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DC-DC for car This DC-DC converter will allow you to use a hifi power audio amplifier in your car to provide good quality sound. It provides split supply rails which can be adjusted to suit your amplifier. 22 SILICON CHIP H igh power amplifiers have become very popular for use in automobiles and for good reason. If you want hifi sound in your car, then high power is the only way to go. That's because of the high ambient noise level that's present inside your car - noise which must be masked out by the music. The idea behind this project is to give you an alternative to buying an expensive commercial car power amplifier. It can be used to power virtually any amplifier module with an output of up to 100 watts which means that you can now build your own. In fact, the power amplifiers described in SILICON CHIP in December 1987 should do the job quite nicely. As it stands, the circuit can be used to power twin 50W amplifier modules or a single 100 watt amplifier module, the latter possibly being used to drive a sub-woofer loudspeaker. Of course, you can also use the circuit to power amplifiers with lower power outputs, provided you tailor the supply rails accordingly. That's done simply by adjusting the number of By JOHN CLARKE & GREG SWAIN turns on the secondary of a transformer which you wind during construction. Basic principle The converter circuit is designed to convert the 12V DC supply from your car's battery to give supply rails of up to ±50V. It does this by alternately switching the 12V supply to each half of a centre-tapped transformer primary. The resulting AC waveform is then stepped up by the transformer secondary (because of the turns ratio) and then rectified and filtered to provide the plus and minus supply rails. To obtain high efficiency and reduce the number of bulky components, the converter operates at a switching frequency of about 22kHz. This high frequency allows us to use a ferrite transformer rather than an iron cored type. The circuit also uses high speed power Mosfets to switch the transformer and fast recovery diodes for the rectifiers. Power Mosfets were used because they are very fast and have low switching losses. In addition, the "on resistance" of a power Mosfet has a positive temperature coefficient, which means that they can be paralleled without the need for current sharing resistors. The complete circuit is housed in a diecast metal case to provide the necessary heatsinking and the ruggedness required for automotive use. Typically, it would be mounted in the boot (under the rear parcel shelf) or under one of the seats, along with the power amplifier modules. Specifications Output Voltage .................................................. ±35 to ±50V (adjustable) Input Voltage ............................................................................ 10-13.BV Power Output ................................................................ 100W continuous No Load Current .................. ,............................ ..... 100mA at 13.8V input Efficiency .. .. .. .. .. .. .... .. .. .. .. .. .. .. ... .. ... .. .. .. .. .. .. ... .. ... .. .. .. 80% at 100W output Line Regulation ........... ,. .. .. . .. .. .. ... . .. .. .. .. .. .. .. ... ... .. .. .. .. .. 2% from 11-13.BV Load Regulation ............................................ 2% from no load to full load Output Ripple .......................................................... 30mV p-p at all loads Operating Frequency .... .. ........................................ ...... .. 22kHz (approx.) Temperature Cutout ...................................... ................ 80°C (adjustable) Low Voltage Cutout . ... .. . ..... .. .. . ..... .. .. ... ...... ... ... .... .. .. .. .. ... .... .. .. . ... .. .. .. 10V Current Cutout ..... .......... .... . .. .. ........ ...... .. 15A primary, 1.15A secondary low, the Mosfet will not fully conduct and this can lead to excessive power dissipation and failure of the device. In addition, the converter circuit also features temperature and overload (or short circuit) protection. The temperature cutout is necessary due to the very high temperatures that can occur in a vehicle during the summer months. If the interior temperature reaches 65°C for example, the Mosfet devices do not need to heat up very much before they are likely to be damaged. The temperature cutout switches off the converter at a preset temperature to guard against this possibility. The overload protection circuitry operates at two levels. First, there is a 15A fuse in the supply line which will blow if there is a drastic fault in the converter itself. Second, the positive and negative output rails are fitted with Polyswitches (these are positive temperature coefficient thermistors) which go open circuit when the current through them exceeds about 1.15A. These protect the converter against output short circuits (eg, if a fault occurs in the amplifier) and