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Simply Solutions

Portable Voltage Regulator

This entire project was made from recycled materials, so nothing new was purchased to create it. I just looked through the random ICs I had and built a circuit around one of them.  This uses a voltage regulating transistor and a pair of resistors (circuit diagram is sharpied onto the inside of the tin) that control the output voltage down to the thousandth of a volt. The formula for the ratio of the two resistances is also scrawled onto the bottom left of the tin, but I have to admit I didn’t use it because it was easier just to balance out the resistors with a jeweler’s screwdriver and then test the resistances with a multimeter. Lazy, I know, but I’m not a mathematician.
The output maximum is roughly 1 volt lower than the maximum input, so 8 volt max out for 9v in, and the minimum is in the micro-volt range.
Tested and works great at recharging a cellphone, just don’t adjust the voltages “while” you’re charging a device because there isn’t currently a way to tell that the voltage is too high and it will send a voltage surge through the USB that your device may not be protected against. Also be aware that some devices are power hogs and will require more amperage than a 9 volt battery can produce through the LM317T.

Future improvements:  clean up wire traces on back of circuit board, add a switch, and add ability to use multiple power sources (option to use AA or 9v, for example).

The last photograph is of a separate project where I essentially “cheated” by disassembling a USB car adapter/charger and attached the power input to a 9v battery and the output to a USB port. The form factor is much smaller and it was designed by someone who just does this all day, so I trust it. Just be mindful that the amperage will be lower than you might desire, so if you decide to take apart a car adapter, choose one with a high amperage rating.



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