Varistor component and method for securing a varistor component

Abstract

A varistor component and a method for securing a varistor component are disclosed. In an embodiment, a varistor includes a first external contact, a second external contact, a varistor electrically connected to the first external contact, a path between the varistor and the second external contact and an active releasing device including a shutter and a heat sensitive element, wherein the heat sensitive element releases the shutter under abnormal operation conditions and the shutter closes the path between the varistor and the second external contact.

Claims

1. A varistor component comprising: a first external contact; a second external contact; a third external contact; a varistor electrically connected to the first external contact; a path between the varistor and the second external contact; and an active releasing device comprising a shutter and a heat sensitive element, wherein the heat sensitive element releases the shutter under abnormal operation conditions and the shutter closes the path between the varistor and the second external contact, and wherein, under abnormal operation conditions, the heat sensitive element electrically connects the second external contact to the third external contact.

2. The varistor component of claim 1, wherein the heat sensitive element is arranged in the path and establishes an electrical connection between the varistor and the second external contact.

3. The varistor component of claim 1, wherein the heat sensitive element is a fuse and has a conducting material with a melting point below 230 C.

4. The varistor component of claim 1, further comprising a spring exerting a force onto the shutter.

5. The varistor component of claim 1, further comprising a housing with a first hole, where the shutter has a second hole arranged adjacent to the first hole, wherein the first and the second holes establish a segment of the path, and wherein the heat sensitive element is a metallic body extending through the first and the second holes and electrically connecting the varistor to the second external contact.

6. The varistor component of claim 5, wherein the shutter has a hub, wherein the housing has a pivot arranged in the hub, and wherein, under abnormal operation conditions, the shutter revolves around the pivot closing the path.

7. The varistor component of claim 5, wherein the housing has a first pin, wherein the shutter has a first pin, and wherein a spring exerts a torque onto the first pins of the shutter and of the housing.

8. The varistor component of claim 1, wherein the first and second external contacts and the third external contact are lead wires.

9. The varistor component of claim 1, wherein the shutter comprises a material consisting essentially of a thermoplastic or a ceramic.

10. The varistor component of claim 1, further comprising a cap, wherein the shutter and the heat sensitive element are arranged in a cavity and the cap covers the cavity.

11. The varistor component of claim 1, wherein the shutter is designated to close the path under abnormal operation conditions independent from an orientation of the varistor component.

12. A method of securing a varistor component according to claim 1 under abnormal operation conditions, the method comprising: actively closing the path and electrically separating the varistor from the second external contact by the shutter.

13. A varistor component comprising: a first external contact; a second external contact; a third external contact; a varistor electrically connected to the first external contact; a path between the varistor and the second external contact; and an active releasing device having a shutter and a heat sensitive element, wherein the heat sensitive element releases the shutter under abnormal operation conditions and the shutter closes the path between the varistor and the second external contact, wherein, under abnormal operation conditions, the heat sensitive element electrically connects the second external contact to the third external contact, and wherein the first, second and third external contacts are lead wires.

14. A varistor component comprising: a first external contact; a second external contact; a third external contact; a varistor electrically connected to the first external contact; a path between the varistor and the second external contact; and an active releasing device having a shutter and a heat sensitive element, wherein the heat sensitive element releases the shutter under abnormal operation conditions and the shutter closes the path between the varistor and the second external contact, wherein, under abnormal operation conditions, the heat sensitive element electrically connects the second external contact to the third external contact, and wherein the shutter comprises a material consisting essentially of a thermoplastic or a ceramic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The varistor component, the working principles of the component and details of preferred embodiments are shown in the accompanied schematic figures.

(2) FIG. 1 shows the working principle of the varistor component.

(3) FIGS. 2 and 3 show an embodiment where a hole of the shutter is moved relative to a hole of a mask when the releasing device is activated.

(4) FIG. 4 shows a perspective view of an embodiment with a cylinder-shaped housing.

(5) FIG. 5 shows a perspective view of a varistor component with a third external contact.