automatically return to their low resistance state when the fault is cleared. Protection circuitry What's one of the most frustrating things that can go wrong with a car? The answer is a flat battery, particularly if it's been flattened by the hifi system. To guard against this possibility, the converter includes under-voltage protection. In effect, the converter monitors the battery voltage and if it drops below a certain level, the converter switches itself off. This not only protects you from the inconvenience of a flat battery but is also necessary to protect the Mosfets from possible destruction. To explain, a Mosfet is triggered into conduction by applying a voltage to its gate. If this voltage is too A metal diecast case is used to house the circuitry of the DC-DC Converter. This not only provides the necessary heatsinking but also makes the assembly very rugged for automotive use. DECEMBER1990 23 > Q The accompanying specifications panel shows the performance of the converter. Note that it achieves an efficiency of about 80% at 100W output. It also has excellent voltage regulation and low output ripple. > Q i Circuit details I· Q "' "' "' ~!,------- 0; a: w 1- ffi > z 0 u > C It) tl ~ C .... J--+ .,; + I At the heart of the circuit (see Fig.1) is a dedicated switchmode IC from Texas Instruments - the TL494. This device contains all the necessary circuitry to generate complementary square wave pulses at its pin 9 and pin 10 outputs to drive the switching circuitry. It also contains control circuitry to provide output voltage regulation and low voltage dropout. Fig.2 shows the internal workings of the TL494. It is a fixed frequency pulse width modulation (PWM) controller and contains a sawtooth osciliator, an error amplifier and a PWM comparator. It also includes an extra error amplifier, a "dead time control" comparator, a precision 5V reference and output control logic so that the device can be set for push-pull or single ended operation. The PWM comparator generates the variable width output pulses. It does this by comparing the sawtooth oscillator waveform with the outputs of the two error amplifiers. In practice, the error amplifier with the highest output voltage sets the pulse width. The dead time comparator inside the TL494 prevents the push-pull outputs from rising and falling at the same time. In other words, it ensures that there is a brief time delay between one output swinging high and the other output swinging low. This time is called the "dead time" and accounts for about 5% of the total output time. Error amplifiers tl II :::;11 ll In our circuit, one of the error amplifiers is used to provide the low Fig. 1: the circuit is based on the TL494 switchmode IC from Texas Instruments. Depending on the feedback signal applied to its E2 input, this device generates complementary variable width pulses to drive Mosfet switching transistors Q6-Q9. These then drive transformer Tl which steps up the voltage & drives bridge rectifier D1-D4 to produce the supply rails. 24 SILICON CHIP ~ STEERING INPUT Tl495 ONLY I I 7 L________ J Ar-----1 r-------7 I I I I I 1 OUTPUT CONTROL I I I 1 16 FEED BACK J 14 4 1J NONINV INPUT}ERROR INV INPUT AMP 2 REF OUT OUTPUT CON T RO L 12 11 Vee C2 DEAD -TI ME CONTROL L _ _ _ _ _ _ _ _,I 1 -L_ _ _J cr - - ERROR{ NQN INV IN PU T AMP 1 INV INPUT er , c, RT GND 6 E1 DEAD TIME ~~~7 CONTROL - C2 PULSE -STEER ING NONl ~~~~TING _ _ _~ 1 E2 Fig.2: block diagram & pinout details for the TL494 pulse width modulation control IC. The device generates a FLIP-FLOP INyi;~~NG ___--1 r--1 NONll~~~~TING 7: r-------7 ERROR ----t.,,.._ I INVERTING ~I_ _-----, INPUT L _ _l!:_42! rcUR NONINVERTING J A !NPUT -cl_:..;:.c.:...::::-=-j INVERTING INPUT variable width pulse train at the PWM I I I I .-R-EF-ER...E-NC_E.., I REGULATOR 1 - - - - - - - - - - - V RE I I I ~---.---' I I I l _ - l_'c~~~L!_ _J voltage dropout feature. This is done by connecting the 12V rail to pin 2 (inverting input) via a voltage divider consisting of two lOkQ resistors. The other input at pin 1 (non-inverting) is connected to the internal 5V reference (VREF) via a 4.7kQ resistor. When the voltage at pin 2 drops below 5V (ie, when the battery voltage goes below 10V), the output of this error amplifier switches high and reduces the pulse width to zero, thus effectively shutting the circuit down. Note the lMQ resistor between pin 1 and the error amplifier output at pin 3. This provides a small amount of hysteresis so that this particular error amplifier operates as a comparator. The second error amplifier, with inputs at pins 15 (inverting) and 16 (non-inverting), is used to control the output voltage of the converter. In operation, a sample of the output voltage is tapped off by trim pot VRl and fed to the non-inverting input of the error amplifier at pin 16. This voltage is also compared to the internal 5V reference which in this case is applied to the inverting input at pin 15. Thus, if the output voltage