Detection circuit for fuse

Abstract

The invention provides a detection circuit for a fuse, the fuse is connected in series between an AC power supply and electric equipment, and the detection circuit comprises a first alarm indication circuit which is connected with a first end and a second end of the fuse to detect whether the fuse is in an open circuit or not, and gives out a first alarm indication when detecting that the fuse is in an open circuit; and the second alarm indication circuit is connected with the second end of the fuse to detect whether the fuse is in an open circuit or not and sends out a second alarm indication when detecting that the fuse is in the open circuit, the first end of the fuse is connected to the alternating current power supply, and the second end of the fuse is connected to the electric equipment. The detection circuit provided by the invention can not only send out the first local alarm indication, but also send out the second remote alarm indication under the condition that the fuse is open-circuited, so that the fuse is informed of a fault in time, and mutual verification can be carried out through the two modes, so that the alarm accuracy is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of fuses, and more particularly, to a detection circuit for a fuse. Background Art

[0002] A surge protective device (SPD) can protect electrical equipment from lightning strikes and can also reduce the overvoltage category (OVC) of the electrical equipment. The design of the power supply equipment and the selection of components can both be carried out according to the reduced OVC standard. The low OVC requirement can reduce the safety distance in product design and the safety voltage withstand requirement of components. For example, the gap requirement of the feedback relay in an Uninterruptible Power Supply (UPS) product can be reduced from 6.3 mm to 3.6 mm. This is the benefit brought about by the reduction of OVC, and it can reduce the product volume and lower the product cost.

[0003] The short-circuit current capacity of the SPD adopted needs to be greater than the system short-circuit current capacity. For example, if the system short-circuit current capacity is 100 kA, then the short-circuit current capacity of the selected SPD should be greater than 100 kA. This will increase the cost and difficulty of SPD selection. The current common practice is to connect a fuse (also called a fuse wire) in series between the SPD and the power grid. The fuse is installed at the front end of the SPD, and can limit the short-circuit current to a very low level (such as 15 kA), and at the same time can prevent the SPD from short-circuiting the power grid due to SPD component failures. The fuse is specially designed to be able to withstand the surge pulse without breaking, so that the SPD system can respond to the surge. Under AC short-circuit conditions, the fuse can well limit the current.

[0004] In addition, most of the fuses and SPDs are installed at the front end of the electrical equipment, which may be far from the protected electrical equipment, or may be placed in the front-end power distribution cabinet to protect the electrical equipment at the back end. The status of the fuse needs to be monitored in real time to ensure that the SPD system can effectively perform the real-time protection function.

[0005] Therefore, a method for effectively monitoring whether the fuse is open is needed. Summary of the Invention

[0006] In view of the above problems, the present disclosure provides a new detection circuit for a fuse. The detection circuit provided by the present disclosure can, when the fuse is open, not only give an alarm indication (such as a first alarm indication) locally, but also give an alarm indication (such as a second alarm indication) remotely externally, so that the detection circuit provided by the present disclosure can give an alarm prompt in the above two ways. This can not only notify the service team in a timely manner that the fuse has failed, but also enable the service team to mutually verify the alarm prompts given in the above two ways to improve the accuracy of the alarm, and further enable the service team to replace the faulty fuse in a timely manner.

[0007] An embodiment of the present disclosure provides a detection circuit for a fuse. The fuse is connected in series between an AC power supply and an electrical device. The detection circuit includes: a first alarm indication circuit connected to the first end and the second end of the fuse to detect whether the fuse is open and give a first alarm indication when it detects that the fuse is open; a second alarm indication circuit connected to the second end of the fuse to detect whether the fuse is open and give a second alarm indication when it detects that the fuse is open, wherein the first end of the fuse is connected to the AC power supply and the second end of the fuse is connected to the electrical device.

[0008] According to an embodiment of the present disclosure, the detection circuit further includes a first rectification circuit and a second rectification circuit for rectifying the AC power supply into direct current. The first alarm indication circuit is connected to the first end of the fuse via the first rectification circuit and the first alarm indication circuit is connected to the second end of the fuse via the second rectification circuit; the second alarm indication circuit is connected to the second end of the fuse via the second rectification circuit.

[0009] According to an embodiment of the present disclosure, the first alarm indication circuit includes an alarm detection circuit and an alarm indication circuit. The alarm detection circuit is configured to send a drive signal to the alarm indication circuit to drive the alarm indication circuit to give the first alarm indication when it detects that the fuse is open.

[0010] According to an embodiment of the present disclosure, the AC power supply is a three-phase four-wire based AC power supply. The fuse includes a first fuse, a second fuse, a third fuse, and a fourth fuse. The first end of the first fuse is connected to the A-phase wire in the three-phase four-wire, the first end of the second fuse is connected to the B-phase wire in the three-phase four-wire, the first end of the third fuse is connected to the C-phase wire in the three-phase four-wire, and the first end of the fourth fuse is connected to the neutral wire in the three-phase four-wire.

[0011] According to an embodiment of the present disclosure, the second rectifying circuit includes a first diode, a second diode, and a third diode. The anode of the first diode is connected to the second end of the first fuse. The anode of the second diode is connected to the second end of the second fuse. The anode of the third diode is connected to the second end of the third fuse. The second alarm indication circuit includes a first resistor and a first optocoupler. The first end of the first resistor is connected to the cathodes of the first diode, the second diode, and the third diode. The second end of the first resistor is connected to the first end of the first optocoupler. The second end of the first optocoupler is connected to the neutral line and grounded. The third end and the fourth end of the first optocoupler are respectively connected to a first external output terminal and a second external output terminal, so as to issue the second alarm indication through the first external output terminal and the second external output terminal when at least one of the first fuse, the second fuse, the third fuse, and the fourth fuse is open.

[0012] According to an embodiment of the present disclosure, the alarm detection circuit includes a second resistor, a second optocoupler, and a third resistor; the alarm indication circuit includes a first switch and an alarm device. Among them, the first end of the second resistor is connected to the cathodes of the first diode, the second diode, and the third diode. The second end of the second resistor is connected to the first end of the second optocoupler. The second end of the second optocoupler is connected to the second end of the first optocoupler. The third end of the second optocoupler is connected to the first end of the third resistor and the first end of the first switch. The fourth end of the second optocoupler is connected to the second end of the first switch and grounded. The third end of the first switch is connected to the first end of the alarm device. The second end of the alarm device is connected to the second end of the third resistor. Among them, when it is detected that the fuse is open, a drive signal is sent to the alarm indication circuit to drive the alarm indication circuit to issue the first alarm indication, including: when it is detected that at least one of the first fuse, the second fuse, the third fuse, and the fourth fuse is open, the drive signal is sent to the first switch to cause the alarm device to issue the first alarm indication by closing the first switch; the first rectifier circuit includes a fourth diode, a fifth diode, a sixth diode, and a seventh diode. Among them, the anode of the fourth diode is connected to the cathode of the sixth diode. The cathode of the fourth diode is connected to the cathode of the fifth diode and the second end of the third resistor. The anode of the fifth diode is connected to the cathode of the seventh diode. The anode of the sixth diode is connected to the anode of the seventh diode and grounded. Among them, the anode of the fourth diode and the anode of the fifth diode are respectively connected to any two of the A-phase line, B-phase line, C-phase line, and neutral line.

[0013] According to an embodiment of the present disclosure, the second rectifier circuit further includes a first capacitor. Among them, the first end of the first capacitor is connected to the cathodes of the first diode, the second diode, and the third diode. The second end of the first capacitor is connected to the neutral line and grounded.

[0014] According to an embodiment of the present disclosure, the second alarm indication circuit further includes an eighth diode. Among them, the anode of the eighth diode is connected to the second end of the first optocoupler. The cathode of the eighth diode is connected to the first end of the first optocoupler.

[0015] According to an embodiment of the present disclosure, the first rectifier circuit further includes a second capacitor. Among them, the first end of the second capacitor is connected to the cathodes of the fourth diode and the fifth diode. The second end of the second capacitor is connected to the anodes of the sixth diode and the seventh diode.

[0016] According to an embodiment of the present disclosure, the first alarm indication circuit further includes: a fourth resistor, wherein a first end of the fourth resistor is connected to a second end of the alarm device, and a second end of the fourth resistor is connected to a second end of the third resistor.

[0017] According to an embodiment of the present disclosure, the first alarm indication circuit further includes: a fifth resistor, a sixth resistor, a ninth diode, a twelfth diode, a first voltage regulator diode, and a third capacitor. A first end of the fifth resistor is connected to an anode of the ninth diode, a second end of the fifth resistor is connected to a first end of the first switch, a cathode of the ninth diode is connected to a third end of the second optocoupler, a first end of the sixth resistor is connected to a cathode of the twelfth diode, a second end of the sixth resistor is connected to the first end of the first switch, an anode of the twelfth diode is connected to the third end of the second optocoupler, a first end of the third capacitor is connected to the first end of the first switch, a second end of the third capacitor is connected to a fourth end of the second optocoupler, an anode of the first voltage regulator diode is connected to the fourth end of the second optocoupler, and a cathode of the first voltage regulator diode is connected to the third end of the second optocoupler; wherein, in the case of detecting that at least one of the first fuse, the second fuse, the third fuse, and the fourth fuse is open, sending the driving signal to the first switch to cause the alarm device to issue the first alarm indication by closing the first switch, including: in the case of detecting that at least one of the first fuse, the second fuse, the third fuse, and the fourth fuse is open for a predetermined time, sending the driving signal to the first switch to cause the alarm device to issue the first alarm indication by closing the first switch.

