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I would like to transform 5V 500mA (from USB power) into 12V with a few cheap components.

Is this possible with the help of some generic parts (and not with the help of some expensive transformer, etc.)?

Also, how many milliamps would this provide?

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    \$\begingroup\$ Assuming perfect efficiency, P=V*I = 5V * 500mA = 2.5W total power. If you convert to 12V, you will get ~208mA. \$\endgroup\$ – dext0rb Nov 11 '13 at 23:00
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    \$\begingroup\$ I searched ebay for "5V 12V step up" and found modules from $5 shipped, some with USB and power plugs attached. I would be surprised if it is economic to make your own. \$\endgroup\$ – markrages Nov 12 '13 at 2:22
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    \$\begingroup\$ @markrages with that attitude, its never economic to make your own. China and India have devastated homebrew \$\endgroup\$ – Passerby Nov 12 '13 at 4:32
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    \$\begingroup\$ @Passerby no attitude, just a price check. \$\endgroup\$ – markrages Nov 12 '13 at 6:26
  • \$\begingroup\$ @markrages do you happen to have the links or the manufacturer's name for those? \$\endgroup\$ – Jeanne Pindar Nov 12 '13 at 15:36
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These are called boost convertors. They take a low dc voltage (such as 5V) and convert it to a higher dc voltage such as 12V. They use an inductor to store energy in one half cycle of a clock and in the other half cycle the energy stored in the inductor charges up a capacitor. The capacitor is naturally charged to a higher voltage than the input voltage because of the way the inductor and switching components are placed. Here is another article: -

Snapshot of pdf 1st page

You can actually build this with op-amps/555s/resistors/diodes and a decent MOSFET (n channel) and if you are not that bothered about super high effciency then a NPN can replace the MOSFET.

Personally I'd go to TI or linear technology and buy one because it'll outperform anything you are likely to make if you are a beginner.

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With some generic parts? The MC34063A is a fairly standard part found in most car usb chargers (And I mean most, even The Dollar Tree $1 car chargers). While it is normally used for buck regulation from 12v to 5v, it can also do inverting and in your specific need, boost regulation by moving the circuit around. The car chargers will have an okay sized capacitor, diode, and typically 220 µh inductor needed, though the timing capacitor would most likely need to be changed.

It's a generic chip made by multiple manufacturers, and can see up to 88% efficiency with an internal switch peak of 1.5A, limiting output current to 750mA unless you go to an external switch. Since you are using an unnamed usb source, and could only expect 500mA, the 750mA output limit is not a problem.

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    \$\begingroup\$ I just grabbed an old car charger that wasn't working well (had to keep pushing it in, was about to throw it away) and I opened it up and found one of these chips. There's a great calculator here: dics.voicecontrol.ro/tutorials/mc34063 \$\endgroup\$ – ntgCleaner Jun 25 '14 at 20:35
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Anyway, a transformer works with AC current. For such a small power, a simple DC/DC converter will do the trick. Unless you want to build one for the sake of doing it yourself, there no point in making it from scratch. At the end of the day, this will take you more time, it will be bigger, and the overall cost will probably be larger than a ready to use DC/DC converter, for instance:

RECOM RI-0512S , 2W , 167 mA ouput ($7.60 at mouser)

TracoPower TMH 0512S, 2W , 165 mA ouput ($8.26 at farnell)

Depending on what you plan to power with that, you might consider regulation and electrical isolation.

  1. regulation to make sure the output stays at 12V as long as the load consumption stays within the specs.
  2. isolation if you plan to power a device which is somehow connected to the mains as well. That way you wont fry your computer if your computer and the device are not on the same phase.

Beware, you are not supposed to draw more than 100mA from an USB port unless you have some USB logic able to ask for more. In real life, stealing 500mA from USB will work on most regular computers, but you may have unpleasant surprises on some cheap mini-PC and some laptops.

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