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I'm trying to build a powered USB hub without buying additional parts. So finding old electronics lying around the house kinda deal.

Anyways I have a 4 USB hub that I took apart to find the PCB was designed to accept an external power source (it has a jack silk screen and a capacitor silkscreen). Good news!

I only was able to find this AC/DC converter however. It outputs 12V and 1700mA. USB devices are built for a Vcc of 5V, usually from 4.8V to 5.3V or so, and amperage varies though I've mostly seen 1A as the top value.

What are my options? I'd love to build a circuit but I'm not very good with Electrical Engineering, and I only have Transistors (PNP and NPN), Capacitors, Resistors and a 595 timing chip to work with.

I should add I have a car inverter that I don't use, one with a USB port on it. Is it viable to take that apart? I'm guessing it doesn't invert from 12v DC to 120V AC then back to 12V DC then drop it down to 5V, it probably just drops the DC to 5V.

Any advice welcome, I'm still very new to circuitry.

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The absolute easiest way to produce 5V out when you have 12V in is with a 3-terminal voltage regulator IC, LM7805 or equivalent. Search for data sheet or articles on that chip for suggested schematics (which may include one or two capacitors), depending on what's already on the USB hub PCB. But then again, you might look a little closer and find that the USB board is intended for a higher voltage AC adapter, and already has a comparable regulator on it.

A 7805 snag is that you may want to draw an amp or more, and the drop from 12V to 5V (which is 7V) would result in the 7805 needing to dissipate 7W of heat. That's fine with a heatsink. Or you can put a physically large resistor in series with the input. A 4 ohm 5W resistor take up 4V of the drop (at one amp) and more than half the heat.

A less wasteful (of electricity) solution would use a 12V-to-5V switching power convertor module. See places like Jameco or Digikey for examples.

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