Circuit protection device with a PTC element and a secondary fuse

Abstract

A circuit protection device (10) comprising:a primary fuse (14) anda positive temperature coefficient (PTC) device (16) and a secondary fuse (20) electrically connected in series with each other and in parallel with the primary fuse (14), wherein the secondary fuse (20) comprises a quantity of solder disposed on a dielectric surface, the dielectric surface having a dewetting property with respect to the solder such that when the solder is melted, the solder (20a, 20b) pulls away from the dielectric surface to create a galvanic opening.

Claims

[1] Circuit protection device (10) comprising: a primary fuse (14) and a positive temperature coefficient (PTC) device (16) and a secondary fuse (20) electrically connected in series with each other and in parallel with the primary fuse (14), the secondary fuse (20) comprising a quantity of solder disposed on a dielectric surface, the dielectric surface having a dewetting property with respect to the solder such that when the solder is melted, the solder (20a, 20b) pulls away from the dielectric surface to create a galvanic opening. [2] The circuit protection device (10) of claim 1, wherein the solder is SAC305 solder and the dielectric surface is formed by perfluoroalkoxy. [3] The circuit protection device (10) of claim 1, wherein the solder is a eutectic solder and the dielectric surface is formed by ethylenetetrafluoroethylene. [4] The circuit protection device (10) of claim 1, wherein the solder is a low melting point solder and the dielectric surface is formed by polyvinylidene fluoride. [5] The circuit protection device (10) of claim 1, wherein the primary fuse (14) is disposed on a first side of a dielectric substrate (12) and the PTC device (16) is connected to a second side of the dielectric substrate (12) opposite the first side by a dielectric cover (18) defining the dielectric surface. [6] Circuit protection device (10) according to claim 5, further comprising a first connecting line (37) and a second connecting line (35) for electrically connecting the circuit protection device (10) within an electrical circuit, wherein the first connecting line (37) is electrically connected to a first terminal (28) of the primary fuse (14) and to the secondary fuse (20), wherein the secondary fuse (20) is connected to a first electrode (38) of the PTC device (16), and wherein the second connecting line (35) is electrically connected to a second terminal (26) of the primary fuse (14) and to a second electrode (36) of the PTC device (16). [7] The circuit protection device (10) of claim 6, wherein the first connecting line (37) is connected to the secondary fuse (20) via an electrically conductive line (40), and wherein the secondary fuse (20) extends from the line (40) across the dielectric surface to the first electrode (38) of the PTC device (16). [8] The circuit protection device (10) of claim 7, wherein the dielectric cover (18) provides an electrically insulating barrier between the PTC device (16) and the first connecting line (37) and the line (40). [9] Circuit protection device (10) according to claim 6, wherein the first (37) and the second connecting line (35) are connected to the first (28) and the second terminal (26) of the primary fuse (14) respectively by a first (33) and a second electrically conductive via (31) formed in the dielectric substrate (12). [10] The circuit protection device (10) of claim 1, wherein the secondary fuse (20) has a melting temperature higher than a tripping temperature of a PTC element (34) of the PTC device (16). [11] The circuit protection device (10) of claim 1, wherein the PTC device (16) has a resistance greater than the resistance of the primary fuse (14) in its normal operating temperature range. [12] Circuit protection device (10) comprising: a dielectric substrate (12), a primary fuse (14) disposed on a first side of the dielectric substrate (12) and having a first (28) and second terminal (26) electrically connected to a corresponding first (32) and second conductor strand (30) on the dielectric substrate (12), a positive temperature coefficient (PTC) device (16) and a secondary fuse (20) electrically connected in series with each other and in parallel with the primary fuse (14), the PTC device (16) being attached to a second side of the dielectric substrate (12) via a dielectric cover (18) covering one end of the PTC device (16), the secondary fuse (20) comprising a quantity of solder extending from a first electrode (38) of the PTC device (16) to the dielectric cover (18), the dielectric cover (18) having a dewetting property with respect to the solder such that when the solder is melted, the solder (20a, 20b) pulls away from the dielectric cover (18) to create a galvanic opening, and a first connecting line (37) and a second connecting line (35) for electrically connecting the circuit protection device (10) within a circuit, wherein the first connecting line (37) is electrically connected to the first terminal (28) of the primary fuse (14) and to the secondary fuse (20), and wherein the second connecting line (35) is electrically connected to the second terminal (26) of the primary fuse (14) and to a second electrode (36) of the PTC device (16), wherein the first (37) and the second connecting line (35) are connected to the first (28) and second terminal (26) of the primary fuse (14) respectively by a first (33) and second electrically conductive via (31) formed in the dielectric substrate (12). [13] Circuit protection device (10) according to claim 12, wherein the first connecting line (37) is connected to the secondary fuse (20) via an electrically conductive line (40). [14] The circuit protection device (10) of claim 13, wherein the dielectric cover (18) provides an electrically insulating barrier between the PTC device (16) and the first connecting line (37) and the line (40). [15] The circuit protection device (10) of claim 12, wherein the solder is SAC305 solder and the dielectric cover (18) is formed from perfluoroalkoxy. [16] The circuit protection device (10) of claim 12, wherein the solder is a eutectic solder and the dielectric cover (18) is formed from ethylenetetrafluoroethylene. [17] The circuit protection device (10) of claim 12, wherein the solder is a low melting point solder and the dielectric cover (18) is formed of polyvinylidene fluoride. [18] Circuit protection device (10) according to claim 12, wherein the secondary fuse (20) has a melting temperature which is higher than the tripping temperature of a PTC element (34) of the PTC device (16). [19] The circuit protection device (10) of claim 12, wherein the PTC device (16) has a resistance in its normal operating temperature range that is greater than a resistance of the primary fuse (14).

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