# Patent

## Title
Dual protection device for circuit

## Abstract

A dual protection device for a circuit includes a first protection unit and a second protection unit functioning independently. The first protection unit includes an elastic contact piece having a first contact point and a conductive member having a second contact point to contact with the first contact point. When overloaded, the elastic contact piece is deformed and bent toward an opposite direction to separate the first contact point from the second contact point, thereby protecting the circuit. The second protection unit has a fuse member and a second terminal. The fuse member is connected between the conductive member and the second terminal. If the first protection unit does not function as expected and the temperature climbs to a predetermined value, the fuse member melts. The conductive member is disconnected from the second terminal, thereby protecting the circuit.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a dual protection device for a circuit and more particularly, to a dual protection device having two protection units functioning independently to ensure that the circuit is protected when overloaded, overheated, or shorted.
2. The Prior Arts
Electricity plays an important part in everyday life. There are innumerable applications of electricity in the world of today, from computers, home appliances, traffic, and education to entertainment. Therefore, using electricity safely is very important.
Generally speaking, a whole circuit includes a main switch which controls the ON and OFF states of the circuit. The main switch has a fuse and/or a circuit breaker to cut off the circuit and prevent the whole circuit from damage, when the circuit is overloaded, overheated, or shorted.
Moreover, the whole circuit may include several sub-circuits and each sub-circuit may have its own switch to control the ON and OFF states. In order to enhance the safety of the circuit, a lot of switches for the sub-circuits are also equipped with protection function. Thus, if the main switch does not function properly or cut off the circuit in time, the switches for the sub-circuits can still protect the whole circuit from over-temperature or over-current.
In addition to the fuses and circuit breakers for the whole circuits, some electric appliances with high power consumption, such as digital processing units, electronic products or heaters, are equipped with individual protection devices to prevent them from damage when these electric appliances are overloaded, overheated, or shorted. Once the individual electric appliance is overload, overheat or short, the protection device cuts off the circuit to protect the appliance and avoid damage to other appliances using the same circuit.
Referring to FIGS. 1 and 2, a conventional protection device for individual electric appliance includes a bi-metallic strip 101 which is slightly curved. The bi-metallic strip 101 bends one way if heated, and in the opposite direction if cooled off. One end of the bi-metallic strip 101 is fixed to a first terminal 102 of the electric appliance and the other end of the bi-metallic strip 101 is a free end having a first contact point 103. A second terminal 104 of the electric appliance has a second contact point 105 which is located corresponding to the first contact point 103. When the appliance is in a normal operation state, the first contact point 103 contacts with the second contact points 105 and a closed circuit is formed as shown in FIG. 1. When the circuit is overloaded, the temperature of the bi-metallic strip 101 is raised so that the bi-metallic strip 101 is bent toward the other direction and the first contact point 103 is separated from the second contact point 105. The circuit is cut off to become an open circuit and the electric appliance is then prevented from being burned.
However, the conventional bi-metallic strip has the following disadvantages. (1) When manufacturing the bi-metallic strip 101, it is difficult to maintain the precision of the thickness, curvature and configuration of the bi-metallic strip 101. Therefore, the predetermined temperature of the bi-metallic strip 101 to bend is difficult to control. (2) Some of the bi-metallic strip 101 is not sensitive enough to the temperature and does not bend to cut off the circuit as expected when the circuit is overloaded. Therefore, the electric appliance and the circuit are not protected from overload, overheat or short. (3) Sometimes the bi-metallic strip 101 bends but does not completely separate the contact points 103 and 105. The circuit remains as a closed circuit. Thus, the appliance and the circuit are still damaged by overload. (4) Furthermore, sometimes the bi-metallic strip 101 does not separate the two contact points 103 and 105 to a sufficient distance. When the temperature slightly cools down, the bi-metallic strip 101 bends and re-connects the two contact points 103 and 105. When the temperature is raised again, the bi-metallic strip 101 bends to separate the two contact points 103 and 105. The repeated separation and re-connection of the circuit in a short period of time may generate sparks, which may cause fire. It also makes the electric current unstable. Thus, the electric appliance can not function properly and even may be damaged.
SUMMARY OF THE INVENTION
A primary objective of the present invention is to provide a dual protection device for a circuit to overcome disadvantages of a conventional protection device that has only one bi-metallic strip to cut off a circuit when overloaded, overheated, or shorted. The disadvantages include that the conventional protection device can not cut off the circuit as expected, can not cut off the circuit completely and repeatedly disconnect and connect the circuit in a short period of time.
Another objective of the present invention is to provide a dual protection device for a circuit that includes two protection units functioning independently. The protection units detect the temperature independently. When the circuit is overloaded, the two protection units can cut off the circuit independently. Thus, it ensures that the circuit is protected.
Still another objective of the present invention is to provide a dual protection device for a circuit that includes a reusable first protection unit. A bi-metallic strip of the first protection unit bends to cut off the circuit when the circuit is overloaded. When the circuit is cooled down, the bi-metallic strip bends toward the opposite direction and the circuit becomes a closed circuit again. Because the bi-metallic strip can disconnect and re-connect the circuit, there is no need to replace the first protection unit. It is cost saving.
Further still another objective of the present invention is to provide a dual protection device for a circuit that has a second protection unit. The second protection unit is activated, if the first protection unit does not work as expected and temperature of the circuit is raised to a predetermined value. A fuse member of the second protection unit melts due to high temperature caused by overload, thereby cutting off the circuit to protect the circuit.
In order to achieve the objectives, a dual protection device for a circuit according to the present invention includes a conductive cover, a first protection unit, a second protection unit and a base. A first terminal is connected to the cover. The first protection unit includes an elastic contact piece and a conductive member. The elastic contact piece has a first end fixed to the cover and a second end having a first contact point. The conductive member is a board and has a second contact point corresponding to the first contact point. The elastic contact piece is deformed and bent to separate the first contact point from the second contact point when a temperature of the elastic contact piece reaches a first predetermined value. The second protection unit includes a fuse member and a second terminal. The fuse member is connected between the conductive member and the second terminal. If the first protection unit does not function as expected, the temperature of the circuit would keep rising. The fuse member melts when a second predetermined temperature is reached. Thus, the conductive member is disconnected from the second terminal, thereby cutting off the circuit. The base has a recess to receive the conductive member and the fuse member.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which:
