JP7339690B2 - surge protection circuit - Google Patents

Description

More particularly, the present invention relates to a surge protection circuit for protecting electrical equipment from abnormal increases in current or voltage.

As a conventional surge protection circuit 100, an electric circuit incorporated in a lightning arrester installed as shown in FIG. 3(a) is known. Surge protection circuit 100 is connected in parallel with power input line 200 . That is, as shown in FIG. 3B, the surge protection circuit 100 includes a varistor 300 and a gas arrester 400, or an equivalent has a circuit. Therefore, even after the varistor 300 is destroyed or broken due to the application of a surge and the function of the surge protection circuit 100 is impaired, it is still possible to conduct electricity between the main power supply and the electrical equipment, thereby protecting the electrical equipment from surges. was difficult.

JP-A-11-97215 Japanese Patent Application Laid-Open No. 2020-38861

In order to solve the above problem, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 11-97215) discloses a protection device comprising a varistor and a thermistor arranged adjacent to the varistor. In the device described in Patent Document 1, the current is cut off when the thermistor detects that the varistor has reached an abnormally high temperature. Further, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2020-38861) discloses a lightning arrester that includes a varistor and a thermal fuse arranged adjacent to the varistor. Japanese Patent Laid-Open No. 2002-200001 discloses that current is interrupted by blowing a thermal fuse due to the heat generated by the varistor when the varistor is destroyed.

Both Patent Document 1 and Patent Document 2 use the heat of varistor breakdown generated when a surge is applied to cut off a circuit. However, varistors are larger than thermistors and thermal fuses, and varistor breakdown occurs instantaneously anywhere on the varistor surface. Therefore, in some cases, such as when varistor destruction occurs on the side that is not in contact with the thermistor or thermal fuse, an abnormally high temperature cannot be accurately detected. In other words, even though the varistor is broken, there are cases where the energization is not interrupted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surge protection circuit that can reliably cut off current flow when a varistor fails due to surge application. It is to be.

The surge protection circuit according to the present embodiment includes a power input line including an ungrounded wire (L) and a grounded wire (N), and an LN connection line that connects the ungrounded wire and the grounded wire. A first varistor that absorbs surges, and a first varistor that is in series with the first varistor and is placed in the LN connection line. and a first failure detection means for responsively cutting off the energization of at least one of the non-grounded wire and the grounded wire.

Preferably, the first failure detection means includes a first resistor arranged in the LN connection line and generating heat in response to the flow of the current, and at least one of the non-grounded wire and the grounded wire. A first thermal fuse is provided in the middle of one of the resistors, is arranged in a position close to the first resistor, and is fused in response to the heat generation temperature of the first resistor exceeding a set value.

Preferably, the power input line includes a ground wire (G). In this case, the surge protection circuit of the present embodiment is arranged in the LG connection line that connects the non-grounded side wire and the ground wire, and the second varistor that absorbs the surge is connected in series with the second varistor. , a first gas arrester arranged on the LG connection line, and a first branch line branched from between the second varistor and the first gas arrester on the LG connection line and connected to the ground side wire. and a second failure detection means arranged to cut off the energization of the non-grounded side wire in response to the energization current flowing through the LG connection line and the first branch line due to a failure of the second varistor.

Preferably, the second failure detection means includes a second resistor disposed in the first branch line and generating heat in response to the flow of the energizing current, and a second resistor provided midway along the non-grounded side wire. and a second thermal fuse that is arranged in close proximity to and melts in response to the heat generated by the second resistor exceeding a set value.

When the power input line includes a ground wire (G), the surge protection circuit of another embodiment is arranged in the NG connection line that connects the ground side wire and the ground wire, and includes a third varistor that absorbs the surge. , a second gas arrester arranged in the NG connection line in series with the third varistor, and branching from between the third varistor and the second gas arrester on the NG connection line, ungrounded It is arranged in the second branch line connected to the side wire, and cuts off the energization of the ground side wire in response to the current flowing through the NG connection line and the second branch line due to the failure of the third varistor. and a third failure detection means.

Preferably, the third failure detection means includes a third resistor disposed in the second branch line and generating heat in response to the flow of the current, and a third resistor provided midway along the ground-side wire. and a third thermal fuse arranged in close proximity and blown in response to the temperature generated by the third resistor exceeding a set value.

