Circuit protection devices comprising PTC element

Claim 2

An electrical circuit which comprises (1) a source of electrical power having a voltage of V volts; (2) a circuit protection device comprising at least two electrodes and a PTC element which has a switching temperature T s and which comprises a polymer component and, dispersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of generally columnar shape; and (3) a damageable circuit component which is damaged if the current flowing through it exceeds a value i damage amps for a time t seconds, where t is 30; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device; (B) said device is at a temperature T dn and has a resistance R dn ; (C) said device is in contact with a medium which is at a temperature T n ; (D) a current less than i damage flows through said damageable circuit component; and (E) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; said device having an electrical power/temperature relationship and being capable of losing heat at a rate such that if new electrical elements comprising a new power source and a switch are introduced into the circuit or a part of the circuit so that a fault test circuit is created in which, when said switch is closed a test cycle is initiated and, (a) there is an initial fault current flowing through said damageable circuit component which exceeds i damage ; (b) there is an initial fault current flowing through said device which results in a computed current density in the PTC element in the first of the test cycles defined below which reaches a maximum of 1000 amps/inch 2 ; (c) said device and said damageable circuit component are in series; and (d) the sum of the iniital potential drop over said device and the initial potential drop over said damageable circuit component is V int , where V int is at least 120 volts and at least 1.5×V; then if the fault test circuit is subjected to N successive test cycles, where N is 5, in each of which test cycles the switch is closed for 5 seconds, the switch is then opened and the device is allowed to cool to T dn before the next test cycle is carried out, then in each of said test cycles, the result of closing the switch is that the device generates heat by H 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the current to fall, and thereafter the current through the damageable circuit component reaches a stable value which is less than i damage , the potential drop over the device reches a stable value which is the higher of 150 volts and 1.5×V, and the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat by I 2 R heating is equal to the rate at which heat is lost from the device; and after said test cycles have been completed, the device has a resistance at T dn which is less than 3×R dn .

Claim 3

A circuit according to claim 1 wherein said source of electrical power is a DC source of voltage at most 75 volts and said new power source is an AC source.

Claim 4

A circuit according to claim 1 wherein said new power source is an AC source of voltage at least 220 volts and in each of the test cycles the potential drop over the device reaches a stable value substantially equal to the voltage of the new power source.

Claim 5

A circuit according to claim 1 which is a line circuit of a telephone system.

Claim 6

A circuit according to claim 4 wherein each leg of the circuit contains a said device.

Claim 7

A circuit according to claim 1 which is a supervisory circuit of a telephone system.

Claim 8

A circuit according to claim 6 wherein each leg of the circuit contains a said device.

Claim 9

A circuit according to claim 1 wherein, in the circuit protection device, the PTC element provides the sole electrical connection means between the electrodes.

Claim 10

An electrical circuit which comprises (1) a source of electrical power having a voltage of V volts; (2) a circuit protection device comprising at least two electrodes and a PTC element which has a switching temperature T s and which comprises a polymer component and, dispersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of generally columnar shape; and (3) a damageable circuit component which is damaged if the current flowing through it exceeds a value i damage amps for a time t seconds, where t is 30; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device: (B) said device is at a temperature T dn and has a resistance R dn ; (C) said device is in contact with a medium which is at a temperature T n ; (D) a current less than i damage flows through said damageable circuit component; and (E) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; said device having an electrical power/temperature relationship and being capable of losing heat at a rate such that if new electrical elements comprising a new power source and a switch are introduced into the circuit or a part of the circuit so that a fault test circuit is created in which, when said switch is closed a test cycle is initiated and, (a) there is an initial fault current flowing through said damageable circuit component which exceeds i damage ; (b) there is an initial fault current flowing through said device which is the higher of 1 amp and 3×i crit where i crit is the maximum current which, when it flows through the device in the circuit, causes the device to generate heat by I 2 R heating at a rate equal to the rate at which heat can be lost from the device; (c) said device and said damageable circuit component are in series; and (d) the voltage is such that the peak potential drop over said device in the first of the test cycles defined below is 240 volts; then if the fault test circuit is subjected to N successive test cycles, where N is 5, in each of which test cycles the switch is closed for 30 seconds, the switch is then opened and the device is allowed to cool to T dn before the next test cycle is carried out, then in each of said test cycles, the result of closing the switch is that the device generates heat by I 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the current through the damageable circuit component reaches a stable value which is less than i damage and the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat by the I 2 R heating is equal to the rate at which heat is lost from the device; and after said test cycles have been completed, the device has a resistance at T dn which is less than 3×R dn .

