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DON’T KEEP BLOWING FUSES! Build the eFuse * A Resettable Circuit Breaker * Ideal for automotive fault-finding * Set for any current between 315mA and 10A This resettable Electronic Fuse (eFuse) can be used temporarily in place of a conventional fuse when fault-finding. It is ideal when tracking down the cause of a blown fuse. The eFuse acts like a circuit breaker, automatically disconnecting power a short time after the current through it exceeds a set value. If it “trips out”, just press the reset button to get the current flowing again! W hen you have blown a fuse for the nth time and you really don’t know why, how often have you wished you could press a button and have the fuse “repair” itself? Well, with the eFuse, now you can! If, for example, you are trying to find out why fuses keep blowing in a car, van or trailer, you have two ways to check them: keep blowing fuses until you track down the problem (and end up with a pocket full of blown fuses) . . . or you can use the SILICON CHIP eFuse to save time and frustration. Mind you, the eFuse is not just limited to automotive applications: it can be used when trouble-shooting any circuit which runs at DC voltages between 9V & 15V. Three LED indicators show when there is voltage present at the eFuse input and output, and also whether it has tripped. In use, the eFuse is connected in place of the conventional fuse by being plugged into the fuseholder of the circuit under investigation (only suitable for vehicles or circuits that have the fuse in the positive supply line). You can set up the eFuse for a trip current that includes standard fuse ratings between 315mA and 10A. ally concerned by the “fuse current”, you could remove the power indicator LEDs (or use high-brightness LEDs with much higher current limiting LEDs) but there still will be around 1.7mA drawn by the eFuse itself. Also the eFuse has a voltage loss that may be a little higher than that of a typical high-current fuse but that should not cause a problem in most circuits. The voltage drop is typically around 0.4V at 10A and proportionally less at lower currents. Configuration The eFuse is housed in a small plastic box with three indicator LEDs, a pushbutton reset switch and a conventional fuse on the front panel. It has three leads, two for connection to the fuseholder (to replace the conventional fuse) while the third lead is to connect to chassis, which provides the negative supply for the eFuse. The positive supply for the eFuse comes from the connection to the fuseholder. A conventional fuse is included in the eFuse just as a safeguard. It would only blow if the eFuse itself fails. Points to consider Table 1 shows the LED indications under various condiNote that the eFuse does draw a slight amount of current tions. If LEDs 1 & 3 are alight, the eFuse is conducting. If when it is connected in-circuit, on top of that consumed LED2 lights, the eFuse has gone “open circuit”. In this case, LED3 will generally be off by the load itself. although it may glow dimly if the load This amounts to around 15mA and is By JOHN CLARKE is disconnected. You can press the Reset mostly due to the indicator LEDs. If you re38  Silicon Chip siliconchip.com.au Features * Adjustable trip current * Reset switch * LED lights when tripped * Capable of withstanding brief overloads * Reverse connection protection * Indication of input and output voltage presence * Transient voltage protection * Output voltage clamping * Onboard safeguard fuse switch after the eFuse has “blown”, to reconnect power to the load. eFuse operation The eFuse operates somewhat like conventional fastblow fuse. Conventional fuses come in several different types including standard, fast and slow blow. Typically, a standard fuse requires twice its rated current to open in one second, a fast-blow fuse requires twice its rated current to blow in 100ms, and a slow-blow fuse requires twice its rated current to blow after tens of seconds. The eFuse operates by limiting the current passing through it and it has two current limits. One is the shortcircuit current limit and the other is the overload current limit. The overload limit is higher than the short-circuit limit. As long as the current flow through the eFuse remains below the overload limit, it operates in full conduction. However, should the overload limit be exceeded, current through the eFuse is limited to the lower short-circuit limit. If the eFuse output is shorted, this will happen almost instantaneously and it will be as if the current was limited to the short-circuit level