[0018] According to an embodiment of the present disclosure, the first alarm indication circuit further includes: an eleventh diode, wherein an anode of the eleventh diode is connected to a second end of the second optocoupler, and a cathode of the eleventh diode is connected to a first end of the second optocoupler.

[0019] According to an embodiment of the present disclosure, the AC power supply is a three-phase three-wire based AC power supply, and the fuses include a fifth fuse, a sixth fuse, and a seventh fuse. A first end of the fifth fuse is connected to the A-phase wire in the three-phase three-wire, a first end of the sixth fuse is connected to the B-phase wire in the three-phase three-wire, and a first end of the seventh fuse is connected to the C-phase wire in the three-phase three-wire.

[0020] According to an embodiment of the present disclosure, the second rectifying circuit includes a twelfth diode, a thirteenth diode, a fourteenth diode, a fifteenth diode, a sixteenth diode, and a seventeenth diode. The cathode of the twelfth diode is connected to the cathodes of the thirteenth diode and the fourteenth diode. The anode of the twelfth diode is connected to the cathode of the fifteenth diode and the second terminal of the fifth fuse. The anode of the thirteenth diode is connected to the cathode of the sixteenth diode and the second terminal of the sixth fuse. The anode of the fourteenth diode is connected to the cathode of the seventeenth diode and the second terminal of the seventh fuse. The anodes of the fifteenth diode, the sixteenth diode, and the seventeenth diode are connected and grounded. The second alarm indication circuit includes a second zener diode, a seventh resistor, and a third optocoupler. The cathode of the second zener diode is connected to the cathode of the fourteenth diode. The anode of the second zener diode is connected to the first terminal of the seventh resistor. The second terminal of the seventh resistor is connected to the first terminal of the third optocoupler. The second terminal of the third optocoupler is connected to the anode of the seventeenth diode. The third terminal and the fourth terminal of the third optocoupler are respectively connected to a third external output terminal and a fourth external output terminal, so as to send out a second alarm indication through the third external output terminal and the fourth external output terminal when at least one of the fifth fuse, the sixth fuse, and the seventh fuse is detected to be open.

[0021] According to an embodiment of the present disclosure, the alarm detection circuit includes an eighth resistor, a fourth optocoupler, a ninth resistor, and a third zener diode; the alarm indication circuit includes a second switch and an alarm device. Among them, the cathode of the third zener diode is connected to the cathode of the fourteenth diode, the anode of the third zener diode is connected to the first end of the eighth resistor, the second end of the eighth resistor is connected to the first end of the fourth optocoupler, the second end of the fourth optocoupler is connected to the second end of the third optocoupler, the third end of the fourth optocoupler is connected to the first end of the ninth resistor and the first end of the second switch, the fourth end of the fourth optocoupler is connected to the second end of the second switch and grounded, the third end of the second switch is connected to the first end of the alarm device, and the second end of the alarm device is connected to the second end of the ninth resistor. Among them, when detecting that the fuse is open, sending a drive signal to the alarm indication circuit to drive the alarm indication circuit to send the first alarm indication includes: when detecting that at least one of the fifth fuse, the sixth fuse, and the seventh fuse is open, sending the drive signal to the second switch to make the alarm device send the first alarm indication by closing the second switch; the first rectifier circuit includes an eighteenth diode, a nineteenth diode, a twenty-second diode, and a twenty-first diode. Among them, the anode of the eighteenth diode is connected to the cathode of the twenty-second diode, the cathode of the eighteenth diode, the cathode of the nineteenth diode are connected to the second end of the ninth resistor, the anode of the nineteenth diode is connected to the cathode of the twenty-first diode, and the anode of the twenty-second diode and the anode of the twenty-first diode are connected and grounded. Among them, the anode of the eighteenth diode and the anode of the nineteenth diode are respectively connected to any two of the A-phase line, the B-phase line, and the C-phase line.

[0022] According to an embodiment of the present disclosure, the second rectifier circuit further includes a fourth capacitor and a tenth resistor. Among them, the first end of the fourth capacitor is connected to the cathode of the fourteenth diode, the second end of the fourth capacitor is connected to the anode of the seventeenth diode, the first end of the tenth resistor is connected to the first end of the fourth capacitor, and the second end of the tenth resistor is connected to the second end of the fourth capacitor.

[0023] According to an embodiment of the present disclosure, the second alarm indication circuit further includes a twenty-second diode. Among them, the anode of the twenty-second diode is connected to the second end of the third optocoupler, and the cathode of the twenty-second diode is connected to the first end of the third optocoupler.

[0024] According to an embodiment of the present disclosure, the first rectifying circuit further includes a fifth capacitor, wherein a first end of the fifth capacitor is connected to the cathodes of the eighteenth diode and the nineteenth diode, and a second end of the fifth capacitor is connected to the anodes of the twenty-second diode and the twenty-first diode.

[0025] According to an embodiment of the present disclosure, the first alarm indication circuit further includes: an eleventh resistor, wherein a first end of the eleventh resistor is connected to a second end of the alarm device, and a second end of the eleventh resistor is connected to a second end of the ninth resistor.

[0026] According to an embodiment of the present disclosure, the first alarm indication circuit further includes: a twelfth resistor, a thirteenth resistor, a twenty-third diode, a twenty-fourth diode, a fourth voltage-regulating diode, and a sixth capacitor, wherein a first end of the twelfth resistor is connected to an anode of the twenty-third diode, a second end of the twelfth resistor is connected to a first end of the second switch, a cathode of the twenty-third diode is connected to a third end of the fourth optocoupler, a first end of the thirteenth resistor is connected to a cathode of the twenty-fourth diode, a second end of the thirteenth resistor is connected to the first end of the second switch, an anode of the twenty-fourth diode is connected to the third end of the fourth optocoupler, a first end of the sixth capacitor is connected to the first end of the second switch, a second end of the sixth capacitor is connected to a fourth end of the fourth optocoupler, an anode of the fourth voltage-regulating diode is connected to the fourth end of the fourth optocoupler, and a cathode of the fourth voltage-regulating diode is connected to the third end of the fourth optocoupler; wherein, when at least one of the fifth fuse, the sixth fuse, and the seventh fuse is detected to be open, sending the driving signal to the second switch to cause the alarm device to give the first alarm indication by closing the second switch includes: when at least one of the fifth fuse, the sixth fuse, and the seventh fuse is detected to be open for a predetermined time, sending the driving signal to the second switch to cause the alarm device to give the first alarm indication by closing the second switch.

[0027] According to an embodiment of the present disclosure, the first alarm indication circuit further includes: a twenty-fifth diode, wherein an anode of the twenty-fifth diode is connected to a second end of the fourth optocoupler, and a cathode of the twenty-fifth diode is connected to a first end of the fourth optocoupler.

[0028] The present disclosure provides a detection circuit for a fuse. The detection circuit provided by the present disclosure can, when the fuse is open, not only give an alarm indication locally, but also output an alarm indication remotely to the outside, so that the detection circuit provided by the present disclosure can give an alarm prompt in the above two ways. This can not only timely notify the service team that the fuse has failed, but also enable the service team to mutually verify the alarm prompts given in the above two ways to improve the accuracy of the alarm, so that the service team can timely replace the faulty fuse. In addition, the detection circuit provided by the present disclosure has the advantages of simple circuit, low cost, flexible remote installation location, and can flexibly use fuses of different packages compared with the existing solutions. When fixed on the metal chassis, high-voltage insulation wires are not required. Moreover, by outputting an indication through two SELV signal lines, it has the advantages of small size, not occupying the space of the detection circuit, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings required to be used in the description of the embodiments. Obviously, the following described drawings are only some exemplary embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 、 Figure 2 and Figure 3 show the existing methods for detecting an open fuse;

[0031] Figure 4 show a schematic diagram of a detection circuit 400 for a fuse according to an embodiment of the present disclosure;

[0032] Figure 5 and Figure 6 respectively show schematic diagrams of the detection circuit for 3P4W according to an embodiment of the present disclosure;

[0033] Figure 7 and Figure 8 respectively show schematic diagrams of the detection circuit for 3P3W according to an embodiment of the present disclosure;

[0034] Figure 9 show at Figure 6 the schematic diagram of the position where signals are collected on the shown detection circuit;

[0035] Figure 10 show the waveform diagram under remote indication when the fuses are all working properly;

[0036] Figure 11Shows the waveform diagram in the case where any one of the first fuse, the second fuse, and the third fuse is open;

[0037] Figure 12 Shows the waveform diagram in the case where any two fuses are open;

[0038] Figure 13 Shows the waveform diagram when the first fuse, the second fuse, and the third fuse are all open or the fourth fuse is open;

[0039] Figure 14 Shows at Figure 6 Schematic diagram of the position where signals are collected on the detection circuit shown;

[0040] Figure 15 Shows the waveform diagram under local indication when the fuses are all working normally;

[0041] Figure 16 Shows the waveform diagram in the case where any one of the first fuse, the second fuse, and the third fuse is open;

[0042] Figure 17 Shows the simulation waveform diagram of the local alarm of the fuse open trigger;