Claim 11

An electrical circuit which comprises (1) a source of electrical power having a voltage of V volts; (2) a circuit protection device comprising at least two electrodes and a PTC element which has a switching temperature T s and which comprises a polymer component and, dispersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of generally columnar shape; and (3) a damageable circuit component which is damaged if the current flowing through it exceeds a value i damage amps for a time t seconds, where t is 30; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device: (B) said device is at a temperature T dn and has a resistance R dn ; (C) said device is in contact with a medium which is at a temperature T n ; (D) a current less than i damage flows through said damageable circuit component; and (E) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; said device having an electrical power/temperature relationship and being capable of losing heat at a rate such that if new electrical elements comprising a new power source and a switch are introduced into the circuit or a part of the circuit so that a fault test circuit is created in which, when said switch is closed a test cycle is initiated and, (a) there is an initial fault current flowing through said damageable circuit component which exceeds i damage ; (b) there is an initial fault current flowing through said device which is the higher of 1 amp and 3×i crit where i crit is the maximum current which, when it flows through the device in the circuit, causes the device to generate heat by I 2 R heating at a rate equal to the rate at which heat can be lost from the device; (c) said device and said damageable circuit component are in series; and (d) the voltage is such that the peak potential drop over said device in the first of the test cycles defined below is 240 volts; then if the fault test circuit is subjected to N successive test cycles, where N is 5, in each of which test cycles the switch is closed for 30 seconds, the switch is then opened and the device is allowed to cool to T dn before the next test cycle is carried out, then in each of said test cycles, the result of closing the switch is that the device generates heat by I 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the current through the damageable circuit component reaches a stable value which is less than i damage and the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat by the I 2 R heating is equal to the rate at which heat is lost from the device; and after said test cycles have been completed, the device has a resistance at T dn which is less than 3×R dn .

Claim 12

A circuit according to claim 9 wherein said source of electrical power is a DC source of voltage at most 75 volts and said new power source is an AC source.

Claim 13

A circuit according to claim 10 wherein said new power source is an AC source of voltage at least 220 volts and in each of the test cycles the potential drop over the device reaches a stable value substantially equal to the voltage of the new power source.

Claim 14

A circuit according to claim 9 which is a line circuit of a telephone system.

Claim 15

A circuit according to claim 12 wherein each leg of the circuit contains a said device.

Claim 16

A circuit according to claim 9 which is a supervisory circuit of a telephone system.

Claim 17

A circuit according to claim 14 wherein each leg of the circuit contains a said device.

Claim 18

A circuit according to claim 9 wherein, in the circuit protection device, the PTC element provides the sole electrical connection means between the electrodes.

