1. Field of the Invention
The invention relates to a voltage-responsive protection device, more particularly to a lamp-string apparatus that incorporates a voltage-responsive protection device.
2. Description of the Related Art
In a string of series connected lamps, the entire string of the lamps is inoperable when one of the lamps breaks down or falls off from the string. The following are two methods proposed in the art in order to overcome the above problem:
1. A protection device, such as a Zener diode, a transistor, a thyristor, etc., is connected electrically in parallel to each of the lamps, and is used to replace a corresponding one of the lamps when the corresponding lamp breaks down or falls off from the string. In use, a voltage applied across the protection device after the latter is activated is generally greater than an operating voltage of each lamp. As such, an increase in the number of the lamps that broke down or that fell off results in decreased brightness of the other lamps in the lamp string.
2. A connecting device, such as a metal oxide wire, is connected in parallel to each lamp of a string of series connected lamps, and a short-circuiting copper piece is installed in each lamp seat for providing a conducting path when any one of the lamps breaks down or falls off from the string. When some of the lamps in the lamp string break down, the load voltage of the other lamps, the current flowing therethrough, and the operating temperature will increase, thereby damaging more lamps.
Therefore, the main object of the present invention is to provide a voltage-responsive protection device for a lamp-string apparatus that can eliminate the aforesaid drawbacks of the prior art.
According to one aspect of the present invention, a voltage-responsive protection device comprises:
a resistive element;
a conductive unit; and
a current blocking unit disposed between the resistive element and the conductive unit, the current blocking unit preventing current flow between the resistive element and the conductive unit when an applied voltage across the voltage-responsive protection device does not exceed a predetermined rated voltage, and permitting current flow between the resistive element and the conductive unit when the applied voltage exceeds the predetermined rated voltage.
According to another aspect of the present invention, a packaged voltage-responsive protection device comprises:
a resistor having opposite first and second ends;
a first diode having a first anode coupled electrically to the first end of the resistor, and a first cathode that serves as a first external electrode; and
a second diode having a second anode coupled electrically to the second end of the resistor, and a second cathode that serves as a second external electrode.
According to a further aspect of the present invention, a lamp-string apparatus comprises:
a string of series connected lamps; and
a plurality of voltage-responsive protection devices, each of which is connected electrically in parallel to a respective of the lamps, each of the voltage-responsive protection devices including
a current blocking unit disposed between the resistive element and the conductive unit, the current blocking unit preventing current flow between the resistive element and the conductive unit when a lamp voltage of the respective one of the lamps does not exceed a predetermined rated voltage, and permitting current flow between the resistive element and the conductive unit when the lamp voltage exceeds the predetermined rated voltage.
According to still another aspect of the present invention, there is provided a method for fabricating a voltage-responsive protection device. The method comprises the steps of:
a) forming a semi-finished product that has a current blocking unit disposed between a resistive element and a conductive unit, the current blocking unit preventing current flow between the resistive element and the conductive unit when an applied voltage across the voltage-responsive protection device does not exceed a predetermined rated voltage, and permitting current flow between the resistive element and the conductive unit when the applied voltage exceeds the predetermined rated voltage; and
b) encapsulating the semi-finished product such that the conductive unit is partly exposed.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which:
Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure.
Referring to
The current blocking unit 3 is disposed between the resistive element 2 and the conductive unit 4. The current blocking unit 3 prevents current flow between the resistive element 2 and the conductive unit 4 when an applied voltage across the voltage-responsive protection device 11 does not exceed a predetermined rated voltage, and permits current flow between the resistive element 2 and the conductive unit 4 when the applied voltage exceed the predetermined rated voltage.
In this embodiment, the resistive element 2 is one of a carbon film resistor, a carbon rod resistor, a metal film resistor, a metal wire-wound resistor, a metal rod resistor, and a metal foil resistor, which are all commercially available. The resistive element 2 is formed with a cylindrical shape, and has opposite ends 20, each of which is formed with a terminal stub 21.