(6) FIG. 6 shows an embodiment where the housing has a second pin establishing a stop for the shutter to confine the shutter's movement.

(7) FIG. 7 shows a perspective view of an embodiment indicating the orientation of the varistor relative to the housing including the releasing device's mechanism.

(8) FIG. 8 shows an exploded view of the varistor component, especially of the releasing device.

(9) FIG. 9 shows a perspective view of the back of the varistor and its electrical connection to the first external contact.

(10) FIG. 10 shows an embodiment where the first external contact is soldered to the back of the varistor.

(11) FIGS. 11 and 12 illustrate the working principle of a revolving type shutter.

(12) FIGS. 13 and 14 indicate the working principles of the third external contact.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(13) FIG. 1 shows the basic working principle of the varistor component VC. The varistor component VC has a varistor V, a first external contact EC1 and a second external contact EC2. The varistor V is electrically connected in series between the first external contact EC1 and the second external contact EC2 under normal operation conditions. The heat-sensitive element HSE is electrically connected between varistor V and the second external contact EC2 and arranged in the path P indicated by the arrow. The varistor component VC further comprises a shutter SH as part of the active releasing device ARD.

(14) Under normal operation conditions, the heat-sensitive element HSE is solid and electrically connects the varistor V to the second external contact EC2. However, when the temperature of the heat-sensitive element HSE exceeds a previously chosen limit, then the heat-sensitive element HSE melts and the shutter SH actively closes the path P and electrically separates the varistor V from the second external contact EC2. The shutter SH can be driven by a spring SP.

(15) The fact that the shutter SH is actively driven reduces the response time of the shutdown of the varistor component and increases the reliability of the varistor component.

(16) FIGS. 2 and 3 illustrate the working principle of an embodiment where the varistor component has a first hole H1 in a mask M and a second hole H2 in the shutter SH. The heat-sensitive element HSE is arranged in the two holes establishing the current path P. When the releasing device is activated (FIG. 3), the heat-sensitive element HSE melts and cannot further withstand the spring's SP force. Thus, the shutter is moved and the hole H2 of the shutter is moved relative to the hole H1 in the mask M and the path is blocked leading to the electrical separation of the varistor V from the second external contact EC2.

(17) It is preferred that the shutter SH, e.g., a segment without a hole, fully closes the hole in the mask M in such a way that residual material of the melted heat-sensitive element HSE cannot establish a remaining electrical connection between the varistor V and the second external contact EC2.

(18) FIG. 4 shows an embodiment where the mask and the shutter have such a geometrical shape that the probability that remaining material of the heat-sensitive element HSE maintains an electrical connection. The varistor component VC has a housing HOU in which the elements of the mechanism of the active releasing device ARD are arranged. The housing HOU has mainly the shape of a cylinder. The backside of the housing HOU establishes the mask M as illustrated in FIG. 3. The shutter has a bell-shaped footprint and a first pin P1. The housing HOU also has a first pin P1 and the first pins P1 of the housing HOU and of the shutter SH support the spring SP, which may be a coil spring or a spiral spring. Further, the housing HOU has a pivot PV establishing an axis around which the shutter SH can revolve. The heat-sensitive element HSE has mainly the shape of a cylinder and is in mechanical contact with the inner walls of the holes of the housing H1 and the shutter SH and is in contact to a wire electrically connected to the second external contact EC2. While the heat-sensitive element HSE is solid, the element holds the shutter SH in the open position with the shutter's hole H2 being arranged directly over the hole H1 of the housing HOU. The heat-sensitive element HSE establishes the electrical contact between the varistor (not shown in FIG. 4 but being arranged directly behind the housing HOU) and the second external contact EC2.

(19) When the temperature of the heat-sensitive element HSE exceeds a critical temperature and the heat-sensitive element melts, then the spring SP revolves the shutter SH by exerting a force onto pin P1 of the shutter SH revolving the shutter SH in a counter-clockwise direction.

