Abstract
A thermal fuse resistor including a ceramic substrate, a resistor body, a temperature sensing body, a first electrode cap, a second electrode cap, a first lead wire, a second lead wire, and a third lead wire. A first end of the ceramic substrate is provided with a first electrode cap, and a second end of the ceramic substrate is provided with a second electrode cap. The first electrode cap includes a main body, an inner end, and an outer end with an opening. The outer end includes an everted edge closely contacting the first end of the ceramic substrate. The main body and the inner end are arranged inside the ceramic substrate. The first lead wire extends outward from an outer end. One end of the third lead wire is electrically connected to the second electrode cap.
Claims
1. A thermal fuse resistor, comprising: a ceramic substrate; a resistor body; a temperature sensing body; a first electrode cap; a second electrode cap; at least two lead wires; and an insulation coating arranged on a surface of the resistor body, wherein the ceramic substrate comprises a first end having a first opening and a second end; the first electrode cap comprises a main body, an inner end, and an outer end having a second opening; the first electrode cap and the second electrode cap are respectively arranged at the first end and the second end of the ceramic substrate; two ends of the resistor body are respectively and electrically connected to the first electrode cap and the second electrode cap; the temperature sensing body is arranged in the first electrode cap; and the temperature sensing body is connected to the lead wire.
2. The thermal fuse resistor of claim 1 wherein, the outer end comprises an everted edge; the everted edge contacts the ceramic substrate; the inner end located close to the second end of the ceramic substrate; and the main body and the inner end are arranged inside the ceramic substrate.
3. The thermal fuse resistor according to claim 1, wherein the at least two lead wires and the temperature sensing body are axially connected and in a same straight line; and the at least two lead wires are centrally led out from the ceramic substrate, respectively.
4. The thermal fuse resistor according to claim 1, wherein the first electrode cap is of a tubular shape.
5. The thermal fuse resistor according to claim 3, wherein the inner end of the first electrode cap is a tapered constrictive port; and one of the at least two lead wires is inserted into the tapered constrictive port.
6. The thermal fuse resistor according to claim 3, wherein one of the at least two lead wires is hermetically connected to the inner end of the first electrode cap, closely.
7. The thermal fuse resistor according to claim 1, wherein the temperature sensing body is a low-melting-point metal wire; and a flux is adhered around the temperature sensing body.
8. The thermal fuse resistor according to claim 3, wherein the outer end of the first electrode cap is sealed by a first insulator; and one of the at least two lead wires extends outward from the first insulator.
9. The thermal fuse resistor according to claim 8, wherein a second insulator is partially filled between the first electrode cap and the ceramic substrate.
10. The thermal fuse resistor according to claim 1, wherein the insulation coating is one or more selected from the group consisting of epoxy resin, silicone resin, silicone rubber, and inorganic material.
11. The thermal fuse resistor according to claim 1, wherein an inner cavity wall of the first electrode cap is attached with a first insulation coating layer; and the first insulation coating layer is one or more selected from the group consisting of acetal paint, polyurethane paint, polyester paint, polyamideimide paint, polyesterimide paint, polyimide paint, alkyd paint, epoxy paint, and organosilicon paint.
12. The thermal fuse resistor according to claim 1, wherein an inner cavity of the first electrode cap is coaxially provided with an insulation sleeve; and the insulation sleeve is arranged around one or two of the at least two lead wires and the temperature sensing body.
13. The thermal fuse resistor according to claim 12, wherein the insulation sleeve comprises a first portion and a second portion; the first portion is located near the first end of the ceramic substrate; the second portion is located near the second end of the ceramic substrate; and an inner diameter of the first portion is smaller than an inner diameter of the second portion.
14. The thermal fuse resistor according to claim 1 further comprising a protective bushing arranged outside the thermal fuse resistor.
15. The thermal fuse resistor according to claim 1, wherein the resistor body is selected from the group consisting of resistance alloy wire, carbon film, metal film and metal oxide film.
