I need a 15 volt power supply. is there any other circuit than using a 7815 and two batteries?
What is the application? details details details! Do you want to step household line voltage (AC) down to 15 volts? Does it need to be portable (working off batteries)? How much current (total wattage) does your application draw? 240 or 120 AC volts should be easily stepped down with a 10:1 transformer, then a bridge rectifier will flip it to DC, then a big capacitor to smooth it out, then your 15V regulator (if you REALLY want smooth power)... If you just want portable DC-DC conversion, I'd recommend a switch-mode power supply. They are far more efficient and can be purchased or designed to run on a variety of input and output values.
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Frollard, I love you. Tell me, in great detail, as if I was very very dumb, how to do EXACTLY what you mentioned in your second paragraph. Because yes, I want to turn 120 AC volts into really smooth 15 volts dc, as high as 28 amps. If you can tell me how to make the amperage adjustable then even better. Keep in mind that I: can disassemble and assemble a v8 with my eyes closed; barely understand what is meant by series and parallel; will be using such a power supply to run a peltier unit.
You have an option or three: Build it yourself power supply would work, again there are many ac to dc power supply listings here on instructables. Variable power supplies get a LOT more complex. If its a peltier you're running they don't need quite as smooth power, and will happily accept Pulse Width Modulation (quickly turning the power on and off in rapid succession to replicate 'lower average power'. What are you peltiering? Sounds fun! 12V peltiers are more common and you will have better luck finding a 12v power supply (such as a modified ATX power supply >> see the related ibles on the right). They do a lot of the conversion, filtering etc at a much more efficient level.
I have not been able to find 12v peltier elements. Well, that is to say, I have found many that are advertised as 12v elements, but they all have a Vmax at or around 15.4. As it turns out, peltiers have a rather steep drop off when they are not supplied a voltage at or near Vmax. Running such a peltier at 12 volts usually results in about half the performance you might expect. I am hoping to peltier a cpu in a mineral oil cooled pc (and thereby eliminate the condensation problem one typically encounters with peltier coolers and computers). I will also be using aluminum casing instead of the typical fish tanks you see people doing this sort of thing in because I actually passed highschool physics and I know that the thermal conductivity of plastic, plexiglass, and glass, are all quite low.
Cool sauce. The container being used will conduct more heat out, but will still need heat-sinking, fins, or active cooling or it will just get hotter and hotter overall.just read this: http://www.dansdata.com/pelt.htmLots of good info. Yes it wil run at 50% less oomph at 12 volts, but its the cheapest possible option to use your existing power supply. Otherwise, as they say, you're best to get a proper power supply. (He links to a few).
Hit Didigkey.com and search for voltage regulators. You'll find that the LM7815 (and similar cloned knock-offs by National Semiconductor competitors) are but one of many choices