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Adjustable 0-45V 8A power supply, Pt.2 This month, we feature the construction and setting-up procedure for the adjustable 0-45V 8A power supply. Virtually all of the components are mounted on one large PC board, leaving only a small amount of hand wiring to be done. By JOHN CLARKE The new power supply is housed in a large instrument case measuring 355 x 250 x 122mm. Available in black, beige and blue (the colour we chose), the case is made exclusively for Altronics and gives a very good appearance to the unit. For this project, the case requires the addition of alu76 SILICON CHIP minium front and rear panels plus a steel baseplate (also available from Altronics). Most of the circuit components are mounted on a PC board measuring 189 x 167mm (coded SC04201921). The remaining components either mount onto the steel baseplate or on the front and rear panels. You can begin assembly of the power supply by checking the copper pattern on the PC board. It should be free from any shorted, missing or open circuit tracks. Check the copper pattern against the published pattern to be sure that the PC board has no faults. Shorted pads and tracks should be cleared with a sharp knife, while breaks in the copper pattern can be repair,ed by soldering a short length of tinned copper wire across the gap. Once the PC board has been checked, you can start mounting the parts onto it. Fig.4 shows the parts layout details. Install the PC stakes first and then the wire links and resistors. The resistors are all 1 % types with the exception of the ½W, 1W and Fig.4: here's how to install the parts on the PC board. Make sure that all polarised parts are correctly oriented & refer to the text for details on mounting the optical fibre link. The text also gives the winding details for L1 & L2. , ~ sV ~-1~R ~ MINAL + I .........-s3 A• • Ke ~="' 0~ • =~ • • 02 '-' _ 5W types. It's easy to mistake the value of the 1 % types when reading the 5band codes, so we recommend that you check each resistor with your multimeter before installing it on the board. The 5W resistors should be mounted about 2mm above the surface of the PC board to allow air to circulate free~ , Several different diode types are used in the power supply. These are the 1N4004 rectifier diodes (Dl, D3D6}, which are· usually black with a silver stripe; the 1N4148 or 1N914 switching diodes (D7, D8-D11) which are smaller than the 1N4004 diodes and have a transparent body and white or black stripe; and the zener diodes. ZD1 will be marked 1N4744, ZD2 will be marked 1N4733 and ZD3 marked 1N4761. ZD4 is a 3-pin device marked 336Z-2.5. When installing the diodes, make sure that each one has the correct orientation. Wrongly installed diodes qm be hard to spot if you have to track them down later. Note that di- _ _ _ __ ode D2, the MUR1515, is not installed at this stage. Optical fibre link The light link components are inserted next. Install LED 1 (the SFH750V) and insert the short length of optical fibre cable into the collet (with the collet loose) and push it in as far as it will go. This done, insert the other end into the SFH5 51 V receiver (!Cl) and check how much length of cable needs to be cut so that IC1 can be installed with just enough CAPACITOR CODES Value 0.1µF 820pF IEC Code 100n 820p EIA Code 104 821 TRIM POT CODES . Value EIA Code 50kQ 503 soon 501 '-' ~;; EAR~ _ _ _ _ _ _ _ CHASSIS _ _____, cable length between the two units. The ends of the optical fibre can be cut to length using a sharp knife but make sure that each end is square and neat. There is no need to polish the ends to prevent end reflections since the optical fibre length is short and light losses are small. !Cl (the receiver) can now be installed with the optical fibre in position. Once LED 1 and !Cl are both soldered in place, their collets are tightened to secure the optical fibre between them. The remaining ICs can now be installed but again pay careful attention to their orientation and type number. When soldering these in place, check that yo~ don't get any solder bridges between the IC pins. Now install the 12V regulator and the transistors . (see Fig.2 in last month's issue for the pinout details) . Don't install Ql (the power Mosfet) at th)s stage. That step comes later, when the PC board is mounted in the case. The capacitors can now be installed on the board. Make sure that the elecFEBRUARY 1992 77 This close-up view shows how the two inductors are wound & secured to the board. Ll is wound using 10 turns of1.2mm enamelled copper wire on the larger of the two cores, while L2 is wound using six turns of1.2mm enamelled copper wire. Make sure that the turns are evenly spaced on each toroid. trolytic