16. The thermal fuse resistor according to claim 1, wherein three lead wires are provided; a first lead wire is led out from the outer end of the first electrode cap; a first end of a second lead wire is connected to the temperature sensing body; a second end of the second lead wire is hermetically connected to the inner end of the first electrode cap; one end of a third lead wire is connected to the second electrode cap; the first lead wire and the third lead wire are centrally led out from two sides of ceramic substrate; and the first lead wire, the temperature sensing body, the second lead wire, and the third lead wire are located in the same straight line.
17. The thermal fuse resistor according to claim 16, wherein the second lead wire is an extension of the temperature sensing body.
18. The thermal fuse resistor according to claim 14, wherein the protective bushing is selected from the group consisting of shrinkable tubing, silicone bushing, rubber bushing, fiberglass bushing, and fiberglass bushing with silica gel layer.
19. The thermal fuse resistor according to claim 14, wherein the protective bushing is selected from the group consisting of plastic, glass, and ceramics.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 shows a structural diagram of embodiment 1 of the present invention;
(2) FIGS. 2 (a)-2 (d) are the sectional views of the device according to embodiment 1 of the present invention; wherein
(3) FIG. 2 (a) is a sectional view showing a mode of the temperature sensing body axially connecting to the first lead wire and the second lead wire;
(4) FIG. 2 (b) is a sectional view showing that the second lead wire is replaced by the extension of the temperature sensing body;
(5) FIG. 2 (c) is a sectional view showing that a gap between the first electrode cap and the ceramic substrate is partially filled with a second insulator;
(6) FIG. 2 (d) is a sectional view showing that the second lead wire is replaced by an extension of the temperature sensing body and the gap between the first electrode cap and the ceramic substrate is partially filled with the second insulator;
(7) FIGS. 3 (a)-3 (d) are sectional views of the device according to embodiment 2 of the present invention; wherein
(8) FIG. 3 (a) is a sectional view showing that the inner cavity of the first electrode cap is attached with an insulation coating layer on the basis of FIG. 2 (c) of embodiment 1;
(9) FIG. 3 (b) is a sectional view showing that the inner cavity of the first electrode cap is attached with an insulation coating layer on the basis of FIG. 2 (d) of embodiment 1;
(10) FIG. 3 (c) is a sectional view showing that the inner cavity of the first electrode cap is provided with an insulation sleeve on the basis of FIG. 2 (c) of embodiment 1;
(11) FIG. 3 (d) is a sectional view showing that the inner cavity of the first electrode cap is provided with an insulation sleeve on the basis of FIG. 2 (d) of embodiment 1;
(12) FIGS. 4 (a)-4 (d) are sectional views of the device according to embodiment 3 of the present invention; wherein
(13) FIG. 4 (a) is a sectional view showing that a stretchable and transformable protective bushing is provided based on FIG. 3 (c);
(14) FIG. 4 (b) is a sectional view showing that a stretchable and transformable protective bushing is provided based on FIG. 3 (d);
(15) FIG. 4 (c) is a sectional view showing that a non-transformable hard protective bushing is provided based on FIG. 3 (c);
(16) FIG. 4 (d) is a sectional view showing that a non-transformable hard protective bushing is provided based on FIG. 3 (d);
(17) FIG. 5 is a circuit diagram showing that the resistor is used as an over-current protection element of a switching mode power supply.
DETAILED DESCRIPTION OF THE EMBODIMENTS
(18) Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are merely used to describe the preferred schemes of the present invention and should not be regarded as limiting the present invention.
Embodiment 1
(19) FIG. 1 and FIGS. 2(a)-2(d) show a structural view (partial sectional view) and a full sectional view of the device according to the first embodiment of the present invention.
