Active material circuit breaker

Abstract

Circuit breaker (32A) comprising: an active material (38A) configured to undergo a change in at least one attribute in response to an activation signal, as a result of which the second electrically conductive element moves between the first and second positions; a first electrically conductive element (26); a second electrically conductive element (30A) selectively movable between a first position in which the second electrically conductive element (30A) contacts the first electrically conductive element (26) and a second position in which the second electrically conductive element (30A) does not contact the first electrically conductive element (26); and an active material (38A) configured to undergo a change in at least one attribute in response to an activation signal, as a result of which the second electrically conductive element (30A) comprising the active material (38A) moves between the first and second positions; a third element (18A) defining a groove (42); wherein the length of the second element (30A) is greater in the first position than in the second position; and wherein the second electrically conductive element (30A) is arranged in the groove (42) over its entire length in the first position.

Description

TECHNICAL FIELD

[0001] This invention relates to circuit breakers for protecting electronic components from excessive current.

[0002] An active material circuit breaker is disclosed, for example, in WO 00 / 58980 A1. BACKGROUND OF THE INVENTION

[0003] Electrical circuits are sometimes prone to overheating as a result of excessive current. Consequently, circuits or components may include circuit breakers that open the circuit in the event of excessive current flow, thereby preventing damage to the circuit components. Circuit breakers include fuses and mechanical circuit breakers.

[0004] Fuses include a conductive element configured to break or blow when the current flowing through them exceeds a predetermined amount, thereby opening the circuit. Mechanical circuit breakers include switches that automatically move to an open position when the current flowing through them exceeds a predetermined amount. In an exemplary mechanical circuit breaker, the current flows through an electromagnet; when the current exceeds a predetermined amount, the magnetic field generated by the electromagnet is sufficiently large to move the switch to the open position. SUMMARY OF THE INVENTION

[0005] According to the invention, a circuit breaker is presented which is characterized by the features of claim 1.

[0006] Unlike fuses, the circuit breaker is resettable. Furthermore, the circuit breaker has less mechanical complexity than prior art circuit breakers, allowing the use of the circuit breaker in applications where the size or cost of prior art circuit breakers would prohibit it.

[0007] Further described is a device comprising an electronic component, an electrical contact, and a circuit breaker, which at least partially define a conductive path between the contact and the electronic component. The circuit breaker comprises an active material configured to undergo a change in at least one attribute in response to an activation signal. The circuit breaker is configured such that the change in at least one attribute changes the resistance of the conductive path between the contact and the electronic component.

[0008] The above features and advantages, as well as other features and advantages of the present invention, will become readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic, cutaway side view of an electronic component and a circuit breaker not according to the invention with a conductor in a first position; Fig. Figure 2 is a schematic, cutaway side view of the electronic component and circuit breaker of Fig. 1 with the conductor in a second position; Fig. Figure 3 is a schematic, cutaway side view of an alternative electronic component and an inventive circuit breaker according to the claimed invention with a conductor in a first position; and Fig. Figure 4 is a schematic, cutaway side view of the electronic component and circuit breaker of Fig. 3 with the conductor in a second position. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In Fig. 1, a portion of an electrical circuit 10 is schematically illustrated. The circuit 10 includes at least one electronic component 14. In the embodiment shown, the electronic component 14 is a microprocessor, i.e., an integrated circuit; however, any electronic component may be used within the scope of the claimed invention. The microprocessor includes an insulating silicon dioxide base plate 18. A microprocessor core 22 is attached to the base plate 18. As those skilled in the art will appreciate, the core 22 includes transistors and other components interconnected by a plurality of conductive elements.

[0010] The electrical circuit 10 includes first and second electrically conductive elements 26, 30 that cooperate to selectively establish electrical connection to and from the microprocessor core 22. The first element 26 in the illustrated embodiment is an input / output pin via which electronic input and / or output signals can be transmitted to the microprocessor core 22. As those skilled in the art will appreciate, the microprocessor 14 includes a plurality of input and output pins via which the microprocessor core 22 sends and receives data in the form of electronic signals. Only one of the pins is shown in the figures. The first element 26 thus serves as an electrical contact that can be engaged, for example, with a complementary contact on a printed circuit board.

[0011] The first element 26 is mounted to the base plate 18. The second element 30 is mounted with respect to and in electrical communication with the microprocessor core 22. The second element 30 is part of an electromechanical circuit breaker 32 not according to the invention and at least partially defines an electrically conductive path from the pin, i.e., the first element 26, to the core 22. The microprocessor 14 also includes an outer casing 34 made of silicon dioxide (or other IC substrate known to those skilled in the art) that is mounted with respect to the base plate 18 and that serves as a heat sink. The circuit breaker 32 also includes an active material element 38 configured to undergo a change in at least one attribute in response to an activation signal.

[0012] The activation signal is generated when the amount of current flowing through the second element 30 exceeds a predetermined amount. The protection switch 32 is configured such that changing the attribute changes the resistance of the conductive path between the first element 26 and the second element 30, limiting or preventing current flow to the microprocessor core 22, and thereby protecting the microprocessor core 22 from excessive current and overheating.

