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By JOHN CLARKE 12V 100W Inverter With Adjustable Output Did you build the 12/24V 3-stage MPPT solar charge controller published in the February 2011 issue? Then you will probably want this companion 12V 100W inverter as well. It will power laptops and other devices which require a DC voltage between 15V & 35V. S MALL SOLAR SYSTEMS are growing increasingly popular, whether it is for mains power, battery charging on boats, recreational vehicles and remote homesteads. But was well as needing solar panels to charge 12V or 24V batteries, you also need DC-DC converters to obtain supplies than cannot be run direct from batteries. Laptop computers are just one example. We last published an adjustable DCDC converter in the June 2003 issue of SILICON CHIP. This unit was powered by a 12V battery and could deliver an output voltage anywhere between 13.8V to 24V. The maximum output current that it could deliver was 2A at 16V, falling to 1.1A at 24V. Unfortunately, this output current is often not sufficient to run a laptop computer or similar equipment. Many 78  Silicon Chip recent laptops require a supply voltage of about 19V and a current of 4A or more possibly more. So the June 2003 unit is simply not up to the job. By contrast, this new design has a much higher output current capability and is suitable not only for powering most laptops from a 12V supply but for powering higher voltage equipment as well. Fig.1 shows the output current capability of the new converter. The graph follows a nominal 100W power curve and as indicated, the circuit can supply just over 4A at 25V and 5A at 20V. As well as its enhanced current capabilities, the new converter also boasts excellent voltage regulation at better than 99%. This means that the output voltage is maintained to within ±0.35V of its open-circuit voltage. However, some additional voltage drop can be expected in the leads running from the DC-DC Converter to the unit being powered. Another excellent specification is the output ripple which is less than 200mV peak-to-peak at full power. However, once the input current exceeds 10A, the unit’s output voltage begins to droop. High efficiency As with any such circuit, there are some power losses involved in converting from 12V to a higher output voltage. For this DC-DC Converter, the efficiency is well over 80% when supplying full power. This means that the unit only runs warm at full power, with any heat dissipated by the diecast box that houses it. siliconchip.com.au OUTPUT CURRENT (AMPS) D2 i2 L1 7 A + K + 6 5 INPUT i1 (Q1) C1 OUTPUT 4 – – 3 2 0 10 15 20 25 30 Fig.2: how the DC-DC Converter operates. When Q1 closes, current i1 flows and stores energy in inductor L1. When Q1 opens, this energy is dumped via D2 into the capacitor C2 (via current path i2). 35 OUTPUT VOLTAGE (VOLTS) MAXIMUM OUTPUT CURRENT VS. OUTPUT VOLTAGE Fig.1: this graph plots the output current capability of the 100W DC-DC Converter. It can supply just over 4A at 25V and 5A at 20V. This box measures 111 x 94 x 54mm and is fitted with a power switch and power-indicator LED at one end. Two cable glands are fitted at the opposite end and these clamp the figure-8 power input and output leads. A cigarette lighter socket can be used to make the connection to a car’s battery. Alternatively, the unit can be connected via 10A-rated wiring in a solar-powered system. How it works Fig.2 shows the basic operating principle of the DC-DC Converter. It comprises an inductor (L1), a switch (Q1), a diode (D2) and a capacitor (C1). When the switch is closed (ie, Q1 is on), current i1 flows through L1 (and the switch) and so energy is stored in the magnetic flux of the inductor. When switch Q1 subsequently opens, this stored energy is dumped via diode D2 to capacitor C1 (and the load). This is shown as current i2. In our DC-DC Converter circuit, switch Q1 is an N-channel Mosfet. This Mosfet is controlled using an On Semiconductor (previously Motorola) MC34063 DC-DC Converter IC. This control device varies the Mosfet’s duty cycle (ie, its on/off ratio) to maintain the desired output voltage. This type of converter can only be used to step up (boost) the input voltage. If switch Q1 is left open, then current simply flows directly through L1 and D2. The resulting output voltage will be slightly lower than the input voltage due to the voltage