(20) As shown in the figures, the thermal fuse resistor in this embodiment includes a ceramic substrate 6 which has a cylindrical shape. The ceramic substrate 6 includes a first end 6-1 and a second end 6-2 at a distance from the first end 6-1. The first end 6-1 has a first opening 6-1a and the second end 6-2 is a closed end. The resistor body 3 is wound around the outer surface of the ceramic substrate 6. The first end 6-1 and the second end 6-2 of the ceramic substrate 6 are respectively provided with first electrode cap 5a and second electrode cap 5b tightly fitted with the ceramic substrate 6. Two ends of the resistor body 3 are respectively and electrically connected to the first electrode cap 5a and the second electrode cap 5b, and are fixed on the ceramic substrate 6 by the first electrode cap 5a and the second electrode cap 5b. The first electrode cap 5a includes a straight tubular main body 5a-1, an outer end 5a-2, and an inner end 5a-3. Both of the outer end 5a-2 and the inner end 5a-3 are second openings 5a-4. The outer end 5a-2 of the first electrode cap 5a has a large inner diameter and includes an everted edge. The everted edge is hermetically connected to the first end 6-1 of the ceramic substrate 6 tightly, and electrically connected to one end of the resistor body 3. The inner end 5a-3 of the first electrode cap 5a has a smaller inner diameter and is a tapered constrictive port 5a-3a. The main body 5a-1 and the tapered constrictive port 5a-3a of the first electrode cap 5a are both arranged in the inner cavity of the ceramic substrate 6. The temperature sensing body 8 is arranged in the inner cavity of the first electrode cap 5a and is a fusible metal wire. Both ends of the temperature sensing body 8 are respectively connected to the first lead wire 1a and the second lead wire 1b. Flux 9 is adhered around the temperature sensing body 8. One end of the first lead wire 1a back in a distance from the temperature sensing body 8, centrally passes through the first end of the first electrode cap 5a and extends outwards to be used as the first pin of the whole product. One end of the second lead wire 1b at a distance from the temperature sensing body 8 is hermetically connected to the tapered constrictive port 5a-3a of the first electrode cap 5a tightly, and is electrically connected to the first electrode cap 5a at the same position. One end of the third lead wire 7 is electrically connected to the top center of the second electrode cap 5b, and the other end extends outward to be used as the second pin of the whole product.
(21) The outer end 5a-2 of the first electrode cap 5a is sealed by first insulator 2a. The first insulator 2a is made of epoxy resin. The outer surfaces of the resistor body 3, the ceramic substrate 6, the first electrode cap 5a, and the second electrode cap 5b are coated with insulation coating layer 4 which is one or combination of more selected from epoxy resin, silicone resin, silicone rubber, and inorganic materials. In the present embodiment, the insulation coating layer 4 is a silicone resin coating and forms an effective insulation layer with good insulation and voltage resistance performance.
(22) It can be derived from FIG. 2 (a) that the temperature sensing body 8 may be extended and the extension thereof may be used as the second lead wire 1b as shown in FIG. 2 (b).
(23) Based on FIG. 2 (a), a gap between the ceramic substrate 6 and the first electrode cap 5a is partially filled with second insulator 2b which is made of a thermally conductive silica gel. The effect of transferring the heat generated by the external resistor 3 to the inside when the circuit is turned on may be further improved. The structure is shown in FIG. 2 (c).
(24) It can be derived from FIG. 2 (c) that the temperature sensing body 8 may be extended and the extension thereof may be used as the second lead wire 1b as shown in FIG. 2 (d).