initially. While the current is being limited in this manner, the eFuse IC heats up and one of two things can happen: it trips off, disconnecting the load or if the overload condition is cleared (eg, output short removed), the eFuse goes back to full conduction. siliconchip.com.au The time it takes the eFuse to “blow” typically ranges from 1-100ms, depending mainly on the current limit setting. The two current limits cannot be set separately; they’re locked together. You set the short-circuit current limit and the overload current limit is automatically set to a somewhat higher value. Typically, you would set the short-circuit current limit to the same value as you would select for a standard fastblow fuse in the circuit being protected. If you’re confused about the two different current limits, think of the difference in the two limits as similar to hysteresis in the comparator which compares the current flow to a reference current limit. It also serves to allow the load to draw more than the Table 1: LED Indicator states Supply indicator (LED1) Output indicator (LED3) Trip indicator (LED2) Normal Lit Lit Off Limiting Lit Dimmed Off Tripped Lit Off or dim Lit Reversed supply/ output connection Off Lit Off eFuse state April 2017  39 8 age which typically must be amplified before being fed to a microcontroller or analog-to-digital converter and the amplification inevitably increases CHARGE VOLTAGE the noise level in the current reading. PUMP REGULATOR The configuration of a SenseFET is shown in CURRENT Fig.2(b). In this case, some small proportion (say 4 LIMIT CURRENT LIMIT 1%) of the current always flows through the smaller OVERFET while the other 99% flows through the larger VOLTAGE CLAMP FET. The drain current and gate voltage is therefore SOURCE 5,6,7 the same as with a regular FET, but this current is THERMAL split between the two source terminals. This allows LATCH a resistor to be inserted in series with the smaller FET such that 1% of the load current (say) flows VOLTAGE SLEW RATE through it while the other 99% flows unimpeded. ENABLE/ This is shown in Fig.2(c). TIMER Since the current through this resistor is so low, say 100mA when the total current is 10A (ie, 10A x dV/dt ENABLE/ TIMER GND 1%), it can have a much higher value, so the sense 3 2 1 voltage is higher and there is no need to amplify it. Fig.1: the block diagram of the NIS5112 is shows the SenseFET Also, despite the higher voltage across this resistor, in the top righthand corner. The charge pump circuit provides the dissipation is much, much lower and there’s the necessary voltage-shifted gate signal to the SenseFET for no need to use a high power resistor. high-side switching. However, the coupling from the charge In practice, in the eFuse circuit, the current sense pump to the SenseFET gate is not shown. resistor has a value of 20Ω or more, dissipation is very low, under 100µW (0.1mW) and the ratio of rated current for brief periods, eg, while charging up ca- the two currents is 1000:1 (ie, 99.9% and 0.1%). pacitors (which a normal fuse would also tolerate). The eFuse cannot be reset to restore power until the Electronic fuse IC details overload or short-circuit has been removed. Depending on Being an N-channel device, the internal Mosfet how soon you reset it, the overload current limit may be (SenseFET) needs a gate voltage higher than Vcc to operate lower than it was initially, until the eFuse IC cools down. as a high-side switch and so the IC has an internal charge The current limiting described above not only provides pump to generate this voltage. the fuse function but also serves to protect the eFuse itself. The NIS5112 also includes a soft-start feature whereby a capacitor connected to the dV/dt input (pin 2) is charged Current sensing from a current source, causing the Mosfet to gradually The main component in the eFuse is an NIS5112 Elec- switch on at power up. dV/dt simply refers to the rate of tronic Fuse IC manufactured by ON Semiconductor. Its in- voltage change (dV) with time (dt). The slow start-up rate ternal function block diagram is shown in Fig.1. is useful when the load would normally have a high initial It contains an internal N-channel Mosfet which conducts surge current. This includes loads that have large filter cacurrent from the Vcc supply at pin 8 to output Source pins pacitors or capacitor banks across their inputs. 