A surge protection circuit according to another aspect of the present embodiment includes a power input line including a non-grounded wire (L), a grounded wire (N), and a ground wire (G); A varistor that is arranged in an earth connection line that connects one of the ground-side wires and the earth wire to absorb surges, a gas arrester that is arranged in the earth connection line in series with the varistor, and the earth connection line. It is installed in a branch line that branches from between the upper varistor and the gas arrester and is connected to either the grounded wire or the non-grounded wire, and if the varistor fails, the current flows through the ground connection line and the branch line. and a failure detection means for interrupting the energization of either the grounded wire or the non-grounded wire in response to the flow.

A surge protection circuit according to another embodiment is incorporated in a three-phase AC circuit having three input lines. A surge protection circuit is arranged in a connection line connecting between any two input lines, and is arranged in the connection line in series with a varistor that absorbs a surge, and if a failure of the varistor occurs, the connection line and fault detection means for de-energizing one or the other of the input lines in response to the flow of current.

A surge protection circuit incorporated in a three-phase AC circuit having three input lines (L1, L2, L3) and a ground wire (G) is one input line of any two input lines, Between a varistor that is arranged in the earth connection line that connects the earth wire and absorbs surges, a gas arrester that is arranged in the earth connection line in series with the varistor, and the varistor and the gas arrester on the earth connection line. in a branch line branching from and connected to the other of any two input lines, and in response to a varistor failure causing energizing current to flow through the grounded line and the branch line, and failure detection means for de-energizing one or the other of the input lines.

Advantageous Effects of Invention According to the present invention, when a varistor fails due to the application of a surge, it is possible to reliably cut off energization and protect electrical equipment.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the surge protection circuit which concerns on this Embodiment, (a) is a schematic diagram, (b) is a circuit diagram. FIG. 10 is a circuit diagram showing a surge protection circuit according to another embodiment; It is a figure which shows the conventional surge protection circuit typically, (a) is a schematic diagram, (b) is a circuit diagram.

(About configuration)
A surge protection circuit according to the present embodiment will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated. In addition, the configurations labeled "first", "second", and "third" are basically of the same or similar performance, and the configurations labeled "second" and later will not be repeated.

FIG. 1 is a diagram showing a surge protection circuit 1 according to this embodiment. FIG. 1(a) is a schematic diagram showing that a surge protection circuit 1 according to the present embodiment is incorporated between a main power supply and electrical equipment. FIG. 1(b) is a circuit diagram showing an electric circuit extracted from the dotted line in FIG. 1(a).

A surge protection circuit 1 comprises a power input line 2 . The power input line 2 includes a non-grounded wire L, a grounded wire N, and a ground wire G. As shown in FIG. The power input line 2 is a line that electrically connects the main power source and the electrical equipment. In addition, although this Embodiment demonstrates the example provided with the earth wire G, it is not essential to provide this.

A surge protection circuit 1 according to the present embodiment includes an LN connection line 3 that connects a non-grounded wire L and a grounded wire N. As shown in FIG. The surge protection circuit 1 includes a first varistor 32 arranged on the LN connection line 3 to absorb the surge, and a first varistor 32 arranged on the LN connection line 3 in a series relationship with the first varistor 32 . a first failure detection means 31 for interrupting the energization of at least one of the non-grounded side wire L and the grounded side wire N in response to the flow of current through the LN connection line 3 due to the failure of .

On the LN connection line 3, the first varistor 32 is provided on the non-grounded wire L side, and the first failure detection means 31 is provided on the grounded wire N side. Since the impedance of the first varistor 32 is high during normal energization, the current flows on the non-grounded side wire L toward the electrical equipment and does not flow to the LN connection line 3 side. When a surge is applied here and the first varistor 32 breaks down, the impedance of the first varistor 32 decreases, so that current flows into the LN connection line 3 . A varistor failure is a state in which the function of the varistor is reduced or lost. In this embodiment, on the LN connection line 3, the first varistor 32 is arranged on the non-grounded wire L side and the first failure detection means 31 is arranged on the grounded wire N side. can be reversed. That is, the first varistor 32 may be arranged on the ground side wire N side, and the first fault detection means 31 may be arranged on the non-ground side wire L side.