Embodiment 2
(25) As shown in the FIGS. 3(a)-3(d), the thermal fuse resistor in this embodiment include ceramic substrate 6 which has a cylindrical shape. The ceramic substrate 6 includes a first end 6-1 and a second end 6-2 at a distance from the first end. The first end 6-1 has a first opening 6-1a and the second end 6-2 is a closed end. Resistor body 3 is wound around the outer surface of the ceramic substrate 6. The first end 6-1 and the second end 6-2 of the ceramic substrate 6 are respectively provided with first electrode cap 5a and second electrode cap 5b, and the first electrode cap 5a and second electrode cap 5b are tightly fitted with the first end 6-1 and the second end 6-2 of the ceramic substrate 6. Two ends of the resistor body 3 are respectively electrically connected to the first electrode cap 5a and the second electrode cap 5b, and are fixed on the ceramic substrate 6 by the first electrode cap 5a and the second electrode cap 5b. The first electrode cap 5a includes a main body 5a-1 having straight tubular shape, an outer end 5a-2, and an inner end 5a-3. Both, the outer end 5a-2 and inner end 5a-3 are second openings 5a-4. The outer end 5a-2 of the first electrode cap 5a has a larger inner diameter and includes an everted edge. The everted edge is hermetically connected to the first end 6-1 of the ceramic substrate 6 tightly, and electrically connected to one end of the resistor body 3. The inner end 5a-3 of the first electrode cap 5a has a smaller inner diameter and is a tapered constrictive port 5a-3a. The main body 5a-1 and the tapered constrictive port 5a-3a of the first electrode cap 5a are both arranged in the inner cavity of the ceramic substrate 6. First insulation coating layer 10 is attached to the inner cavity wall 5a-5 of the first electrode cap 5a. The first insulation coating layer 10 may be made of acetal paint, polyurethane paint, polyesterimide paint, polyester paint, polyamideimide paint, polyimide paint, alkyd paint, epoxy paint, and organosilicon paint, etc. Preferably, the first insulation coating layer 10 is made of polyimide paint. The first insulation coating layer 10 can provide sufficient creepage distance and electrical clearance between the first lead wire 1a and the first electrode cap 5a after the opening of the temperature sensing body 8 because of overheating. The inner cavity of the first electrode cap 5a is provided with temperature sensing body 8 which is a fusible metal wire. Two ends of the temperature sensing body 8 are respectively connected to first lead wire 1a and second lead wire 1b. Flux 9 is adhered around the temperature sensing body 8. One end of the first lead wire 1a at a distance from the temperature sensing body 8 centrally passes through the first end of the first electrode cap 5a and extends outwards to be used as the first pin of the whole product. One end of the second lead wire 1b at a distance from the temperature sensing body 8 is hermetically connected to the tapered constrictive port 5a-3a of the first electrode cap 5a tightly, and is electrically connected to the first electrode cap 5a at this position. One end of the third lead wire 7 is electrically connected to the top center of the second electrode cap 5b, and the other end of the same extends outward to be used as the second pin of the whole product.
(26) It can be derived from FIG. 3 (a) that the temperature sensing body 8 may be extended and the extension thereof may be used as the second lead wire 1b as shown in FIG. 3 (b).
(27) The outer end 5a-2 of the first electrode cap 5a and the gap between the first electrode cap 5a and the ceramic substrate 6 are partially sealed by second insulator 2b. Here, the second insulator 2b is epoxy resin for improving the strength. The outer surfaces of the resistor body 3, the ceramic substrate 6, the first electrode cap 5a, and the second electrode cap 5b are coated with insulation coating layer 4, which is one or combination of more selected from epoxy resin, silicone resin, silicone rubber, and inorganic materials. In the present embodiment, the insulation coating layer 4 is a silicone resin coating which forms an effective insulation layer, thus, the present invention has a good insulation and voltage endurance performance.
(28) On the basis of FIG. 3(a) and FIG. 3(b), the first insulation coating layer 10 may be replaced with insulation sleeve 11, namely, the insulation sleeve 11 is arranged in the inner cavity of the first electrode cap 5a to ensure that the first lead wire 1a and the first electrode cap 5a have sufficient electrical clearance and creepage distance after the temperature sensing body 8 is fused and cut-off. The insulation sleeve may be made of inorganic materials such as glass, ceramics, plastics, rubbers etc. or organic materials or composite materials. In this embodiment, the insulation sleeve 11 is a ceramic sleeve. The insulation sleeve 11 in this embodiment includes a first portion 11-1 located near the first electrode cap 5a and a second portion 11-2 located near the second electrode cap 5b. The inner diameter of the first portion 11-1 is smaller than that of the second portion 11-2 and slightly larger than the diameter of the first lead wire 1a, so as to ensure that the first lead wire 1a is centrally led out from the first portion 11-1 of the insulating sleeve 11 and the outer end 5a-2 of the first electrode cap 5a. The first portion 11-1 and the second portion 11-2 of the insulation sleeve 11 are tapered transition which facilitates the first lead wire 1a to pass through the insulation sleeve 11 smoothly during product assembly process. By doing so, the first lead wire 1a and the third lead wire 7 are symmetrically led out from the center of the cross section of the ceramic substrate 6 to form two pins of the thermal fuse resistor, so that the two pins of the thermal fuse resistor of the present invention are in the same straight line, which facilitates the axial taping of the thermal fuse resistor and the automatic plug-in of the printed circuit board. On the basis of FIG. 3(a), the first insulation coating layer 10 is replaced by the insulation sleeve 11 to form the structure of FIG. 3(c). On the basis of FIG. 3(b), the first insulation coating layer 10 is replaced by the insulation sleeve 11 to form the structure of FIG. 3(d).