In this embodiment, the conductive unit 4 includes a pair of conductive members 41.
In this embodiment, the current blocking unit 3 is made from an insulator material selected from SiO2 and Al2O3, and includes a pair of dielectric members 31, each of which is provided between a respective one of the conductive members 41 and a respective one of the opposite ends 20 of the resistive element 2. Each of the conductive members 41 is capped on the terminal stub 21 on a respective one of the opposite ends 20 of the resistive element 2. In this embodiment, each of the dielectric members 31 is in the form of a circular dielectric plate disposed between the respective one of the conductive members 41 and the terminal stub 21 on the respective one of the opposite ends 20 of the resistive element 2. Preferably, the predetermined rated voltage ranges from 20 volts to 80 volts.
As such, in actual use, if each lamp 12 of the lamp-string apparatus is normal, each lamp 12 has an operating voltage of about 2.4 volts, which is greatly less than the predetermined rated voltage, such that the respective voltage-responsive protection device 11 prevents current flow between the resistive element 2 and the conductive unit 4 thereof. Therefore, the voltage-responsive protection devices 11 incorporated in the lamp-string apparatus do not affect operation of the lamps 12.
In contrast, if one of the lamps 12 breaks down or falls off from the string, an applied voltage at a location corresponding to said one of the lamps 12 increases quickly up to about 120 volts, which is greater than the predetermined rated voltage of 20˜80 volts, such that the voltage-responsive protection device 11 corresponding to the lamp 12 that broke down or that fell off permits current flow between the resistive element 2 and the conductive unit 4 thereof, and replaces the lamp 12 that broke down or that fell off due to the impedance of the resistive element 2 of the voltage-responsive protection device 11 being equal to that of each lamp 12, thereby enabling the lamp-string apparatus to continue operation in a normal state.
It is noted that the power source applied to the lamp-string apparatus is not limited to the 120-volt AC power source, and that the number of the lamps 12 is also not limited to 50. The thickness of the dielectric member 31, and the predetermined rated voltage can be decided based on the applied power source and the number of the lamps 12.
In this embodiment, the resistive element (2b) is made from a semiconductor material, which can be a p-type semiconductor material, and has opposite surfaces 22. When the voltage-responsive protection device (11b) is incorporated in the above-mentioned lamp-string apparatus, the p-type semiconductor material of the resistive element (2b) is fabricated to have an adequate thickness so that the resistive element (2b) has an impedance corresponding to that of a corresponding lamp 12 of the above-mentioned lamp-string apparatus.
In this embodiment, the current blocking unit (3b) includes a pair of dielectric layers (31b) made from an insulator material selected from SiO2 and Al2O3. Each of the dielectric layers (31b) is formed on a respective one of the opposite surfaces 22 of the resistive element (2b) using convnetional CVD or PVD techniques such that each dielectric layer (31b) has an adequate thickness so as to match the requirements related to the predetermined rated voltage that ranges from 20 volts to 80 volts.
In this embodiment, the conductive unit (4b) includes a pair of metal layers (41b), which are made from Cu or Al. Each of the metal layers (41b) is formed on a respective one of the dielectric layers (31b) without extending therethrough.
Referring to
The current blocking unit is made from a second semiconductor material, and is in the form of a pair of doped regions (31c), each of which is formed on a respective one of the opposite surfaces 23 of the resistive element (2c). In this embodiment, the second semiconductor material is an n-type semiconductor material.
The conductive unit includes a pair of metal layers (41c), each of which is formed on a respective one of the doped regions (31c) without extending therethrough.
Furthermore, there are two oxide layers 5 made from SiO2. Each of the oxide layers 5 is formed on a respective one of the opposite surfaces 23 of the resistive element (2c) for isolating the resistive element (2c) from a respective one of the metal layers (41c).
In such a configuration, two p-n junctions, each of which constitutes a diode, are formed. Therefore, an equivalent circuit diagram of the configuration shown in
While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.