LED Array Short Detection Circuit Using Voltage Change Rate

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Solution Overview

Problem

Conventional LED driving apparatuses incorrectly detect temporary increases in feedback voltage as shorts in LED arrays, leading to false detection of faults.

Innovation Solution

A detection circuit that measures feedback voltages and uses preset reference voltages to differentiate between normal and abnormal conditions, with a hysteresis comparator controlling the detection to prevent false positives during abnormal feedback voltage fluctuations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If feedback voltage measurement is used to detect LED array shorts, then short detection capability is provided, but false detection occurs during temporary voltage increases

Engineering Contradiction:

Improveshort detection accuracyVSAvoidfeedback voltage measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the detection parameter from absolute feedback voltage level to voltage change rate (dV/dt). By detecting the rate of change rather than the absolute value, the system can distinguish between normal temporary voltage increases (slow change) and actual short conditions (rapid change), thereby resolving the false detection problem while maintaining detection accuracy

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a voltage change rate calculation unit as an intermediary between the feedback voltage measurement and the short detection decision. This intermediary processes the raw voltage signal to extract the change rate, which then serves as the actual detection criterion, filtering out false positives caused by temporary voltage fluctuations

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If constant current source settling time is considered, then stable current delivery is achieved, but temporary feedback voltage increases are detected as shorts

Engineering Contradiction:

Improvecurrent stabilityVSAvoidshort detection reliability

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent applies preliminary action by implementing a delay mechanism that waits for the constant current source to settle before performing short detection. This ensures that temporary voltage increases during the settling period are not misinterpreted as faults, while still enabling timely detection of actual shorts after stabilization

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent makes the detection system dynamic by introducing time-based conditions and delay mechanisms. The detection timing is adjusted dynamically based on the settling state of the constant current source, allowing the system to adapt its detection behavior to different operational phases and avoid false detections during transient periods

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS9888552B2Detecting circuit for short of LED array and LED driving apparatus using the same

Publication Date: 2018.02.06 MAGNACHIP SEMICON LTD

AI summary

A detection circuit configured to detect a short in a plurality of LED arrays is provided. The detection circuit includes a voltage measuring unit, a short detecting unit, and a detection control unit. The voltage measuring unit is configured to measure respective feedback voltages of the plurality of LED arrays and output a lowest measured feedback voltage as a first feedback voltage. The short detecting unit is configured to detect the short in the LED arrays using the measured feedback voltages. The detection control unit is configured to control the short detecting unit to stop short detection operation, when the first feedback voltage exceeds a first preset reference voltage.