types are inserted the right way around. Wiring the toroids Ll is wound on the larger ironpowdered toroidal core. First, wind on 10 turns of 1.2mm enamelled copper wire, evenly spaced around the core. This done, strip the enamel insulation back on each end and tin the bared copper ends. The toroid is then mounted vertically on the PC board and secured by a loop of tinned copper wire. To do this, solder one end of this wire loop to the PC board, then solder the other end while pulling it tight with a pair of pliers. Finally, solder the toroid windings to their respective PC stakes. L2 is wound with six turns ofl.2mm enamelled copper wire evenly spaced around the core. It is mounted on the board and secured in a similar manner to Ll. Mounting the hardware With the PC board complete, work can now begin on the case. We will assume that most readers who elect to build this power supply will purchase a complete kit of parts with the necessary metalwork ready to assemble. At the time of writing, Altronics has indicated that they will have kits available shortly after publication of this article. The price will be $375 .00. The method of assembly is to first 78 SILICON CHIP mount all the hardware (ie, the two transformers, bridge rectifier and terminal blocks) on the baseplate, which is then installed into the case. The front and rear panel hardware is then mounted and the wiring installed. Fig.6 shows the assembly details. The main toroidal transformer is mounted using a single bolt, one large · clamping plate, rubber washers at top and bottom, and a nut and lockwasher. Its 240VAC primary input wires (check the colour code supplied) are connected to an insulated terminal block, while its secondary wires are con- .........____ M!CA. BiJSH WAS\HEII SC11EW NUT \ -~~~ J PCB .le \ FINNED ilEATSIIK Fig.5: transistor Ql & diode 02 must both be isolated from the rear panel using a mica washer & insulating bush. Smear all mating surfaces with heatsink compound before bolting the assemblies together, then use your DMM to check that each · device is correctly isolated. . nected to the AC terminals on the bridge rectifier (BRIDGE 1). Apply a smear ofheatsink compound between the face of the bridge rectifier and the baseplate to provide good thermal contact. The small power transformer is mounted near the bridge rectifier and its 240VAC primary wires terminated to the same insulated terminal block as before. The two secondary wires are terminated to an adjacent 2-way insulated terminal block. The solder lugs for the various earth connections to the baseplate and front and rear panels should each be secured using a machine screw, nut and star washer to ensure reliable contacts. The PC board is mounted on 6mm spacers and secured using machine screws and nuts. Note that a solder lug is installed under one of the board mounting screws - see Fig.6. This provides an earth path for the output filter network. Rear panel assembly The single sided heatsink (ie, fins on one side only) is bolted to the rear panel using a single screw and nut. Apply a smear ofheatsink compound to the back of the heatsink and rear panel before they are fastened together. You can now mount diode D2 and Mosfet Ql in position. The metal tabs of these two device must both be insulated from the rear panel using a mica washer and insulating bush. Fig.5 shows the mounting details. Apply a smear ofheatsink compound between the mating surfaces of both devices before bolting them to the rear panel. Now switch your multimeter to the OHMS range and check that the metal tabs of both D2 and Ql are indeed isolated from the rear panel. If not, remove them and clear the fault. The rear panel assembly can now be completed by installing the fuseholder and the mains cord. Make sure that the mains cord is securely clamped with a cordgrip grommet. Front panel assembly Assuming that you have purchased the kit from Altronics, the front panel will be supplied with all cutouts and holes drilled and screen printed. However, before installing the meters, you will have to fit the new meter scales included in the kit. ~FUSE (~,~HOLDER REAR ALUMINIUM PANEL ----~===============~~ ' ,'-..._ _ _ _ _ _ _ _ - - - - - - - - - - - - - 12.6V _ ..... ~--------------------- PCB ROWN 2• 8• 10• EARTHT' CHASSIS 10 EARTH 13• 5• 14• 9• •3 •4 •12 e11 •1 •6 1• <at> METAL BASE PLATE ~ S1 POWER FRONT ALUMINIUM PANEL Fig.6: exercise care with the mains wiring & be sure to use heavy duty cable where specified in the text. FEBRUARY1992 79 This close-up view shows how Qt & D2 are bolted to the rear panel & their leads soldered to adjacent pins on the PC board. Note that their metal tabs must be isolated from the metal rear panel as shown in Fig.5. The finned heatsink is