Parallel PTC Circuit Protection Structure for Thermal Stability
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Solution Overview
Problem
Existing circuit protection devices face issues with poor resistance recovery, high electrical resistance, and thermal instability due to thermal expansion, which limits their miniaturization and application in modern electronic devices requiring larger current flow.
Innovation Solution
A circuit protection device with two temperature-sensitive resistors connected in parallel, featuring insulating layers with lower thermal expansion coefficients, external electrodes for enhanced heat dissipation, and notches to mitigate thermal stress, packaged with insulation material to stabilize the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of the circuit protection device is reduced, then the device occupies less space, but heat accumulates more easily leading to low hold current and poor thermal stability
Solution Approach 1:
The device is divided into multiple PTC layers (first PTC layer and second PTC layer) with insulating layers in between, allowing heat dissipation through multiple pathways and reducing heat accumulation in a compact form factor
Solution Approach 2:
Insulating layers with lower CTE than the PTC material are introduced as intermediary elements between PTC layers and metal foils. These insulating layers act as thermal and mechanical buffers, improving heat management and structural stability in the miniaturized device
2Reliability
If the PTC material undergoes phase transition during tripping, then over-current protection is achieved, but the tremendous volume change causes the material to cannot fully return to original structure resulting in poor resistance recovery
Solution Approach 1:
The patent introduces insulating layers with specific CTE parameters lower than the PTC material to compensate for the volume expansion during phase transition. This parameter matching approach allows the PTC material to undergo necessary volume changes for protection while maintaining structural integrity and resistance recovery through the constraining effect of the insulating layers
3Strength
If the electrically conductive layers are thickened to increase structural strength, then resistance recovery improves, but the device size increases
Solution Approach 1:
The patent uses composite material structures combining PTC material layers with insulating layers having lower CTE. This composite approach provides structural strength and thermal management without requiring thick metal foils, maintaining device compactness while improving resistance recovery through the composite layer system
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 solution reduces electrical resistance, increases current flow, and enhances thermal stability, allowing for a smaller device size while maintaining low resistance and improved resistance recovery.
Implementation Method 1
the electrical resistance of conductive composite materials having a positive temperature coefficient (PTC) characteristic is very sensitive to temperature variation
Implementation Method 2
When the current passing through the conductive paths and makes the temperature of device increase to a temperature exceeding the phase transition temperature of the polymer (e.g., the melting point of the polymer)
Implementation Method 3
Both the upper insulating layer and the lower insulating layer have thermal expansion coefficients lower than that of a positive temperature coefficient (PTC) layer of the circuit protection device
Implementation Method 4
at least one external electrode is provided. Its surface area, position to be placed, and length to be extended are taken into consideration and adjusted accordingly, by which heat dissipation is enhanced
Data Source
AI summary
A circuit protection device includes a first temperature sensitive resistor, a second temperature sensitive resistor, an electrically insulating multilayer, a first and second electrode layer, and at least one external electrode. The first temperature sensitive resistor and the second temperature sensitive resistor are electrically connected in parallel, and have a first upper electrically conductive layer and a second lower electrically conductive layer, respectively. The electrically insulating multilayer includes an upper insulating layer, a middle insulating layer, and a lower insulating layer. The upper insulating layer is between the first upper electrically conductive layer and the first electrode layer. The middle layer is laminated between the first temperature sensitive resistor and the second temperature sensitive resistor. The lower insulating layer is between the second lower electrically conductive layer and the second electrode layer. The external electrode is disposed on the first electrode layer, and extends beyond a peripheral wall along a horizontal direction.