Overcurrent protection circuits comprising combinations of PTC devices and switches

Claim 2

An electrical protection system which can be connected in series between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a control element which (1) has a relatively low resistance, R LOW , when a relatively low current, I NORMAL , is passing through it, and (2) is converted to a relatively high resistance, R FAULT , when the current through it increases from I NORMAL to a relatively high current, I FAULT ; b. a circuit interruption element which (1) is connected in series with the control element, (2) has a normal state when the current I NORMAL is passing through the control element, the normal state permitting the current I NORMAL to pass through the system, and (3) has a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; and c. a bypass element which (1) is connected in parallel with the series combination of the control element and the circuit interruption element, (2) is functionally linked to the circuit interruption element so that an increase in current passing through the bypass element can convert the circuit interruption element into the fault state, and (3) comprises (a) a relay coil which causes the circuit interruption element to move from its normal state to its fault state in response to increased current flowing in the bypass element, (b) a bypass resistor connected in series with the relay coil, and (c) a bypass switch which (i) is connected in series with the relay coil and in parallel with the bypass resistor, and (ii) is closed when the circuit switch is closed and open when the circuit switch is open; whereby, when the current through the system increases from I NORMAL to I FAULT d. the resistance of the control element increases from R LOW to R FAULT , e. an increased current passes through the bypass element, and f. the circuit interruption element is converted into the fault state.

Claim 3

A system according to claim 1 wherein the control element comprises a first PTC device.

Claim 4

A system according to claim 2 wherein the control element comprises a voltage clamping device connected in parallel with the first PTC device.

Claim 5

A system according to claim 1 wherein the circuit interruption element comprises a circuit switch having a normal state in which it is closed and a fault state in which it is open.

Claim 6

A system according to claim 1 wherein the bypass element comprises a PTC device, which a. is connected in series with the relay coil and the bypass resistor, and b. has a trip current which is less than the current which, when passed through the relay coil, will cause the circuit interruption element to change from its normal state to its fault state.

Claim 7

An electrical protection system which can be connected in series between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a control element which (1) has a relatively low resistance, R LOW when a relatively low current, I NORMAL , is passing through it, and (2) is converted to a relatively high resistance, R FAULT , when the current through it increases from I NORMAL to a relatively high current, I FAULT ; b. a circuit interruption element which (1) is connected in series with the control element, (2) has a normal state when the current I NORMAL is passing through the control element, the normal state permitting the current I NORMAL to pass through the system, and (3) has a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; c. a bypass element which (1) is connected in parallel with the series combination of the control element and the circuit interruption element, and (2) is functionally linked to the circuit interruption element so that an increase in current passing through the bypass element can convert the circuit interruption element into the fault state; and d. an auxiliary double pole circuit switch and an auxiliary resistor, (1) the auxiliary double pole circuit switch (i) when the circuit interruption element is in its normal fault state connecting the load to the electrical power supply, and (ii) when the circuit interruption element is in its fault state disconnecting the load from the electrical power supply and connecting the auxiliary resistor to the electrical power supply, and (2) the auxiliary resistor having a resistance which is small enough to permit sufficient current to flow in the bypass element to maintain the circuit interruption element in its fault state; whereby, when the current through the system increases from I NORMAL to I FAULT (i) the resistance of the control element increases from R LOW to R FAULT , (ii) an increased current passes through the bypass element and (iii) the circuit interruption element is converted into the fault state.

Claim 8

An electrical protection system which can be connected in series between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a control element which (1) has a relatively low resistance, R LOW when a relatively low current, I NORMAL , is passing through it, and (2) is converted to a relatively high resistance, R FAULT , when the current through it increases from I NORMAL to a relatively high current, I FAULT ; b. a circuit interruption element which (1) is connected in series with the control element, (2) has a normal state when the current I NORMAL is passing through the control element, the normal state permitting the current I NORMAL to pass through the system, and (3) has a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; c. a bypass element which (1) is connected in parallel with the series combination of the control element and the circuit interruption element, and (2) is functionally linked to the circuit interruption element so that an increase in current passing through the bypass element can convert the circuit interruption element into the fault state; and d. an auxiliary double pole circuit switch and an auxiliary resistor, (1) the auxiliary double pole circuit switch (i) when the circuit interruption element is in its normal fault state connecting the load to the electrical power supply, and (ii) when the circuit interruption element is in its fault state disconnecting the load from the electrical power supply and connecting the auxiliary resistor to the electrical power supply, and (2) the auxiliary resistor having a resistance which is small enough to permit sufficient current to flow in the bypass element to maintain the circuit interruption element in its fault state; whereby, when the current through the system increases from I NORMAL to I FAULT (i) the resistance of the control element increases from R LOW to R FAULT , (ii) an increased current passes through the bypass element and (iii) the circuit interruption element is converted into the fault state.