Claim 19

An electrical circuit which comprises (1) a circuit protection device comprising at least two electrodes and a PTC element composed of a PTC composition which has a switching temperature T s and which comprises a polymer component and, dispersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of a generally columnar shape; (2) a source of electrical power having a voltage of V 1 volts which is at least 120 volts; and (3) other circuit elements which are connected in series with said PTC element and which have an impedance R L ohms; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device; (B) said device is at a temperature T dn and has a resistance R dn which is less than 0.5×R L ohm and less than V 1 ohms; (C) said device is in contact with a medium which is at a temperature T n ; and (D) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; and said device having an electrical power/temperature relationship and being capable of losing heat to said medium at a rate such that (a) if elements of the circuit are changed so that the current flowing through said device increases slowly from i n while maintaining T n substantially constant, then the temperature of the device increases slowly until the circuit reaches a critical operating condition in which (i) the equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device is unstable, (ii) the device is at a temperature T d trip and has a resistance R d trip, (iii) the rate at which the resistance of the devices changes with temperature ( dR d trip/ dT d trip), is positive, and (iv) the current has a value i crit ; and (b) if elements of the circuit are further changed so that the current flowing through the device increases to 2×i crit , while maintaining T n substantially constant, then the rate at which the device generates heat by I 2 R heating exceeds the rate at which heat can be lost from the device and thus causes the temperature and the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the circuit reaches a high temperature high resistance stable operating condition in which (i) the rate at which the device generates heat by I 2 R heating is equal to the rate at which heat is lost from the device; and (ii) the device is at a temperature T d latch which is such that the ratio of the power in the circuit in the normal operating condition to the power in the circuit in the high temperature high resistance stable operating condition, the Switching Ratio, is at least 8; and said device, after having been subjected to the test routine defined below, (i) having a resistance at T dn which is less than 3×R dn , less than 0.5×R L , and less than V 1 ohms; and (ii) having an electrical power/temperature relationship such that, when the device is replaced in said electrical circuit after having been subjected to said test routine, the electrical circuit (a) has a normal operating condition as defined, and (b) when the elements of the circuit are changed so as to increase the current in the circuit, the circuit first reaches a critical operating condition as defined and then reaches a high temperature high resistance stable operating condition as defined; said test routine consisting of placing the device in a test circuit which consists essentially of the device, a switch, a fixed resistor of resistance of R 1 ohms and a source of electrical power having a voltage of V 1 volts, the device being in contact with said medium at said temperature T n and R 1 being such that the computed current density in the PTC element in the first of the test cycles defined below reaches a maximum of 1000 amp/inch 2 , and subjecting the test circuit to N successive test cycles, where N is 5; in each of which test cycles the switch is closed for 5 seconds, whereby the device initially generates heat by I 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat is equal to the rate at which heat is lost from the device; the switch is opened; and the device is allowed to cool to T n before the next test cycle is carried out.

Claim 20

An electrical circuit which comprises (1) a circuit protection device comprising at least two electrodes and a PTC element composed of a PTC composition which has a switching temperature T s and which comprises a polymer component and, dispersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of a generally columnar shape; (2) a source of electrical power having a voltage of V 1 volts which is at least 120 volts; and (3) other circuit elements which are connected in series with said PTC element and which have an impedance R L ohms; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device; (B) said device is at a temperature T dn and has a resistance R dn which is less than 0.5×R L ohm and less than V 1 ohms; (C) said device is in contact with a medium which is at a temperature T n ; and (D) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; and said device having an electrical power/temperature relationship and being capable of losing heat to said medium at a rate such that (a) if elements of the circuit are changed so that the current flowing through said device increases slowly from i n while maintaining T n substantially constant, then the temperature of the device increases slowly until the circuit reaches a critical operating condition in which (i) the equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device is unstable, (ii) the device is at a temperature T d trip and has a resistance R d trip, (iii) the rate at which the resistance of the devices changes with temperature ( dR d trip/ dT d trip), is positive, and (iv) the current has a value i crit ; and (b) if elements of the circuit are further changed so that the current flowing through the device increases to 2×i crit , while maintaining T n substantially constant, then the rate at which the device generates heat by I 2 R heating exceeds the rate at which heat can be lost from the device and thus causes the temperature and the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the circuit reaches a high temperature high resistance stable operating condition in which (i) the rate at which the device generates heat by I 2 R heating is equal to the rate at which heat is lost from the device; and (ii) the device is at a temperature T d latch which is such that the ratio of the power in the circuit in the normal operating condition to the power in the circuit in the high temperature high resistance stable operating condition, the Switching Ratio, is at least 8; and said device, after having been subjected to the test routine defined below, (i) having a resistance at T dn which is less than 3×R dn , less than 0.5×R L , and less than V 1 ohms; and (ii) having an electrical power/temperature relationship such that, when the device is replaced in said electrical circuit after having been subjected to said test routine, the electrical circuit (a) has a normal operating condition as defined, and (b) when the elements of the circuit are changed so as to increase the current in the circuit, the circuit first reaches a critical operating condition as defined and then reaches a high temperature high resistance stable operating condition as defined; said test routine consisting of placing the device in a test circuit which consists essentially of the device, a switch, a fixed resistor of resistance of R 1 ohms and a source of electrical power having a voltage of V 1 volts, the device being in contact with said medium at said temperature T n and R 1 being such that the computed current density in the PTC element in the first of the test cycles defined below reaches a maximum of 1000 amp/inch 2 , and subjecting the test circuit to N successive test cycles, where N is 5; in each of which test cycles the switch is closed for 5 seconds, whereby the device initially generates heat by I 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat is equal to the rate at which heat is lost from the device; the switch is opened; and the device is allowed to cool to T n before the next test cycle is carried out.

