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I have a project that requires me to make a portable power pack that can be charged up and then power different devices. The product needs to have two USB charging ports and hold around 7Ah.

The problem I have is that the devices it will charge vary in minimum/max current and voltage and I would like to not damage the devices it is charging. What is the best way to do this as the only way I would know is to state the rails, yet I cant list all the devices it could charge so should I go for a general voltage and current.

Also what are some of the important circuits I should be looking to make sure the device has to make it more safe. Any answers are appreciated

Dean Millard
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  • If you're charging devices via USB ports you just give them 5V and let them take the current they need. – Finbarr Nov 28 '17 at 16:11

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If you are using a USB 2.x connector then you should supply only 5 V.
Configuration of the D+/D- lines can advise of the peripheral charging current required. If you don't use these lines then you will simply provide the current defined by the peripheral.

If you are using a USB 3.x connector then you can negotiate the output voltage based on the connected peripheral device.

This answer provides a starting point for your research. Short answer.... read the USB 3 spec.

Jack Creasey
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