rises above its preset value, the output of the error amplifier also rises and this reduces the output pulse width from IC1. Conversely, if the output voltage falls, the error amplifier output also falls and the pulse width increases. The gain of this amplifier is set by the lMQ feedback resistor between pins 3 and 15 for frequencies below This oscilloscope photograph shows the PWM waveforms at the E1 & E2 (pins 9 & 10) outputs of the TL494. The duty cycle here is only slightly less than 50% but, if the error voltage goes up, the pulses become narrower. comparator output by comparing the signal from a sawtooth oscillator with two error amplifier outputs. The following logic circuitry is then used to derive the out-of-phase output signals which drive transistors Qt & Q2. about 33Hz. For higher frequencies, the gain is set to a lower value by the 47kQ feedback resistor in series with the O. lµF capacitor. This is done to prevent the error amplifier from responding to high frequency hash on the supply lines. The 27kQ resistor and .OOlµF capacitor on pins 6 & 5 set the internal oscillator to a frequency of about 44kHz. Because the TL494 is operated in push-pull inode, this means the switching frequency for the output transistors is about 22kHz. Dead time control The dead time control input is at pin 4. When this input is at the VREF voltage, the output transistors are off and as the voltage drops to ground, The top trace in this photograph shows the El (pin 9) output of the TL494 at low duty cycle while the bottom trace shows the corresponding sawtooth oscillator waveform at pin 5. DECEMBER 1990 25 TO BATTERY + TERMINAL TO Sl TO BATTERY - TERMINAL OR CHASSIS \ CORO GRIP GROMMET SOLDER LUG t , - OUTSIDE CASE ~ .....- SOLDER LUG sistors when a preset temperature is exceeded. IC4, an LM334 adjustable current source, functions as the temperature sensor. It produces an output current which is directly proportional to temperature and this current flows through the series 10kQ resistor. The resultant voltage across the resistor (approximately 14.5mV per °K) is then applied to the inverting input (pin 2) of IC3 where it is compared with the reference voltage. When the voltage across the 10kQ resistor reaches +5V (ie, at 85°C), pin 6 of IC3 switches low and turns on Q5 via D7 and the serie~)-kQ resistor. Q5 now effectively conne cts the dead time input (pin 4) to VREF (pin 14) and this shuts down the output transistors inside ICl. VR2 allows the cutout temperature to be set to the required value. D7 is necessary because the output of IC3 can swing much higher than VREF, to almost the +12V rail. Without the diode, Q5's base would be pulled higher than its emitter and this could damage the transistor. Complementary outputs HINKS REQUIRED IF TH1, TH2 NOT USED Fig.3: take care to ensure that all polarised parts are correctly oriented when installing them on the PC board. The two thermistors are optional and can be replaced by wire links if not required. Note that transistors Q6-Q9 must be correctly isolated from the case (see Fig.4). the dead time decreases to a minimum. The dead time input is used to control the duty cycle of the output driver tran,,istors in two ways. First, at initial switch on, the l0µF capacitor across transistor Q5 pulls the dead time input (pin 4) to VREF and thus prevents the output transistors inside ICl from switching on. 26 SILICON CHIP The lOµF capacitor then charges to VREF and as it does so, the duty cycle of the output transistors increases until full control is gained by the error amplifiers. Temperature cutout The second use for the dead time input is to shut down the output tran- Pins 9 and 10 (El & E2) are the complementary transistor outputs for !Cl. These transistors are uncommitted within the IC which means that both the collector and emitter of each transistor are connected to external pins of the IC, so the circuit designer can arrange tham as needed. The collectors at pins 8 and 11 are connected to the +12V supply rail while the emitters are tied to ground via l0kQ resistors. IC2a, IC2b & IC2c (4050) buffer the emitter 2 output at pin 10, while IC2d, IC2e & IC2f buffer the emitter 1 output at pin 9. These non-inverting buffer stages then drive transistors Ql & Q2 on one phase of the output waveform and Q3 & Q4 on the other. Thus, when pin 10 of !Cl goes high, Ql turns on and turns Mosfets Q6 & Q7 on. When pin 10 goes low again, Ql switches off and Q2 turns on and pulls the gates of Q6 & Q7 low again. Q6 & Q7 now turn off again while Q3 switches on Q8 & Q9 to drive the other half of the transformer primary. Ql, Q2, Q3 & Q4 have been included to ensure that the Mosfet transistors are switched on and off as quickly as possible. The idea here is to minimise the time that the Mosfets spend in the linear region where they of turns on the transformer secondary. If the values shown on the circuit are used, the converter will produce supply rails of ±50V. Fast recovery diodes The four