I want to use a USB connector for charging battery and also for outputting battery voltage, depending on what is connected. I am also thinking of two micro USB connectors. One for charging. The other for a load, like an simple LED module.

This is what I thought of:

enter image description here

I do not know what happens if I loop the battery voltage back to the input of the charging IC...

Is something like this possible? Are there any alternatives?

  • 1
    \$\begingroup\$ It would not be a great idea to output battery voltage out from the same connector, not even via diode. If you accidentally plug that into something that can't handle it, like a laptop or desktop computer, it can damage the motherboard. Use a custom connector for custom loads. \$\endgroup\$
    – Justme
    Jul 1, 2021 at 13:37
  • \$\begingroup\$ I saw some chinese module which are capable of charging and even apply a load onto it. How can they do it? \$\endgroup\$
    – Cpt. Balu
    Jul 1, 2021 at 13:40
  • \$\begingroup\$ They have one input for battery charger and one output from boost converter? USB is 5V so a battery would not be directly connected to the USB connector for output. \$\endgroup\$
    – Justme
    Jul 1, 2021 at 13:47
  • \$\begingroup\$ Be carefull ... Some can do the two things ! Charging and boost converter ! There is two USB port (one mini, one micro) tied together ... \$\endgroup\$
    – Antonio51
    Jul 1, 2021 at 15:56

1 Answer 1


Unless you intend to support USB-C bidirectional power delivery (and all the complexity it entails), do not use USB this way. Have separate charge and output ports.

This is why USB power banks that aren't USB-C use the following:

  • USB-micro-B for charge in
  • USB-A or micro-A for power out

Prior to USB3.1, USB supported a 'dual role' mode with the OTG specification; such a device would have a 'micro-AB' connector on it. This has been superceded in USB3.1 by the USB-C method.

More here: https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go/

  • \$\begingroup\$ The ones that do do not tend to have isolated 5V rails and can often be used as a pass through. The use of a usb a and usb b mini/micro is more due to not needing special cables. The same cable can be used to charge the bank and the phone etc. \$\endgroup\$
    – Passerby
    Jul 1, 2021 at 21:08
  • \$\begingroup\$ Disagree. The device that has micro-B fpr charge and A for output will have a power-path control that prevents back-powering the USB-B side, but can support charge-and-run too if can request enough current from the host. It's not a straight pass-through. \$\endgroup\$ Jul 1, 2021 at 23:01
  • \$\begingroup\$ Plenty of teardown of cheap power banks online. You can see yourself. \$\endgroup\$
    – Passerby
    Jul 2, 2021 at 1:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.