5, 6 & 7. This Mosfet has a typical on-resistance of 30mΩ, The slow start allows these capacitor(s) to charge withcurrent ratings of 5.3A continuous and 25A peak and is a out tripping the eFuse. The same slow start-up procedure current-sensing type, known as a “SenseFET”. This con- applies when the eFuse is reset. sists of two Mosfets in parallel, one of which is much bigFuse tripping is handled by monitoring the Mosfet temger than the other. perature and the IC switches it off quickly when the die Most of the current flows through the LOAD LOAD bigger Mosfet and the ratio of the curCURRENT CURRENT rents flowing through the two Mosfets D D LOAD is constant. A small resistor connected MAIN MAIN SENSING SENSING CURRENT MOSFET MOSFET MOSFET MOSFET D in series with the smaller Mosfet allows the total current to be sensed, without G G G needing to pass the full current through S this resistor. MIRROR R To explain the benefit of a SenseFET, R consider the conventional method for SOURCE sensing current through a Mosfet, as SOURCE MIRROR Fig.2b Fig.2a Fig.2c shown in Fig.2(a). The problem with CURRENT this approach is that since the entire Fig.2: these diagrams show the operation of a SenseFET. Fig.2(a) show a current load current flows through the sense sensing resistor in the source circuit of a normal FET. This resistor would need to resistor, it must have a very low value be a very low value to keep power dissipation low in high current applications. and high power rating to avoid exces- A SenseFET has two FETs with the smaller FET “mirroring” the current in the sive dissipation, reduced efficiency and main FET (Fig.2(b)). So the sensing FET can have a much higher value of sensing overheating. This results in a small volt- resistor without consequent high power dissipation, as in Fig.2(c). VCC 40  Silicon Chip siliconchip.com.au temperature reaches about 135°C. There are two versions of the NIS5112 which differ in regards to how tripping is handled. In one version, the Mosfet stays off once it is tripped until reset and this is the version we are using. The other version restores fuse operation automatically when the temperature drops below 95°C. Another feature of the NIS5112 is over-voltage clamping which limits the output voltage to 15V. Clamping is done by controlling gate drive to the Mosfet to adjust the drainsource resistance to maintain the 15V maximum output. Note though that if the input voltage is very far above 15V and stays that way for a significant time, the Mosfet is likely to overheat and trip the fuse. SPECIFICATIONS Supply voltage: ........ 9-15V Polarity: .................... for fuses connected in series with the positive supply line Current drain: ........... 15mA typical (1.7mA with LED1 and LED3 removed) Trip current range: ... See Table 1 Trip response time: .. typically 10ms Overload current: .....13.6A (with two fuse ICs fitted; self-limiting) Supply voltage: ........ 15V maximum Paralleling eFuse ICs Typically, if two NIS5112 ICs are connected in parallel, they will automatically current share the current, ie, 50% of the overall current is carried in the Mosfet within each IC. Thus, the actual trip level will be twice the set trip level for each IC. The reason is as follows. At 25°C, the internal Mosfets in IC1 and IC2 have an onresistance of around 28mΩ. If one Mosfet has a slightly lower on-resistance, it will conduct more current and so heat up a little more than its companion. Mosfet on-resistance rises with temperature (to around 37mΩ at 100°C) and the increased resistance will reduce the current through this Mosfet so more current flows through the other Mosfet. The Mosfets will stabilise in temperature as each Mosfet shares current more or less equally. It may not be obvious that the Mosfet with the lower onresistance will heat up more since the resistance is one factor in calculation the dissipation, but note that the equation is I2R and since the current will increase proportionally as the on-resistance decreases, the fact that the current is squared in this equation means that its increase will more 2.2k eFUSE IN + 8 VCC TO CHASSIS (15V) The circuit for the SILICON CHIP eFuse is shown in Fig.3 and it can use one or two NIS5112 electronic fuse ICs. With a single IC fitted, the eFuse will work up to 5A whereas with two, you can set the trip current as high as 10A. Resistors R1 and R2 set the trip current for IC1 and IC2 LED2  SOURCE F1 TVS1 SA15A Circuit description K Q1 SUP53P06 TRIPPED SAFEGUARD FUSE (9–15V) A than compensate from the reduction in dissipation due to lower resistance. One small wrinkle when paralleling NIS5112 ICs is that while they will share current before either trips, inevitably one will trip before the other (due to differences in onresistance, external resistor value, temperature sensor accuracy etc), leaving the remaining