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MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP some not so recent) projects described in the magazine. Order online or phone (02) 9939 3295. FOR SALE TALK TO THE WORLD: get into Ham Radio. Study for the Standard or Advanced Licence with my books. Graeme Scott, VK2KE. Visit www.gscott.com. au PO Box 385, Albury, NSW 2640. LEDs! Nichia, Cree and other brand name LEDs at excellent prices. LED drivers, including ultra-reliable linear driver options. Many other interesting and hard-to-find electronic items! www.ledsales.com.au questronix.com.au – audiovisual experts solve home, corporate security and devotional installation & editing woes. QuestAV CYP, Kramer TVone (02) 4343 1970 or sales<at>questronix. com.au PCBs MADE, ONE OR MANY. Any format, hobbyists welcome. Sesame Electronics Phone (02) 8068 2713. sesame<at>sesame.com.au www.sesame.com.au PCBs & Micros: Silicon Chip Pub­ lications can supply PCBs and programmed micros for all recent (and SOLAR PANELS LOW COST: full range 5W to 250W, eg: 40W/12V Poly $69, 130W/12V $169, 190W/24V $165, 200W/12V $225, 250W/24V $225, 230W Poly $190. AGM Batteries: 7AH $19.50, 9AH $24.50, 20AH $52.50, 55AH $129, 105AH $199, 220AH $399. (03) 94705851 or (03) 9478 0080 chris<at>lowenergydevelopments.com.au www.lowenergydevelopments.com.au 544 High St, Preston 3072, Melbourne. KIT ASSEMBLY & REPAIR KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith 0409 662 794. keith.rippon<at>gmail.com ENGINEERING SERVICES  NSW/ACT - Electronics IT Specialist 25 years experience – aerospace – IPC J-STD-001ES – SMD/SMT – electronics & PCB design – embedded systems – hardware & software development – installations – repairs: www.elcomtel. com.au WANTED NATIONAL DIGITALKER Speech Processor MM54104 OR USPAT4214125 and any Speech Roms. Wanted price? reply pjhennessy34<at>yahoo.com.au CIRCUIT & DESIGN IDEAS: SILICON CHIP pays up to $60 for Circut Notebook items or you could win a $150 gift voucher from Hare & Forbes. See the Circuit Notebook pages for details. SERVICES Un-manned Aviation Systems (UAS). Civil Aviation Service Australia (CASA) Application Specialist. Advantage Partnership Lawyers, Tel: (02) 9221 7555. Email: legal.one<at>advantagepartnership.net Web: www.advantagepartnership.net ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words plus 95 cents for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. Ask SILICON CHIP . . . continued from page 101 speaker enclosures I cannot listen to anymore. Can you come up with a loop system or connection with earphones? (A. H., via email). •  We published a hearing-aid loop receiver in September 2010 and a signal conditioner for a loop drive amplifier in September 2011. The September and October 2011 issues had feature siliconchip.com.au articles on installing a hearing aid loop – see www.siliconchip.com.au for these articles. Altronics (www. altronics.com.au) have the kit for the hearing loop receiver (Cat K5547). However, we cannot see how using headphones will solve the problem; instead, it might make it worse. Tinnitus has a number of causes, including excessive exposure to loud noise (music?) but there can be more serious causes, including Meniere’s disease. In some cases, Tinnitus can gradually fade but you would be wise to consult your doctor if you haven’t done so. Current boost regulator circuit gets too hot This question is not regarding a SILICON CHIP article but refers to a circuit in the Jaycar catalog on page 198 labelled “increasing the output current”. I require a 12V DC power supply at around 2A and I reasoned continued on page 104 August 2013  103 Advertising Index ADM Instrument Engineering....... 39 Altronics.................................. 68-71 Australasian Exhibitions & Events.. 27 Elcomtel..................................... 103 Element14...................................... 3 Embedded Logic Solutions.......... 80 Emona Instruments........................ 5 Futurlec........................................ 10 Hare & Forbes.......................... OBC Ask SILICON CHIP . . . continued from page 103 that this circuit would meet my needs. Accordingly, I built the circuit on a Veroboard layout. I have doubled-checked, even-triple checked, my layout and can find no fault, however even with a modest load of half an amp the 7812 becomes so hot it is impossible to touch it within 15-20 seconds. Surely this is not normal? I have checked the pinout of the TIP2955 and the 7812 and as I mentioned earlier, cannot fault my layout connections. I know this is presumptuous of me but is the circuit and component listing correct to provide the resultant 12V at up to 3A? Could you perhaps suggest an alternative power supply, published by SILICON CHIP, that I could use? (K. J., via email). •  That Jaycar current boost circuit is fairly standard (see www.eleccircuit. com/boosting-regulator-current-foric-78xx-by-mj2955/). The 3.3Ω resistor between the base and emitter of the TIP2955 means that there will be 0.6V across the resistor when the transistor is conducting, allowing the transistor to bypass some of the current that would otherwise pass through the regulator to the output. When the transistor is conducting, the current supplied by the regulator will be 0.6V/3.3Ω or 182mA. Whether the regulator runs hot or not when delivering current depends on the voltage difference between the input and output. If you are feeding in, say, 15V to the input for a 12V output, there is about 3V minus the 0.6V drop across the 3.3Ω resistor. The regulator then dissipates 2.4V x 182mA or 437mW. 104  Silicon Chip DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305  Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au Harbuch Electronics..................... 95 Instant PCBs.............................. 103 Jaycar .............................. IFC,49-56 Keith Rippon .............................. 103 KitStop.......................................... 10 LED Sales.................................. 103 Notes & Errata Low Energy Developments........ 103 CLASSiC DAC, February-May 2013: the element14 part number listed for the AP5002S IC was wrong (page 41, April 2013). It should be 1825351. Mikroelektronika......................... IBC Demonstration Circuits for Human Colour Vision, July 2013: The RGB LED specified for the circuit of Fig.3 is a common cathode type and its Jaycar catalog number is ZD-0012. Do not use the ZD-0010 which is a common anode type. Radio, TV & Hobbies DVD.............. 8 Microchip Technology................... 23 Oatley Electronics........................ 79 Ocean Controls............................ 37 Quest Electronics....................... 103 RF Modules................................ 104 Rockby Electronics....................... 89 Sesame Electronics................... 103 Silicon Chip Binders..................... 95 Silicon Chip Online Shop........ 96-97 The thermal resistance of a TO-3 package is typically 4°C/W junction to case and 35°C/W case to ambient. The thermal resistance of a TO-220 package is typically 4°C/W junction to case and 50°C/W case to ambient. So for a TO-3 package, the regulator will run some 39°C/W x 437mW. That’s 17°C above the ambient temperature. For a TO-220 style package, the regulator will run at 54°C/W x 437mW or 23.6°C above ambient. The 23.6°C above ambient (for a TO-220 device) would mean that the regulator tab will be 48.6°C and that is fairly hot. If you have a higher input voltage, then the regulator will run hotter again. One way to reduce temperature is to reduce power dissipation within the Silicon Chip Subscriptions......... 102 Syndetic Pty Ltd........................... 11 Tekmark Australia...................... 7,59 Tenrod.......................................... 81 Verbatim Australia.......................... 9 Wiltronics...................................... 33 Worldwide Elect. Components... 104 xLogic............................................. 8 regulator. To do that, the input voltage needs to be reduced. Note that you do require at least 2V between the input and output of the regulator in order to maintain output regulation. Otherwise, use a heatsink to keep the regulator SC running cooler. siliconchip.com.au