Mosfet transistors are bolted to the side of the case using TO-220 insulating kits and their leads soldered to PC stakes on the board. Make sure that the mounting surfaces are free of metal swarf before installing the devices. dissipate high power. In addition, the gates of the Mosfets are driven via ion resistors to ensure that parallel devices switch on simultaneously. D5, D6, ZD2 & ZD3 protect the Mosfets by suppressing any switching spikes genMICA INSULATING BUSH WAS!HER w,}j ~ SCREW r ~ -----CASE ' T0220 DEVICE Fig.4: mounting details for the four Mosfet transistors (Q6-Q9). Smear all mating surfaces with heatsink compound before bolting each assembly together. After each device is mounted, use a multimeter to check that the metal tab of the device & the case are correctly isolated. erated by the transformer. In summary then, the power Mosfets in each phase of the circuit alternately switch the Sl and F2 terminals of the transformer primary to ground, so that the transformer is driven in push-pull mode. For example, when Q6 & Q7 are on, the 12V supply is connected between Fl and Sl. By transformer action, 12V appears across the other half the transformer primary which means that there is a total of 24V across the whole transformer primary (ie, F2 at 24V, Sl at ground). Conversely, when QB & Q9 are on, F2 is connected to ground while Sl goes to 24V. This alternating voltage is stepped up by the transformer secondary and applied to bridge rectifier Dl-D4 which produces positive and negative supply rails with respect to the secondary centre tap. Note that the actual DC voltages produced will depend on the number As mentioned before, Dl-D4 are fast recovery diodes and are necessary to minimise switching losses. Because they operate at high speed, each has been paralleled with a 470pF capacitor to suppress switching hash. At the outputs of the bridge rectifier, the supply rails are filtered using inductors 12, 13 and four lO00µF electrolytic capacitors. From there, the supply rails go to the (optional) Polyswitches THl and TH2 which provide output short circuit protection. The lOkQ resistors across the output rails set the minimum load current, while the parallel .0lµF capacitors provide further filtering of RF components. Voltage regulation To provide the voltage regulation feature, the positive . supply rail is sampled at the junction of 12 and THl and fed to a voltage divider consisting of a 47kQ resistor and VRl. The divided output voltage is then taken from the wiper of VRl and fed to the E2 (pin 16) input of one of the error amplifiers inside ICl. Thus, dependi:µg on this error voltage, ICl adjusts the duty cycle of its PWM output as described previously. Power for the converter is derived CAPACITOR CODES 0 0 0 Value IEC Code EIA Code 0.1µF 470pF 100n 470p 104 471 RESISTOR CODES 0 0 0 0 0 0 0 0 0 No. Value 4-Band Code {5%) 5-Band Code {1%) 2 1MQ 47kQ 27kQ 10kQ 4.7kQ 1kQ 47g 10n brown black green gold yellow violet orange gold red violet orange gold brown black orange gold yellow violet red gold brown black red gold yellow violet black gold brown black black gold brown black black yellow brown yellow violet black red brown red violet black red brown brown black black red brown yellow violet black brown brown brown black black brown brown yellow violet black gold brown brown black black gold brown 3 1 8 2 1 3 4 DECEMBER 1990 27 This close-up view shows how the face of the LM334Z temperature sensor sits against the end of the threaded metal specer. Smear the mating surfaces with heatsink compound before installing the PC board to ensure efficient heat transfer from the case to the sensor. from the car's battery via a 15A fuse and fed to the transformer primary via inductor Ll. This inductor, together with the 0. lµF capacitor at the input, prevents the converter from radiating RF hash from the supply lead. Switch Sl supplies power to the low-current part of the circuit. This supply path is decoupled using 16V zener diode ZDl, a 47Q resistor and a S1 S2 F1 F2 PRIMARY S3 S4 F3 F4 SECONDARY T1 WINDINGS Fig.5: when winding the transformer, be sure to terminate the windings exactly as shown here. Step-by-step winding details for the transformer are given in the text. 47µF capacitor to prevent voltage spikes from elsewhere in the car's electrical system from destroying the !Cs or transistors. Construction Virtually all the parts for the ±50V DC Converter are mounted on a PC board coded SC05111901 and measuring 177 x 100mm. Fig.3 shows the assembly details. Before actually mounting any of the components though, take a few minutes to thoroughly examine the copper side of the PC board. It's far easier to locate and repair any defects before any of the parts are installed. This done, check that the board will fit inside the recommended diecast case and file the edges if necessary. Now you can begin the board assembly. The first step is to install PC pins at all external wiring points and at the Mosfet (Q6-Q9) pin locations. Once these are in position, install the 21 wire links on the board. You don't have to follow any particular sequence when installing the Winding Details For Transformer T1 Output Voltage No. of Secondary Turns Wire Gauge ±50V ±45V ±40V ±35V 47.5 turns 42.5 turns 38.5 turns 33.5 turns 0.5mm 0.6mm 0.6mm 0.6mm bifilar bifilar bifilar bifilar I 28 SILICON CHIP ECW ECW ECW ECW remaining parts, although it's best to install the smaller components first. Check the orientation of the !Cs, diodes and transistors carefully when installing them on the board, since polarity is important here. Similarly, take care to ensure correct polarity of the electrolytic capacitors. Note particularly that Dl & D3 are oriented differently to DZ & D4, so don't be caught here (see Fig.1 for the pinout details). The two thermistors can be regarded as optional and should be replaced with wire links if not used. We strongly recommend them but some readers may prefer to leave them out. It's a good idea to check all resistor values with a digital multimeter before installing them on the board. You can also refer to the accompanying tables for the resistor and capacitor codes, if you're not familiar with these. Don't mount the four Mosfet transistors at this stage - that step comes later. The LM334 temperature sensor should be installed at full lead length. Winding the transformer This is a job that most people hate but it's really quite straightforward provided you follow the step-by-step procedure set out below. First, you will have to decide what voltage you need at the output of your converter, then check the accompanying table for the winding details. This gives winding information fof voltages ranging from ±35V up to ±50V in 5V steps (note: only the secondary winding changes). The transformer is supplied as a bobbin with two E cores, one for the top and another for the bottom. These cores are held together with a Ushaped clamp which is installed after the transformer is wound. Take a look now at Fig.5; this shows how the primary and secondary windings are terminated on the transformer bobbin. Note that the 4-pin side of the bobbin terminates the primary leads while the 5-pin side is for the secondary. To wind the primary, you will need 1-metre of 1.25mm enamelled copper wire (ECW). First, strip off the insulation from one end and solder it to the S1 pin. Now, starting from the bottom, wind on 8.5 turns, with the windings laid side by side as you progress up the bobbin. Once you have wound on the 8.5 turns, run the lead directly down the side of the bobbin (ie, at right angles to the winding), trim to size and terminate the end on the Fl pin. Wrap a layer on insulating tape tightly around the winding to secure the turns firmly in place. The other half of the primary winding starts at S2 and is wound directly over the top of the first winding and in the same direction as the first. Wind on 8.5 turns as before and terminate at the F2 pin. Another layer of insulating tape should then be used to secure this winding. That completes the primary; now for the secondary. First, check the table for the number of turns required and the gauge of wire to be used. You will need a 7-metre length of 0.5mm or 0.6mm enamelled copper wire. Fold the 7-metre length of wire in half and clamp the folded end in the chuck of a hand drill. The other end of the wire should now be clamped in a vyce, the wires pulled taut, and the drill handle turned to twist the wires together. Continue turning the drill handle until there is about one twist every 10mm. Next, cut the wire at the fold, strip the ends of enamel and tin them with solder. Connect these to the S3 and S4 terminals (ie, the two starts). Wind the appropriate number of turns evenly onto the bobbin in the same direction as the primary winding (note: there should be several layers which fill the entire length of the bobbin), then use your multimeter to determine which winding end is F3 and which is F4 (ie, check for on between S3 & F3 and on between S4 & F4). The secondary winding can now be completed by connecting these two leads to F3 & F4 and winding on another layer of insulation tape. This done, fit the top and bottom cores to the bobbin and clamp the transformer assembly to the PC board as shown in Fig.3. Tighten the clamp nuts firmly but don't overtighten them, otherwise you'll crack the ferrite cores. Finally, solder the various transformer pins to the PC pattern. Inductors The three inductors, Ll-L3, are all wound on Neosid iron powder toroids. Inductor Ll is wound using 38 turns of 1.25mm enamelled cop- PARTS LIST 1 PC board, code SC05111901, 177 x 100mm 1 Dynamark label, 170mm x 100mm 1 diecast case, 190 x 120 x 63mm 1 Neosid 17-745-10 iron powder toroid (L 1) 2 Neosid 17-742-1 0 iron powder toroids (L2,L3) 1 Siemens EC-41 N27 ferrite transformer core, bobbin and clamp 4 T0-220 mica washers and insulating mounting bushes 1 panel mount 3AG fuse holder 1 15A 3AG fuse 2 cord grip grommets 1 2.5-metre length 1.25mm enamelled copper wire 1 1-metre length 1.25mm enamelled copper wire 1 2.5-metre length 0.8mm enamelled copper wire 1 ?