IC to continue passing the full load current for a brief period. Before this second IC trips, it will continue to limit the current to one half the value compared to when the two ICs were conducting. However, normally the second IC will trip very soon after the first due to the increased dissipation in this condition so it isn’t really an issue. IC 1 IC1 NIS5112 2.2k K SOURCE SOURCE A SUPPLY LIMIT IN A EN/T  LED1 3 GND 5 D 6 7 4 C dv/dt B 2 1 K 15k 1 F 8 FUSE RESET VCC SOURCE IC2 NIS5112 S1 SOURCE SOURCE LIMIT 1 F EN/T 3 GND 1 100k G 100k R1 100nF eFUSE OUT S Q2 BC 547 2.2k SUPPLY OUT A  LED3 E K 5 6 7 4 BC547 LEDS R2 B K A dv/dt 2 E 1 F C SUP53P06 NIS5112 SC 20 1 7 ELECTRONIC FUSE SA15A A 8 K 4 1 G D D S Fig.3: one or two NIS5112 ICs can be used in the circuit, giving a trip current rating of 5A or 10A. Mosfet Q1 provides protection against input/output reversal. The safeguard fuse (F1) is included just in case the whole circuit fails. siliconchip.com.au April 2017  41 1 F RESET NO NC 2.2k 2.2k 100k SUP53P06-20 Electronic Fuse 1 F LED1 S1 C Q2 BC547 Q1 2.2k IC2 100nF 100k TVS1 R2 IC1 R1 NIS5112 15k eFUSE eFUSE IN GND OUT Safeguard FUSE F1 1 F A Supply IN LED2 eFuse Trip A LED3 A Supply OUT 17120140 04102171 C 2017 REV.C Fig.4: the safeguard fuse is a standard automotive blade type, mounted on the top left corner of the PCB. The external connections can be made via a 3-way terminal block, as shown on the component overlay at left, or wired directly, as shown in the photo at right. respectively. Assuming both ICs are fitted, both resistors must be the same value so the trip current is the same for each. Table 2 shows the various trip currents that can be selected with one IC fitted while Table 3 shows the values for R1 & R2 with IC1 & IC2 fitted. Note that for a given short-circuit trip current ratings, there will difference in the overload current rating, depending on whether you use one or two ICs. For example, a 3A eFuse with just IC1 fitted has an overload rating of 4.6A but with IC1 and IC2 fitted, has an overload rating of 7.6A instead. So fitting both ICs is to be preferred since a normal fuse will typically handle overloads up to twice its rated current (ie, 6A in this case) for around one minute before blowing. The dV/dt inputs for IC1 and IC2 (pin 2) each connect to a 1F capacitor so that after resetting or during power up, the eFuse output will slowly rise in voltage to supply the load over about 80ms, ie, it “slew rate” limits. A second 1F capacitor across reset switch S1 provides a slight delay after resetting and serves as a contact de-bounce for the switch. The input supply indicator, LED1, lights whenever power is connected to the eFuse. LED2 lights when the eFuse trips and LED3 lights when there is a supply to the load. Circuit protection Note that the output from IC1 (and IC2 if used) passes current to the eFuse output via P-channel Mosfet Q1. This Table 2: Only IC1 installed Mosfet provides reverse connection protection (ie, if power is incorrectly applied to the eFuse output rather than its input). While we could have used a schottky diode to provide the same reverse polarity protection, its forward voltage drop of about 0.5V at 10A, is much higher than the conduction voltage of Q1. It works as follows. Once IC1/IC2 switch on, the output voltage turns on NPN transistor Q2 via a 100kΩ/15kΩ resistive divider and current limiting network. Q2 pulls the gate of Q1 low, switching it on. It will have started conducting current to the load anyway, via its body diode, however this has a high forward voltage drop and that diode is effectively shorted out once the Mosfet switches on, so only its low on-resistance of around 20mΩ affects the load voltage slightly. If the circuit is connected in reverse, with a voltage source connected to the output, Q1’s body diode is reverse-biased so will not conduct and since its gate pin is pulled up by the 100kΩ resistor from its source, it will remain switched off. The 100nF capacitor and 15kΩ resistor across Q2’s baseemitter junction ensures that it too remains off, despite any voltage coupled across Q1’s gate/source or drain/source capacitance. This condition is indicated by LED3 being lit while LED1 is off so you can easily identify and rectify it. Q1 also protects the circuit if the connections are swapped both in terms of input/output and also polarity; ie, if the “eFuse out” terminal is connected to 0V and 0V Table 3: IC1 and IC2 installed Short Circuit Trip Current Overload Current Safeguard Fuse rating R1 Short Circuit Trip Current Overload Current Safeguard Fuse rating R1 & R2 (IC2 installed) 