Embodiment 3
(29) As shown in FIGS. 4(a)-4(d), the thermal fuse resistor in this embodiment includes ceramic substrate 6 having a cylindrical shape. The ceramic substrate 6 includes a first end 6-1 and a second end 6-2 at a distance from the first end. The first end 6-1 has a first opening 6-1a and the second end 6-2 is a closed end. The resistor body 3 is wound around the outer surface of the ceramic substrate 6. The first end 6-1 and the second end 6-2 of the ceramic substrate 6 are respectively provided with first electrode cap 5a and second electrode cap 5b, and the first electrode cap 5a and second electrode cap 5b are tightly fitted with the first end 6-1 and the second end 6-2 of the ceramic substrate 6. Two ends of the resistor body 3 are respectively electrically connected to the first electrode cap 5a and the second electrode cap 5b, and are fixed on the ceramic substrate 6 by the first electrode cap 5a and the second electrode cap 5b. The first electrode cap 5a includes a main body 5a-1 having a straight tubular shape, an outer end 5a-2, and an inner end 5a-3. Both of the outer end 5a-2 and the inner end 5a-3 are second openings 5a-4. The outer end 5a-2 of the first electrode cap 5a has a larger inner diameter and includes an everted edge. The everted edge is hermetically connected to the first end 6-1 of the ceramic substrate 6 tightly, and electrically connected to one end of the resistor body 3. The inner end 5a-3 of the first electrode cap 5a has a smaller inner diameter and is a tapered constrictive port 5a-3a. The main body 5a-1 and the tapered constrictive port 5a-3a of the first electrode cap 5a are both arranged in the inner cavity of the ceramic substrate 6. The inner cavity of the first electrode cap 5a is provided with insulation sleeve 11 having openings at both ends. The inner cavity of the first electrode cap 5a is further provided with temperature sensing body 8 which is a fusible metal wire. Both ends of the temperature sensing body 8 are respectively electrically connected to the first lead wire 1a and the second lead wire 1b. Flux 9 is adhered around the temperature sensing body 8. One end of the first lead wire 1a back in a distance from the temperature sensing body 8 centrally passes through insulation sleeve 11 and the first end of the first electrode cap 5a and extends outwards to be used as the first pin of the whole product. The insulation sleeve 11 ensures that the first lead wire 1a and the first electrode cap 5a have sufficient electrical clearance and the creepage distance after the temperature sensing body 8 is fused and cut-off. The insulation sleeve may be made of inorganic materials such as glass, ceramics, plastics, rubbers etc. or organic materials or a composite material. In this embodiment, the insulation sleeve 11 is a ceramic sleeve. The insulation sleeve 11 in this embodiment includes a first portion 11-1 located near the first electrode cap 5a and the second portion 11-2 located near the second electrode cap 5b. The inner diameter of the first portion 11-1 is smaller than that of the second portion 11-2 and slightly larger than the diameter of the first lead wire 1a, so as to ensure that the first lead wire 1a is centrally led out from the first portion 11-1 of the insulation sleeve 11 and the outer end 5a-2 of the first electrode cap 5a. One end of the second lead wire 1b at a distance from the temperature sensing body 8 is hermetically connected to the tapered constrictive port 5a-3a of the first electrode cap 5a tightly, and is electrically connected to the first electrode cap 5a at this position. One end of the third lead wire 7 is electrically connected to the top center of the second electrode cap 5b, and the other end of the same extends outward to be used as the second pin of the whole product.
