Conventional light-emitting element drive devices may misdetect an output ground fault during device startup, leading to malfunctions such as incorrect flag signal outputs due to the output voltage being 0 V, causing abnormality flags to be sent incorrectly.
Innovation Solution
A light-emitting element drive device with a transistor control unit, an output ground fault detection unit, a stop control unit, and a mask signal generation unit to manage the output ground fault detection signal during startup, ensuring accurate flag signaling and preventing premature transistor shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output ground fault protection unit detects the output voltage to determine ground fault, then the ground fault protection function is achieved, but during device startup the 0V output voltage causes misdetection and malfunction
Solution Approach 1:
The patent introduces a mask signal as an intermediary element that mediates between the output voltage detection and the ground fault determination. The mask signal temporarily suppresses the ground fault detection function during startup when output voltage is 0V, preventing misdetection. This allows the protection function to operate reliably only when output voltage exceeds a threshold, resolving the contradiction between achieving protection and avoiding false positives during initialization.
2Reliability
If the controller turns off the transistor when output voltage is low, then thermal breakdown is prevented, but during startup this causes premature shutdown and malfunction
Solution Approach 1:
The patent applies preliminary action by establishing a voltage threshold condition before the ground fault protection function becomes active. During startup, the output voltage naturally remains below this threshold, which preliminarily disables the protection function until the voltage rises above the threshold. This preliminary conditioning prevents premature transistor shutdown during normal startup while maintaining protection capability when voltage is low due to actual ground faults.
3Reliability
If the output ground fault detection is activated immediately on power on, then protection is available, but misdetection occurs due to 0V output voltage
Solution Approach 1:
The patent implements a dynamic ground fault detection mechanism where the detection threshold and functionality change based on output voltage level. When output voltage is below the threshold (including during startup at 0V), the detection function is suppressed. When voltage exceeds the threshold, detection becomes active. This dynamic adaptation resolves the contradiction by making protection availability conditional on voltage level, ensuring accurate detection only when meaningful voltage levels are present.
Data Source
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AI summary
Provided is a light-emitting element drive device including a transistor control unit arranged to drive and control a transistor connected to a light-emitting element, an output ground fault detection unit arranged to output an output ground fault detection signal corresponding to the voltage level at a connection node between the light-emitting element and the transistor, a stop control unit arranged to stop driving the transistor when the output ground fault detection signal indicates an output ground fault, and a mask signal generation unit arranged to generate a mask signal that masks the output ground fault detection signal on device startup.