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Build this miniature 1.5V to 9V DC converter This tiny project allows you to replace those expensive 9V batteries with more cost-efficient 1.5V cells. It uses only three components and is smaller than the 9V battery it replaces. By DARREN YATES Back in November 1990, we published our smallest project ever. It used just three electronic components and allowed a 1.5V cell to replace a more expensive 9V battery. You could use any type of 1.5V cell as well either AA, C, D, N or AAA. Of course, the bigger the cell, the longer it lasted. There was just one drawback - the unit was larger than a 9V battery which meant that it could not be fitted inside the device to be powered. This revised unit overcomes that problem by using a much smaller toroid core and a revised PC board. It now measures just 17 x 43 x 16mm which means that it will fit comfortably inside a 9V battery compartment. The new toroid core is cheaper than the original unit too, which means that the new unit costs a few dollars less than the previous version. Circuit diagram Fig.1 shows what's inside the TL- 496, while Fig.2 shows the circuit details. At the heart of the circuit is ICl which is a TL496CP switching inverter. We gave a detailed explanation of how this IC works in the No- PARTS LIST 1 PC board, code SC11111921, 42x 17mm 1 Neosid 17-732-22 toroid core, 14.8 (OD) x 8 (ID) x 6.35mm (H) 1 1.SV battery holder to suit battery 1 AA, C or D-size battery 2 metres of 0.63mm enamelled copper wire. Semiconductors 1 TL496 DC converter (IC1) Capacitors 1 220µF 16VW PC electrolytic vember 1990 issue, so we'll just briefly cover the circuit operation here. Inside ICl is an oscillator that drives_ a switching transistor at a rate that depends on the load current. The higher the load current, the higher the switching frequency, which can be anywhere from a few Hertz up to 2kHz. This internal transistor alternately switches the current through inductor L1 on and off. When the transistor is on, current flows and energy is stored in the inductor. When the transistor turns off, the voltage across Ll rises and the inductor dumps its stored energy into the 220µF capacitor. An internal feedback and voltage regulator circuit ensure that the output is maintained at 9V. The maximum output current which can be drawn from the circuit is about 40mA. At this current, a typical 9V battery would not last long at all. By contrast, a 1.5V alkaline D-cell will last for about 20 hours, despite the considerably higher input current required. Note that because the circuit steps the voltage up six times (from 1.5V to 9V) and because the circuit is not 100% efficient, the current consumed goes up by a factor of twelve (eg, if the load current is 2mA, the input current is 25mA). Putting it another way, the circuit T INPUT (4) 9V SERIES REGULATOR 2C INPUT (3V) (~) SWITCHING VOLTAGE REGULATOR CONTROL lC INPUT (1.5V) (3) GNO (5) - - - - - (6) SWITCH GND (7) Fig.1: block diagram of the TL496 switching converter IC. It uses a.variable-frequency oscillator to drive a switching transistor. 36 SILICON CHIP g QUALITY NO BRAND DISKETTES =l,;1= 3 1C 2 SW IC1 Tl496 2C 5.25" 5.25" 3.5" 3.5" OUT B GND GND 7 5 +9V 220 + 16VW OUTPUT _ _ _ _ _ _...,._ _ _ _ _oov Fig.3: install the parts on the PC board as shown here. The inductor (Ll) consists of 60 turns (approx.) of 0.63mm ECW on a small toroid core. L1 : &OT, 0.63mm ENCU ON 17ll32/22 NEOSIO POWDERED IRON TOROID 1.SV TO 9V DC CONVERTER Fig.2: in addition to the IC, the final circuit uses an inductor, a single capacitor & a 1.5V battery. The circuit can also be powered from a 3V supply, in which case the connection to pin 3 is deleted. Fig.4: the etching pattern for the PC board measures just 42 x 17mm. DSDD DSHD DSDD DSHD $4.70 $8.95 $8.50 $16.95 II I *************** JAPANESE BRAND -~':--1/ +·- /;";,{ FLOPPY DRIVES <:,.-- SUPER ~ 3.5" 1.44M $99.00 7- SPECI~~ 5.25" 1.2M $125.00 "h~\~"""' EPROMS 2716 .... .. ....... $9.95 2732A ........... $7.50 27C32 ...... .. . $11.50 2764 ·············$6.50 27C64 ........... $7.00 27128 ........... $7.50 27C128 ... .... .. $8.00 27256 ......... .. $8.50 27C256 ......... $9.00 27512 ......... $12.50 27C512 ..... .. $13.50 27C1001 ..... $23.50 - -- RAMS 6116 ... ... ....... $4.50 6264 ......... ... . $9.50 62256 ......... $17.50 628128 ....... $60.00 SERIAL PORT CHIPS 8250 ············ · $7.50 82450 ......... $17.50 16C450 .. ... .. $18. 