(20) The external contact EC2 can have a rod shaped body and a bolt shaped head thicker than the rod shaped body. The bolt shaped head can have a rectangular cross section to be connected to the heat sensitive element HSE.

(21) FIG. 5 shows an embodiment where the varistor component VC has a third external contact EC3 that is electrically connected to a metallization within the cavity in the housing HOU. Under normal operation conditions, the third electrical contact EC3 is electrically separated from the first and from the second external contacts EC1, EC2. However, once the heat-sensitive element HSE is molten, the residual material can electrically connect the third external contact EC3 to the second external contact EC2 to indicate the activation of the active release device ARD to an external circuit environment.

(22) FIG. 6 shows a further embodiment where the housing HOU has a second pin P2 which defines a stop position for the shutter SH.

(23) FIG. 7 shows a perspective view of a varistor component indicating the position of the varistor V relative to the housing HOU including the elements of the mechanism of the active release device ARD. The varistor V is arranged behind the housing HOU. The varistor V also can have a cylinder shape and one side of the cylinder points at the varistor component's housing HOU is such a way that it can be electrically connected to the second external contact via the current path P.

(24) The first external contact EC1 electrically connects the respective backside of the varistor V that points away from the housing HOU.

(25) FIG. 8 shows an exploded view of the main components of the mechanism of the active release device ARD to emphasize the construction and the working principle of the corresponding embodiment.

(26) The housing HOU has a cavity CAV in which a first pin P1 of the housing HOU and a pivot PV of the housing HOU extend from a backside of the housing HOU. The bell-shaped shutter SH has a hole that acts as a hub HU and a hole H2 establishing a segment of the path during normal mode. Further, the shutter SH has its first pin P1 to support the spring SP. During normal operation, the hub HU surrounds the pivot PV of the housing HOU and the shutter SH can rotate around the corresponding axis through the pivot PV. The spring SP uses the first pin P1 of the housing HOU to exert a torque onto the shutter SH via the shutter's pin P1. The heat-sensitive element HSE is arranged in the hole of the housing HOU and the hole H2 in the shutter SH. Further, the heat-sensitive element HSE electrically connects the side of the varistor V pointing towards the housing HOU to the hook-shaped conductor segment of the second external contact EC2. The cavity CAV is covered by cap C to protect the mechanism against environmental influences and to protect the environment against molten material of the heat-sensitive element SHE.

(27) FIG. 9 shows the backside of the varistor V with a wire W attached to its backside establishing the connection between the varistor V and the conductor of the external connection EC1.

(28) FIG. 10 shows a preferred embodiment of the backside of the varistor V where the wire W is mechanically and electrically connected to the backside of the varistor V using a solder material S.

(29) FIGS. 11 and 12 illustrate the working principle of the shutter SH being in the position of normal operation in FIG. 11 and being in the activated position in FIG. 12. In the position of the normal operation, the hole H1 of the housing HOU and the hole H2 of the shutter SH are directly arranged one above the other and the path between the varistor and the second external contact is open.

(30) After activating the active release device ARD, the shutter SH is revolved around the hub HU in a counter-clockwise direction until the shutter SH hits the second pin P2 defining a stop position. The hole H2 of the shutter SH is moved relative to the hole H1 of the housing HOU leaving the path blocked by the shutter SH.

(31) FIGS. 13 and 14 illustrate the basic principle of the third external contact EC3. The third external contact EC3 is electrically separated from the other two external contacts EC1, EC2 during normal operation as the heat-sensitive element HSE is in its position to connect the varistor to the second external contact EC2. FIG. 14 illustrates the situation after activation. The material of the heat-sensitive element HSE is removed from its original position. The electric path between the varistor and the external contact EC2 is blocked (open circuit) and material of the heat-sensitive element HSE electrically connects the second external contact EC2 to the third external contact EC3.

(32) The varistor component can have additional elements such as additional shutters, fuses, springs, electrical connections, and the housing can have a polygon shape, e.g., a rectangular shape basic area. The shutter can be a rotating shutter or a shutter with a linear movement.