[0013] In particular, in the embodiment shown, the second element 30 is movable between a first position as shown in Fig. 1, and a second position as shown in Fig. 2, is selectively movable. When the second element 30 is in the first position, the second element 30 is in contact with the first element 26, thereby establishing a direct electrical connection from the first element 26 to the second element 30. Thus, when the second element 30 is in its first position, electrical current can flow from the first element 26 via the second element 30 to the core 22. Fig. 2, when the second element 30 is in its second position, the second element 30 does not contact the first element 26, thus there is an air gap in the conductive path from the first element 26 to the core 22, which creates a large amount of resistance and prevents the flow of current from the first element 26 to the core 22.

[0014] The active material element 38 is attached to the outer housing 34 and to the second conductive element 30. In the embodiment shown, the active material of the element 38 is a shape memory alloy (SMA). A shape memory alloy is characterized by a cold state, ie, when the temperature of the alloy is below its martensite final temperature M f A shape memory alloy is also characterized by a hot state, ie when the temperature of the alloy exceeds its austenite final temperature A f An object formed from the alloy may be characterized by a predetermined shape. If the object has undergone pseudoplastic deformation from its predetermined shape in the cold state, the deformation can be reversed by heating the object to a temperature above its austenite final temperature A fis heated, ie the application of a thermal activation signal sufficient to heat the object beyond its A f Heating beyond this temperature causes the object to return to its predetermined shape. Furthermore, the elastic modulus and yield strength of an SMA are significantly lower in the cold state than in the hot state. As those skilled in the art will understand, pseudoplastic deformation is similar to plastic deformation in that the deformation remains despite the removal of the stress that caused the deformation. However, unlike plastic deformation, pseudoplastic deformation is reversible when the object is heated to its hot state.

[0015] The element 38 is defined by a given shape as shown in Fig. 2, and a pseudoplastic deformed state as shown in Fig. 1. In particular, the element 38 is configured to be characterized by pseudoplastic tensile deformation when the second element 30 is in its first position and in contact with the first element 26, as shown in Fig. 1, such that the height of the element 38 is greater than its predetermined height. Heating the active material element 38 to its hot state (i.e., by applying a thermal activation signal to the active material element 38) makes the pseudoplastic tensile deformation shown in Fig. 1 is reversed, whereby the element 38 retains its predetermined shape as shown in Fig. 2. When the element 38 assumes its predetermined shape, the element 38 pulls the second element 30 out of contact with the first element 26 into its second position, thereby increasing the resistance in the conductive path and preventing current flow to the microprocessor core 22.

[0016] The active material element 38 is in contact with the second element 30, thus placing the active material element 38 in direct conductive heat transfer relationship with the second element 30. The austenite finish temperature of the active material element 38 is set to a temperature reached by the second element 30 due to ohmic heating when the amount of current flowing through the second element 30 exceeds a predetermined amount. The predetermined amount of current in the illustrated embodiment is the maximum amount of current that the core 22 can safely receive without damage.Accordingly, the circuit breaker 32 is configured such that when the current flow in the second element 30 exceeds a predetermined amount, the active material element 38 assumes its predetermined shape, moving the second element 30 out of contact with the first element 26, thereby preventing current flow from the first element 26 to the core 22 and protecting the core 22 from overheating.

[0017] Alternatively, and within the scope of the claimed invention, the activation signal may be generated when, as a result of a cooling system failure, environmental conditions, etc., the temperature of core 22, element 30, element 26, etc., exceeds a predetermined amount. More specifically, heat is transferred from core 22, element 30, element 26, etc., to element 38. Element 38 may be heated by core 22, element 30, element 26, etc., to a temperature above its austenite final temperature, thereby stopping the flow of electrical current.

[0018] In the illustrated embodiment, the circuit breaker 32 automatically resets when the temperature of the second element 30 (and thus the temperature of the active material element 38) becomes colder. In particular, the circuit breaker 32 includes a spring that biases the second element 30 to its first position. In the illustrated embodiment, the second element 30 acts as a spring: the second element 30 has elastically deformed upon moving from its first position to its second position, and thus urges to return to its first position. In an alternative embodiment, and within the scope of the claimed invention, a separate spring may urge the second element toward its first position. For example, a coil spring may be disposed between the second element 30 and the outer housing 34.

[0019] When the active material of element 38 is in its hot state, the modulus of element 38 is sufficiently high to withstand the preload of the spring. However, as thermal energy is transferred from the second element 30 and the active material element 38 to the outer casing 34, the modulus of the active material element 38 decreases as the element 38 cools to a temperature below the austenite final temperature, the force of the spring being sufficient to deform the element 38 and return the second element 30 to its first position, thereby restoring the direct electrical connection from the first element 26 through the second element 30 to the core 22. The circuit breaker can also be manually reset if temperature conditions permit.

[0020] In Fig. 3, wherein like reference numerals refer to like components from the Fig. 1 and Fig. 2, a portion of an alternative circuit 10A is shown schematically. The circuit 10A includes at least one electronic component 14A. In the illustrated embodiment, the electronic component 14A is a microprocessor; however, any electronic component may be used within the scope of the claimed invention. The microprocessor includes an insulating base plate 18A. A microprocessor core 22 is attached to the base plate 18A.