In the present embodiment, when a current flows into the LN connection line 3, the first fault detection means 31 detects this and cuts off the energization of the non-grounded side wire L. FIG. The first failure detection means 31 may be any means as long as it cuts off the energization of the power input line 2 . The first failure detection means 31 in the present embodiment is arranged in the LN connection line 3, and includes a first resistor 33 that generates heat in response to the flow of current, the non-grounded wire L and the grounded wire. N, is arranged in a position close to the first resistor 33, and is fused in response to the heat generation temperature of the first resistor 33 exceeding a set value. and a thermal fuse 34 .

The first resistor 33 generates heat when the LN connection line 3 is energized. That is, the first resistor 33 does not generate heat during normal energization, but generates heat when the first varistor 32 fails due to the application of a surge and current flows through the LN connection line 3 . From the viewpoint of interrupting the energization of the non-grounded side wire L as soon as possible, it is preferable to use the first resistor 33 whose temperature rises to 100° C. or more in several seconds to several tens of seconds.

The first thermal fuse 34 of the present embodiment is provided in the middle of the non-grounded electric wire L. As shown in FIG. The first thermal fuse 34 and the first resistor 33 are arranged at positions close to each other. The term "proximity" as used herein typically refers to a state in which at least a portion of the first thermal fuse 34 and the first resistor 33 are in contact with each other, and the temperature of the first resistor 33 can sufficiently affect the temperature. It is sufficient that the first thermal fuse 34 is arranged at a position where it is possible. Thereby, the first thermal fuse 34 can be fused by the heat generated from the first resistor 33 . From the viewpoint of practicality, it is preferable to use the first thermal fuse 34 that melts at 100° C. or higher.

Note that the first resistor 33 and the first thermal fuse 34 may be bundled with a tape or the like and adhered to each other from the viewpoint of reliable fusing.

A surge protection circuit 1 according to this embodiment includes an LG connection line 4 . In this case, the surge protection circuit 1 is arranged in the LG connection line 4 that connects the non-grounded side wire L and the ground wire G, and the second varistor 42 that absorbs the surge and the second varistor 42 are connected in series. and a first gas arrester 45 arranged on the LG connection line. Also, the surge protection circuit 1 is arranged in the first branch line 40 branched from between the second varistor 42 and the first gas arrester 45 on the LG connection line 4 and connected to the ground side wire N. A second failure detection means 41 is provided.

On the LG connection line 4, the second varistor 42 is provided on the non-grounded wire L side, and the first gas arrester 45 is provided on the ground wire G side. Since the impedances of the second varistor 42 and the first gas arrester 45 are high during normal energization, the current flows through the non-grounded wire L and does not flow through the LG connection line 4 side. When a surge is applied here, the second varistor 42 absorbs the surge by changing impedance, and the first gas arrester 45 absorbs the surge by discharging. When the second varistor 42 fails due to the application of a surge, the impedance of the second varistor 42 becomes low, and the impedance of the first gas arrester 45 becomes high. . A second resistor 43 is arranged on the first branch line 40 , and the second failure detection means 41 functions when a current flows through the first branch line 40 .

The second failure detection means 41 cuts off the energization of the non-grounded side wire L when a surge is applied to the LG connection line 4 and the second varistor 42 fails. The second failure detection means 41 of the present embodiment is arranged in the first branch line 40 and provided in the middle of the second resistor 43 that generates heat in response to the applied current and the non-grounded side wire L. It includes a second thermal fuse 44 that is arranged in a position close to the two resistors 43 and melts in response to the temperature of the heat generated by the second resistor 43 exceeding a set value.

The second resistor 43 generates heat when an electric current flows into the first branch line 40 . Since the impedance of the first gas arrester 45 is high, almost no current flows to the ground wire G side. That is, the current that flows into the LG connection line 4 after the breakage of the second varistor 42 does not flow into the ground line G, but flows into the first branch line 40. This ensures that the second resistor 43 heats up. Thermal fuse 44 can be blown.