(30) The outer end 5a-2 of the first electrode cap 5a and the gap between the first electrode cap 5a and the ceramic substrate 6 are partially sealed by second insulator 2b. Here, the second insulator 2b is epoxy resin for improving the strength. The outer surfaces of the resistor body 3, the ceramic substrate 6, the first electrode cap 5a, and the second electrode cap 5b are coated with insulation coating layer 4 which is one or combination of more selected from epoxy resin, silicone resin, silicone rubber, and inorganic materials. In the present embodiment, the insulation coating layer 4 is silicone resin coating which forms an effective insulation layer. Therefore, the present invention has good insulation and voltage resistance performance.
(31) It can be derived from FIG. 4 (a) that the temperature sensing body 8 may be extended and the extension thereof may be used as the second lead wire 1b as shown in FIG. 4 (b).
(32) It can also be derived from FIG. 4 (c) that the temperature sensing body 8 may be extended and the extension thereof may be used as the second lead wire 1b as shown in FIG. 4 (d).
(33) In addition, protective bushing 12 is provided outside the insulation coating layer 4. As shown in FIGS. 4(a) and 4 (b), the protective bushing may be a soft protective bushing which has openings at two ends and is stretchable and transformable, or as shown in FIG. 4(c) and FIG. 4(d), the protective bushing may be a hard protective bushing which is non-transformable. The soft protective bushing may be one selected from heat shrinkable tubing, silicone bushing, rubber bushing, fiberglass bushing, fiberglass bushing with silica gel layer etc. Preferably, soft protective bushing is heat shrinkable tubing. The non-deformable hard protective bushing may be made of materials having similar functions such as plastic, glass, ceramics etc. Preferably, the non-deformable hard protective bushing is made of ceramic materials. FIG. 4(a) shows that a stretchable and deformable protective bushing with openings at two ends is arranged outside the insulation coating layer based on FIG. 3(c) of embodiment 2. The first lead wire 1a and the third lead wire 7 are respectively centrally led out from two ends of the opening of the protective bushing to be used as two pins of the whole product. FIG. 4(b) shows that a stretchable and deformable protective bushing with openings at two ends is arranged outside the insulation coating layer based on FIG. 3(d) of embodiment 2. The first lead wire 1a and the third lead wire 7 are respectively centrally led out from two ends of the opening of the protective sleeve to be used as two pins of the whole product. FIG. 4(c) shows that a non-transformable hard protective bushing with openings at two ends is arranged outside the insulation coating layer based on FIG. 3(c) of embodiment 2. The first lead wire 1a and the third lead wire 7 are respectively centrally led out from two ends of the opening of the protective sleeve to be used as two pins of the whole product. FIG. 4(d) shows that a non-transformable hard protective bushing with openings at two ends is arranged outside the insulation coating layer based on FIG. 3(d) of embodiment 2. The first lead wire and the third lead wire are respectively centrally led out from two ends of the opening of the protective sleeve to be used as two pins of the whole product. By arranging the protective bushing, the explosion of device caused by severe overload can be suppressed, and fragments generated by explosion can be kept inside the protective bushing even if the device is exploded due to a severe overload, thereby reducing the explosion noise, and improving the anti-explosion performance. Also, the protective sleeve can improve the insulation and pressure performance of the device.
(34) In summary, the device can be used for over-temperature and over-current protection of the circuit. When the ambient temperature reaches the melting point of the temperature sensing body inside the device, the temperature sensing body fuses, retracts towards the lead wires under the action of the flux, so that the temperature sensing body is cut-off and the circuit is protected. When a small fault current occurs in the circuit, the resistance wire in the device heats up, and the heat is effectively transferred to the temperature sensing body located inside. When the melting point of the temperature sensing body is reached, the temperature sensing body retracts towards two ends of the lead wires under the action of the flux, so that the temperature sensing body is cut-off, and the circuit is protected. When a large fault current occurs in the circuit, the resistor body in the device will heat up sharply to the melting point thereof so that the resistor body is cut-off, and the circuit is effectively protected.