-metre length 0.6mm enamelled copper wire (see table) 1 ?-metre length 0.5mm enamelled copper wire (see table) 1 500mm length 0.5mm tinned copper wire 2 solder lugs 19 PC stakes 4 6mm standoffs 1 tapped 6mm standoff 2 RN3415 Polyswitches (optional) 1 10kQ miniature horizontal trimpot 1 500Q miniature vertical trimpot Semiconductors 1 TL494 switchmode controller (IC1) per wire on the larger 17-745-10 core. Begin with a 2.5-metre length of wire and feed half of this length through the centre of the core and wind on about half the number of turns. The remaining turns can then be wound on using the other end of the wire. L2 and L3 are wound in identical fashion using 28 turns of 0.8mm wire. You will need about 1.2 metres of wire for each of these inductors. Once the inductors have all been wound, they can be mounted on the PC board at the locations shown. Note that each inductor is strapped firmly to the PC board using a tinned copper wire loop that passes through the 1 4050 hex buffer (IC2) 1 LF351, TL071 op amp (IC3) 1 LM334Z adjustable current source (IC4) 2 BC338 NPN transistors (01 ,Q3) 3 BC328 PNP transistors (Q2,Q4,Q5) 4 MTP3055, BUZ71 Mosfets (Q6-Q9) 4 MUR1550, BYW29 fast recovery diodes (D1 -D4) 2 1N4002 1A diodes (D5,D6) 1 1N4148 signal diode (D7) 1 16V 1W zener diode (2D1) 2 30V 1W zener diodes (2D2,2D3) Capacitors 1 2200µF 25VW PC electrolytic 4 1000µF 63VW PC electrolytic 1 47µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.1µF disc ceramic (near S1) 2 0.1 µF monolithic ceramic 3 0.1 µF metallised polyester 2 .01µF ceramic 1 .001 µF metallised polyester 4 470pF ceramic Resistors (0.25W, 5%) 21Mn 24.?kn 3 47kn 1 1kQ 1 27kn 3 47Q 2 10kn 0.5W 410n 610kn Miscellaneous Screws, nuts, heatsink compound, heavy-duty automotive wire for 12V input, 3-way heavy-duty wire for output voltage leads centre of the core. The ends of these loops are soldered to adjacent pads on the PC board (not shown in Fig.3). Make sure that you don't confuse these holes with the holes for the inductor leads. By the way, if you intend using the unit in your car, it would be a good idea to further secure the inductors using a generous amount of silicone sealant. Run it around each inductor to "glue it" to the PC board. This will prevent the inductors from vibrating and eventually breaking their leads. Metalwork With the PC board assembly comDECEMBER 1990 29 1-9 .... 10+ ·//f- 10+ 31/2"DD $19.95 $18.95 31/2"HD $39.95 $37.95 31/2"HD $45.95 $42.95 $8.95 51/4"DD $14.95 $12.95 51/4"HD $19.95 $17.95 51/2"HD $23.95 $22.95 $9.95 51/4"DD r-. 1-9 ..... 31/2"DD $19.95 $18.95 "'··· VERBATIM DYSAN 1-9•- 1-9 .... 10+ 1-9 loan 10+ 10+ ~ '~ 31/2"0D $22.95 $21.95 31/2"0D $29.95 $27.95 31/2"0D $28.50$27.95 31/2"HD $3~.95 $37.95 3 1/2"HD $49.95 $47.95 31/2"HD $53.50$52.50 3 1/2".HD $69.95 $67.95 51/4"0D $19.95 $18.95 51/4"0D $19.95 $17.95 5 1/4"0D $22.95$21.95 5 1/4"0D $19.95 $18.95 5 1/4"HD $31.95 $29.95 51/4"HD $29.95 $27.95 5 1/4"HD ., '-'._ i-.t '-'._ i-.t $24.95 $23.9 ( ?l/1 .~ 5 1/4"HD $39.95 $37.95 ALL PRICES PER PKT/BOX OF TEN ' - '. _ ; - -. , ' - '. _ ; -. , ' - ' " :( -. t1 I .·•. "8 PAGES PER MINUTE!" Oi<ILASER 800 9PECIACATIONS: th'" waye to daCftbe the OllllaMr 800. ttgh quality printing, eturdy conatrvction and compact •.ign In one prfntar. sa.Ulb&lty la a m1Jor faeture OldlaMr aoo. 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A range of p..,~ ....... ,. 1vall ■ ble fo, •II - pofUu paper MEN ph• Printer Type: LED la. . prinW Printing ~ : 8 pega/mlnula Wsm up time: 45 N .c onda Anoludon: Mai 3CIJ Jt 300 dota/lndl Aulom..c paper fNd Standard: 200 .t.Nta Option: a tuther 200 ahNta Paper formats (automallc fNd): M, AS, A6, 85 (weight I0-90g/m2) Manual PIS:- fNd : Envolopea, S.lf-«lhHtve labtla ovemead traMPfianclH TyptfaCH 3& font (wtth HP ....,ttlon) l-14.4 pointa IC font c:arda Downloadable .oft fonta lnttrfac:ei: Centronlc. paraUel or Mriat RS-232 CN.24 2 a: Centronl~ par.... (option) 2 a: ....... RS-232 C/V.24 tlgh rnolutlon (300 ll 300 dpl) Single and Dual ba'I ;:9',:;:•~:;,':rm,.~":nt,,.,.. llcMMar memory to 4.5 MBylN EXPANDED DYNAMI RAM RANGE 24 PIN MICROLINE 391 . . t The OKI Mlcrollne 391 I• a result SPECIACATIONS: of a combination of the very PRINTER MECHANSM: latest technology Prinlltr method: Dot matrh: and OKI'• many years of Mnt head: 24 pin• (dl1n.ter 0.2) experience. The OKI 391 provldas exceptional paper handling and professional quality print whllS1 being axtreamly quiet. Th• foll-covarad touch kays on th• control panel aro cl■arly lit to avoid confusion. The OKI 391 can print up to 270 characters a second and 90 characters a HCOnd at latter quality. Tha OKI 391 Head operatl~l:~llon c:h■ractDra PRINTER SPEED: Data: 270 cpa (12cpl) proce..lng: 225 cps (10cpi) Letter: 90 cpa (12cpi) quality: 75 cpa (10cpl) ;::~clllr• ~~line: 12 cpl 163 ,s c-pl 204 11.1 cp 233 20 cpl 272 PRINTER CHARACTERtSTICS: =~= also ha■ 1norm_ou■ paper Courier, tlgh Speed handling ver■ ltdlty. 