across the inductor (due to its resistance) and the forward voltage of the diode. It is only when Q1 is rapidly switched on and off that the output voltage is increased above the input voltage. siliconchip.com.au Main Features Fig.3 shows the internal arrangement of the MC34063. Its components include a 1.25V reference, a comparator, an oscillator, an RS flipflop and output transistors QA and QB. The oscillator’s frequency is set by a capacitor connected to pin 3. This oscillator drives the flipflop which in turn drives the output transistors to control the external Mosfet. The comparator monitors a sample of the output voltage at pin 5. If the output voltage is low, the comparator’s inverting input will be below the +1.25V reference. As a result, the comparator’s output switches high and sets the RS flipflop. This in turn allows the output transistors to be toggled (via the RS flipflop) at the rate set by the oscillator. The transistors are not held on permanently. Instead, the oscillator periodically resets the flipflop, either after a maximum period or if the peak inductor current, as sensed at pin 7, reaches a certain level. On the other hand, if the output voltage is too high, the comparator’s output Ipk SENSE 7 V+ 6 • • • • • Steps up a 12V DC input to between 15V and 35V DC Maximum input current 10A Efficient switchmode design Fuse & reverse polarity protection Power switch and indicator goes low to keep the flipflop from setting. This holds transistors QA & QB off so that the output voltage falls. Circuit details Take a look now at Fig.4 for the circuit details. It’s based on the MC34063 DC-DC Converter IC (IC1) but the internal transistors are not used to directly switch the supply current. Instead, they are used to drive power Mosfet Q1 which has a current rating of 118A at 100°C (the current rating is even higher at lower temperatures). This rating is far more than is required for this circuit. What’s more, the Mosfet’s low 5.3mΩ “on resistance” with a 10V gate voltage ensures that it runs cool, even at 10A. Power for the circuit is applied via DRIVER COLLECTOR 8 FLIPFLOP S Q QA R OSCILLATOR 1 SWITCH COLLECTOR QB COMPARATOR 1.25V REFERENCE 2 SWITCH EMITTER 5 COMP – INPUT 3 TIMING CAPACITOR 4 GND Fig.3: block diagram of the MC34063 DCDC Converter IC. The oscillator drives the flipflop which in turn drives transistors QA & QB. The internal comparator holds the flipflop reset & shuts down the drive to QB & QB if the converter’s output goes too high. INSIDE THE MC34063 May 2011  79 12V INPUT + D1 MBR20100CT F1 10A CON1 L1 100 µH 3x 4700 µF 16V OUTPUT A1 + K K A2 – D2 MBR20100CT R1 0.025 Ω 5W A1 A2 S1b S1a – 3x 1000 µF 35V CONVERTER POWER CON2 LOW ESR LOW ESR 47Ω 7 Ips 6 Vcc 1k POWER A LED1 λ K DrC SwC IC1 MC34063 100nF GND 4 Ct 3 D D3 1N4148 8 SwE A 1 2 Cin5 10Ω K E B Q2 BC327 C 1k Q1 IRF1405N G K A ZD1 18V 1W S 22k 1nF D3 A K ZD1 A SC  2011 750Ω VR1 2k SET OUTPUT VOLTAGE K BC327 LED 100W DC-DC CONVERTER B K A E MBR20100CT A1 C K IRF1405N K G A2 D D S Fig.4: the circuit uses IC1 to drive the gate of Mosfet Q1 via diode D3, while transistor Q2 quickly discharges Q1’s gate capacitance each time pin 2 of IC1 goes low. Voltage regulation is achieved by the feedback network connected to pin 5 of IC1, while current monitoring is achieved by monitoring the voltage across resistor R1. fuse F1 and double diode D1. Fuse F1 protects against excessive current being drawn by the circuit (eg, if there is a short at the output), while D1 provides reverse polarity protection. D1 is necessary although it does slightly reduce the efficiency of the circuit due to its forward voltage drop. However, without this diode a reverse polarity supply connection would cause current to flow in the reverse direction through the integral diode within Q1 and then through inductor L1, resistor R1 and the fuse. As a result, the fuse would blow. This would not result in any damage but having the fuse blow due to a reverse supply connection is inconvenient. D1 solves that problem. Note that D1 is shown as two diodes in parallel. These diodes are in the same package and are connected in parallel to increase the single diode continuous current rating from 10A to 20A. A double diode has been specified because parallelling diodes in separate packages does not normally result in even current sharing between them. That’s because the separate diodes are 80  Silicon