(35) Comparing the resistor (the resistance value of the resistor body is 10, and the melting-point of the temperature sensing body is 218 C.) shown in FIG. 4 (a) of this embodiment with a commonly used wire-wound resistor having the same volume, resistor body, and resistance value, the comparison results of the surface temperature and the fusing-cut-off time under different test currents are shown in table 1 below. The surface temperature of the device before fusing and cut-off in this embodiment does not exceed 221 C., so the device used as an over-temperature over-current protection element of the circuit can ensure that there is no hidden danger of overheat. While using the commonly used wire-wound resistor, when a small fault current occurs in the circuit, the surface temperature can reach hundreds of degrees Celsius, which may cause the shells of chargers, LED lights etc. fusing and even start fire. In addition, low-melting-point metals with different fusing points may be selected as the temperature sensing body, thereby forming different levels of temperature protection and having wider selectivity.
(36) TABLE-US-00001 TABLE 1 Test Resistor of embodiment 3 Common wire-wound resistor current Temperature Cut-off time Temperature Cut-off time (A) ( C.) (s) ( C.) (s) 0 27.5 C. No cut-off 27.5 C. No cut-off 0.1 36.2 C. No cut-off 36.5 C. No cut-off 0.15 50.8 C. No cut-off 51.1 C. No cut-off 0.2 72.3 C. No cut-off 73.0 C. No cut-off 0.25 90.5 C. No cut-off 91.3 C. No cut-off 0.30 128.0 C. No cut-off 129.5 C. No cut-off 0.35 171.5 C. No cut-off 172.3 C. No cut-off 0.40 214.1 C. No cut-off 215.5 C. No cut-off 0.45 219.3 C. 135 s 245 C. No cut-off 0.50 279 C. No cut-off 0.60 388 C. No cut-off 0.70 467 C. No cut-off 0.80 582 C. No cut-off 0.90 729 C. No cut-off 1.00 905 C. 128 s
(37) In table 1, the temperature of the device of embodiment 3 is the temperature at the middle position of the outer surface of the protective bushing, and the temperature of the common wire-wound resistor is the temperature at the middle position of outer surface of the main body.
(38) FIG. 5 is a circuit diagram showing that the resistor (hereinafter referred to as FR) is used as an over-current protection element of the charger used as switching mode power supply. In the process of charging, elements such as rectifier bridge, filtering capacitor or metal oxide semiconductor (MOS transistor) etc. may be broken down and shorted out, at this time, the resistor will withstand a short circuit voltage ranged 100V a.c.-240V a.c. If the resistor is the existing coating-fusing resistor, such as wire-wound resistor, the moment when the resistor is cut-off, is followed with a high electric arc which makes the fragile coating splashing around with a loud blasting sound, which would frighten people around the charger. However, if the resistor is the device with protective bushing in the embodiment, the electric arc occurring at the moment when the resistor is cut-off can be suppressed, the fragile coating is limited inside the protective bushing without obvious blasting sound, thereby greatly improving the safety of using the charger.
(39) The existing coating resistor and the resistor with protective bushing shown in FIG. 4 (a) of embodiment 3 were tested with short circuit under the same short circuit voltage, and the test results are shown in table 2.
(40) TABLE-US-00002 TABLE 2 Comparison of short-circuit anti-explosion performance test results Short-circuit Existing voltage (V a.c.) coating resistor Resistor of embodiment 3 220 Large sparks and loud No spark and blasting blasting sound sound 240 Large sparks and loud No spark and blasting blasting sound sound
(41) The foregoing merely shows the preferred embodiments of the present invention, rather than limiting the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the above-mentioned embodiments or substitute some of the technical features to similar objects. Any modification, substitution, improvement etc. without departing from the spirit and principles of the present invention, however, shall be considered as falling within the scope of the present invention.