A surge protection circuit 1 according to this embodiment includes an NG connection line 5 . In this case, the surge protection circuit 1 is arranged in the NG connection line 5 that connects the ground-side wire N and the ground wire G, and is connected in series with the third varistor 52 that absorbs the surge and the third varistor 52. , and a second gas arrester 55 arranged on the NG connection line 5 . Also, the surge protection circuit 1 is arranged in the second branch line 50 branched from between the third varistor 52 and the second gas arrester 55 on the NG connection line 5 and connected to the non-grounded side wire L. A third failure detection means 51 is provided.

On the NG connection line 5, the third varistor 52 is provided on the ground wire N side, and the second gas arrester 55 is provided on the ground wire G side. Since the impedances of the third varistor 52 and the second gas arrester 55 are high during normal energization, current flows through the ground side wire N and does not flow through the NG connection line 5 side. When a surge is applied here, the third varistor 52 absorbs the surge by changing impedance, and the second gas arrester 55 absorbs the surge by discharging. When the third varistor 52 fails due to the application of a surge, the impedance of the third varistor 52 becomes low, and the impedance of the second gas arrester 55 becomes high. . A third resistor 53 is arranged on the second branch line 50 , and the third failure detection means 51 functions when a current flows through the second branch line 50 .

When a surge is applied to the NG connection line 5 and the third varistor 52 fails, the third failure detection means 51 cuts off the energization of the ground-side wire N. FIG. The third failure detection means 51 of the present embodiment is arranged in the second branch line 50 and provided in the middle of the third resistor 53 that generates heat in response to the applied current and the ground side wire N. It also includes a third thermal fuse 54 that is arranged in close proximity to the resistor 53 and melts in response to the temperature of the heat generated by the third resistor 53 exceeding a set value.

The third resistor 53 generates heat when a current flows into the second branch line 50 . Since the impedance of the second gas arrester 55 is high, almost no current flows to the ground line G side. That is, the current that flows into the NG connection line 5 after the breakage of the third varistor 52 does not flow into the ground line G, but flows into the second branch line 50. This ensures that the third resistor 53 heats up. The third thermal fuse 54 can be fused.

(About effect)
A first gas arrester 45 is provided on the LG connection line 4 and a second gas arrester 55 is provided on the NG connection line 5 . Here, the first and second gas arresters 45 and 55 have the characteristic that they do not conduct electricity at the voltage during normal energization due to their high impedance. That is, the first and second gas arresters 45 and 55 function so that the energizing currents flowing into the LG connection line 4 and the NG connection line 5 flow through the first and second branch lines 40 and 50, respectively. As a result, electricity is supplied between L and N. Therefore, the energization between L and N after the failure of the varistor is carried out via the first and second branch lines 40,50. The second and third resistors 43 and 53 provided on the first and second branch lines 40 and 50 generate heat due to the current flowing through the branch lines 40 and 50 . As a result, the second and third thermal fuses 44, 54 can be reliably fused.

According to the surge protection circuit 1 according to the present embodiment, since the energization to the electrical equipment is surely interrupted, it is possible to easily recognize the failure. In addition, since the electrical equipment is not used continuously after the varistor has failed, it is possible to prevent damage caused by the next surge.

A conventional surge protection circuit detects heat generation of a varistor when the varistor is destroyed and the shape and heat detection are unstable. The surge protection circuit according to the present embodiment is different from such a configuration of the prior art, in that the current passing through the broken or faulty varistor causes the resistor to generate heat, and the heat generated by the resistor reliably The thermal fuse can be fused to cut off the power input line.

Note that the surge protection circuit 1 of the present embodiment only needs to have at least one failure detection means. However, when two or more, especially the second and third failure detection means 41, 51 are provided, further effects can be obtained. When a surge is applied to the power input line 2 , surge current also flows through the first branch line 40 and the second branch line 50 . As a result, in the surge protection circuit 1 of the present embodiment, three parallel circuits connecting between L and N are formed. Each varistor and/or gas arrestor provided in each of the lines 5 can absorb the distributed surge. That is, the surge protection circuit 1 of this embodiment can improve the surge tolerance.

