Patent ID: 6862164

Claim:
A circuit protection arrangement which comprises (1) a first PTC device which (i) has a first switching temperature T s1 , (ii) has a resistance at 20° C. R 1 , (iii) has a hold current at a first specified temperature I H1 , and (iv) comprises (a) a first PTC resistive element composed of a first conductive polymer composition comprising a polymeric component, and, dispersed therein, a particulate conductive filler, and (b) first and second electrodes which are attached to the first PTC element; and (2) a second PTC device which (i) is electrically connected in series with the first PTC device, (ii) has a second switching temperature T s2 which is less than T s1 , (iii) has a resistance at 20° C. R 2 which is less than R 1 , (iv) has a hold current at the first specified temperature I H2 which is greater than I H1 , and (v) comprises (a) a second PTC resistive element composed of a second conductive polymer composition comprising a polymeric component, and, dispersed therein, a particulate conductive filler, and (b) third and fourth electrodes which are attached to the second PTC element; I H1 equaling I H2 at a critical temperature T crit , which is greater than the first specified temperature such that (A) at temperatures less than T crit , the first PTC device switches into a high resistance state and the circuit protection arrangement is resettable, and (B) at temperatures greater than T crit , the second PTC device switches into a high resistance state and initiates an action causing the circuit protection arrangement to permanently open.