bolted to the back of the rear panel, directly behind these devices. To change a meter scale, first remove the clear plastic escutcheon by undoing the screws on either side of the meter. The original scale is then removed by undoing the small screws on either side of the meter movement and by then sliding the scale away from the meter without damaging the pointer. Finally, the new scale is installed and the meter re-assembled RESISTOR COLOUR CODES 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 No. Value 5-Band Code (1%) 1 1 9 3 1 2 2 4 2 1 6 470kQ 270kQ 100kQ 47kQ 27kQ yellow violet black orange brown red violet black orange brown brown black black orange brown yellow violet black red brown red violet black red brown red red black red brown brown grey black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown red red black brown brown brown green black brown brown brown brown black brown brown brown black black brown brown grey red black black brown yellow violet black black brown orange white brown gold (4-band code) red violet brown gold (4-band code) red red black black brown brown black black black brown yellow violet black gold brown 1 1 6 1 3 1 1 1 2 1 SILICON CHIP 22kQ 18kQ 10kQ 6.8kQ 4.7kQ 2.2kQ 1.5kQ 1.1kQ 1kQ 820Q 470Q 390Q 270Q 220Q 100Q 47Q using the reverse procedure. Before mounting the meters, install an earth solder lug adjacent to the voltmeter as shown on Fig.6. This is secured using a screw, nut and star washer. This done , install the meters and secure them using the nuts supplied. The two pot shafts can now be cut to a length suitable for the knobs, after which the pots can be mounted on the front panel. Orient the pots exactly as shown on Fig.6 and install the knobs. Finally, complete the front panel assembly by installing the switches, LEDs (use bezels) and the output terminals. We used green for the earth terminal, black for the negative terminal and red for the positive terminal. Wiring Once all the hardware has been mounted, the power supply can be wired up. Follow the wiring diagram (Fig.6) carefully to avoid mistakes and be sure to use 250VAC insulated cable for all mains wiring (ie, to the fuseholder, earth lugs, 3-way terminal block and switch S1). Before soldering the Active (brown) leads to the fuseholder, slide a length of heatshrink tubing over both wires so that the fuseholder can be completely sheathed. Similarly, when wiring the mains switch, slide the wires • RAM Card SELLOUT NEW PRODUCT 2MB XT Card Complete with 2MB fitted This card does it all $299.00 SAVE $75.00 IDE2 x Hard Disk controller with 2 x Floppy Disk Controller and 2 Serial Ports, 1 Parallel and 1 Games port. Introductory SPECIAL for this month only 2MB AT Card Complete with 2~ fitted $299.00 SAVE $75.00 $49.00 32MB AT Card complete with 4MB fitted $599.00 SAVE $146.00 ·Normalpricewillbe$75.00 We also stock a range of motherboards, external disk drives, hard disk drives, add-on interface cards, as well as a huge range of cables, adaptors, switch boxes and chips. Call today for competitive pricing. DEALER INQUIRIES WELCOME BUILD YOUR OWN FAX/MODEM ONLY $299.00 Time saving The Comma Fax/Modem will also receive faxes in background while you continue to work. When faxing out the Fax/Modem will redial an engaged number so you can be sure your faxes are sent. The software also automatically keeps a complete log of both incoming and outgoing faxes. Also supported are cover pages, broadcast faxes, and scheduling. The software keeps a database type register of regularly used fax numbers for easy retrieval This is a fully featured kit The Comma Fax/Modem is a commercially designed kit you can build. It will turn your PC (or Macintosh) into both a fax machine which can transmit faxes up to 9600 baud, as well as a Modem which supports both 1200 and 2400 baud. You get all the necessary components as well as a professional case, and power supply. You also receive FREE Fax/Modem software. All this for less than $300. The Comma Fax/Modem uses the latest technology in digital signal processing to ensure lasting troublefree operation. Send faxes from home The Comma Fax/Modem is a fully featured fax machine similar to units costing over $1000, which will transmit faxes at up to 9600bp. Your faxes can now be sent directly from your PC without having to print them first. Programs supported such as Ventura Publisher, Wordperfect, Windows, TIFF and Dr Halo to name but a few. You can view incoming faxes on-screen or print them using a standard dot matrix printer. Incoming files can also be exported in either TIFF or PCX format for use in most popular graphic packages. Only print the faxes you want to keep - just think of the savings on expensive fax paper. As well it's also a modem The Comma Fax/Modem is a fully AT command series V compatible modem. Features include V22/V22bis standards (V21/23 is an option) both 1200 and 2400 baud rates are supported as well as auto answer, dialing and disconnect. You will find it compatible with all popular communication services including most bulletin boards. 