Claim 9

A circuit which comprises a power supply having a voltage V NORMAL , an electrical load, and a protection system, and which circuit has a normal operating condition in which a normal current, I NORMAL , passes through the protection system, which system comprises: a. a control element which (1) has a relatively low resistance, R LOW , when a relatively low current, I NORMAL , is passing through it, and (2) is converted to a relatively high resistance, R FAULT , when the current through it increases from I NORMAL to a relatively high current, I FAULT ; b. a circuit interruption element, connected in series with the control element and having (1) a rating to carry a current, I CARRY , which is greater than I NORMAL , (2) a rating to interrupt a current, I INTERRUPT , which is substantially less than I FAULT , at a voltage equal to V NORMAL , (3) a normal state when the current I NORMAL is passing through the control element, the normal state permitting the current I NORMAL to pass through the system, and (4) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; and c. a bypass element which (1) is connected in parallel with the series combination of the control element and the circuit interruption element, (2) is functionally linked to the circuit interruption element so that an increase in current passing through the bypass element can convert the circuit interruption element into the fault state, and (3) comprises (a) a relay coil which causes the circuit interruption element to move from its normal state to its fault state in response to increased current flowing in the bypass element, (b) a bypass resistor connected in series with the relay coil, and (c) a bypass switch which (i) is connected in series with the relay coil and in parallel with the bypass resistor, and (ii) is closed when the circuit interruption element is in its normal state and open when the circuit interruption element is in its fault state; such that when the current in the protection system increases to I FAULT , the resistance of the control element increases from R LOW to R FAULT , an increased current passes through the bypass element, the circuit current is reduced below I INTERRUPT , thereby permitting the circuit interruption element to convert to the fault state and interrupt circuit current.

Claim 10

A circuit which comprises a power supply having a voltage V NORMAL , an electrical load, and a protection system, and which circuit has a normal operating condition in which a normal current, I NORMAL , passes through the protection system, which system comprises: a. a control element which (1) has a relatively low resistance, R LOW , when a relatively low current, I NORMAL , is passing through it, and (2) is converted to a relatively high resistance, R FAULT , when the current through it increases from I NORMAL to a relatively high current, I FAULT ; b. a circuit interruption element, connected in series with the control element and having (1) a rating to carry a current, I CARRY , which is greater than I NORMAL , (2) a rating to interrupt a current, I INTERRUPT , which is substantially less than I FAULT , at a voltage equal to V NORMAL , (3) a normal state when the current I NORMAL is passing through the control element, the normal state permitting the current I NORMAL to pass through the system, and (4) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; and c. a bypass element which (1) is connected in parallel with the series combination of the control element and the circuit interruption element, (2) is functionally linked to the circuit interruption element so that an increase in current passing through the bypass element can convert the circuit interruption element into the fault state, and (3) comprises (a) a relay coil which causes the circuit interruption element to move from its normal state to its fault state in response to increased current flowing in the bypass element, (b) a bypass resistor connected in series with the relay coil, and (c) a bypass switch which (i) is connected in series with the relay coil and in parallel with the bypass resistor, and (ii) is closed when the circuit interruption element is in its normal state and open when the circuit interruption element is in its fault state; such that when the current in the protection system increases to I FAULT , the resistance of the control element increases from R LOW to R FAULT , an increased current passes through the bypass element, the circuit current is reduced below I INTERRUPT , thereby permitting the circuit interruption element to convert to the fault state and interrupt circuit current.

Claim 11

An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a circuit interruption element having (1) a normal state which permits the flow of a normal current, I NORMAL , and (2) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; b. a control element which (1) is connected in series with the circuit interruption element; (2) has a variable resistance which (a) is low compared to the load when the current in the circuit is the normal current, I NORMAL , and (b) increases substantially when the current in the load substantially exceeds the normal current, I NORMAL ; (3) comprises a comparator which compares (a) the current, I CONTROL , in the control element at a control comparison point, and (b) the current, I LOAD , in the load at a load comparison point, and (4) changes the circuit interruption element from its normal state to its fault state when I CONTROL differs from I LOAD by more than a predetermined current imbalance value, I DIFF ; and c. a bypass element which (1) is connected in parallel with the control element, and (2) has a resistance such that (a) when the circuit current is I NORMAL , the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by less than I DIFF , and (b) when the circuit current exceeds I NORMAL by a predetermined current amount, the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by more than I DIFF .

