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I am thinking about modding some sort of system where it would be necessary to connect a MOLEX (Internal PSU connection) to a Micro-USB 5V (VCC) connection.

Molex Pinout

Molex Pinout

Micro-USB Pinout

Micro-USB Pinout

Now, since I'm not fully aware of the steps, is it necessary to set up a NPN BJT transistor connection to run it through? Could I instead just connect the 5V molex connection straight to the 5V Micro-USB connection in-line, or will that fry the Pi?

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  • 5V is 5V. I would not hesitate for an instant. Personally I'd power via the more accessible expansion header pins but be aware that does bypass the polyfuse. – joan Dec 27 '15 at 10:22
  • I am aware that it bypasses the polyfuse, but do I need to run it through the transistor as mentioned above between the PSU and the RPi? – Brandon White Dec 28 '15 at 2:45
  • I came by looking for a pinout for a micro-usb. Be warned: the above image is the FEMALE pinout, but OP's pic shows the MALE connector for molex. I don't care if people call that molex connector "female" as you stick that plug into things. If you were converting a normal PSU molex to micro USB male and followed the above images, you'd having your vcc and ground backwards. – Anonymous Jan 29 '17 at 10:13
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You can connect directly.

You'd use a transistor only if the current used by the Pi was greater than the current supplied by the device that the Molex cable is connected to, or if you were using a different supply voltage. In either case, you would need a different supply as well as the 5v supply.

In other words: if whatever is attached to the Molex end provides at least 1 amp at 5 volts, you should be able to run a Pi. If it provides 2.5 amps at 5 volts, you will be able to run a Pi 2 with all USB ports.

The official power requirements can be found here: https://www.raspberrypi.org/help/faqs/#powerReqs

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