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Unless insurance is declined it will be charged at P.O. Box 1100 Lane Cove 1% of total purchase. This is for your protection. NSW2066 PRICES CURRENT FOR MONTH OF PUBLICATION OR WHILE STOCKS LAST e SERVICE IS THE DIFFERENCE e SERVICE JS THE DIFFERENCE e I SERVICE IS THE DIFFERENCE The terminals of the fuseholder & the mains switch are sleeved in heatshrink tubing to prevent accidental contact with the mains. Note that the power transformers, terminal blocks & PC board are all mounted on a steel baseplate which is securely earthed. The front & rear panels are also earthed - see Fig.6. through some heatshrink tubing before soldering them to the switch terminals. After soldering, push the heatshrink tubing over the switch body and shrink it into position. When wiring the unit, use heavyduty hookup wire between the PC board and the (-) output terminal, and between the board, switch S3 and the (+) output terminal. Similarly, use heavy duty wiring between the bridge rectifier and the PC board. The remaining wiring can be run using medium-duty hookup wire. Use various colours so that it is easy to check your wiring after it has been completed and the wires are all bundled together. We installed insulating sleeving over the LED leads to prevent shorts to the case. Diode DZ and Mosfet Ql can now be soldered to their respective PC stakes on the PC board. The leads are 82 SILICON CHIP simply bent towards the PC stakes and soldered. Testing & setting up Before switching on the power supply, check your construction and wiring carefully. Make sure that the transformer and rectifier leads run to their correct destinations and check that all capacitors are correctly oriented. In particular, check the 4700µF and lO00µF electrolytic capacitors since they may overheat and leak if incorrectly connected. When you are sure that everything is correct, you can perform the following voltage checks: • set your multimeter to the 20V DC range and connect it across zener diode ZD1. This done, apply power and check that the voltage across ZD1 is 15V ±1.5V. • check that there is 15V between pins 7 & 14 of ICZ and that the voltage across ZDZ is 4. 7V ±0.5V. • check that pin 3 of IC3, pin 3 of IC4 and pin 4 of IC5 are all at +12V with respect to the tab of the 7812 (GND) . • check that there is 2.5V across trimpot VR4. If these checks are all OK, connect your multimeter between the (+) and (-) output terminals and check that the output voltage can be adjusted from 0-45V (make sure that the Load switch is on and that S4 is set so that the voltage can be adjusted). If any of these tests give an incorrect reading, switch off the power immediately and attempt to·find out why before switching the power on again. In particular, check for wiring errors, incorrectly oriented components, and for missing solder joints and shorted and open circuit tracks on the PC board. If these checks don't reveal the fault, refer to the troubleshooting procedure below. Assuming everything is OK so far, you can calibrate the voltmeter by wax, FOR CHIPS... WOXI FOR CHIPS... WOXl FOR CHIPS... WCXJD FOR CHIPS... WOOD FOR CHIPS... WOOD FOR CHIPS... WOOD FOR CHIPS... WOOD Why pay up to $150 for a label? Take a close look at these APPA 90 SERIES Look lamlllar? That's NEW mulUmeters. because they're sold under different Loot at lh• feature,brand names. And that means you • Lll'p8 high fOntrasl d/1p/,y · pay a lot more than you need T,,. 96 and 118 hw• analog ,,,,. 100 could to. graph• too We'lle seen the top of the line • Colour co•d Input llrmlnat, SERIES model selling at around $150 more and tuncllan lwitch tar •asy than our price. So you're paying that much extra Just for the brand label! 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Aac 200uA. 2mA, 20mA, 200mA, 2A, 20A Ohms 2000, 2kn, 20kn, 200kO, 2MO, 20MO Frequency 2kHz, 20kHz, 200kHz Ca~~tance 2nF, 20nF, 200nF, 2µf, MlJJ1 J1Jeg't'Ss Rang_ss nning · • Pro/M 11Drag1 cl/pi bu/11 In tar 11a,y two hlnMd n.asuremsntr • T/111 96 lr wallr resistance tar /nduslr/1/un •• Shod/proof fora drop al 1.5ml Bui/I-In II/I stand - -.. . .Rack . .---~-~ - - - -• §o Cases &........ 