Claim 12

An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a circuit interruption element having (1) a normal state which permits the flow of a normal current, I NORMAL , and (2) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; b. a control element which (1) is connected in series with the circuit interruption element; (2) has a variable resistance which (a) is low compared to the load when the current in the circuit is the normal current, I NORMAL , and (b) increases substantially when the current in the load substantially exceeds the normal current, I NORMAL ; (3) comprises a comparator which compares (a) the current, I CONTROL , in the control element at a control comparison point, and (b) the current, I LOAD , in the load at a load comparison point, and (4) changes the circuit interruption element from its normal state to its fault state when I CONTROL differs from I LOAD by more than a predetermined current imbalance value, I DIFF ; and c. a bypass element which (1) is connected in parallel with the control element, and (2) has a resistance such that (a) when the circuit current is I NORMAL , the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by less than I DIFF , and (b) when the circuit current exceeds I NORMAL by a predetermined current amount, the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by more than I DIFF .

Claim 13

A system according to claim 8 wherein the control element comprises a PTC device.

Claim 14

A system according to claim 9 wherein the control element comprises a voltage clamping device connected in parallel with the PTC device.

Claim 15

A system according to claim 8 wherein the bypass element comprises a bypass resistor whose resistance is substantially independent of temperature.

Claim 16

A circuit which comprises a power supply having a voltage V NORMAL , an electrical load, and a protection system, and which has a normal operating condition in which a normal current, I NORMAL , passes through the protection system, which system comprises: a. a circuit interruption element comprising a mechanical switch and having (1) a rating to carry a current, I CARRY , which is greater than I NORMAL , (2) a rating to interrupt a current, I INTERRUPT , which is substantially less than a current, I TRIP , at a voltage equal to V NORMAL ; (3) a normal state which permits the flow of a normal current, I NORMAL , and (4) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; b. a control element which (1) is connected in series with the circuit interruption element; (2) has a variable resistance which (a) is low compared to the load when the current in the circuit is the normal current, I NORMAL , and (b) increases substantially when the current in the load exceeds a trip current, I TRIP , which is greater than I NORMAL , (3) comprises a comparator which compares (a) the current, I CONTROL , in the control element at a control comparison point, and (b) the current, I LOAD , in the load at a load comparison point, and (4) changes the circuit interruption element from its normal state to its fault state when I CONTROL differs from I LOAD by more than a predetermined current imbalance value, I DIFF ; and c. a bypass element which (1) is connected in parallel with the control element, and (2) has a resistance such that (a) when the circuit current is I NORMAL , the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by less than I DIFF , and (b) when the circuit current exceeds I NORMAL by a predetermined current amount, the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by more than I DIFF ; such that when the circuit current exceeds I TRIP , the control element reduces the circuit current below I INTERRUPT , thereby permitting the circuit interruption element to interrupt circuit current.

Claim 17

A circuit which comprises a power supply having a voltage V NORMAL , an electrical load, and a protection system, and which has a normal operating condition in which a normal current, I NORMAL , passes through the protection system, which system comprises: a. a circuit interruption element comprising a mechanical switch and having (1) a rating to carry a current, I CARRY , which is greater than I NORMAL , (2) a rating to interrupt a current, I INTERRUPT , which is substantially less than a current, I TRIP , at a voltage equal to V NORMAL ; (3) a normal state which permits the flow of a normal current, I NORMAL , and (4) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; b. a control element which (1) is connected in series with the circuit interruption element; (2) has a variable resistance which (a) is low compared to the load when the current in the circuit is the normal current, I NORMAL , and (b) increases substantially when the current in the load exceeds a trip current, I TRIP , which is greater than I NORMAL , (3) comprises a comparator which compares (a) the current, I CONTROL , in the control element at a control comparison point, and (b) the current, I LOAD , in the load at a load comparison point, and (4) changes the circuit interruption element from its normal state to its fault state when I CONTROL differs from I LOAD by more than a predetermined current imbalance value, I DIFF ; and c. a bypass element which (1) is connected in parallel with the control element, and (2) has a resistance such that (a) when the circuit current is I NORMAL , the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by less than I DIFF , and (b) when the circuit current exceeds I NORMAL by a predetermined current amount, the ratio of the resistance of the bypass element to the resistance of the control element is such that I CONTROL differs from I LOAD by more than I DIFF ; such that when the circuit current exceeds I TRIP , the control element reduces the circuit current below I INTERRUPT , thereby permitting the circuit interruption element to interrupt circuit current.