[0043] Figure 18 Shows the flowchart for remote indication of fuse open for 3P4W;

[0044] Figure 19 Shows at Figure 8 Schematic diagram of the position where signals are collected on the detection circuit shown;

[0045] Figure 20 Shows the waveform diagram related to the second zener diode and the third zener diode;

[0046] Figure 21 and Figure 22 Respectively show the waveform diagrams in the normal mode when the fuses are all working normally at 176Vac and 277Vac;

[0047] Figure 23 and Figure 24 Respectively show the waveform diagrams in the case where any one of the fifth fuse, the sixth fuse, and the seventh fuse is open at 176Vac and 277Vac;

[0048] Figure 25 and Figure 26 Respectively show the waveform diagrams in the case where any two of the fifth fuse, the sixth fuse, and the seventh fuse are open or all fuses are open at 176Vac and 277Vac;

[0049] Figure 27 shows the schematic diagram of the position where signals are collected on the Figure 8 detecting circuit shown;

[0050] Figure 28 shows the waveform diagram in the case where any one of the fifth fuse, sixth fuse, and seventh fuse is open at 277Vac;

[0051] Figure 29 shows the simulation waveform diagram of the local alarm of the fuse open trigger. Detailed implementation mode

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0053] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure shall have the ordinary meaning as understood by those of ordinary skill in the art to which the present disclosure pertains. The "first", "second", and similar terms used in the present disclosure do not denote any order, quantity, or importance, but are only used to distinguish different components. Similarly, the terms such as "a", "an", or "the" do not denote a quantity limitation, but mean that there is at least one. The terms such as "comprising" or "including" mean that the elements or items appearing before the term cover the elements or items listed after the term and their equivalents, without excluding other elements or items. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left", "right", etc. are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0054] Figure 1 , Figure 2 and Figure 3 shows the existing method for detecting fuse open.

[0055] Figure 1 Corresponds to the method for detecting fuse open used in a three-phase four-wire (3P4W) system. Figure 2 Corresponds to the method for detecting fuse open used in a three-phase three-wire (3P3W) system. In Figure 1Among them, the four wires are four wires corresponding to phase A, phase B, phase C, and the neutral wire respectively, namely L1, L2, L3, and N. In Figure 2 Among them, the three wires are three wires corresponding to phase A, phase B, and phase C respectively, namely L1, L2, and L3.

[0056] In Figure 1 Among them, four fuses (denoted as L_1, L_2, L_3, and N respectively) and sampling resistors (denoted as R_1, R_2, R_3, R_4, R_5, R_6, R_7, and R_8 respectively) connected correspondingly are provided. The voltages across the fuses and the correspondingly connected sampling resistors are led out through wires to a sampling circuit board arranged in the protected power system. As Figure 1 shown, this sampling circuit board includes a logic unit and a controller. Among them, a complex sampling and processing circuit (for example, complex logic circuits, operational amplifiers, comparators, etc.) is adopted in the logic unit to send the processed signal to the processor for fault judgment and corresponding operations. Since these wires are connected to the grid voltage, they are not safety extra-low voltage (SELV), and high-voltage insulated wires are required to achieve insulation from the metal chassis and meet the requirements of safety regulations. Therefore, Figure 1 the method shown in

[0057] In Figure 2 Among them, three fuses (denoted as L_1, L_2, and L_3 respectively) and sampling resistors (denoted as R_1, R_2, R_3, R_4, R_5, and R_6 respectively) connected correspondingly are provided. The voltages across the fuses and the correspondingly connected sampling resistors are led out through wires to a sampling circuit board arranged in the protected power system. As Figure 2 shown, this sampling circuit board includes a logic unit and a controller. Among them, a complex sampling and processing circuit (for example, complex logic circuits, operational amplifiers, comparators, etc.) is adopted in the logic unit to send the processed signal to the processor for fault judgment and corresponding operations. Since these wires are connected to the grid voltage, they are not safety extra-low voltage SELV, and high-voltage insulated wires are required to achieve insulation from the metal chassis and meet the requirements of safety regulations. Therefore, Figure 2 the method shown in

[0058] In addition, it can be seen from the two methods shown in the above Figure 1 and Figure 2 that they can only perform remote indication, and the number of high-voltage insulated wires is large, the cost is high, the number of connectors is large, the occupied space is large, and the installation position is not flexible. In addition, inFigure 1 And Figure 2 In the manner shown, it is necessary to match specific and complex sampling and processing circuits on the protected device to detect whether the fuse is open.

[0059] Figure 3 The prior art corresponding to the local indication of the fuse. Currently, many manufacturers adopt the manner as shown in Figure 3 In the manner shown. The fuse comes with a base. An indicator light is set on the base to determine whether the fuse is open by the indicator light. Figure 3 The manner shown can only provide local indication and is very inflexible. The relevant accessories need to be purchased from specific manufacturers and matched with fuses with specific packaged signals. This makes Figure 3 The manner shown also has problems such as high cost and incompatibility with fuses of other package models.

[0060] To solve at least one of the above problems in the existing manner, the present disclosure provides a new detection circuit for a fuse. The detection circuit provided by the present disclosure can, when the fuse is open, not only give an alarm indication locally, but also output an alarm indication remotely externally, so that the detection circuit provided by the present disclosure can give an alarm prompt through the above two methods. This can not only timely notify the service team that the fuse has failed, but also enable the service team to mutually verify the alarm prompts given by the above two methods to improve the accuracy of the alarm, and further enable the service team to timely replace the faulty fuse.

[0061] Now, the detection circuit for a fuse provided by the present disclosure will be described in detail with reference to the accompanying drawings.

[0062] Figure 4 Fig. shows a schematic diagram of a detection circuit 400 for a fuse according to an embodiment of the present disclosure.

[0063] According to an embodiment of the present disclosure, the fuse is connected in series between an AC power supply and an electrical device. As an example, the AC power supply may be a three-phase four-wire based AC power supply. Optionally, the AC power supply may be a three-phase three-wire based AC power supply.

[0064] Referring to Figure 4 , the detection circuit 400 may include: a first alarm indication circuit 410 and a second alarm indication circuit 420.

[0065] According to an embodiment of the present disclosure, the first alarm indication circuit 410 may be connected to the first end and the second end of the fuse to detect whether the fuse is open, and issue a first alarm indication when it detects that the fuse is open. According to an embodiment of the present disclosure, the second alarm indication circuit 420 may be connected to the second end of the fuse to detect whether the fuse is open, and issue a second alarm indication when it detects that the fuse is open. Wherein, the first end of the fuse is connected to the AC power supply, and the second end of the fuse is connected to the electrical equipment.

[0066] As an example, the first alarm indication may be issued locally. For example, when it detects that the fuse is open, the first alarm indication circuit may issue the first alarm indication locally in one or more of the following ways: emit a specific light (such as red light) through an LED, etc., emit a specific sound through a speaker, etc., and emit a specific vibration through a vibrator, etc.

[0067] When it detects that the fuse is working properly, the first alarm indication circuit may indicate to the local that the fuse is working properly by not emitting any light, sound, vibration, etc. Alternatively, when it detects that the fuse is working properly, the first alarm indication circuit may indicate to the local that the fuse is working properly by emitting a soft light (such as green light), a soft sound, etc.

[0068] As an example, the second alarm indication may be sent remotely to the outside. For example, when the fuse is open, the second alarm indication circuit may output an alarm indication to the outside by outputting a high-impedance state signal to the outside, such as a high-level signal.

[0069] When the fuse is working properly, the second alarm indication circuit may output an indication that the fuse is working properly to the outside by outputting a low-impedance state signal to the outside, such as a low-level signal.

[0070] As an example, it may be determined that the fuse is open based on at least one of the above first alarm indication and second alarm indication.

[0071] According to an embodiment of the present disclosure, the detection circuit further includes a first rectification circuit and a second rectification circuit for rectifying the AC power supply into direct current. Wherein, the first alarm indication circuit is connected to the first end of the fuse via the first rectification circuit, and the first alarm indication circuit is connected to the second end of the fuse via the second rectification circuit; the second alarm indication circuit is connected to the second end of the fuse via the second rectification circuit. In this embodiment, the first alarm indication circuit and the second alarm indication circuit share the second rectification circuit to connect to the second end of the fuse. Optionally, in another embodiment, the detection circuit may also respectively provide rectification circuits connected to the second end of the fuse for the first alarm indication circuit and the second alarm indication circuit, so that the first alarm indication circuit and the second alarm indication circuit are respectively connected to the second end of the fuse through their respective rectification circuits.

[0072] According to an embodiment of the present disclosure, the first alarm indication circuit may include an alarm detection circuit and an alarm indication circuit. Wherein, the alarm detection circuit may be configured to send a drive signal to the alarm indication circuit to drive the alarm indication circuit to give the first alarm indication when detecting that the fuse is open.

[0073] From the detection circuit provided by the present disclosure described above in combination Figure 4 it can be seen that the detection circuit provided by the present disclosure can, when the fuse is open, not only give an alarm indication locally, but also output an alarm indication remotely to the outside, so that the detection circuit provided by the present disclosure can give an alarm prompt in the above two ways. This can not only timely notify the service team that the fuse has failed, but also enable the service team to mutually verify the alarm prompts given in the above two ways to improve the accuracy of the alarm, and further enable the service team to timely replace the faulty fuse.

[0074] Next, the above detection circuit provided by the present disclosure will be described in detail by way of examples.