Chip not matched for voltage drop and so the diode with the lowest voltage drop would carry most of the current. As a result, it will heat up more than the other diode and this then makes the situation worse. A diode’s voltage drop decreases with increasing temperature and so the hotter diode will further increase its share of the load. With a double diode, the two diodes are manufactured on the same silicon die and so have the same characteristics, including a matched forward voltage drop with current. The diodes also operate at the same temperature because they share the same package. This ensures consistent and almost equal current sharing over a wide temperature range. Following D1, the supply is filtered using three parallel 4700µF low-ESR capacitors. These provide a reservoir of current for the following switchmode circuit which draws short highcurrent pulses. Without the capacitors, the available current would drop markedly due to the inductance of the supply leads going to the 12V battery. Because of this lead inductance, the initial current available via the supply leads when Q1 turns on is low (it builds up over time). If not for the filter capacitors, the full current capability would never be reached due to the 30kHz switching rate of the MC34063 DC-DC Converter IC (IC1). Power for IC1 is applied to pin 6 via switch S1a from the nominal 12V supply. A 100nF capacitor filters this supply rail, while LED1 provides “power on” indication. The 1kΩ series resistor limits the LED’s current to around 10mA. Note that the power switch (S1) switches power to the DC-DC Converter step-up circuitry only. When S1 is off, power is no longer applied to IC1 but there is still a current path from the 12V input to the output via fuse F1, D1, R1, L1 and D2. As a result, the output voltage sits approximately 1.2V below the input voltage (eg, if the battery voltage is 13.8V, the DC-DC Converter’s output will be at 12.6V). If the laptop requires an 18V supply, this will not be sufficient to charge the laptop’s battery and so no current will be drawn from the converter. However, other loads could continue to draw siliconchip.com.au Parts List 1 PCB, code 11105111, 111 x 85mm 1 diecast box, 119 x 94 x 57mm 1 panel label, 79 x 103mm 1 powdered iron toroidal core, 42 x 22 x 17mm (Jaycar LO-1246 or equivalent) (L1) 4 2-way PC-mount screw terminals with 5.08mm pin spacing 2 M205 PC-mount fuse clips 1 M205 10A fast blow fuse (F1) 2 cable glands for 3-6.5mm diameter cable 1 DPDT toggle switch (S1) or 1 x SPST 15A toggle switch (eg, Jaycar SK-0976 – see text) 4 M3 x 15mm tapped Nylon spacers 4 M3 x 6m countersunk screws 4 M4 x 6mm machine screws 3 M3 x 10mm machine screws 3 M3 nuts 3 TO-220 insulating bushes 3 TO-220 silicone insulating washers 1 150mm length of medium-duty hookup wire 1 6.5m length of 1.25mm enamelled copper wire 1 25mm length of 0.7mm tinned copper wire 2 100mm cable ties 1 40mm length of 3mm heatshrink tubing power. If this is not desirable, then an alternative arrangement using a 15A switch to fully disconnect power can be used, as described later. Of course, if power is derived via a car’s cigarette lighter socket, this will be switched off when the ignition is switched off. Current monitoring Resistor R1 is included so that the current into the inductor can be monitored. IC1 does this by monitoring the voltage at pin 7. When pin 7 drops about 300mV below pin 6, IC1 ceases operation and current pulses cease flowing through L1. R1 has a value of 0.025Ω and so the peak current is restricted to 12A. Mosfet Q1 is driven via IC1’s transistor emitter output at pin 2 (SwE). Each time pin 2 goes high (ie, when the internal transistors turn on), it drives the gate of Mosfet Q1 via diode D3 and a 10Ω resistor. D3 is included to ensure that transistor Q2 is off dursiliconchip.com.au 1 2kΩ horizontal trimpot Semiconductors 1 MC34063AP DC-DC Converter (IC1) 1 IRF1405N 169A 55V N-channel Mosfet (Q1) 1 BC327 PNP transistor (Q2) 2 MBR20100CT 10A 100V double diodes (D1,D2) 1 1N4148 switching diode (D3) 1 18V 1W zener diode (ZD1) 1 3mm green LED (LED1) Capacitors 3 4700µF 16V low-ESR electrolytic capacitors 3 1000µF 35V low-ESR electrolytic capacitors 1 100nF MKT polyester 1 1nF MKT polyester Resistors (0.25W 1%) 1 22kΩ 1 47Ω 2 1kΩ 1 10Ω 1 750Ω 1 0.025Ω 5W (Welwyn OAR5R025FI) (from http://au.element14. com/ – Cat. 120-0377) Miscellaneous 