1neer1 Cuda: Latter Gothic, Thi bidirectional push tractor I ■ PrHtlge Ell11t ■tandard In the OKI 391, a ■ ls Software Input: upto 251 automatic single sheet fled. Thi. characte,. u required paper handllng faaturH are Fonta: 1a national fonta. numerous making this printer :".~:!~h• ::.::.•~.~~eon, capable on the Butter: 4164-10 4464-10 4464-08 41256-10 41256- 08 44256-10 44256- 08 lM- 10 lM- 08 (64K X 1) (4 X 64K) (4 X 64K) (256K X 1) (256K X 1) (256K X 4) (256K X 4) (lM X 1) (lM X 1) $4.95 $5.50 $5.95 $4.50 $4.95 $4.50 $4.95 $5.50 $3.95 $4.50 $10.9S $9.9S $11.9S $10.9 4t? K BylN. rl rl rl rl rl rl rl rl rl ah ~ ~ . MEG . ' . _ AT. ., . _ ROD IRVINGS SPECIAL VGA 40Mb PACKAGE! . . . .~ l , T.♦ ♦.r ,.. ~w:.a I•· ..... . • 16 MHZ LANDMARK • MINI CASE & P.S • 1.2M FDD • 1M RAM • 101 KEYBOARD • IDE/FDC CARD • 12M MB , EGA CARD • 40M HO/ 28MS 16 MHZ LANDMARK MINI CASE & P.S 1M RAM • G7 CARD 101 KEYBOARD IDE/ FDC CARD 40M HD/28MS 12 MB • 1.2M FFD monitor extra • 16 MHZ LANDMARK • MINI CASE &P.S • 1 M RAM • 40M HD / 28MS •12M MB • 101 KEYBOARD • IDE/ FDC CARD • VGA 256K CARD • 1.2 FDD $1,179'monitor extra $1,199 ~2}!~E G• I: · E~M ! $875 ! !G HD • 101 KEYBOARD , FDC / HO CARD •360K FFD , 640K RAM • G 7 CARD $ monitor extra ~ A~ E~ P~ • 101 KEYBOARD • FOCI HO CARD EGA CARD monitor extra ., -• • 1 ,159 ., • - $1,179 # 4lt I P:o :~~a: -# ~ 12! JB •1 M RAM • 1.2M FFD • 20 M HO *****REMEMBER THAT WE HA VE BEEN IN THE ELECTRONICS BUSINESS SINCE19'77., WE HA VE GROWN UP WITH PERSONAL COMPUTERS " " • " " WE ARE ALSO lOO'll> AUSTRALIAN OWNED AND MANAGED • WE THOROUGHLY SERVICE OUR OWN PRODUCTS AND DON'T LEA VE TIIE PROBLEMS FOR ANOTHER COMPANY. • ALL SYSTEMS ARE ASSEMBLED AND TESTED IN AUSTRALIA. • 101 KEYBOARD • 1 M RAM , FOCI HO CARD • 1.2M FFD , VGA 256 CARD , 20 M HO - "AND NOW THE FREEBIES •• • FREE ON/SITE WARRANTY FOR 12 MONTHS (within a 50km radiua of o..- MIibourne eervlce crnter) monitor extra FREE TELEPHONE HELP AND INFORMATION LINE 9am• 5pm. From our ""Technical Service Manager" Valid for 12 months after date of purchaN. FREE S'll> V.LP CUSTOMER DISCOUNT VOUCHER (valid for 12 month• after date of purchaee of au ayatema valued over $2,000 ) OKILASER PRINTER ONLV... $1695 < inc. Iax1 Introducing the new generation in page prtnters, the OKILASER 400. The affordable LED page printer designed ~ f r the small business. Reliable and compact, the OKILASER 400 fits neatlt into the smallest of 1?ffices. Highly rellabte due to the latest LED imaging tachnology, the OKILASER 400 offers excellent print quality, superior paper handling, and• variety of fonts which revival some ot the more expensive laser printer on the martet. MICROLI~ ~ lncl. sales tax & 12 months warranty v~ ~ Le,_, Quollty: 60 CPS 30 x l8<at> l2 cpl UtHlty: 180 CPS 9 x 17<at> 12 cpl Print r.atures· 1 1 2 :::::f.:"cC:~ ,~: 1 ~~ of4000 holM"a and a printhead life of 12000 houR. 3 L Q Relident W:;, SPECIFICATIONS: Speed and Prln1 Chlracterl1dco. 24-pin (20 mm diamelllr) lmopct Dot Matrl1 Gr1phlco Reaotudon: 80 x 72 dpl minimum 180 x 360 dpi maximum Feed rate : 2.2 lpe Character Seta: Standard ASCII Epeon Charater Set IBM Set I and II Foreign Language Nia Zero/Staehed Zero \llrtlc1I Une Spacing: Flud Vw1lble S lpl n/80"" 8 lpl n/180"" Bkllrec11onal, llhort Uno -1"9: Technology, Print Method: 1// t-:J . • 40 MB Hard Disk Drive. • 101 Key Keyboard • MS DOS 4.01 Enhanced ao.m. Width Condnuoue Underlining Super/Suboclpt Outllne/Shldow Retlabllty: . MTBF :4000 houra (25% duty cycle 35% page Oo!Me height denllty) MTTR: 15 mlnutee Prlntheld Ille: 12000 houra (25% duty cycle 35% pege denllty) Prlnthelld Life : 200,000,000 characten 1vg In 10 cpl draft mode<at> normal 25% duty 35% pege denolty (uaer repl1clble) Net weight: 7,7 kg (171be) Pow• conaumtlon: Operating Idle &&VA 22VA Sia: 15.T' (w) X 13.8"" (d) X 4,7 (h) [39,aan (w) x 34.5 cm (d) x 12,0 cm(h) ~ ------------- • 80386-25 CPU • 1MB RAM • 1.2 MB Floppy Disk Drive . . A~~Jr~i~S . -.✓ -- PRINTER only / --/., ' /""'---.... ,. . . ' .-:~ $269 Finally, a Dot Matrix printer for under $300. But don't let the price fool you. The Mlcrollne 172 offers you the perfect combination of performance and advanced engineering at a price which Is extremely economical. The Mlcrollne 172 has every1hlng you'd expect In a quality printer, advanced paper handling, speed and print versltlllty, The Mlcrollne 172 ls Ideal tor the small business or home office being compact, reliable and having the speed to meet your needs, And you won't find It cheaper than at Rod Irving Electronlcs. 088 335757 TOLL FREE MAIL ORDER HOTLINE FOR CREDIT CARD ORDERS! ~ ' ' ••'h~ ..