Integrated NTC Resistor Fuse for Inrush Current Limiting

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Solution Overview

Problem

Existing circuit protection devices require separate components for overcurrent protection and current limitation, which occupy more space and are costly, whereas a single device capable of providing both functions is desirable, especially in electronic devices that experience high initial currents during startup.

Innovation Solution

An integral circuit protection device is developed, featuring a substrate with a resistive material and a fuse element in electrical series, where the resistive material is a negative temperature coefficient (NTC) thermistor that reduces resistance with increasing temperature, allowing for both inrush current limitation and overcurrent protection in a compact form.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If separate fuse element and resistor are used for overcurrent protection and current limitation, then protection function is provided, but device occupies more space and increases cost

Engineering Contradiction:

Improveovercurrent protectionVSAvoiddevice space

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent combines a fuse element and a resistor into a single integrated circuit protection device. The fuse element and resistor are disposed in electrical series between first and second terminals within a single device structure, eliminating the need for separate components and reducing the overall space occupied while maintaining both overcurrent protection and current limitation functions.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If separate fuse element and resistor are used, then protection function is provided, but manufacturing cost increases

Engineering Contradiction:

Improveovercurrent protectionVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

3Use of energy by moving object

If NTC material is used for resistive substrate, then inrush current limitation is improved, but temperature management becomes critical

Engineering Contradiction:

Improveinrush current limitationVSAvoidtemperature management

Core Design Contradiction:

Use of energy by moving objectVSTemperature

Solution Approach 1:

The patent introduces a thermally conductive substrate that couples the fuse element to a heat sink. The substrate has higher thermal conductivity than the surrounding environment, facilitating heat transfer from the fuse element to the heat sink. This thermal management mechanism allows the NTC resistor to operate at optimal temperatures while preventing excessive heat buildup that would affect its resistance characteristics.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The integrated device effectively limits initial inrush currents and provides overcurrent protection, reducing the risk of component damage while minimizing space and cost, with enhanced performance during overload faults and efficient energy usage.

Implementation Method 1

the resistive material is a negative temperature coefficient (NTC) thermistor that reduces resistance with increasing temperature

Methodology Applied

Scientific EffectNegative temperature coefficient (NTC): Thermistor

Implementation Method 2

In the case of a short circuit, an overcurrent fuse will open if the current exceeds a predetermined value

Methodology Applied

Scientific EffectFusing: Melting

Data Source

PatentUS8076751B2Circuit protection device including resistor and fuse element

Publication Date: 2011.12.13 LITTELFUSE INC

AI summary

An integral circuit protection device includes a substrate disposed between first and second terminals. The substrate is composed of a resistive material. A first conductive layer is disposed on a first surface of the substrate and in electrical contact with the first terminal. A second conductive layer is disposed on a second surface of the substrate. A first electrically insulating layer is disposed on the second conductive layer and substantially covers the second conductive layer. The first electrically insulating layer includes an aperture. A fuse element is disposed on the first electrically insulating layer and is in electrical contact with the second conductive layer through the aperture and in electrical contact with the second terminal. The fuse element is in electrical series with the resistive material. A second electrically insulating layer is disposed over the fuse element.