10A figure-8 wire, solder, etc ing this time, by keeping its base 0.6V above its emitter. Zener diode ZD1 protects Q1’s gate from voltage spikes above 18V which could otherwise damage the Mosfet. The gate rise-time for 0-10V with a 12V supply is 500ns. When Q1’s gate is high, Q1 turns on and current flows through Q1 and inductor L1 which then stores energy. When the transistors within IC1 switch off, pin 2 is pulled to 0V via a 1kΩ resistor. Transistor Q2 now has its base connected to 0V and so this transistor switches on and quickly pulls Q1’s gate voltage down to near 0V, thus switching the Mosfet off. Q2 is necessary to ensure that Q1’s gate capacitance quickly discharges (it would discharge too slowly through the 1kΩ pull-down resistor). The gate fall time from 10V to 1V is about 500ns and a 1V gate voltage is sufficient to fully switch Q1 off (the gate fall time from 10V to 0V is 1µs). Give your lighting projects a SEOUL AS FEATURED IN ZZLER SILICON CHIP LED DA 11) (P24, FEBRUARY 20 Acriche A4 4W Pure White AC LED Mounted on PCB No Electronics Needed, Just add power AW3231-240V $16.00 +GST P7 Power LED 10W Pure White Emitter Approx. 900lm <at> 2.8A Ideal for torch applications PCB available to suit W724C0-D1 $16.00+GST P4 Star 4W LEDs Power LEDs mounted on 20mm Star PCB. Various Colours available. Pure White W42182 $3.90+GST Nat. White S42182 $3.90+GST Warm White N42182 $3.90+GST P3-II Star 2W LEDs Power LEDs mounted on 20mm Star PCB. Various Colours available. Pure White WS2182 $2.95+GST Warm White NS2182 $2.95+GST P5-II RGB Power LED High power RGB LED mounted On 20mm Star PCB Drive each colour <at> 350mA Ideal for wall wash applications F50360-STAR $14.95+GST SMD RGB LED General purpose RGB LED in PLCC-6 package Drive each colour <at> 20mA SFT722N-S $0.95ea+GST Top View SMD White LED High Brightness pure white LED in small PLCC package Great for strip lighting Typical luminous intensity 1600mcd KWT803-S $0.30ea+GST AUSTRALIAN DISTRIBUTOR Ph. 07 3390 3302 Fx. 07 3390 3329 Email: sales<at>rmsparts.com.au www.rmsparts.com.au May 2011  81 MBR20100CT D1 + INPUT * + + + 4700 µF 16V 4700 µF 16V 4700 µF 16V * F1 Fig.5: follow this layout diagram to install the parts on the PCB. Make sure that all polarised parts are correctly orientated and refer to the text for details on installing Mosfet Q1, diodes D1 & D2 and the LED. – CON1 1000 µF + * S1 IC1 L1 100 µH 35V 47Ω 34063 1000 µF 1nF 1k 100nF 22k 35V A LED1 D2 Q1 MBR20100CT IRF1405N With Q1 off, the energy stored in L1 is transferred to the output via double diode D2. This energy is then stored in three 1000µF low-ESR electrolytic capacitors. These reduce the ripple to less than 200mV peak-to-peak. The resulting output voltage is sampled using a voltage divider consisting of a 22kΩ resistor, a series 750Ω resistor and a 2kΩ trimpot (VR1). This provides a proportion of the output voltage to the comparator input at pin 5 of IC1. In operation, IC1 adjusts its duty cycle to regulate the output voltage so that the voltage at pin 5 is 1.25V. VR1 allows the output voltage to be adjusted between the recommended limits of 15V and 35V. Setting the trimpot to 64.8Ω gives a 35V output, while a 1.25kΩ setting gives a 15V output. A setting between these two values gives an intermediate voltage. Construction The DC-DC Converter circuit is built ZD1 D3 750Ω K 1k * 4148 * CON2 18V Q2 – 10Ω OUTPUT + 35V RETREV N O C CD- CD + 0.025 Ω 5W 1000 µF + BC327 11150111 VR1 2k * USE 1.25MM ENAMELLED COPPER WIRE – SEE TEXT * USE 10A-RATED CABLE FOR INPUT & OUTPUT LEADS on a PCB coded 11105111 and measuring 111 x 85mm. This is mounted inside a diecast box measuring 119 x 94 x 57mm and has cut-outs to clear the pillars at each corner. Fig.5 shows the assembly details for the PCB. The first job is to check that the indicated corner cut-outs have been made and that the board fits inside the case. If not, you will have to cut and file the corner cut-outs yourself. That done, carefully inspect the board for defects, such as breaks in the copper tracks and shorts between tracks and pads. Check also that the hole sizes are correct by test fitting the larger parts (fuse clips, screw terminals, Mosfet Q1, diodes D1 & D2 and the trimpot). The screw terminal holes must all be 1.25mm in diameter, while 1.3mm holes are required for those wire links marked with an asterisk (*). Larger holes again are required for the