[0075] Figure 5 and Figure 6 respectively show schematic diagrams of the detection circuit for 3P4W according to an embodiment of the present disclosure.

[0076] The external alternating current may be alternating current based on three-phase four-wire.

[0077] The fuse may include a first fuse L1, a second fuse L2, a third fuse L3, and a fourth fuse N.

[0078] The first end 1 of the first fuse L1 may be connected to the A phase wire (such as Figure 5 L1 in

[0079] The first end 1 of the second fuse L2 can be connected to the B-phase line in the three-phase four-wire system (such as Figure 5 L2 in

[0080] The first end 1 of the third fuse L3 can be connected to the C-phase line in the three-phase four-wire system (such as Figure 5 L3 in

[0081] The first end 1 of the fourth fuse N can be connected to the neutral line in the three-phase four-wire system (such as Figure 5 N in

[0082] The second rectifying circuit may include a first diode D1, a second diode D2, and a third diode D3. The anode of the first diode D1 can be connected to the second end 2 of the first fuse L1. The anode of the second diode D2 can be connected to the second end 2 of the second fuse L2. The anode of the third diode D3 can be connected to the second end 2 of the third fuse L3.

[0083] The second alarm indication circuit may include a first resistor R1 and a first optocoupler U1. The first end 1 of the first resistor R1 is connected to the cathodes of the first diode D1, the second diode D2, and the third diode D3. The second end 2 of the first resistor R1 can be connected to the first end 1 of the first optocoupler U1. The second end 2 of the first optocoupler U2 can be connected to the neutral line and grounded to GND1. The third end 3 and the fourth end 4 of the first optocoupler U1 are respectively connected to a first external output terminal OUT_1 and a second external output terminal OUT_2, so as to output a second alarm indication through the first external output terminal OUT_1 and the second external output terminal OUT_2 when at least one of the first fuse L1, the second fuse L2, the third fuse L3, and the fourth fuse N is open. This second alarm indication can be output to the remote end through a line that meets SELV, such as Figure 5 for making judgments and subsequent operations in the logic circuit of the protected power system at the remote end as shown in Figure 5 As shown in

[0084] The alarm detection circuit may include a second resistor R2, a second optocoupler U2, and a third resistor R3. The alarm indication circuit may include a first switch S1 and an alarm device (Figure 5 shown as an LED, a speaker, etc.). The first end 1 of the second resistor R2 may be connected to the cathodes of the first diode D1, the second diode D2, and the third diode D3. The second end 2 of the second resistor R2 may be connected to the first end 1 of the second optocoupler U2. The second end 2 of the second optocoupler U2 may be connected to the second end 2 of the first optocoupler U1. The third end 3 of the second optocoupler U2 is connected to the first end 1 of the third resistor R3 and the first end 1 of the first switch S1. The fourth end 4 of the second optocoupler U2 may be connected to the second end 2 of the first switch S1 and grounded to GND2. The third end 3 of the first switch S1 may be connected to the first end 1 of the alarm device. The second end 2 of the alarm device may be connected to the second end 2 of the third resistor R3. When detecting that the fuse is open, sending a drive signal to the alarm indication circuit to drive the alarm indication circuit to issue the first alarm indication, including: when detecting that at least one of the first fuse L1, the second fuse L2, the third fuse L3, and the fourth fuse N is open, sending the drive signal to the first switch S1 to make the alarm device issue the first alarm indication by closing the first switch S1.

[0085] The first rectifier circuit may include a fourth diode D4, a fifth diode D5, a sixth diode D6, and a seventh diode D7. The anode of the fourth diode D4 is connected to the cathode of the sixth diode D6. The cathode of the fourth diode D4 is connected to the cathode of the fifth diode D5 and the second end 2 of the third resistor R3. The anode of the fifth diode D5 is connected to the cathode of the seventh diode D7. The anode of the sixth diode D6 is connected to the anode of the seventh diode D7 and grounded to GND2. The anode of the fourth diode D4 and the anode of the fifth diode D5 are respectively connected to any two of the A-phase line, B-phase line, C-phase line, and neutral line. For example, Figure 5 shown as being respectively connected to L3 and N.

[0086] The diodes described above and hereinafter can be any suitable diodes selected according to actual needs, such as diodes with small current. The resistors described above and hereinafter can be any suitable resistors selected according to actual needs, such as resistors ranging from a few ohms to several kiloohms. The switches (such as the first switch and the second switch) described above and hereinafter can be any suitable switches selected according to actual needs, such as switches based on relays, metal devices, power semiconductors (such as Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)), etc. The capacitors described hereinafter can be any suitable capacitors selected according to actual needs, such as capacitors ranging from a few picofarads to a few microfarads. The zener diodes described above and hereinafter can be any suitable zener diodes selected according to actual needs. The optocouplers described above and hereinafter can be any suitable optocouplers selected according to actual needs. The costs of the above-mentioned components are usually relatively low.

[0087] Therefore, the detection circuit provided by the present disclosure has the advantages of low cost and simple circuit structure compared with the prior art. In addition, the designed detection circuit board can be compatible with different types of fuses, and has the advantages of flexibility and wide application range.

[0088] According to an embodiment of the present disclosure, as Figure 6 shown, the second rectifying circuit may further include a first capacitor C1. The first end 1 of the first capacitor C1 is connected to the cathodes of the first diode D1, the second diode D2, and the third diode D3. The second end 2 of the first capacitor C1 is connected to the neutral line and grounded at GND1. By setting the first capacitor C1, the detection circuit provided by the present disclosure can effectively absorb some transient spikes existing in the power grid, thereby avoiding problems such as false alarms and damage of the detection circuit caused by poor power grid quality.

[0089] According to an embodiment of the present disclosure, as Figure 6 shown, the second alarm indication circuit may further include an eighth diode D8. The anode of the eighth diode D8 is connected to the second end 2 of the first optocoupler U1. The cathode of the eighth diode D8 is connected to the first end 1 of the first optocoupler U1. By setting the eighth diode D8, the detection circuit provided by the present disclosure can further protect the first optocoupler U1 to avoid excessive reverse voltage between the first end and the second end of the optocoupler caused by certain abnormal conditions, thereby preventing problems such as false alarms and damage of the detection circuit.

[0090] According to an embodiment of the present disclosure, as Figure 6As shown, the first rectification circuit may further include a second capacitor C2. A first terminal 1 of the second capacitor C2 is connected to the cathodes of the fourth diode D4 and the fifth diode D5. A second terminal 2 of the second capacitor C2 is connected to the anodes of the sixth diode D6 and the seventh diode D7. By providing the second capacitor C2 in the detection circuit provided by the present disclosure, a stable DC power supply can be obtained after rectification by the first rectification circuit. In this way, a stable voltage can be provided for the subsequent alarm device, which helps to expand the selection range of the alarm device. At the same time, it also helps to make the first alarm indication stable, without situations such as suddenly large or small, suddenly bright or dark, etc.

[0091] According to an embodiment of the present disclosure, as Figure 6 shown, the first alarm indication circuit may further include a fourth resistor R4. A first terminal 1 of the fourth resistor R4 is connected to a second terminal 2 of the alarm device. A second terminal 2 of the fourth resistor R4 is connected to a second terminal 2 of the third resistor R3. By providing the fourth resistor R4 in the detection circuit provided by the present disclosure for voltage division and / or current limiting, the voltage on the alarm device can be stabilized within a suitable range, which helps to flexibly select the alarm device.

[0092] According to an embodiment of the present disclosure, as Figure 6As shown, the first alarm indication circuit may further include: a fifth resistor R5, a sixth resistor R6, a ninth diode D9, a tenth diode D10, a first zener diode ZD1, and a third capacitor C3. The first end 1 of the fifth resistor R5 is connected to the anode of the ninth diode D9. The second end 2 of the fifth resistor R5 is connected to the first end 1 of the first switch S1. The cathode of the ninth diode D9 is connected to the third end 3 of the second optocoupler U2. The first end 1 of the sixth resistor R6 is connected to the cathode of the tenth diode D10. The second end of the sixth resistor R6 is connected to the first end 1 of the first switch S1. The anode of the tenth diode D10 is connected to the third end 3 of the second optocoupler U2. The first end 1 of the third capacitor C3 is connected to the first end 1 of the first switch S1. The second end 2 of the third capacitor C3 is connected to the fourth end of the second optocoupler U2. The anode of the first zener diode ZD1 is connected to the fourth end 4 of the second optocoupler U2. The cathode of the first zener diode ZD1 is connected to the third end of the second optocoupler U2. When at least one of the first fuse L1, the second fuse L2, the third fuse L3, and the fourth fuse N is detected to be open, sending the drive signal to the first switch S1 to cause the alarm device to issue the first alarm indication by closing the first switch S1 includes: when at least one of the first fuse L1, the second fuse L2, the third fuse L3, and the fourth fuse N is detected to be open for a predetermined time, sending the drive signal to the first switch S1 to cause the alarm device to issue the first alarm indication by closing the first switch S1.