315mA 350mA 500mA 800mA 1A 1.6A 2A 2.5A 3A 3.15A 4A 5A 3.5A 3.5A 3.6A 3.7A 3.8A 3.9A 4.1A 4.5A 4.6A 4.6A 5.5 6.8A 1A 1A 1A 1A 1A 2A 2A 3A 3A 3A 5A 5A 430Ω 390Ω 330Ω 180Ω 120Ω 91Ω 62Ω 47Ω 39Ω 36Ω 27Ω 20Ω 800mA 1A 1.25A 2A 2.5A 3A 3.15A 4A 5A 6.5A 7.5A 10A 7A 7.2A 3.9A 7A 7.2A 7.6A 7.7A 8.2A 8.4A 9.2A 10.6A 13.6A 1A 1A 1A 2A 3A 3A 3A 5A 5A 7.5A 10A 10A 360Ω 330Ω 220Ω 150Ω 120Ω 91Ω 82Ω 62Ω 43Ω 36Ω 30Ω 20Ω 42  Silicon Chip siliconchip.com.au terminal to +15V, little current will flow and no damage will result. However, if the input is connected with reverse polarity – ie, with “eFuse in” to 0V and the 0V terminal to +15V, TVS1 will conduct a large amount of current and safeguard fuse F1 will blow. In normal use, with the correct supply polarity, TVS1 is used to clamp transient voltages over about 18V and thus to protect IC1 and IC2 from over-voltage damage. As well as protecting against reverse polarity, F1 prevents further damage in the case of any other catastrophic faults. Construction 1 double-sided PCB coded 04102171, 74 x 47mm 1 UB5 plastic box, 83 x 54 x31mm 1 panel label, 78 x 48mm 1 SPDT PCB-mount momentary pushbutton switch (Altronics S1393) (S1) 1 6073B-type flag heatsink, 19 x 19 x 10mm (Jaycar HH8502, Altronics H0630) (for Q1) 1 PCB-mount ATO/ATC blade fuse holder (Altronics S6040) (F1) 1 ATO/ATC blade fuse (see Table 2&3) 1 blown fuse (to connect eFuse to circuit being protected) 1 cable gland for 6mm diameter cable 1 M3 x 10mm machine screw and nut (to mount Q1) 1 crimp eyelet or alligator clip (for 0V lead) 1 1m length of light or medium-duty black insulated wire 1 1m length of red insulated wire, rated to suit eFuse configuration 1 1m length of yellow insulated wire, rated to suit eFuse configuration Semiconductors 1 NIS5112D1R2G latch-off electronic fuse (IC1) 1 SUP53P06 P-channel Mosfet (Q1) 1 BC547 NPN transistor (Q2) 1 500W 15V Transient Voltage Suppressor (eg, SA15A) (TVS1) 2 3mm green LEDs (LED1 & LED3) 1 3mm red LED (LED2) Capacitors 2 1F 25V (or 63V) PC electrolytic 1 100nF 63V or 100V MKT polyester Resistors (0.25W 1%) 2 100kΩ 1 15kΩ plus R1 & R2 (see Table 2&3) Fig.5: reproduced from the data sheet, this graph shows the short circuit and overload current limits of a single NIS5112 IC for various values of limiting resistor (ie, R1). Note that we have selected a minimum value of 20Ω, giving the device the ability to carry 5A continuously. Lower values of R1 will allow higher currents to be carried for short periods until it reaches its internal temperature limit and then trips out. So in fact, lower values for R1 are not practical. siliconchip.com.au 3 2.2kΩ Additional parts if fitting IC2 1 NIS5112D1R2G latch-off electronic fuse (IC2) 1 1F 25V or 63V PC electrolytic 1 0.25W 1% resistor for R2 (see Table 3) I Limit (A) The eFuse is built on a PCB coded 04102171 and measuring 74 x 47mm. It can be housed in a small plastic box measuring 83 x 54 x 31mm. A panel label measuring 78 x 48mm can also be glued to the base of the box which is normally fitted with a cable gland at one end for the wires to pass through. Before starting construction, decide on the current rating you require and whether or not to install both IC1 and IC2. If you only install IC1, use Table 2 to select the value of R1. If you install both IC1 & IC2, select R1 & R2 from Table 3. Use the overlay diagram, Fig.4, as an assembly guide. IC1 (and IC2 if used) are installed first. Start by aligning pin 1 of the IC on the marking on the PCB. Solder pin 1 first, then check that the IC pins are correctly aligned. If not oriented correctly, re-melt the solder and adjust placement until the IC is correctly positioned. Finally, solder the remaining pins and refresh the initially tacked pin. Any solder bridges between the pins can be removed with solder wick. Note that pins 5, 6 and 7 are meant to be connected together. Install the resistors next and then TVS1. The resistors are colour coded with the resistance value and the table overleaf shows the colour bands for each resistor used. A digital multimeter should also be used to check the values as the colour bands can be hard to identify. Make sure that TVS1 is installed with the correct polarity, with the striped end oriented as shown in the overlay diagram. The P-channel Mosfet Q1 is fitted with a heatsink. Bend its leads over by 90° and insert them into the PCB holes, then secure both the Mosfet tab and heatsink using an M3 x 10mm screw and nut before soldering the leads. Switch S1 is mounted next. We have arranged the 100 PCB so that S1 can be oriented either way. Follow with the capacitors. The electrolytic types