Claim 21

A circuit according to claim 17 wherein V 1 is at least 150 volts AC.

Claim 22

A circuit according to claim 18 wherein V 1 is at least 240 volts AC.

Claim 23

A circuit according to claim 17 wherein, in the circuit protection device, the PTC element provides the sole electrical connection means between the electrodes.

Claim 24

An electrical circuit which comprises (1) a circuit protection device comprising at least two electrodes and a PTC element composed of a PTC composition which has a switching temperature T s and which comprises a polymer component and, despersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of a generally columnar shape; (2) a source of electrical power having a voltage V 2 volts which is at least 240 volts; and (3) other circuit elements which are connected in series with said PTC element and which have an impedance R L ohms; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device; (B) said device is at a temperature T dn and has a resistance R dn which is less than 0.5×R L ohm and less than V 2 ohms; (C) said device is in contact with a medium which is at a temperature T n ; and (D) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; and said device having an electrical power/temperature relationship and being capable of losing heat to said medium at a rate such that (a) if elements of the circuit are changed so that the current flowing through said device increases slowly from i n while maintaining T n substantially constant, then the temperature of the device increases slowly until the circuit reaches a critical operating condition in which (i) the equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device is unstable, (ii) the device is at a temperature T d trip and has a resistance R d trip, (iii) the rate at which the resistance of the devices changes with temperature ( dR d trip/ dT d trip), is positive, and (iv) the current has a value i crit ; and (b) if elements of the circuit are further changed so that the current flowing through the device increases to 2×i crit , while maintaining T n substantially constant, then the rate at which the device generates heat by I 2 R heating exceeds the rate at which heat can be lost from the device and thus causes the temperature and the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the circuit reaches a high temperature high resistance stable operating condition in which (i) the rate at which the device generates heat by I 2 R heating is equal to the rate at which heat is lost from the device; and (ii) the device is at a temperature T d latch which is such that the ratio of the power in the circuit in the normal operating condition to the power in the circuit in the high temperature high resistance stable operating condition, the Switching Ratio, is at least 8; and said device, after having been subjected to the test routine defined below, (1) having a resistance at T dn which is less then 3×R dn , less than 0.5×R L , and less than V 2 ohms; and (ii) having an electrical power/temperature relationship such that, when the device is replaced in said electrical circuit after having been subjected to said test routine, the electrical circuit (a) has a normal operating condition as defined, and (b) when the elements of the circuit are changed so as to increase the current in the circuit, the circuit first reaches a high resistance stable operating condition as defined; said test routine consisting of placing the device in a test circuit which consists essentially of the device, a switch, a fixed resistor of resistance R 2 ohms and a source of electrical power having a voltage of V 2 volts, the device being in contact with said medium at said temperature T n , and R 2 being such that in the first of the test cycles defined below the peak current through the device is the higher of 1 amp and 3×i crit , and subjecting the test circuit to N successive test cycles, where N is 5; in each of which test cycles the switch is closed for 30 seconds, whereby the device initially generates heat by I 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat is equal to the rate at which heat is lost from the device; the switch is opened; and the device is allowed to cool to T n before the next cycle is carried out.