[0093] The circuit composed of the fifth resistor R5, the sixth resistor R6, the ninth diode D9, the tenth diode D10, the first zener diode ZD1, and the third capacitor C3 is used to implement the counting and driving functions. For example, when the fuse is truly open, the third capacitor C3 is continuously charged, and then after the third capacitor C3 is charged to a predetermined value, it will drive the first switch S1 to close, so that the alarm device issues an alarm indication. Another example is that when the fuse is not truly open (such as an instantaneous fault illusion caused by other reasons), the third capacitor C3 will not be continuously charged, and thus the third capacitor C3 cannot be charged to a predetermined value, so it will not drive the first switch S1 to close, and thus the alarm device will not issue an alarm indication. This circuit setting for implementing the counting and driving functions can effectively avoid false alarms, thereby improving the accuracy of the detection circuit provided by the present disclosure.

[0094] According to an embodiment of the present disclosure, as Figure 6As shown, the first alarm indication circuit may further include the eleventh diode D11. The anode of the eleventh diode D11 is connected to the second terminal 2 of the second optocoupler U2. The cathode of the eleventh diode D11 is connected to the first terminal 1 of the second optocoupler U2. By providing the eleventh diode D11, the detection circuit provided by the present disclosure can further protect the second optocoupler U2 to avoid excessive reverse voltage between the first terminal and the second terminal of the optocoupler caused by certain abnormal conditions, thereby preventing problems such as false alarms and damage of the detection circuit.

[0095] Figure 7 and Figure 8 respectively show schematic diagrams of the detection circuit for 3P3W according to embodiments of the present disclosure.

[0096] The external alternating current may be a three-phase three-wire based alternating current.

[0097] The fuse includes a fifth fuse L5, a sixth fuse L6, and a seventh fuse L7. Among them, the first terminal 1 of the fifth fuse L5 is connected to the A-phase wire (such as Figure 7 L1 in Figure 7 the three-phase three-wire), the first terminal 1 of the sixth fuse L6 is connected to the B-phase wire (such as Figure 7 L2 in

[0098] the three-phase three-wire), and the first terminal 1 of the seventh fuse L7 is connected to the C-phase wire (such as

[0099] The second alarm prompt circuit includes a second voltage stabilizing diode ZD2, a seventh resistor, and a third optocoupler U3. The cathode of the second voltage stabilizing diode ZD2 is connected to the cathode of the fourteenth diode D14. The anode of the second voltage stabilizing diode ZD2 is connected to the first terminal 1 of the seventh resistor R7. The second terminal 2 of the seventh resistor R7 is connected to the first terminal of the third optocoupler U3. The second terminal 2 of the third optocoupler U3 is connected to the anode of the seventeenth diode D17. The third terminal 3 and the fourth terminal 4 of the third optocoupler U3 are respectively connected to a third external output terminal OUT_3 and a fourth external output terminal OUT_4, so as to issue a second alarm indication through the third external output terminal and the fourth external output terminal when at least one of the fifth fuse L5, the sixth fuse L6, and the seventh fuse L7 is open.

[0100] The alarm detection circuit may include an eighth resistor R8, a fourth optocoupler U4, a ninth resistor R9, and a third voltage stabilizing diode ZD3. The alarm indication circuit may include a second switch S2 and an alarm device (such as an LED, a speaker, etc. in the figure). The cathode of the third voltage stabilizing diode ZD3 is connected to the cathode of the fourteenth diode D14. The anode of the third voltage stabilizing diode ZD3 is connected to the first terminal 1 of the eighth resistor R8. The second terminal 2 of the eighth resistor R8 is connected to the first terminal 1 of the fourth optocoupler U4. The second terminal 2 of the fourth optocoupler U4 is connected to the second terminal 2 of the third optocoupler U3. The third terminal 3 of the fourth optocoupler U4 is connected to the first terminal 1 of the ninth resistor R9 and the first terminal 1 of the second switch S2. The fourth terminal 4 of the fourth optocoupler U4 is connected to the second terminal 2 of the second switch S2 and grounded to GND2. The third terminal 3 of the second switch S2 is connected to the first terminal of the alarm device. The second terminal 2 of the alarm device is connected to the second terminal 2 of the ninth resistor R9. The step of, when detecting that the fuse is open, sending a driving signal to the alarm indication circuit to drive the alarm indication circuit to issue the first alarm indication includes: when detecting that at least one of the fifth fuse L5, the sixth fuse L6, and the seventh fuse L7 is open, sending the driving signal to the second switch S2 to cause the alarm device to issue the first alarm indication by closing the second switch S2.

[0101] The first rectifier circuit includes the eighteenth diode D18, the nineteenth diode D19, the twentieth diode D20, and the twenty - first diode D21. The anode of the eighteenth diode D18 is connected to the cathode of the twentieth diode D20. The cathode of the eighteenth diode D18, the cathode of the nineteenth diode D19, and the second terminal 2 of the ninth resistor R9 are connected. The anode of the nineteenth diode D19 is connected to the cathode of the twenty - first diode D21. The anode of the twentieth diode D20 and the anode of the twenty - first diode D21 are connected and grounded to GND2. The anode of the eighteenth diode D18 and the anode of the nineteenth diode D19 are respectively connected to any two of the A - phase line, B - phase line, and C - phase line.

[0102] According to an embodiment of the present disclosure, as Figure 8 shown, the second rectifier circuit further includes a fourth capacitor C4 and a tenth resistor R10. The first terminal 1 of the fourth capacitor C4 is connected to the cathode of the fourteenth diode D14. The second terminal 2 of the fourth capacitor C4 is connected to the anode of the seventeenth diode D17. The first terminal 1 of the tenth resistor R10 is connected to the first terminal 1 of the fourth capacitor C4. The second terminal 2 of the tenth resistor R10 is connected to the second terminal 2 of the fourth capacitor C4. By providing the fourth capacitor C4, the detection circuit provided by the present disclosure can effectively absorb some transient spikes existing in the power grid, thereby avoiding problems such as false alarms and damage of the detection circuit caused by poor power grid quality.

[0103] According to an embodiment of the present disclosure, as Figure 8 shown, the second alarm indication circuit further includes a twenty - second diode D22. The anode of the twenty - second diode D22 is connected to the second terminal 2 of the third optocoupler U3. The cathode of the twenty - second diode D22 is connected to the first terminal 1 of the third optocoupler U3. By providing the twenty - second diode D22, the detection circuit provided by the present disclosure can further protect the third optocoupler U3 to avoid excessive reverse voltage between the first terminal and the second terminal of the optocoupler caused by certain abnormal conditions, thereby preventing problems such as false alarms and damage of the detection circuit.

[0104] According to an embodiment of the present disclosure, as Figure 8As shown, the first rectifying circuit further includes a fifth capacitor C5. A first terminal 1 of the fifth capacitor C5 is connected to the cathodes of the eighteenth diode D18 and the nineteenth diode D19. A second terminal 2 of the fifth capacitor C5 is connected to the anodes of the twentieth diode D20 and the twenty-first diode D21. By providing the fifth capacitor C5 in the detection circuit provided by the present disclosure, a stable DC power supply can be rectified by the first rectifying circuit. In this way, a stable voltage can be provided for the subsequent alarm device, which helps to expand the selection range of the alarm device, and at the same time helps the first alarm indication to be stable and will not occur, for example, the situation of being large and small, bright and dark, etc.

[0105] According to an embodiment of the present disclosure, as Figure 8 As shown, the first alarm indication circuit further includes: an eleventh resistor R11. A first terminal 1 of the eleventh resistor R11 is connected to a second terminal 2 of the alarm device. A second terminal 2 of the eleventh resistor R11 is connected to a second terminal 2 of the ninth resistor R9. By providing the eleventh resistor R11 in the detection circuit provided by the present disclosure for voltage division and / or current limiting, the voltage on the alarm device can be stabilized within a suitable range, which helps to flexibly select the alarm device.

[0106] According to an embodiment of the present disclosure, as Figure 8As shown, the first alarm indication circuit further includes: a twelfth resistor R12, a thirteenth resistor R13, a twenty-third diode D23, a twenty-fourth diode D24, a fourth voltage regulator diode ZD4, and a sixth capacitor C6. A first end 1 of the twelfth resistor R12 is connected to an anode of the twenty-third diode D23. A second end 2 of the twelfth resistor R12 is connected to a first end 1 of the second switch S2. A cathode of the twenty-third diode D23 is connected to a third end of the fourth optocoupler U4. A first end 1 of the thirteenth resistor R13 is connected to a cathode of the twenty-fourth diode D24. A second end 2 of the thirteenth resistor R13 is connected to a first end 1 of the second switch S2. An anode of the twenty-fourth diode D24 is connected to a third end 3 of the fourth optocoupler U4. A first end 1 of the sixth capacitor C6 is connected to a first end 1 of the second switch S2. A second end 2 of the sixth capacitor C6 is connected to a fourth end 4 of the fourth optocoupler U4. An anode of the fourth voltage regulator diode ZD4 is connected to the fourth end 4 of the fourth optocoupler U4. A cathode of the fourth voltage regulator diode ZD4 is connected to the third end 3 of the fourth optocoupler U4. When it is detected that at least one of the fifth fuse L5, the sixth fuse L6, and the seventh fuse L7 is open, sending the drive signal to the second switch S2 to cause the alarm device to give the first alarm indication by closing the second switch S2 includes: when it is detected that at least one of the fifth fuse L5, the sixth fuse L6, and the seventh fuse L7 has been open for a predetermined time, sending the drive signal to the second switch S2 to cause the alarm device to give the first alarm indication by closing the second switch S2.