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CLASS-2.5 MU-65 ~ l. CLASS -2.5 MU-65 First, a word of warning if you are troubleshooting with an oscilloscope. The various sections of this power supply circuit operate at different potentials so, to obtain meaningful results, make sure that the oscilloscope probe earth is connected to the relevant section of the circuit. If using two probes, avoid using more than one earth point to prevent shorting out different DC potential sections of the circuit. If the output voltage is always above 40V and cannot be controlled with the voltage adjust control, check the voltage at the gate of Ql with respect to its source pin. Ifit is at 15V or close to it, check the voltage on pin 1 ofIC2. If this voltage is different, then suspect IC2. If pin 1 of IC2 is at 15V, check the base of QZ. If this is at about 0.6V, then the transistor is not functioning. If the output voltage is always OV, check the voltage at the gate of Q1 with respect to its source pin. If this is close to OV then check pin 1 of IC2. If this has a different voltage, then suspect IC2. If pin 1 ofIC2 is at OV, check the base ofQZ. If this is at OV, then the transistor is short circuit from collector to emitter. Control circuit checks Fig.7: here are actual-size artworks for the two meter scales. adjusting VR5 until the reading on the voltmeter matches that on your digital multimeter. Note that the voltmeter is not as accurate (typically only ±2.5% of full scale deflection) as a digital multimeter. This means that it will not track your digital multimeter exactly over the full output voltage range. The 13.8V fixed supply can now be calibrated. To do this, set S4 to the 13.8V position and adjust VR6 so that the output voltage is 13.8V. The ammeter is calibrated by setting your multimeter to the 5A range and connecting it in series with a 0.22Q 5W resistor across the output (ie, between the + and - terminals). Adjust the output voltage until the multimeter indicates a current of 4A, then adjust VR2 to get a reading of 4A on the ammeter. If the current over84 SILICON CI-IJP load LED lights during this procedure and you cannot obtain the 4A setting, just wind up the current adjustment knob. Now, with the resistor and multimeter still in circuit, press the current set switch and wind back the current adjust control until the current overload LED just lights. If you now wind the control back further, the current should reduce. That completes the construction and setting up procedure of the power supply. Troubleshooting Apart from the simple voltage checks that were made in the testing and setting up section, there are some further checks that can be made to test various sections of the circuit if you cannot get it working. You may also need to test the control section of the circuit. Note that the common ground supply for this section is at a different potential to the circuit for IC1 and IC2. For this reason, connect the negative lead of your multimeter to the tab of the 12V regulator (GND) when testing the control circuitry. IC3a is the triangular waveform generator and this should produce a waveform which swings between 4V and 8V peak to peak. The DC voltage at pin 14 of IC3a should be at about 6V while an AC measurement should give a reading of about 1V RMS, depending on the frequency response of your multimeter. If the voltages measured here are significantly different from those stated above, suspect the IC3a oscillator stage. Under normal operation, with no load on the power supply, the DC voltage at pin 1 of IC3 (as measured by your multimeter) will be close to ground, since the pulses to LED 1 are relatively short. If this voltage is at 12V, suspect comparator stage IC3b or the error input voltages. Fig.8: use this full-size PC artwork to make your own board & to check the finished board for etching defects. The error input voltage at pin 7 of IC3b should be close to 4V. If it is much higher or much lower than this, then suspect the current, voltage and overcurrent error outputs. These error output voltages are easy to check. First, measure the voltage on pin 7 of IC5 with no load on the supply. It should be about 3.4V. Pin 8 ofIC5 should be above 10V, while pin 13 of IC3 should be above 11 V. Pin 5 of IC5 should be adjustable from 02.5V using VR4 when S4 is switched to the voltage adjust position. These checks should enable you to at least locate the faulty circuit section. After that, it's a matter of checking the relevant circuitry carefully until you locate the fault but remember that most problems with projects are due to incorrect wiring or faulty soldering (solder bridges between IC pins, missed or bad solder joints, etc). It is very unusual for new !Cs to be faulty unless they are incorrectly oriented on the PC board, so don't be in too much of a hurry to replace ICs if you strike problems. The same goes for the other parts - only rarely will new parts be faulty. SC FEBRUARY1992 85