Claim 25

An electrical circuit which comprises (1) a circuit protection device comprising at least two electrodes and a PTC element composed of a PTC composition which has a switching temperature T s and which comprises a polymer component and, despersed in said polymer component, a particulate filler component which comprises a conductive filler, each of said electrodes being in the form of a wire or strip which is at least partially embedded in the PTC element so that it has an electrically active surface of a generally columnar shape; (2) a source of electrical power having a voltage V 2 volts which is at least 240 volts; and (3) other circuit elements which are connected in series with said PTC element and which have an impedance R L ohms; said electrical circuit having a normal operating condition in which said device is in a low temperature low resistance stable operating condition and (A) a current i n flows through said device; (B) said device is at a temperature T dn and has a resistance R dn which is less than 0.5×R L ohm and less than V 2 ohms; (C) said device is in contact with a medium which is at a temperature T n ; and (D) there is a stable equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device; and said device having an electrical power/temperature relationship and being capable of losing heat to said medium at a rate such that (a) if elements of the circuit are changed so that the current flowing through said device increases slowly from i n while maintaining T n substantially constant, then the temperature of the device increases slowly until the circuit reaches a critical operating condition in which (i) the equilibrium between the rate at which the device generates heat by I 2 R heating and the rate at which heat is lost from the device is unstable, (ii) the device is at a temperature T d trip and has a resistance R d trip, (iii) the rate at which the resistance of the devices changes with temperature ( dR d trip/ dT d trip), is positive, and (iv) the current has a value i crit ; and (b) if elements of the circuit are further changed so that the current flowing through the device increases to 2×i crit , while maintaining T n substantially constant, then the rate at which the device generates heat by I 2 R heating exceeds the rate at which heat can be lost from the device and thus causes the temperature and the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the circuit reaches a high temperature high resistance stable operating condition in which (i) the rate at which the device generates heat by I 2 R heating is equal to the rate at which heat is lost from the device; and (ii) the device is at a temperature T d latch which is such that the ratio of the power in the circuit in the normal operating condition to the power in the circuit in the high temperature high resistance stable operating condition, the Switching Ratio, is at least 8; and said device, after having been subjected to the test routine defined below, (1) having a resistance at T dn which is less then 3×R dn , less than 0.5×R L , and less than V 2 ohms; and (ii) having an electrical power/temperature relationship such that, when the device is replaced in said electrical circuit after having been subjected to said test routine, the electrical circuit (a) has a normal operating condition as defined, and (b) when the elements of the circuit are changed so as to increase the current in the circuit, the circuit first reaches a high resistance stable operating condition as defined; said test routine consisting of placing the device in a test circuit which consists essentially of the device, a switch, a fixed resistor of resistance R 2 ohms and a source of electrical power having a voltage of V 2 volts, the device being in contact with said medium at said temperature T n , and R 2 being such that in the first of the test cycles defined below the peak current through the device is the higher of 1 amp and 3×i crit , and subjecting the test circuit to N successive test cycles, where N is 5; in each of which test cycles the switch is closed for 30 seconds, whereby the device initially generates heat by I 2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the resistance of the device to rise rapidly and the circuit current to fall, and thereafter the device reaches a high temperature high resistance stable operating condition in which the rate at which the device generates heat is equal to the rate at which heat is lost from the device; the switch is opened; and the device is allowed to cool to T n before the next cycle is carried out.

Claim 26

A circuit according to claim 21 wherein V is at least 150 volts AC.

Claim 27

A circuit according to claim 22 wherein V 2 is at least 240 volts AC.

Claim 28

A circuit according to claim 21 wherein, in the circuit protection device, the PTC element provides the sole electrical connection means between the electrodes.