PTC Over-Current Protection Device Mitigating NTC Behavior
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Solution Overview
Problem
Traditional over-current protection devices exhibit negative temperature coefficient (NTC) behavior after tripping, leading to incomplete current elimination, reduced voltage endurance, and inability to handle large currents and high power, especially in small-sized electronic products and high-temperature environments.
Innovation Solution
An over-current protection device comprising a PTC material layer with a fluoropolymer matrix, conductive ceramic filler, and a carbon-containing conductive filler, along with an inner filler like aluminum nitride or boron nitride, which maintains high hold current and power endurance while mitigating NTC behavior, ensuring suitable performance in small-sized electronic products and high-temperature applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnesium hydroxide is added to avoid hydrofluoric acid generation, then safety is improved, but NTC behavior occurs after trip causing incomplete current elimination
Solution Approach 1:
The patent removes magnesium hydroxide from the PTC material composition to eliminate the source of NTC behavior. By extracting this harmful component, the device achieves complete current elimination after trip without resistance decrease, while alternative safety measures are implemented elsewhere in the system.
Solution Approach 2:
The patent uses a composite PTC material consisting of fluoropolymer matrix combined with conductive ceramic powder and carbon-containing conductive filler. This composite formulation achieves both safety (no hydrofluoric acid generation) and performance (no NTC behavior) by selecting compatible materials that work together synergistically.
2Area of stationary object
If top-view area of PTC material layer is decreased to reduce device size, then miniaturization is achieved, but resistance increases and voltage endurance decreases
Solution Approach 1:
The patent changes the material parameters of the PTC layer by selecting fluoropolymer with specific melting point (>150°C) and optimizing conductive filler composition and distribution. These parameter changes enable high hold current density and voltage endurance even in miniaturized devices with reduced area.
Solution Approach 2:
The patent employs a composite material system with fluoropolymer matrix and optimized conductive filler combination that achieves superior electrical properties. This composite formulation allows the device to maintain high voltage endurance and hold current capability despite reduced top-view area, enabling successful miniaturization.
3Length of stationary object
If thickness of PTC material layer is reduced to minimize device profile, then compactness is improved, but voltage endurance is reduced making device susceptible to breakdown
Solution Approach 1:
The patent uses a composite PTC material with fluoropolymer matrix and optimized conductive filler that provides enhanced electrical strength. This composite structure maintains excellent voltage endurance even at reduced thickness, allowing the device to achieve compact profile without sacrificing breakdown resistance.
Solution Approach 2:
The patent optimizes material parameters including fluoropolymer selection with melting point above 150°C and precise control of conductive filler content and distribution. These parameter optimizations enable the thin PTC layer to withstand high voltages, achieving both compactness and high voltage endurance.
4Reliability
If conventional PTC material is used to achieve low resistance, then normal operation is enabled, but NTC behavior occurs after trip preventing complete current elimination
Solution Approach 1:
The patent extracts magnesium hydroxide from the material composition to eliminate NTC behavior. By removing this component, the device achieves reliable current elimination after trip, and the material complexity is managed through simplified formulation with fluoropolymer, conductive ceramic, and carbon-containing filler only.
Solution Approach 2:
The patent develops a composite PTC material with fluoropolymer matrix and conductive fillers that inherently prevents NTC behavior. This composite approach achieves both low resistance for normal operation and complete current elimination after trip, with material complexity optimized through careful selection of compatible components.
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 device achieves high hold current and power per unit area, excellent voltage endurance, and resistance retention within specific ratios, preventing NTC behavior, thus effectively protecting against large currents and high power in compact, high-temperature environments.
Implementation Method 1
the resistance of the PTC material layer remains extremely low at normal temperatures... when an over-current or an over-temperature event occurs in the circuit or cell, the resistance will instantaneously increase to a high resistance state
Implementation Method 2
a polymer matrix comprising at least one fluoropolymer with a melting point temperature higher than 150° C.
Implementation Method 3
The PTC material layer has a resistivity less than 0.05 Ω·cm... A conductive ceramic filler of a resistivity less than 500μΩ·cm is dispersed in the polymer matrix
Data Source
AI summary
An over-current protection device comprises first and second electrode layers and a PTC material layer laminated therebetween. The PTC material layer comprises a polymer matrix, a conductive ceramic filler, a carbon-containing conductive filler, and an inner filler. The polymer matrix comprises a fluoropolymer having a melting point higher than 150° C. The inner filler is selected from one of aluminum nitride, silicon carbide, zirconium oxide, boron nitride, graphene, aluminum oxide, or any mixtures thereof, and comprises 2-10% by volume of the PTC material layer. The over-current protection device is able to mitigate negative temperature coefficient (NTC) behavior after trip of device, and achieves high hold current and high endurable power.