must be installed with the polarity shown, ie, longer lead through the holes marked +. These will need to be laid over sideways so they sit no taller than the switch body. Transistor Q2 can also be fitted now. 10 The LEDs are mounted with the top of each lens Parts list – eFuse ILIMIT_OL 1 ILIMIT_SS 0.1 10 20 100 RexternalLimit () 1000 April 2017  43 Resistor Colour Codes                      No. 2 1 1 * * * * * * * * * * * * * * * * * * Value 100kΩ 15kΩ 2.2kΩ 430Ω 390Ω 360Ω 330Ω 220Ω 180Ω 150Ω 120Ω 91Ω 82Ω 62Ω 47Ω 43Ω 39Ω 36Ω 30Ω 27Ω 20Ω 4-Band Code (1%) brown black yellow brown brown green orange brown red red red brown yellow orange brown brown orange white brown brown orange blue brown brown orange orange black brown red red brown brown brown grey brown brown brown green brown brown brown red brown brown white brown black brown grey red black brown blue red black brown yellow purple black brown yellow orange black brown orange white black brown orange blue black brown orange black black brown red purple black brown red black brown brown 5-Band Code (1%) brown black black orange brown brown green black red brown red red black brown brown yellow orange brown brown orange white black blackbrown orange blue black black brown orange orange black black brown red red black black brown brown grey black black brown brown green black black brown brown red black black brown white brown black gold brown grey red black gold brown blue red black gold brown yellow purple black gold brown yellow orange black gold brown orange white black gold brown orange blue black gold brown orange black black gold brown red purple black gold brown red black black gold brown * A selection of these resistors is used for R1 and/or R2 – see Table 2 and Table 3 for details. dome 17mm above the PCB surface. Make sure the LEDs are oriented correctly with the anode (longer lead) soldered to the pad marked “A”. The Supply In and Supply Out LEDs are green (LED1 and LED3) and the trip indicator (LED2) is red. The input supply and output (load) wires can be soldered directly to the PCB or secured in a 3-way terminal block, as we show on the component overlay. We used red for the eFuse input, black for the 0V wire and yellow for the eFuse output wire. Note that although the 0V wire carries little current, it’s probably a good idea to use the same type of wire for all three connections. The eFuse PCB is installed upsidedown in the plastic case with the PCB clipped into the side flanges and the LEDs, switch and safeguard fuse protruding through the base. A copy of the front panel artwork can also be used as a drilling diagram. Drill and file to shape the required holes for the LEDs, switch and fuse. You will also need to drill a hole for the cable gland, centred on the end of the box near to the safeguard fuse. To produce a front panel label, you have a variety of choices available, ranging from “quick’n’easy” through to quite professional finishes. 44  Silicon Chip These are discussed on the S ILICON C HIP website at www. siliconchip.com.au/fp ate one by directly connecting a lowcurrent fuse across a vehicle battery. Wear safety goggles when doing this. Finishing it Testing The PCB can now be installed in the Plug the fuse plug into the circuit to box. First, place a nut on the switch be protected and attach the negative shaft and screw it down onto the lead to chassis with a clip or with a switch body. Leave the safeguard fuse screw. Check that the supply in and out of its fuseholder. Pass the wires supply out LEDs (LED1 and LED3 rethrough the gland and place the PCB spectively) light. If only the supply into the box and make sure the LEDs out LED lights, the fuse is most likely and switch enter the holes. connected in reverse. Table 3 shows Pull the wires through as you clip the various LED indications. the PCB into place. Clamp down the Assuming they do both light, the SC cable gland over the wires and refit the eFuse is ready for action. safegard fuse. The eFuse input and output wires can be solwww.siliconchip.com.au dered to either end of a blown fuse so it can Safeguard be plugged into a fuseFuse holder in the circuit be(9-15VDC) ing protected. Blade fuses normally have exposed metal SUPPLY TRIP SUPPLY RESET on the top of the fuse IN OUT (presumably intended + + + + to allow you to probe the fuse while it’s fitted) that can be used This same-size artwork can be copied and printed to solder the wires to. If you don’t have a to make a label for the eFuse. Alternatively, you can blown fuse, you can cre- download a PDF from www.siliconchip.com.au SILICON CHIP eFuse siliconchip.com.au