fuse clips. Once these checks are complete, start the assembly by the installing the wire links. Note that you must use 1.25mm-diameter enamelled copper wire for the three links marked with an asterisk, to ensure sufficient current-carrying capacity. The unmarked link can be run using 0.7mm tinned copper wire. Bend each wire link so that it fits neatly in position and be sure to scrape away the enamel from the ends of the enamelled wire links before soldering them. The resistors are next. Table 1 below shows the resistor colour codes but it’s a good idea to also use a digital Table 2: Capacitor Codes Value µF Value IEC Code EIA Code 100nF 0.1µF 100n 104 1nF 0.001µF    1n 102 Table 1: Resistor Colour Codes o o o o o o No.   1   2   1   1   1 82  Silicon Chip Value 22kΩ 1kΩ 750Ω 47Ω 10Ω 4-Band Code (1%) red red orange brown brown black red brown violet green brown brown yellow violet black brown brown black black brown 5-Band Code (1%) red red black red brown brown black black brown brown violet green black black brown yellow violet black gold brown brown black black gold brown siliconchip.com.au multimeter (DMM) to check each one before soldering it into circuit. The 0.025Ω 5W resistor looks like a thin U-shaped strip of metal. It can go in after the other resistors have been installed, after which you can install diode D3 and zener diode ZD1. Be sure to orientate D3 and ZD1 as shown (D1 & D2 are installed later). IC1 can either be mounted directly on the PCB or via a socket if you prefer. Install it now, again making sure that it’s correctly orientated, then install the trimpot (VR1) and the capacitors. Check that electrolytic capacitors go in with the correct polarity. Follow these with the screw terminal blocks. The 4-way terminal block is made using two 2-way blocks that are dovetailed together before mounting them on the PCB. They must all go in with their wire entry openings facing outwards. The fuse clips can now be fitted. These must be mounted with their end stops towards the outside, otherwise you won’t be able to install the fuse later on. The easiest way to ensure this is to fit the fuse into the clips before installing them on the PCB. Tack solder one leg of each clip, then remove the fuse and complete the soldering (this prevents the end caps from getting too hot and possibly melting the solder that secures the fuse wire to the caps). Mosfet Q1 and diodes D1 & D2 are next on the list. These should all be mounted so that the hole centre in each tab is 21mm above the PCB. In practice, this means mounting each device with 9mm lead lengths. The easy way to do this is to cut a 9mm cardboard spacer, insert it between the leads and push the device down onto it before tack soldering one of the leads. The cardboard spacer can then be removed and the soldering completed. LED1 must be mounted with 25mm lead lengths, so that the top of its lens is 30mm above the PCB. This can also be done using a cardboard spacer (25mm high). Take care with the orientation – the anode lead is the longer of the two. Once the LED is in, it’s bent over at 90° some 18mm above the PCB so that it’s lens later goes into a hole in the side of the box. This view shows the completed PCB assembly. The inductor is secured using two cable ties. The two external cables and the switch leads must all be secured to the terminal blocks before the PCB is slid into the case. M3 x 10mm SCREW SIDE OF CASE INSULATING WASHER INSULATING BUSH M3 NUT D1, D2 OR Q1 PC BOARD Winding L1 Inductor L1 is wound with 34 turns of 1.25mm-diameter enamelled copper wire (ECW). Wind each turn tightly siliconchip.com.au Fig.6: Mosfet Q1 and double diodes D1 & D2 must each be isolated from the metal case using an insulating washer and insulating bush. May 2011  83 Alternative Power Switch Arrangement INPUT + * * + + + – OUTPUT * + + + LED1 18V – 4148 CABLE GLANDS + RETREV N O C CD- CD * * USE 10A-RATED CABLE FOR INPUT, OUTPUT & SWITCH LEADS 11150110 15A SWITCH Fig.7: this diagram shows the alternative power switch arrangement. In some cases, it may be preferable to switch the unit off completely, rather than just switching it to standby mode using switch S1. This can be done by wiring a 15A SPST switch in series with the incoming +12V rail and linking out the poles for switch S1 at the 4-way screw terminal block – see Fig.7. The 15A power switch can be mounted on one side of the