FIG. 1 is a schematic view showing a conventional protection device in a closed circuit state;
FIG. 2 is a schematic view showing the conventional protection device of FIG. 1 in an open circuit state;
FIG. 3 is an exploded view showing a dual protection device for a circuit according to an embodiment of the present invention;
FIG. 4 is a perspective view showing the dual protection device of FIG. 3;
FIG. 5 is a schematic top view showing the dual protection device of FIG. 3, wherein the dual protection device is in a closed circuit state;
FIG. 6 is a side cross sectional view showing the dual protection device of FIG. 3, wherein the dual protection device is in a closed circuit state;
FIG. 7 is a side cross sectional view showing the dual protection device of FIG. 3, wherein a first protection unit cuts off the circuit and the dual protection device is in an open circuit state; and
FIG. 8 is a schematic top view showing the dual protection device of FIG. 3, wherein a second protection unit cuts off the circuit and the dual protection device is in an open circuit state.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to the drawings and in particular to FIGS. 3 to 6, a dual protection device for a circuit according to the present invention includes a cover 10, a first protection unit 20, a second protection unit 30 and a base 40.
The cover 10 is made of a conductive material and has a first terminal 11 connected thereto.
The first protection unit 20 has an elastic contact piece 21 and a conductive member 22. The elastic contact piece 21 is a flexible metal strip, slightly curved in shape and can be bent toward two opposite directions due to temperature change. The elastic contact piece 21 may be made of a bi-metallic material. A first end of the elastic contact piece 21 is fixed to an inner side of the cover 10 and a second end of the elastic contact piece 21 is a free bendable end. The second end of the elastic contact piece 21 is provided with a first contact point 211. The conductive member 22 is a thin board and a second contact point 221 is disposed on a top of the conductive member 22. The first contact point 211 is located corresponding to the second contact point 221. The conductive member 22 includes an assembly hole 223 and extends a narrow first connection end 222 extended from a side thereof.
The second protection unit 30 includes an elongated fuse member 31 and a second terminal 32. The second terminal 32 includes a narrow second connection end 321 extended from a side facing the conductive member 22. A first end of the fuse member 31 is connected with the first connection end 222 of the conductive member 22 and a second end of the fuse member 31 is connected with the second connection end 321 of the second terminal 32, thereby electrically connecting the conductive member 22 with the second terminal 32. According to an embodiment of the present invention, the fuse member 31 may be welded to the first and second connection ends 222, 321. Welding flux may be applied on the both ends of the fuse member 31 to lower the welding temperature and make welding process easier.
The cross-section area of the first connection end 222 of the conductive member 22 and the second connection end 321 of the second terminal 32 is smaller than that of the conductive member 22 and the second terminal 32. The smaller the cross-section area is, the higher the temperature generated by the current flowing through the area is. Thus, the fuse member 31 that contacts with the first connection end 222 and the second connection ends 321 would have a higher temperature than the conductive member 22 and the second terminal 32, thereby speeding the melting of the fuse member 31 and enhancing the safety of the circuit.
The base 40 includes a recess 41 defined therein so as to receive the conductive member 22 and the fuse member 31. The base 40 includes an assembly post 42 extending from the floor of the recess 41. The base 40 also has a slit 44 corresponding to the second terminal 32 disposed at a side wall thereof.
Referring to FIG. 5, when the conductive member 22 and the fuse member 31 are received in the recess 41, the assembly post 42 is fitted into the assembly hole 223 of the conductive member 22. The second terminal 32 is fixed with the slit 44. The fuse member 31 connects the first connection end 222 with the second connection end 321.
When the dual protection device is in use, the elastic contact piece 21 bends downward and the first contact point 211 contacts with the second contact points 221. Thus, the electric current passes the first terminal 11, the cover 10, the elastic contact piece 21, the first contact point 211, the second contact point 221, the conductive member 22, the first connection end 222, the fuse member 31, the second connection end 321 and the second terminal 32 to form a closed circuit as shown in FIGS. 5 and 6.
When the circuit is overloaded and reaches a first predetermined temperature, the first protection unit 20 is activated and the elastic contact piece 21 is deformed and bent upward to separate the first contact points 211 from the second contact points 221 as shown in FIG. 7, thereby cutting off the circuit. The circuit becomes an open circuit. When the temperature is decreased, the elastic contact piece 21 is deformed and bent downward. Thus, the first contact point 211 and the second contact point 221 are in contact with each other as shown in FIG. 6, and the circuit becomes a closed circuit again.
If the elastic contact piece 21 of the first protection unit 20 does not function properly to cut off the circuit, the temperature of the circuit keeps climbing. Then, when the circuit reaches a second predetermined temperature, the fuse member 31 melts and breaks to form two spherical pieces 31′ attached on the first connection end 222 and the second connection end 321 due to surface tension. In this situation, the circuit becomes an open circuit. Because the melted fuse member 31 no longer connects the conductive member 22 with the second terminal 32, the circuit cannot re-connect again by itself after the temperature is decreased. The circuit is permanently cut off.
The first predetermined temperature of the first protection unit 20 is set up lower than the second predetermined temperature of the second protection unit 30. Thus, the dual protection device in accordance with the present invention uses the first protection unit 20 and the second protection unit 30 to provide first-line and second-line protections, respectively. When the circuit is overloaded and reaches the first predetermined temperature, the elastic contact piece 21 of the first protection unit 20 is deformed to separate the first contact point 211 from second contact point 221, thereby protecting the circuit. The second protection unit 30 is activated to cut off the circuit if the first protection unit 20 does not function properly and temperature of the circuit keeps rising. The fuse member 31 melts when the circuit reaches the second predetermined temperature, thereby separating the conductive member 22 from the second terminal 32. The first protection unit 20 and the second protection unit 30 function independently, and therefore the dual protection device for a circuit according to the present invention ensures that the circuit is protected.
Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.