In the above description, the surge protection circuit 1 of the present embodiment is provided with the LN connection line 3, the LG connection line 4, and the NG connection line 5. The effect of the present invention can be exhibited only by providing a failure detection means in one of the connection lines. Therefore, a surge protection circuit 1 according to another aspect of the present invention includes a power input line 2 having a non-grounded wire (L), a grounded wire (N), and a ground wire (G), and a grounded wire or non-grounded wire. Varistors 42, 52 for absorbing surges, which are arranged in the ground connection lines 4, 5 connecting one of the ground-side electric wires and the ground wire, and the ground connection lines 4, 52 are connected in series with the varistors 42, 52. gas arresters 45, 55 arranged at 5, branched from between the varistors 42, 52 on the ground connection lines 4, 5 and the gas arresters 45, 55, either the ground side wire L or the non-ground side wire N are arranged in the branch lines 40, 50 connected to the other, and in response to current flowing through the ground connection lines 4, 5 and the branch lines 40, 50 due to the failure of the varistors 42, 52, the ground side wire N or Failure detection means 41 and 51 for interrupting the energization of either one of the non-grounded side wires L are provided.

(About other embodiments)
Next, a surge protection circuit 1A according to another embodiment will be described with reference to FIG. The surge protection circuit 1 according to the present invention is used for a single-phase AC electric circuit, but the surge protection circuit 1A according to another embodiment is designed for a surge protection circuit used for a three-phase AC electric circuit. This is the protection circuit 1A. A three-phase AC circuit is substantially a combination of three single-phase AC circuits, and the above-described surge protection circuit 1 for single-phase AC circuits can also be applied to the three-phase AC circuit.

The varistor and failure detection means of the surge protection circuit 1A shown in FIG. 2 are provided between any two input lines out of the three input lines L1, L2 and L3. That is, varistors 32A, 42A, 52A for absorbing surges and failure detection means 31A, 41A, 51A are provided in the L1-L2 connection line 3A, the L2-L3 connection line 4A and the L3-L1 connection line 5A, respectively. A current flows through each connection line 3A, 4A, 5A due to failure of each varistor 32A, 42A, 52A. In response to the flow of current, the failure detection means 31A, 41A, 51A cut off the current to one input line or the other input line.

The failure detection means 31A, 41A, 51A are provided with resistors 33A, 43A, 53A that generate heat in response to the flow of current on the connection lines 3A, 4A, 5A. It is provided in the middle of the input line or the other input line, is arranged in a position close to the resistors 33A, 43A, 53A, and is fused in response to the heat generation temperature of the resistors 33A, 43A, 53A exceeding the set value. Thermal fuses 34A, 44A, 54A are provided.

Further, when the power input line 2A includes a ground line G, the surge protection circuit 1A has an L1-G connection line 6A, an L2-G connection line 7A, and an L3-G connection line 8A. Varistors 62A, 72A, 82A and gas arresters 65A, 75A, 85A may be provided on 7A, 8A. Even in this case, branching from between the varistors 62A, 72A, 82A and the gas arresters 65A, 75A, 85A of the ground connection lines 6A, 7A, 8A and connecting to the corresponding lines of the power input line 2A When current flows through the lines 60A, 70A and 80A, the failure detection means 61A, 71A and 81A cut off the current.

The fault detection means 61A, 71A, 81A comprise resistors 63A, 73A, 83A that heat in response to conducting current on the branch lines 60A, 70A, 80A and are connected to either one or the other of the power inputs. Thermal fuses 64A, 74A which are provided in the middle of the line, are arranged in the vicinity of the resistors 63A, 73A, 83A, and are fused in response to the heat generation temperature of the resistors 63A, 73A, 83A exceeding a set value. , 84A.

The embodiments disclosed this time are illustrative in all respects and should be considered not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

1 surge protection circuit 2 power input line 3 LN connection line 4 LG connection line 5 NG connection line 31 first failure detection means 32 first varistor 33 first resistor 34 First thermal fuse 40 First branch line 41 Second failure detection means 42 Second varistor 43 Second resistor 44 Second thermal fuse 45 First gas arrester 50 Second branch line 51 Third third Failure detection means, 52 third varistor, 53 third resistor, 54 third thermal fuse, 55 second gas arrester, 1A surge protection circuit, 2A power input line, 3A L1-L2 connection line, 4A L2-L3 connection line , 5A L3-L1 connection line, 6A L1-G connection line, 7A L2-G connection line, 8A L3-G connection line, 60A, 70A, 80A branch line, 31A, 41A, 51A, 61A, 71A, 81A failure detection means, 32A, 42A, 52A, 62A, 72A, 82A varistors, 33A, 43A, 53A, 63A, 73A, 83A resistors, 34A, 44A, 54A, 64A, 74A, 84A thermal fuses, 65A, 75A, 85A gas arresters .

