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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?

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    \$\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 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 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 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 at 15:56
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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 This has been superceded in USB3.1 by the USB-C method.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/

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  • \$\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 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 at 23:01
  • \$\begingroup\$ Plenty of teardown of cheap power banks online. You can see yourself. \$\endgroup\$
    – Passerby
    Jul 2 at 1:06

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