## Claims

1. A dual protection device for a circuit, comprising:
a cover made of a conductive material and having a first terminal connected thereto;
a first protection unit comprising an elastic contact piece and a conductive member, the elastic contact piece including a first end fixed to the cover and a second end having a first contact point disposed on a bottom thereof, the elastic contact piece being made of metal, slightly curved, and capable of bending toward two opposite directions due to temperature change, the conductive member having a second contact point disposed on a top thereof, the first contact point located corresponding to the second contact point, the first contact point contacted with the second contact point;
a second protection unit comprising a fuse member and a second terminal, a first end of the fuse member connected to the conductive member and a second end of the fuse member connected to the second terminal, thereby electrically connecting the conductive member with the second terminal; and
a base having a recess defined therein so as to receive the conductive member and the fuse member;
wherein the elastic contact piece of the first protection unit is deformed and bent toward another direction to separate the first contact point from the second contact point when the elastic contact piece reaches a first predetermined temperature; when the temperature of the fuse member is raised to a second predetermined temperature, the fuse member melts and the conductive member is disconnected from the second terminal, thereby cutting off the circuit.

2. The dual protection device as claimed in claim 1, wherein the elastic contact piece is bi-metallic strip.

3. The dual protection device as claimed in claim 1, wherein the conductive member extends to form a narrow first connection end from a side thereof, the second terminal extends to form a narrow second connection end from a side thereof, the elongated fuse member is connected between the first connection end and the second connection end, thereby electrically connecting the conductive member with the second terminal.

4. The dual protection device as claimed in claim 1, wherein the base includes a slit defined at a side thereof and the second terminal is engaged with the slit.