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Self Protecting Switch

IP.com Disclosure Number: IPCOM000115703D
Publication Date: 2005-Mar-30
Document File: 1 page(s) / 14K

Publishing Venue

The IP.com Prior Art Database

Abstract

Switches using a carbon pill to bridge two printed circuit board contacts are now common in automotive applications.

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Self Protecting Switch

Switches using a carbon pill to bridge two printed circuit board contacts are now common in automotive applications. Figure 1. illustrates the principle.

               
   
 
     
   

Simplified view of carbon pill supported by flexible rubber membrane over fingers on PCB track

 
 
       
 
 

Figure 1.

Polymers loaded with a critical amount of carbon are used as PTC (positive temperature coefficient) devices. These devices are used as self resetting fuses. A pill of PTC material connected in series with an electrical circuit will present a relatively low resistance at normal temperatures, but will become high resistance at elevated temperature, thus protecting itself and the circuit in which it is connected from overheating.

A pill of PTC material used to replace the carbon pill in a switch as illustrated in figure 1 will protect the switch and the associated circuit against over-current and its thermal effects.

Carbon is not the only PTC material and other PTC materials currently used in PTC devices could also be used in this type of self protected switch, subject to their mechanical and electrical properties.

Disclosed anonymously