___________ fonts Emphaelzed hallca , :.:•.; • 12 Month Warranty •VGA Colour monitor (1024 x 768) The Mlcrollne 380 lo the perfe<:t letter quollty printer. Ideal for lhe lffllll bualneH or home, lt'a alza allow• tt to fit on the amalleat deak In the :!: ~:: . -~~t;t~-.. . . . RITRON EXECUTIVE 386-25 24 PIN Combine 1Na with the high quailty of prtnl and you've got I prlnllr lhat will wortr; with you for many year■ to come. • ~ ,:..., * * * * * *** * * * * * ** ~ SPECIFICATIONSOL400 : Printing speed: 4 pages p.m Resolution: 300 x 300 DPI Emulation: HP laserjet series II Data Buffer : 512K byte (standard) 1 M/8 expansion {option) 2 M/8 expansion (option) Max. 2.SM/B Interface: Centronics Parallel or RS232 Serial Resident fonts: 25 various Standard paper input: 200 sheets Standard paper output: 200 sheets face up 100 sheets $2,795 380 'Ills ' I $ 7 '"lt I r'95 #f • VGA COLOUR MONITOR 'IDE INTERFACE AND FDD CONTROLLER CARD (The iww atandarcl) • 40M 28MS HARD DISK DRIVE (Weatem Dlaltal) "OPI'IONAL EXTllA'S FOR TIUS PACKAGE I" • 1.4M FOO 3 1/2"" JAPANESE DRIVE ADD $195 • 9 PIN DOT MATRIX PRINTER ADD $269 , 24 PIN DOT IIATIIIX PRINTER (OKI) ADD $525 • OKI LASER PRINTER ADD $1695 . .~~!~.~-~:... If~.!~~.~~~~~ • 101 KEYBOARD • 20M HD • FDC/ HD CARD • 12M MB • G 7 CARD • 1.2 M FFD • 80286-12 MOTHERBOARD ( Elllremely rellable J ■paneee Sunlec Technology) ... •-. • 16 MHZ LANDMARK SPEED TEST ~ • EXPANDABLE TO 8 MEG OF RAM ON BOARD~ '» ~ • EMS LIM 4.00 SUPPORTED ~ (Eaeentlal for Deaktop PubHahlng) ~ Q1t., • FREE DOS4.D1 '2MEGRAM ~ • SERIAL, PARELL AND GAMES PORTS. ~ I •1.2M FDD 5 1/4"" JAPANESE DRIVE ~ , ~URADUTY 101 KEY KEYBOARD . ._ - _ _ __,, 1/ ,, Fig.6: you can use this full-size artwork to make your own PC board or buy a ready-etched board from the usual retail outlets. Compare your board to this artwork carefully to make sure there are no damaged or shorted tracks. pleted, work can now begin on the case. First, slide the PC board into the case and mark out the positions for the four corner mounting holes. Drill these and temporarily mount the PC board on the 6mm standoffs. This will now allow you to mark out the mounting holes for the Mosfets. These holes should be located 25mm down from the top edge of the case and directly in line with the PC stakes for each device. After drilling, carefully deburr each hole using an oversize drill. If you leave any metal swarf here, it can punch through a mica insulating washer (see Fig.4) and short the case of the device to chassis. You will also have to mark out and drill holes in the case for the fuse holder, the cord entry grommets and the solder lug mounting screw (see Fig.3). A further mounting hole is also necessary to secure the tapped spacer. This is located directly opposite the LM334Z temperature sensor and is positioned so that it sits flush against the face of the sensor (see photo). The four Mosfet transistors (Q6-Q9) must be insulated from the case using mica washers and insulating bushes. Fig.4 shows the mounting details. 32 SILICON CHIP Smear heatsink compound on each of the mating surfaces before screwing each assembly together and note how the leads of the devices are bent to mate with the PC stakes on the board. As each device is mounted, use your multimeter to confirm that its tab is indeed correctly isolated from the case. If you do get a short circuit, be sure to clear the problem before proceeding further. Heatsink compound should also be smeared over the mating surfaces of the tapped spacer and the LM334Z temperature sensor to ensure good thermal transfer. This done, the external wiring can be hooked up and the board permanently installed in the case. Use heavy-duty automotive cable (or 240V AC cable) for all external leads. Testing To test the converter, you will need a 12V DC supply with a current rating of at least 0.5A and a multimeter. Set the multimeter to the 100V DC range and connect it between the positive and negative output rails. Trimpots VRl and VRZ should initially be set to their midpoint positions. Connect up the power supply, switch on and check that you obtain a voltage above ±35V (ie, above 70V). If not, switch off immediate! y and check your work for wiring errors. Assuming an output voltage is obtained, adjust VRl to give the desired value. If you have a variable power supply, check that the output remains rock steady for supply variations over the range 10-13.BV. Below lOV, the converter should be switched off uy the low voltage dropout circuit. To set the temperature cutout, connect a multimeter across the lOkQ resistor at pin 2 of IC3 and adjust VR2 for 4.2V at room temperature; ie, at 25°C. Add or subtract 14.5mV/°C for temperatures above or below this figure. This sets the sensor to give the required 5V across the l0kQ resistor at 80°C - the point of temperature cutout. Installation Finally, make sure that you install the unit in a professional manner. Use automotive crimp connectors to connect all wiring leads to the existing wiring and be sure to connect the positive supply lead via an in-line fuse at the battery end. This simple precaution will prevent the possibility of fire in the (unlikely) event of a short between the postive supply lead and ground.