[0107] The circuit composed of the twelfth resistor R12, the thirteenth resistor R13, the twenty-third diode D23, the twenty-fourth diode D24, the fourth voltage regulator diode ZD4, and the sixth capacitor C6 is used to implement counting and driving functions. For example, when the fuse is truly open, the sixth capacitor C6 is continuously charged, and after the sixth capacitor C3 is charged to a predetermined value, it will drive the second switch S2 to close, thereby causing the alarm device to give an alarm indication. Another example is that when the fuse is not truly open (such as an instantaneous fault illusion caused by other reasons), the sixth capacitor C6 cannot be charged to the predetermined value after being charged, so it will not drive the second switch S2 to close, and thus the alarm device will not give an alarm indication. This circuit arrangement for implementing counting and driving functions can effectively avoid false alarms, thereby improving the accuracy of the detection circuit provided in the present disclosure.

[0108] According to an embodiment of the present disclosure, as Figure 8As shown, the first alarm indication circuit further includes: the twenty-fifth diode D25. The anode of the twenty-fifth diode D25 is connected to the second terminal 2 of the fourth optocoupler U4. The cathode of the twenty-fifth diode D25 is connected to the first terminal 1 of the fourth optocoupler U4. By providing the twenty-fifth diode D25, the detection circuit provided by the present disclosure can further protect the fourth optocoupler U4 to avoid excessive reverse voltage between the first terminal and the second terminal of the optocoupler caused by certain abnormal conditions, thereby preventing problems such as false alarms and damage of the detection circuit.

[0109] To better understand the detection circuit provided by the present disclosure, the following will be described with reference to a schematic waveform diagram (where the horizontal axis of the waveform diagram represents time in all cases).

[0110] Figure 9 shows the positions where signals are collected on the Figure 6 detection circuit shown. They respectively collect the voltage signal VC1 between the first terminal of the second resistor R2 and the second terminal of the first optocoupler U1, and the voltage signal VU1 at the remote end, for showing the situation of remote indication.

[0111] Figure 10 shows the waveform diagram under remote indication when the fuses are all working properly. As Figure 10 shown, when the fuses are all working properly, since the VC1 voltage is continuous and the first optocoupler U1 is always conducting, the output VU1 is always at a low level.

[0112] Figure 11 shows the waveform diagram in the case where any one of the first fuse, the second fuse, and the third fuse is open. As Figure 11 shown, Figure 11 specifically shows the situation where the third fuse is open. Because the VC1 voltage is interrupted due to the fuse open circuit fault. The first optocoupler U1 does not conduct continuously, but does not conduct at the point corresponding to the open fuse. During the duration when U1 is not conducting, the high impedance state output by U1 (i.e., Figure 11The high-level signal detected in []. The output state of the high-impedance state is pulled up to, for example, 5V by the pull-up resistor R_p in the remote sampling circuit of the protected power system, generating a high-level state. This high-level state will be processed, filtered, and sent to the internal controller for judgment. If the high-level state persists for a predetermined time, it is judged that the fuse is open. In addition, since the pulse width of the high-impedance state corresponds to a situation of one fuse open circuit, it can also be further judged that there is a fuse fault. It should be noted that through experiments in advance, the situation of the pulse width of the high-impedance state corresponding to one fuse fault, the situation of the pulse width of the high-impedance state corresponding to two fuse faults, etc. can be known. In addition, this method can also detect whether there are problems such as open circuit, missed connection, and wrong connection in the two wires connecting the first external output port and the second external output port to the external remote sampling circuit.

[0113] Figure 12 shows the waveform diagram in the case of any two fuses being open. As Figure 12 shown, Figure 12 specifically shows the situation where the second fuse and the third fuse are open. Similar to Figure 11 , because the VC1 voltage is interrupted due to the fuse open circuit fault. The first optocoupler U1 does not conduct continuously, but does not conduct at the point corresponding to the open fuse. During the duration when U1 does not conduct, the high-impedance state output by U1 (that is, Figure 12 the high-level signal detected in []) The output state of the high-impedance state is pulled up to, for example, 5V by the pull-up resistor R_p in the remote sampling circuit of the protected power system, generating a high-level state. This high-level state will be processed, filtered, and sent to the internal controller for judgment. If the high-level state persists for a predetermined time, it is judged that the fuse is open, and since the pulse width of the high-impedance state corresponds to the situation of two fuses being open, it can also be further judged that there are two fuse faults. It should be noted that through experiments in advance, the situation of the pulse width of the high-impedance state corresponding to one fuse fault, the situation of the pulse width of the high-impedance state corresponding to two fuse faults, etc. can be known. In addition, this method can also detect whether there are problems such as open circuit, missed connection, and wrong connection in the two wires connecting the first external output port and the second external output port to the external remote sampling circuit.

[0114] Figure 13 shows the waveform diagram when the first fuse, the second fuse, and the third fuse are all open or the fourth fuse is open. As Figure 13As shown, when the first fuse, the second fuse, and the third fuse are all open or the fourth fuse is open, the first optocoupler U1 is never turned on, resulting in a high-impedance state being always output. The output state of the high-impedance state is pulled up to, for example, 5V by the pull-up resistor R_p in the remote sampling circuit of the protected power system, generating a high-level state. This high-level state will be processed, filtered, and sent to the internal controller for judgment, and is judged to be all fuses open if the high-level state lasts for a predetermined time. In addition, this method can also detect problems such as open circuits, missed connections, and wrong connections of the two wires connecting the first external output port and the second external output port to the external remote sampling circuit.

[0115] Figure 14 show the positions where signals are collected on the detection circuit shown in Figure 6 They respectively collect the voltage signal VC1 between the first end of the second resistor R2 and the second end of the first optocoupler, the voltage signal VU2 between the anode and the cathode of the first zener diode, the voltage signal VC3 between the first end and the second end of the third capacitor, and the voltage signal VLED / speaker between the first end and the second end of the alarm device, for showing the situation of local indication.

[0116] Figure 15 shows the waveform diagram under local indication when the fuses are all working properly. As Figure 15 shown, similar to the remote indication circuit, since the VC1 voltage is continuous and the second optocoupler is always on, the output VU2 is always at a low level.

[0117] Figure 16 shows the waveform diagram when any one of the first fuse, the second fuse, and the third fuse is open. As Figure 16 shown, Figure 16Specifically shows the case where the third fuse is open. In this case, the output voltage at the third and fourth terminals of the second optocoupler U2 will have a "high level state" period, and the voltage in the "high level state" can be limited by the rated voltage of the first zener diode ZD1. During the high level period, the voltage signal output by U2 will charge C3 through R6; during the low level period, C3 will discharge through R5. By reasonably setting the values of the rated voltage of ZD1, R5, R6, and C3, it is possible to ensure that while meeting the high level pulse width, a certain number of pulses are accumulated. After the capacitor C3 is charged to the threshold voltage value, the first switch S1 is in the "closed" state, thereby triggering the alarm device (such as an LED) to give an alarm. When the first fuse, the second fuse, and the third fuse are all open or the fourth fuse is open, VU2 will always be in the "high level state", and the capacitor C3 can be quickly charged to the threshold voltage through a constant high level. The first switch S1 will be in the "off" state, then trigger the alarm device (such as an LED) and give an alarm. In addition, this method can also detect problems such as open circuits, missed connections, and incorrect connections of the two wires connecting the first external output port and the second external output port to the external remote sampling circuit.

[0118] Figure 17 Shows the simulation waveform diagram of the fuse open circuit trigger local alarm. As Figure 17 shown, during the simulation, the voltage that drives the first switch to close is set to 4V. The alarm device (LED, speaker, etc.) is replaced by a resistor to observe the voltage across the resistor to determine whether the switch is closed. In the actual circuit, the resistor voltage drop can be adjusted through different voltage dividing resistors.

[0119] Figure 18 Shows the flow chart for remote indication of fuse open circuit for 3P4W. Referring to Figure 18 , at S1810, the remote sampling circuit in the protected power system continuously samples the VU1 voltage signal. At S1820, does the remote sampling circuit determine whether a fuse open circuit signal is detected? For example, whether a high impedance state signal is detected. If not detected, return to S1810. If detected, at S1830, the remote sampling circuit communicates the obtained open circuit signal to the controller. At S1840, does the controller determine whether the fuse is truly open? If multiple open circuit signals (such as the multiple high impedance state signals mentioned above) are detected within a predetermined time, it can be determined that the fuse is truly open. If not truly open, return to S1810. If truly open, proceed to S1850 to handle the fuse open circuit fault. Then at S1860, give an alarm and execute the process related to "fuse open circuit fault".

[0120] Figure 19 Is shown in Figure 8The positions for collecting signals on the detection circuit shown, which respectively collect the voltage signal VC1 between the first end and the second end of the tenth resistor R10, the voltage signal VZD1 across the second zener diode, and the voltage signal VU1 between the third external output terminal and the fourth external output terminal, are used to show the situation of remote indication.

[0121] Figure 20 Waveform diagrams related to the second zener diode and the third zener diode are shown. Refer to Figure 20 , the rated voltage VZ of the second zener diode ZD2 and the third zener diode ZD3 is used as the voltage threshold for triggering the fuse open circuit fault. The voltage threshold determines the duration of the fuse open circuit fault state, which needs to be appropriately selected and coordinated with software processing and local protection.

