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 component 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 having a shutter and a heat sensitive element, wherein, under abnormal operation conditions, the heat sensitive element releases the shutter, and the shutter moves along a straight line and 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; an active releasing device having a shutter and a heat sensitive element, wherein, under abnormal operation conditions, the heat sensitive element is configured to release the shutter, and the shutter is configured to move along a straight line and close the path between the varistor and the second external contact; and a linear guide rail, wherein the shutter is arranged in the guide rail, wherein the heat sensitive element is a metallic body extending through the guide rail and through the shutter and electrically connecting the varistor to the second external contact, wherein the shutter is a mainly cuboid shaped slider with a hole or a notch, wherein the guide rail has a mainly cuboid shape and houses the slider and an element configured to exert a force onto the shutter, wherein, under normal operation conditions, the heat sensitive element is a bolt that extends through two holes in the guide rail—with one hole at each side—and through the hole of the slider, wherein the guide rail establishes a mask, and wherein the mask and the shutter have such a geometrical shape that a probability that remaining material of the heat sensitive element maintains an electrical connection is reduced.

2. The varistor component of claim 1, where the heat sensitive element is a fuse and has a conducting material with a melting point.

3. The varistor component of claim 1, wherein the element is a spring.

4. The varistor component of claim 1, wherein the shutter and the guide rail comprise a ceramic material, a metal oxide, an aluminum oxide, or a thermoplastic material.

5. The varistor component of claim 1, wherein the first-to-third external contacts are lead wires or metal strap electrodes.

6. The varistor component of claim 1, wherein the shutter comprises a ceramic material, a metal oxide, an aluminum oxide, or a thermoplastic material.

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

8. A method for securing the varistor component of claim 1, the method comprising: actively closing, under the abnormal operation conditions, the path by the shutter thereby electrically separating the varistor from the second external contact.

9. The varistor component of claim 1, wherein the heat sensitive element is a solder with a melting temperature between 185° C. and 230° C.

10. The varistor component of claim 1, wherein the heat sensitive element is a SnBi alloy or SnAgCu alloy solder paste or solder wire.

11. The varistor component of claim 1, wherein the element is a thermo-expansion material.

12. The varistor component of claim 1, wherein the element is a memory metal.

13. The varistor component of claim 1, wherein the shutter comprises a dielectric material with a high temperature resistance relative to a temperature resistance of the heat sensitive element.

14. The varistor component of claim 1, further comprising a housing, wherein the releasing device is located in the housing.

15. The varistor component of claim 1, wherein the optical indicator is an LED.

16. The varistor component of claim 1, wherein, under the normal operation conditions, the heat sensitive element electrically connects the second external contact to the third external contact, and wherein, under the abnormal operation conditions, the heat sensitive element is configured to electrically disconnect the second external contact from the third external contact.

17. The varistor component of claim 16, further comprising an optical indicator connected to the third external contact, wherein the optical indicator is configured to be activated under the normal operation conditions and deactivated under the abnormal operation conditions.

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 cuboid shaped guide rail;

(5) FIG. 5 shows a perspective view of a cross section through the guide rail;

(6) FIG. 6 shows a perspective view of a varistor component with a third external contact;

(7) FIG. 7 shows a perspective view of the back of the varistor and its electrical connection to the first external contact;

(8) FIG. 8 shows an embodiment where the first external contact is soldered to the back of the varistor; and

(9) FIGS. 9 and 10 indicate the working principles of the third external contact.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(10) 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. The varistor V and the release device ARD can be placed in a housing HO.

(11) 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.

(12) 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.

(13) 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.

(14) 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 an electrical connection between the varistor V and the second external contact EC2.

(15) FIG. 4 shows an exploded view of an embodiment where shutter SH is a mainly cuboid shaped slider SL with a hole H or a notch. The guide rail GR has also a mainly cuboid shape and houses the slider SL and the spring SP. During normal operation the heat-sensitive element HSE is a bolt that extends through the two holes in the rail (one hole at each side) and through the hole H of the slider SL. The rail GR establishes the mask. 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 is reduced.

(16) The heat-sensitive element HSE has mainly the shape of a cylinder and is in mechanical contact with the walls of the guide rail GR 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 H arranged directly over the hole H of the guide rail GR. The heat-sensitive element HSE establishes the electrical contact between the varistor and the second external contact EC2.

(17) When the temperature of the heat-sensitive element HSE exceeds a critical temperature and the heat-sensitive element melts, then the spring SP pushes the shutter SH along the straight line STL and the electrical contact is discontinued.

(18) 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.

(19) FIG. 5 shows a perspective view of a cross section through the guide rail GR. The guide rail's body is hollow and houses the Spring SP and the shutter SH. The spring SP is under stress pushing against the shutter SH under normal operating conditions. The heat-sensitive element (not shown in FIG. 5) holds the shutter in its position. When the heat-sensitive element melts the resistance against the pushing force of the spring SP ends and the spring SP pushes the shutter SH to interrupt the electrical connection between the varistor V and the second external contact EC2 (not shown in FIG. 5)

(20) FIG. 6 shows an embodiment where the varistor component VC has a third external contact EC3 that is electrically connected to a metallization. Under normal operation conditions, the third electrical contact EC3 is electrically connected to the second external contact EC2. However, once the heat-sensitive element HSE is molten, the residual material can electrically disconnect the third external contact EC3 from the second external contact EC2 to indicate the activation of the active release device ARD to an external circuit environment.

(21) An optical indicator OI, such as a LED, can be used to display whether the mode of operation is normal or abnormal. An LED connected to the third external contact can be deactivated when the releasing device is activated.

(22) However, it is also possible that during normal operation a galvanic connection between the third external contact EC3 and a connection selected from the first EC1 and the second external contact EC2 exists during normal operation that is interrupted by the activation of the releasing device. Then, is possible that an active LED indicates normal operation and a deactivated LED indicated an error.

(23) FIG. 7 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.

(24) FIG. 8 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.

(25) FIGS. 9 and 10 illustrate the basic principle of the third external contact EC3. The third external contact EC3 is electrically connected to the second external contact 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. 10 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 no longer electrically connects the second external contact EC2 to the third external contact EC3.

(26) 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.