case. The incoming supply lead goes to one terminal while the other terminal is connected to the screw terminal block. Be sure to use 10A rated leads for the switch wiring. A suitable 15A SPST switch is available from Jaycar, Cat. SK-0976. around the toroid, keeping each turn alongside the previous turn. The wire ends are terminated on the PCB as shown. Note that one wire end passes around the outside of the core to insert into a hole adjacent to Q1 (see photo). The entire toroid assembly is then secured in place using two cable ties that pass through the centre of the core and through holes in the PCB. Drilling the case With the PCB assembly now completed, it can be installed in the box. The first step is to temporarily place the board inside the base and mark out the four corner mounting holes. Drill these holes to 3mm, then countersink them from outside the case. That done, the four M3 x 15mm Nylon stand-offs can be secured in position using M3 x 5mm countersink Nylon screws. The PCB is then again temporarily placed in position and the mounting holes for Mosfet Q1 and diodes D1 & D2 marked out. Drill these holes to 3mm, then carefully remove any metal swarf using an oversize drill so that the mating areas are nice and smooth. This is necessary to pre84  Silicon Chip vent punch-though of the insulating washers later on. The next step is to drill the two holes for the cable glands at one end of the box (see photo). These cable glands each require a 12.5mm hole and should have their hole centres some 15mm down from the top of the base and about 20mm in from the top edge (so that they later line up with the 2-way screw terminal blocks). A small pilot drill should be used to start these holes, after which they can be enlarged to size using a tapered reamer. Two holes are required at the other end of the box: (1) a 4.5mm hole to accept toggle switch S1; and (2) a 3mm hole for the LED. Position the switch hole about 10mm down from the top and in line with the centre of the 4-way screw terminal block. The hole for the LED is positioned 15mm down from the top. As before, remove any metal swarf from around these holes using an oversize drill. Final assembly Before mounting the PCB, it’s necessary to connect the input and output leads to the 2-way terminal blocks. Similarly, the switch must be wired to the 4-way terminal block. The input and output leads must be rated at 10A (or more). They are installed by first sliding them though the cable glands, then connecting them to their respective screw terminal connectors (watch the polarity). Switch S1 is wired using 60mm lengths of hook-up wire and the solder connections covered in heatshrink tubing (this prevents the wires from breaking). The leads are then connected to the terminal block and a small cable tie used to further secure them. Once the wiring is complete, the PCB can be slid into place and secured using four M3 x 6mm screws. It’s then simply a matter of pushing LED1 through its hole in the case and securing the Mosfet Q1 and diodes D1 & D2 to the side of the case as shown in Fig.6. Note that the device tabs must each be electrically isolated from the case using a silicone washer and insulating bush. Once the devices are in place, use a multimeter set to a high ohms range to confirm that the device tabs are indeed isolated from the case. If a low ohms reading is measured, check that relevant the silicone washer has not been punctured. Front panel label Once the assembly is complete, the front panel label can be downloaded in PDF format from the SILICON CHIP website. This can then be printed out, laminated and attached to the case lid using a smear of silicone sealant. Testing To test the unit, apply power to the input and check that the output voltage can be adjusted over the range from 15V to 35V DC using VR1. Note that if the output is unloaded, it will take a few seconds to drop down to the set voltage if VR1 is adjusted for a lower voltage. Alternatively, if you have a 1kΩ 5W resistor, this can be placed across the output to hasten any changes as VR1 is adjusted. Assuming all is well, adjust VR1 to give the output voltage required for your equipment. Finally, make sure that the output is connected to your equipment with the correct polarity. A suitable plug to make a power connection to your equipment can be obtained from an SC electronics parts supplier. siliconchip.com.au