Claims (5)

a power input line comprising a non-grounded wire (L), a grounded wire (N), and a ground wire (G) ;
a first varistor arranged on an LN connection line connecting the non-grounded wire and the grounded wire to absorb a surge;
Disposed in the LN connection line in series with the first varistor, the non-grounded side wire in response to an energizing current flowing through the LN connection line due to a failure of the first varistor and first failure detection means for interrupting the energization of at least one of the ground-side wires ;
a second varistor disposed on the LG connection line connecting the non-grounded side wire and the ground wire and absorbing a surge;
a first gas arrester disposed on the LG connection line in series relationship with the second varistor;
Branched from between the second varistor and the first gas arrester on the LG connection line and arranged in the first branch line connected to the ground side wire, the failure of the second varistor causes the a second failure detection means for interrupting the energization of the non-grounded side wire in response to the energization current flowing through the LG connection line and the first branch line ;
The first failure detection means is
a first resistor disposed on the LN connection line and generating heat in response to the flow of current;
provided in the middle of at least one of the non-grounded side wire and the grounded side wire, is arranged in a position close to the first resistor, and the heat generation temperature of the first resistor exceeds a set value. a first thermal fuse that blows in response to a surge protection circuit.
The second failure detection means is
a second resistor disposed in the first branch line and generating heat in response to the flow of current;
a second thermal fuse that is provided in the middle of the non-grounded electric wire, is arranged in a position close to the second resistor, and is fused in response to the heat generation temperature of the second resistor exceeding a set value; 2. The surge protection circuit of claim 1 , comprising: a power input line comprising a non-grounded wire (L), a grounded wire (N), and a ground wire (G);
a first varistor arranged on an LN connection line connecting the non-grounded wire and the grounded wire to absorb a surge;
Disposed in the LN connection line in series with the first varistor, the non-grounded side wire in response to an energizing current flowing through the LN connection line due to a failure of the first varistor and first failure detection means for interrupting the energization of at least one of the ground-side wires;
a third varistor disposed on the NG connection line connecting the ground-side wire and the ground wire and absorbing a surge;
a second gas arrester disposed on the NG connection line in series relationship with the third varistor;
branched from between the third varistor and the second gas arrester on the NG connection line and arranged in a second branch line connected to the non-grounded electric wire, and when the third varistor fails, a third failure detection means for interrupting the energization of the ground-side wire in response to the energization current flowing through the NG connection line and the second branch line;
The first failure detection means is
a first resistor disposed on the LN connection line and generating heat in response to the flow of current;
provided in the middle of at least one of the non-grounded side wire and the grounded side wire, is arranged in a position close to the first resistor, and the heat generation temperature of the first resistor exceeds a set value. a first thermal fuse that blows in response to a surge protection circuit. The third failure detection means is
a third resistor disposed in the second branch line and generating heat in response to the flow of current;
a third thermal fuse provided in the middle of the ground-side wire, arranged in a position close to the third resistor, and fused in response to the temperature of the heat generated by the third resistor exceeding a set value; 4. The surge protection circuit of claim 3 , comprising: A surge protection circuit incorporated in a three-phase AC circuit comprising three input lines (L1, L2, L3) and a ground wire (G),
a varistor arranged in a ground connection line connecting one of two arbitrary input lines and a ground line to absorb a surge;
a gas arrester disposed on the ground connection line in series relationship with the varistor;
is arranged in a branch line branched from between the varistor and the gas arrester on the ground connection line and connected to the other input line of any two input lines, and the failure of the varistor causes the fault detection means for interrupting the energization of the one or the other input line in response to the flow of current through the ground connection line and the branch line;
The failure detection means is
a resistor disposed in the branch line and generating heat in response to the flow of the energizing current;
a thermal fuse provided in the middle of one of the input lines, arranged in proximity to the resistor, and blown in response to the heat generated by the resistor exceeding a set value. protection circuit.

Images