[0122] Figure 21 and Figure 22 respectively show the waveform diagrams in the normal mode where the fuses are all working normally at 176Vac and 277Vac. Refer to Figure 21 、 Figure 22 , at 176Vac and 277Vac, the value of VC1 is always greater than the rated voltage VZ of the second zener diode ZD2. The third optocoupler is always in the conducting state, and thus outputs a low level. VU1 will remain in the "low level state".

[0123] Figure 23 and Figure 24 respectively show the waveform diagrams when any one of the fifth fuse, the sixth fuse, and the seventh fuse is open at 176Vac and 277Vac. Figure 23 and Figure 24 both specifically show the waveform diagram when the seventh fuse is open. Refer to Figure 23 and Figure 24 , at this time, VC1 will be lower than VZ of the second zener diode ZD2 at a certain moment, and the third optocoupler will not conduct, so there will be a "high level state" period for the third optocoupler. The controller can detect the "high level state", and after processing and filtering, if the "high level state" is true, the controller will trigger an "alarm" and handle the "fuse open circuit fault". In addition, this method can also check whether there are problems such as open circuit, missing connection, and wrong connection of the two wires connecting the third external output port and the fourth external output port to the external remote sampling circuit.

[0124] Figure 25 and Figure 26 respectively show the waveform diagrams when any two of the fifth fuse, the sixth fuse, and the seventh fuse are open or all fuses are open at 176Vac and 277Vac. Refer to Figure 25 and 26, at this time, VC1 will be zero and lower than the VZ of the second voltage regulator diode ZD2, and the third optocoupler will not conduct. Therefore, the output of the third optocoupler will always be in the "high level state", and the "high level state" can be detected by the controller. After filtering the signal, if the "high level state" is true, then the controller will trigger an "alarm" and handle the "fuse open circuit fault". In addition, this method can also check whether there are problems such as open circuit, missed connection, and wrong connection in the two wires connecting the third external output port and the fourth external output port to the external remote sampling circuit.

[0125] Figure 27 shows the positions where signals are collected on the Figure 8 detection circuit shown. They respectively collect the voltage signal VC1 across the tenth resistor, the voltage signal VZD2 across the third voltage regulator diode, the voltage signal VU2 across the fourth voltage regulator diode, the voltage signal VC3 across the sixth capacitor, and the voltage signal VLED / speaker across the alarm device, for showing the situation of local indication.

[0126] Figure 28 shows the waveform diagram in the case of any one of the fifth fuse, sixth fuse, and seventh fuse being open at 277Vac. Specifically, Figure 28 shows the situation where the seventh fuse is open. Referring to Figure 28 , at this time, the output of the fourth optocoupler will have a "high level state" period, and the "high level state" voltage can be limited by the rated voltage VZ of the fourth voltage regulator diode ZD4. During the high level period, the VU2 voltage will charge C6 through R13. During the low level period, C6 will discharge through R12. By reasonably setting the values of VZ, R12, R13, and C6, it can be ensured that while meeting the high level pulse width, a certain number of pulses are accumulated, the capacitor C6 is charged to the threshold voltage value, the second switch is in the "closed" state, triggering the LED and emitting an alarm. When any two of the fifth fuse, sixth fuse, and seventh fuse are open or all fuses are open, VU2 will always be in the "high level state", and the capacitor C6 can be quickly charged to the threshold voltage through the constant high level. The second switch will be in the "off" state, and then trigger the LED and emit an alarm.

[0127] Figure 29 shows the simulation waveform diagram of the local alarm of the fuse open circuit trigger. As Figure 29 shown, during the simulation, the voltage driving the second switch to close is set to 4V. The alarm device (LED, speaker, etc.) is replaced by a resistor to observe the voltage across the resistor to judge whether the switch is closed. In the actual circuit, the resistor voltage drop can be adjusted through different voltage dividing resistors.

[0128] The process for remote indication of the open circuit of the 3P3W fuse is the same as the process described above for Figure 18 and will not be elaborated here.

[0129] From the detection circuit provided by the present disclosure described in combination with the above Figures 4 - 29 it can be seen that the detection circuit provided by the present disclosure can, in the case of a fuse open circuit, not only give an alarm indication locally, but also output an alarm indication remotely to the outside, so that the detection circuit provided by the present disclosure can give an alarm prompt in the above two ways. This can not only timely notify the service team that the fuse has failed, but also enable the service team to mutually verify the alarm prompts given in the above two ways to improve the accuracy of the alarm, and further enable the service team to timely replace the faulty fuse. In addition, the detection circuit provided by the present disclosure has the advantages of simple circuit, low cost, flexible remote installation location, and can flexibly use fuses of different packages compared with the existing solutions. When fixed on the metal chassis, high-voltage insulated wires are not required. Moreover, by outputting indications through two SELV signal lines, it has the advantages of small volume, not occupying the space of the detection circuit, and low cost.

[0130] The block diagrams of the circuits, units, devices, apparatuses, equipment, and systems involved in the present disclosure are only exemplary examples and do not intend to require or imply that they must be connected, arranged, and configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these circuits, units, devices, apparatuses, equipment, and systems can be connected, arranged, and configured in any way as long as the desired purpose can be achieved. The circuits, units, and devices involved in the present invention can be implemented in any suitable way, such as using application-specific integrated circuits, field-programmable gate arrays (FPGAs), etc.

[0131] Those skilled in the art should understand that the above specific embodiments are only examples and not limitations, and various modifications, combinations, partial combinations, and substitutions can be made to the embodiments of the present invention according to design requirements and other factors, as long as they are within the scope of the appended claims or their equivalents, that is, within the scope of the rights to be protected by the present invention.

Claims

1. A detection circuit for a fuse, the fuse being connected in series between an AC power supply and an electrical device, the detection circuit comprising: A first alarm indication circuit, connected to the first end and the second end of the fuse to detect whether the fuse is open, and giving out a first alarm indication when it detects that the fuse is open; A second alarm indication circuit, connected to the second end of the fuse to detect whether the fuse is open, and giving out a second alarm indication when it detects that the fuse is open, wherein, the first end of the fuse is connected to the AC power supply, and the second end of the fuse is connected to the electrical device.

2. The detection circuit according to claim 1, wherein the detection circuit further comprises a first rectification circuit and a second rectification circuit for rectifying the AC power supply into direct current, wherein, the first alarm indication circuit is connected to the first end of the fuse via the first rectification circuit, and the first alarm indication circuit is connected to the second end of the fuse via the second rectification circuit; the second alarm indication circuit is connected to the second end of the fuse via the second rectification circuit.

3. The detection circuit according to claim 2, wherein, the first alarm indication circuit comprises an alarm detection circuit and an alarm indication circuit, wherein the alarm detection circuit is used for giving out a drive signal to the alarm indication circuit to drive the alarm indication circuit to give out the first alarm indication when it detects that the fuse is open.

4. The detection circuit according to claim 3, wherein, the AC power supply is a three-phase four-wire based AC power supply, the fuse comprises a first fuse, a second fuse, a third fuse and a fourth fuse, wherein, the first end of the first fuse is connected to the A-phase wire in the three-phase four-wire system, the first end of the second fuse is connected to the B-phase wire in the three-phase four-wire system, the first end of the third fuse is connected to the C-phase wire in the three-phase four-wire system, and the first end of the fourth fuse is connected to the neutral wire in the three-phase four-wire system.

5. The detection circuit according to claim 4, wherein, the second rectification circuit comprises a first diode, a second diode and a third diode, wherein, the anode of the first diode is connected to the second end of the first fuse, the anode of the second diode is connected to the second end of the second fuse, and the anode of the third diode is connected to the second end of the third fuse; The second alarm indication circuit includes a first resistor and a first optocoupler. Wherein, a first end of the first resistor is connected to the cathodes of the first diode, the second diode, and the third diode. A second end of the first resistor is connected to a first end of the first optocoupler. A second end of the first optocoupler is connected to the neutral line and grounded. A third end and a fourth end of the first optocoupler are respectively connected to a first external output terminal and a second external output terminal, so as to send out the second alarm indication through the first external output terminal and the second external output terminal when at least one of the first fuse, the second fuse, the third fuse, and the fourth fuse is open.

6. The detection circuit according to claim 5, wherein, The alarm detection circuit includes a second resistor, a second optocoupler, and a third resistor; the alarm indication circuit includes a first switch and an alarm device. Wherein, a first end of the second resistor is connected to the cathodes of the first diode, the second diode, and the third diode. A second end of the second resistor is connected to a first end of the second optocoupler. A second end of the second optocoupler is connected to a second end of the first optocoupler. A third end of the second optocoupler is connected to a first end of the third resistor and a first end of the first switch. A fourth end of the second optocoupler is connected to a second end of the first switch and grounded. A third end of the first switch is connected to a first end of the alarm device. A second end of the alarm device is connected to a second end of the third resistor. Wherein, when it is detected that the fuse is open, a drive signal is sent to the alarm indication circuit to drive the alarm indication circuit to send out the first alarm indication, including: when it is detected that at least one of the first fuse, the second fuse, the third fuse, and the fourth fuse is open, the drive signal is sent to the first switch, so that the alarm device sends out the first alarm indication by closing the first switch; The first rectifier circuit includes a fourth diode, a fifth diode, a sixth diode, and a seventh diode. Wherein, an anode of the fourth diode is connected to a cathode of the sixth diode. A cathode of the fourth diode is connected to a cathode of the fifth diode and a second end of the third resistor. An anode of the fifth diode is connected to a cathode of the seventh diode. An anode of the sixth diode is connected to an anode of the seventh diode and grounded. Wherein, the anode of the fourth diode and the anode of the fifth diode are respectively connected to any two of the A-phase line, B-phase line, C-phase line, and the neutral line.