[0021] The electrical circuit 10A includes first and second electrically conductive elements 26, 30A, which cooperate to selectively establish electrical connection to and from the microprocessor core 22. The first element 26 in the illustrated embodiment is an input / output pin through which electronic input and / or output signals are transmittable to and from the microprocessor core 22.

[0022] The first element 26 is mounted on the base plate 18A. The second element 30A is mounted with respect to the microprocessor core 22 and is in electrical communication therewith. The second element 30A is part of an electromechanical circuit breaker 32A according to the invention and at least partially defines an electrically conductive path from the pin, i.e., the first element 26, to the core 22. The microprocessor 14 also includes an outer housing 34 mounted with respect to the base plate 18 and serving as a heat sink.

[0023] The base plate 18A defines a groove 42 extending from the core 22 to the pin 26. The second element 30A is at least partially disposed in the groove 42. The second element comprises an active material, ie, a shape memory alloy, whereby the second element 30A is also an active material element 38A. The second element 30A is in Fig. 3 in a first position and in Fig. 4 in a second position. When element 30A is in its first position, it is in contact with element 26, thus establishing the direct electrical connection between element 26 and core 22. When element 30A is in its second position, it does not contact element 26; an air gap between element 26 and element 30A provides sufficient resistance in the conductive path to prevent the flow of current from pin 26 to core 22.

[0024] The second element 30A is characterized by a predetermined shape (length) which is Fig. 4 corresponds to its second position. The second element 30A is in its first position, as shown in Fig. 3, characterized by pseudoplastic tensile deformation. Accordingly, the length of the element 30A is greater in the first position than in the second position. The second element 30A is configured to reach its austenite final temperature due to ohmic heating when the amount of current flowing therethrough exceeds a predetermined amount. When the austenite final temperature is reached, the pseudoplastic tensile deformation is reversed, with the second element 30A returning to its second position, which is shown in Fig. 4, thereby stopping the flow of current.

[0025] The circuit breaker 32A automatically resets when the SMA element 38A cools. In one embodiment, the second element 30A comprises a two-way shape memory alloy, where the phase change in the alloy achieves both the shrinking and stretching effects. Alternatively to one-way SMA, as the element 30A cools, the diameter increases; thus, the walls of the groove 42 provide a restoring force urging the element 30A to return to its first position and into contact with the element 26. That is, the groove 42 or features along the groove 42 force the SMA element 30A, 38A to stretch and shrink in a predictable manner, eliminating the need for return springs. In addition to a two-way SMA, the circuit board itself or other spring elements could be attached to the element 30A and provide the restoring force.

[0026] It should be noted that although shape memory alloys are used herein, other active materials such as electroactive polymers, piezoelectric materials, and magnetostrictive and electrostrictive materials may be used within the scope of the claimed invention.

[0027] Those skilled in the art will recognize a variety of applications for the circuit breakers 32, 32A in the fields of avionics electronics, telecommunications, audio-visual equipment, automotive systems, aerospace, etc. By way of example and within the scope of the claimed invention, the circuit breakers may be used in connection with electronic data backup driver systems, power transistors, printed circuit boards, wiring, cellular telephones, video telegraphy, cabled lines, video cassette recorders, televisions, radios, compact disc players, video cameras, video game machines, engine controllers, vehicle body controllers, automotive cooling systems, hydrogen fuel cell charging systems, battery systems for hybrid vehicles, heating and cooling controls, battery charging, engine protection, navigation systems, etc.

[0028] The circuit breakers 32, 32A can increase the possibility of recovering data from damaged computers, can provide a visible indicator of which circuit has failed, thereby reducing the time required for troubleshooting and repairing the circuit, can conversely be used as a temporary shutdown, etc. It should also be noted that an atypical hysteresis curve may result for the circuit cooling time. It should also be noted that the active material elements may require a non-standard transition temperature. It may be desirable to use a backup circuit arrangement for certain systems.

Claims

[1] Circuit breaker (32A) comprising: an active material (38A) configured to undergo a change in at least one attribute in response to an activation signal, as a result of which the second electrically conductive element moves between the first and second positions; a first electrically conductive element (26); a second electrically conductive element (30A) selectively movable between a first position in which the second electrically conductive element (30A) contacts the first electrically conductive element (26) and a second position in which the second electrically conductive element (30A) does not contact the first electrically conductive element (26); and an active material (38A) configured to undergo a change in at least one attribute in response to an activation signal, as a result of which the second electrically conductive element (30A) comprising the active material (38A) moves between the first and second positions; a third element (18A) defining a groove (42); wherein the length of the second element (30A) is greater in the first position than in the second position; and wherein the second electrically conductive element (30A) is arranged in the groove (42) over its entire length in the first position. [2] The circuit breaker (32A) of claim 1, wherein changing at least one attribute comprises changing the shape of the active material (38A). [3] The circuit breaker (32A) of claim 2, wherein the active material (38A) comprises a shape memory alloy and / or a shape memory polymer. [4] The circuit breaker (32A) of claim 1, wherein the activation signal is thermal.

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