00 16C550 ... ... . $29.50 *** * ** *** ** *** * is about 50% efficient, since the input current goes up by a factor of twelve, not six. Even so, it is still cheaper to use the converter than a 9V battery. , <~'~!!!~~~ , ?~ ~ TABLE 1 Load Current Input Current no load 50uA Construction 0.1mA 1mA The PC board for this project is coded SC11111921 and measures 42 x 17mm. Fig.3 shows the assembly details. The inductor consists of two layers of 0.63mm diameter enamelled copper wire (ECW) . To wind the inductor, first take a 2-metre length of wire and thread it half-way through the toroid core. The first layer is now wound using one end of the wire, followed by the second layer using the other end. Keep the turns tight and as closely spaced together as possible. There should be about 60 turns total, although the exact figure is not critical. Clean and tin the ends of the leads carefully before soldering the inductor to the board. The external leads to the 1.5V battery can be wired to a suitable 1.5V battery holder. When the assembly is corpplete, install the battery and measure the output voltage from the board. It should be very close to 9V. Exercise extreme caution if you intend soldering a battery snap connector to the output terminals, to mate with an existing snap connector. In this case, you will have to connect the red lead to the negative(-) terminal of the board and the black lead to the positive (+)terminal to ensure correct 0.SmA 6mA 1mA 12mA 2mA 25mA SmA 65mA 10mA 134mA 20mA 250mA 40mA 460mA polarity at the battery snap terminals. Alternatively, you can use output terminals that have been salvaged from a discarded 9V battery. Check the output polarity carefully with your multimeter before connecting the project to any equipment. Depending on your situation, you can use either an AA, C or D-size battery with the circuit. Table 1 shows the expected input currents for loads ranging from 0. lmA to 40mA, A Dsize cell will last longer than AA or C cells, especially for high input currents, while alkaline cells will last longer than carbon zinc types, Finally, you can modify the unit so that it functions as a 3V to 9V converter by cutting the track to pin 3 of the TL496. This will not make the circuit any more efficient but, because the input current is halved, will approximately double battery life: SC DYNAMIC RAMS 4164-10 ........... $3.25 41464-08 ...... $2.75 41256-08 ......... $2.75 414256-08 ....... $7.95 411000-08 ...... $7.95 256KSIM,SIP . $23.50 IM,SIM,SIP .... $79.00 4M SIM.SIP. $335.00 REGULATDRS 7805T .............. $0.50 7812T .............. $0.50 7815T .... .......... $0.50 7905T .............. $0.60 7912T .............. $0.60 7915T .............. $0.60 317T ................ $1.50 337T ......... ....... $2.10 723 .................. $0.80 DIODES IN4148 ............ $0.04 IN914 . ........ $0.05 IN4004 ........... . $0.08 IN4007 ............ $0.10 IN5404 ..... $0.20 IN5408 ............ $0.25 BRIDGES W04 ................ $0.50 BR64 .. ... ... ....... $1.50 BR104 ....... ...... $2.50 BR254 ............. $3.50 BR354 ............. $3.95 LEDS 5mm RED ........ $0.15 5mm Green ..... $0.25 5mm Yellow .... $0.25 ~ )iY TRANSISTDRS BC547/8/9 ........ $0.15 BC557/8/9 ........ $0. 15 8D139 ....... $0.45 8D140 .............. $0.45 · TIP31C ............. $0.80 TIP32C ............. $0.80 MJ15003 ......... $6.50 MJ15004 ......... $6.50 MJ2955 ........... $2.50 2N3055 ............ $1.50 LINEAR & SPECIAL FUNCTION 1488 ................ $0.50 1489 ................ $0.50 8250 ... $7.50 82C450 .......... $17.50 16C450 .......... $18.00 16C550 ·.......... $29.50 XR2206 ............ $8.50 ICL7106 ......... $14.00 324 ............. . $0.75 339 .................. $0.50 358 .................. $0.90 555 ......... ......... $0.45 741 .................. $0.55 FREE PRICE LIST UPON REQUEST IECS ELECTRONICS & COMPUTER SUPPLIERS 289 LATROBE ST MELBOURNE, VICTORIA 3000 PHONE: (03) 602 3499 FAX: (03) 670 6006 MAIL ORDER HOTLINE: (008) 33 5901 ALL MAJOR CREDIT CARDS WELCOME POSTAGE RATES $1 .00-$9.99 ......... $3.00 $10.00-$24.99 ..... $3.50 $25.00-$49.99 .... . $4.50 $50.00-$99.99 .... $5.50 $100.00-$199.00 $6.00 $200.00+ .. ........... 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