7. The detection circuit according to claim 6, wherein, The second rectifier circuit further includes a first capacitor. Wherein, a first end of the first capacitor is connected to the cathodes of the first diode, the second diode, and the third diode. A second end of the first capacitor is connected to the neutral line and grounded.

8. The detection circuit according to claim 6, wherein, the second alarm indication circuit further includes an eighth diode, wherein the anode of the eighth diode is connected to the second end of the first optocoupler, and the cathode of the eighth diode is connected to the first end of the first optocoupler.

9. The detection circuit according to claim 6, wherein, the first rectification circuit further includes a second capacitor, wherein the first end of the second capacitor is connected to the cathodes of the fourth diode and the fifth diode, and the second end of the second capacitor is connected to the anodes of the sixth diode and the seventh diode.

10. The detection circuit according to claim 6, wherein, the first alarm indication circuit further includes: a fourth resistor, wherein the first end of the fourth resistor is connected to the second end of the alarm device, and the second end of the fourth resistor is connected to the second end of the third resistor.

11. The detection circuit according to claim 6 or 10, wherein, the first alarm indication circuit further includes: a fifth resistor, a sixth resistor, a ninth diode, a twelfth diode, a first voltage stabilizing diode and a third capacitor, wherein the first end of the fifth resistor is connected to the anode of the ninth diode, the second end of the fifth resistor is connected to the first end of the first switch, the cathode of the ninth diode is connected to the third end of the second optocoupler, the first end of the sixth resistor is connected to the cathode of the twelfth diode, the second end of the sixth resistor is connected to the first end of the first switch, the anode of the twelfth diode is connected to the third end of the second optocoupler, the first end of the third capacitor is connected to the first end of the first switch, the second end of the third capacitor is connected to the fourth end of the second optocoupler, the anode of the first voltage stabilizing diode is connected to the fourth end of the second optocoupler, and the cathode of the first voltage stabilizing diode is connected to the third end of the second optocoupler; wherein, in the case that at least one of the first fuse, the second fuse, the third fuse and the fourth fuse is detected to be open, sending the driving signal to the first switch to cause the alarm device to give the first alarm indication by closing the first switch includes: in the case that at least one of the first fuse, the second fuse, the third fuse and the fourth fuse is detected to be open for a predetermined time, sending the driving signal to the first switch to cause the alarm device to give the first alarm indication by closing the first switch.

12. The detection circuit according to claim 6, wherein, the first alarm indication circuit further includes: an eleventh diode, wherein the anode of the eleventh diode is connected to the second end of the second optocoupler, and the cathode of the eleventh diode is connected to the first end of the second optocoupler.

13. The detection circuit according to claim 3, wherein, the AC power supply is a three-phase three-wire based AC power supply. The fuse includes a fifth fuse, a sixth fuse and a seventh fuse. Among them, the first end of the fifth fuse is connected to the A-phase wire in the three-phase three-wire system, the first end of the sixth fuse is connected to the B-phase wire in the three-phase three-wire system, and the first end of the seventh fuse is connected to the C-phase wire in the three-phase three-wire system.

14. The detection circuit according to claim 13, wherein The second rectifying circuit includes a twelfth diode, a thirteenth diode, a fourteenth diode, a fifteenth diode, a sixteenth diode and a seventeenth diode. Among them, the cathode of the twelfth diode is connected to the cathodes of the thirteenth diode and the fourteenth diode, the anode of the twelfth diode is connected to the cathode of the fifteenth diode and the second end of the fifth fuse, the anode of the thirteenth diode is connected to the cathode of the sixteenth diode and the second end of the sixth fuse, the anode of the fourteenth diode is connected to the cathode of the seventeenth diode and the second end of the seventh fuse, and the anodes of the fifteenth diode, the sixteenth diode and the seventeenth diode are connected and grounded; The second alarm indicating circuit includes a second zener diode, a seventh resistor and a third optocoupler. Among them, the cathode of the second zener diode is connected to the cathode of the fourteenth diode, the anode of the second zener diode is connected to the first end of the seventh resistor, the second end of the seventh resistor is connected to the first end of the third optocoupler, the second end of the third optocoupler is connected to the anode of the seventeenth diode, and the third and fourth ends of the third optocoupler are respectively connected to a third external output terminal and a fourth external output terminal, so as to send out a second alarm indication through the third external output terminal and the fourth external output terminal when at least one of the fifth fuse, the sixth fuse and the seventh fuse is open.

15. The detection circuit according to claim 14, wherein The alarm detection circuit includes an eighth resistor, a fourth optocoupler, a ninth resistor, and a third zener diode; the alarm indication circuit includes a second switch and an alarm device. Among them, the cathode of the third zener diode is connected to the cathode of the fourteenth diode, the anode of the third zener diode is connected to the first end of the eighth resistor, the second end of the eighth resistor is connected to the first end of the fourth optocoupler, the second end of the fourth optocoupler is connected to the second end of the third optocoupler, the third end of the fourth optocoupler is connected to the first end of the ninth resistor and the first end of the second switch, the fourth end of the fourth optocoupler is connected to the second end of the second switch and grounded, the third end of the second switch is connected to the first end of the alarm device, and the second end of the alarm device is connected to the second end of the ninth resistor. Among them, when detecting that the fuse is open, sending a drive signal to the alarm indication circuit to drive the alarm indication circuit to issue the first alarm indication includes: when detecting that at least one of the fifth fuse, the sixth fuse, and the seventh fuse is open, sending the drive signal to the second switch to make the alarm device issue the first alarm indication by closing the second switch; The first rectification circuit includes an eighteenth diode, a nineteenth diode, a twenty-second diode, and a twenty-first diode. Among them, the anode of the eighteenth diode is connected to the cathode of the twenty-second diode, the cathode of the eighteenth diode, the cathode of the nineteenth diode, and the second end of the ninth resistor are connected, the anode of the nineteenth diode is connected to the cathode of the twenty-first diode, and the anode of the twenty-second diode and the anode of the twenty-first diode are connected and grounded. Among them, the anode of the eighteenth diode and the anode of the nineteenth diode are respectively connected to any two of the A-phase line, B-phase line, and C-phase line.

16. The detection circuit according to claim 15, wherein, The second rectification circuit further includes a fourth capacitor and a tenth resistor. Among them, the first end of the fourth capacitor is connected to the cathode of the fourteenth diode, the second end of the fourth capacitor is connected to the anode of the seventeenth diode, the first end of the tenth resistor is connected to the first end of the fourth capacitor, and the second end of the tenth resistor is connected to the second end of the fourth capacitor.

17. The detection circuit according to claim 15, wherein, The second alarm indication circuit further includes a twenty-second diode. Among them, the anode of the twenty-second diode is connected to the second end of the third optocoupler, and the cathode of the twenty-second diode is connected to the first end of the third optocoupler.

18. The detection circuit according to claim 15, wherein, The first rectifying circuit further includes a fifth capacitor, wherein a first end of the fifth capacitor is connected to cathodes of the eighteenth diode and the nineteenth diode, and a second end of the fifth capacitor is connected to anodes of the twenty-second diode and the twenty-first diode.

19. The detection circuit according to claim 15, wherein the first alarm indication circuit further includes: an eleventh resistor, wherein a first end of the eleventh resistor is connected to a second end of the alarm device, and a second end of the eleventh resistor is connected to a second end of the ninth resistor.

20. The detection circuit according to claim 15 or 19, wherein the first alarm indication circuit further includes: a twelfth resistor, a thirteenth resistor, a twenty-third diode, a twenty-fourth diode, a fourth voltage stabilizing diode, and a sixth capacitor wherein a first end of the twelfth resistor is connected to an anode of the twenty-third diode, a second end of the twelfth resistor is connected to a first end of the second switch, a cathode of the twenty-third diode is connected to a third end of the fourth optocoupler, a first end of the thirteenth resistor is connected to a cathode of the twenty-fourth diode, a second end of the thirteenth resistor is connected to a first end of the second switch, an anode of the twenty-fourth diode is connected to a third end of the fourth optocoupler, a first end of the sixth capacitor is connected to a first end of the second switch, a second end of the sixth capacitor is connected to a fourth end of the fourth optocoupler, an anode of the fourth voltage stabilizing diode is connected to the fourth end of the fourth optocoupler, and a cathode of the fourth voltage stabilizing diode is connected to the third end of the fourth optocoupler; wherein, when at least one of the fifth fuse, the sixth fuse, and the seventh fuse is detected to be open, sending the drive signal to the second switch to cause the alarm device to give the first alarm indication by closing the second switch includes: when at least one of the fifth fuse, the sixth fuse, and the seventh fuse is detected to be open for a predetermined time, sending the drive signal to the second switch to cause the alarm device to give the first alarm indication by closing the second switch.

21. The detection circuit according to claim 15, wherein the first alarm indication circuit further includes: a twenty-fifth diode, wherein an anode of the twenty-fifth diode is connected to a second end of the fourth optocoupler, and a cathode of the twenty-fifth diode is connected to a first end of the fourth optocoupler.

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