Series LED Short Circuit Detection Using Parallel Resistors

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Solution Overview

Problem

Existing semiconductor light source devices connected in series face challenges in detecting short circuits due to variations in LED drive characteristics and operating voltages, making it difficult to set a threshold voltage for abnormality detection, especially as the number of LEDs increases.

Innovation Solution

Incorporating a plurality of resistors connected in parallel with each semiconductor light source element, with a determination unit that determines the number of short-circuited elements by measuring voltages applied to the resistors when the light source elements are not driven, allowing for accurate detection of short circuits without being affected by variations in the LEDs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If voltage monitoring is used to detect short circuits in series-connected LEDs, then abnormality detection capability is improved, but measurement precision deteriorates due to variations in LED drive characteristics and operating voltages

Engineering Contradiction:

Improveabnormality detection capabilityVSAvoidshort circuit detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The invention divides the series-connected LED string into individual LED units by connecting a resistor in parallel with each LED. This segmentation allows independent monitoring of each LED's voltage state, enabling precise detection of short circuits without being affected by variations in other LEDs' operating characteristics

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention introduces resistors as intermediary elements connected in parallel with each LED. These resistors serve as mediators that convert the hard-to-measure LED voltage variations into easily detectable voltage signals across the resistors, enabling accurate short circuit detection while isolating the measurement from LED characteristic variations

Inventive Principle:

Principle #24Intermediary (Mediator)

2Illumination intensity

If the number of LEDs connected in series is increased to achieve desired light output, then illumination intensity is improved, but difficulty of detecting and measuring short circuits increases

Engineering Contradiction:

Improvelight outputVSAvoidshort circuit detection difficulty

Core Design Contradiction:

Illumination intensityVSDifficulty of detecting and measuring

Solution Approach 1:

By segmenting the long LED string into individually monitored units through parallel resistors, the invention makes it feasible to detect short circuits in high-count LED strings. Each segment can be independently monitored, transforming an unmanageable measurement problem into a series of simple binary detection tasks

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The parallel resistors enable each LED to essentially monitor itself through the voltage drop across its associated resistor. When an LED shorts, the voltage across its parallel resistor changes detectably, allowing the system to self-diagnose without complex external measurement equipment

Inventive Principle:

Principle #25Self-service

3Speed

If threshold voltage is set for abnormality detection in series-connected LEDs, then detection speed is improved, but reliability deteriorates due to inability to distinguish normal voltage variations from actual short circuits

Engineering Contradiction:

Improvedetection speedVSAvoiddetection accuracy

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The invention applies local quality by making each LED's monitoring independent through its dedicated parallel resistor. This localized approach allows threshold detection to be applied reliably to each individual LED based on its own characteristics, rather than using a global threshold that must accommodate all LEDs' variations

Inventive Principle:

Principle #3Local quality

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

This configuration enables reliable detection of short circuits with high accuracy, maintaining simplicity in the circuit design and reducing production costs, while ensuring consistent voltage measurement across the light source unit.

Implementation Method 1

a plurality of resistors, each of which is connected in parallel with one of the semiconductor light source elements, respectively; and a determination unit configured to determine the number of elements short-circuited in the semiconductor light source elements based on voltages applied to the resistors when driving of each of the semiconductor light source elements is being stopped

Methodology Applied

Scientific EffectOhm's Law: Ohm's Law

Data Source

PatentUS8684539B2Semiconductor light source device, semiconductor light source control method, and projection apparatus

Publication Date: 2014.04.01 CASIO COMPUTER CO LTD

AI summary

There is provided a semiconductor light source device including a plurality of semiconductor light source elements connected in series, a drive circuit configured to drive the semiconductor light source elements, a plurality of resistors, each of which is connected in parallel with one of the semiconductor light source elements, respectively, and a determination unit configured to determine the number of elements short-circuited in the semiconductor light source elements based on voltages applied to the resistors when driving of each of the semiconductor light source elements is being stopped.