Jelly Roll PTC Device for High Hold Current in Compact Form Factor
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Solution Overview
Problem
Existing PTC devices face limitations in achieving high hold currents in compact form factors due to restricted maximum surface area of PTC material, which is often constrained by the application's form factor, making it difficult to vary the thickness effectively.
Innovation Solution
A jelly roll-type PTC device configuration is employed, comprising a PTC material layer between overlapping electrode layers with an insulation layer, providing an electrically conductive pathway and insulating barrier, allowing for a larger surface area and higher hold currents in compact designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface area of PTC material is increased to achieve higher hold currents, then the hold current increases, but the device size increases beyond the compact form factor requirement
Solution Approach 1:
The patent transitions from a planar PTC material arrangement to a three-dimensional rolled configuration. Multiple layers of PTC material are stacked and rolled into a jelly roll structure, effectively utilizing the third dimension (depth/height) to increase the total surface area of PTC material without expanding the device's footprint. This dimensional transformation allows the device to maintain a compact form factor while achieving higher hold currents through increased PTC material surface area.
Solution Approach 2:
The patent employs a nested structure where multiple layers of PTC material, electrodes, and insulation are stacked one within another and rolled into a compact jelly roll configuration. Each layer is nested within the overall rolled structure, maximizing the density of PTC material within the constrained form factor. This nesting approach enables high surface area utilization in a compact volume.
2Reliability
If the thickness of PTC material is increased to achieve higher hold currents, then the hold current increases, but the manufacturing complexity increases due to difficulty in varying thickness
Solution Approach 1:
The patent divides the PTC material into multiple separate thin layers rather than using a single thick layer. Each layer can be manufactured with standard thickness using conventional processes, and then multiple layers are stacked and rolled together. This segmentation approach maintains manufacturing simplicity while achieving the equivalent electrical effect of a thicker material through increased surface area from multiple layers.
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 jelly roll configuration enables significantly higher hold currents in compact applications, effectively addressing the challenge of overcurrent and overtemperature protection in devices like cellular telephones by increasing the surface area of the PTC material within the same form factor.
Implementation Method 1
the PTC material layer providing an electrically conductive pathway between the overlapping first and second electrode layers
Implementation Method 2
the insulation layer providing an electrically insulating barrier between the first and second electrode layers
Implementation Method 3
When the temperature of the PTC material reaches an 'activation temperature,' the resistance of the PTC material increases sharply. This increase in resistance mitigates the current flowing through the PTC device
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
A jelly roll-type positive temperature coefficient (PTC) device comprising an insulation layer; a first electrode layer and a second electrode layer disposed on the insulation layer, the first and second electrode layers disposed in a coplanar, side-by-side, interdigitated relationship; and a PTC material layer disposed on the first and second electrode layers and covering interdigitated portions of the first and second electrode layers; wherein the insulation layer, first electrode layer, the second electrode layer, and the PTC material layer are rolled together to define a jelly roll structure with the PTC material layer providing an electrically conductive pathway between the interdigitated first and second electrode layers, and with the insulation layer providing an electrically insulating barrier between the first and second electrode layers.