Claim 18

An electrical protection system which can be connected in series between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a circuit interruption element having (1) a normal state which permits the flow of a normal current, I NORMAL , and (2) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; and b. a control element comprising (1) a PTC device which (a) is connected in series with the circuit interruption element, and (b) has a variable resistance which (i) is low compared to the load when the current is the normal current, I NORMAL , and (ii) increases substantially when the current substantially exceeds the normal current, I NORMAL , (2) a relay coil, coupled in parallel with the load, and (3) back-to-back coupled Zener diodes connected in parallel with the relay coil, whereby when the voltage across the coupled Zener diodes exceeds a predetermined voltage amount current passes through the coupled Zener diodes thereby causing the current in the PTC device to increase by an amount sufficient to cause the resistance of the PTC device to increase by a predetermined resistance amount, which in turn causes the current through the relay coil to increase, thus changing the circuit interruption element from its normal state to its fault state.

Claim 19

An electrical protection system which can be connected in series between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a circuit interruption element having (1) a normal state which permits the flow of a normal current, I NORMAL , and (2) a fault state which permits the flow of at most a reduced current, substantially less than I NORMAL ; and b. a control element comprising (1) a PTC device which (a) is connected in series with the circuit interruption element, and (b) has a variable resistance which (i) is low compared to the load when the current is the normal current, I NORMAL , and (ii) increases substantially when the current substantially exceeds the normal current, I NORMAL , (2) a relay coil, coupled in parallel with the load, and (3) back-to-back coupled Zener diodes connected in parallel with the relay coil, whereby when the voltage across the coupled Zener diodes exceeds a predetermined voltage amount current passes through the coupled Zener diodes thereby causing the current in the PTC device to increase by an amount sufficient to cause the resistance of the PTC device to increase by a predetermined resistance amount, which in turn causes the current through the relay coil to increase, thus changing the circuit interruption element from its normal state to its fault state.

Claim 20

A system according to claim 13 wherein the control element comprises a voltage clamping device connected in parallel with the PTC device.

Claim 21

An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a circuit interruption element which is a double pole circuit switch, and an auxiliary resistor, the double pole circuit switch having (1) a normal state which connects the load to the electrical power supply and permits the flow of a normal current, I NORMAL , and (2) a fault state which disconnects the load from the electrical power supply and connects the auxiliary resistor to the electrical power supply; b. a control element (1) connected in series with the circuit interruption element, and (2) having a variable resistance which (a) is low compared to the load when the current is the normal current, I NORMAL , and (b) increases a first predetermined resistance amount if the current substantially exceeds the normal current, I NORMAL ; and c. a bypass element (1) connected in parallel with the control element, and (2) having a resistance which (a) is substantially higher than the resistance of the control element when the circuit is in the normal operating condition, (b) is substantially lower than the resistance of the control element when the resistance of the control element has increased by the first predetermined resistance amount, and (c) increases by a second predetermined resistance amount when the resistance of the control element has increased by the first predetermined resistance amount; with the double pole circuit switch changing from its normal state to its fault state when the resistance of the control element has increased by the first predetermined resistance amount and the resistance of the bypass element has increased by the second predetermined resistance amount.

Claim 22

An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises: a. a circuit interruption element which is a double pole circuit switch, and an auxiliary resistor, the double pole circuit switch having (1) a normal state which connects the load to the electrical power supply and permits the flow of a normal current, I NORMAL , and (2) a fault state which disconnects the load from the electrical power supply and connects the auxiliary resistor to the electrical power supply; b. a control element (1) connected in series with the circuit interruption element, and (2) having a variable resistance which (a) is low compared to the load when the current is the normal current, I NORMAL , and (b) increases a first predetermined resistance amount if the current substantially exceeds the normal current, I NORMAL ; and c. a bypass element (1) connected in parallel with the control element, and (2) having a resistance which (a) is substantially higher than the resistance of the control element when the circuit is in the normal operating condition, (b) is substantially lower than the resistance of the control element when the resistance of the control element has increased by the first predetermined resistance amount, and (c) increases by a second predetermined resistance amount when the resistance of the control element has increased by the first predetermined resistance amount; with the double pole circuit switch changing from its normal state to its fault state when the resistance of the control element has increased by the first predetermined resistance amount and the resistance of the bypass element has increased by the second predetermined resistance amount.

Claim 23

A system according to claim 15 wherein the bypass element comprises a PTC device.

Claim 24

A system according to claim 16 wherein the bypass element comprises a voltage clamping device connected in parallel with the PTC device.

Claim 25

A system according to claim 15 wherein the auxiliary resistor is a PTC device.

Claim 26

A system according to claim 15 wherein the double pole circuit switch comprises a double pole bimetal switch which a. is thermally coupled with the bypass element so that when the resistance of the bypass element increases by the second predetermined resistance amount, heat generated by the bypass element causes the double pole bimetal switch to move from its normal state to its fault state; and b. is thermally coupled with the auxiliary resistor so that when the auxiliary resistor is connected to the electrical power supply, heat generated by the auxiliary resistor causes the double pole bimetal switch to latch in its fault state.