I'm trying to power a small microcontroller board using the USB-C of a smartphone, to do so I took a USB C - USB A that has 4 lines (Vcc, GND and 2 data), but I'm not able to get 5V out of it.

Simply testing the power line gets less then 1V and drops to 0V if a load is applied, I also tried putting data lines in pull-down with no results.

I don't need high power, so I'm fine with a simple solution (I can't implement any software protocol on data lines) to get few Watts.

Edit: I also tried with a USB-C phone charger with similar results.

  • \$\begingroup\$ Important details are missing. Is the adapter with a Type-A plug or receptacle? And the other end of the adapter has Type-C plug to a smartphone? Also not needing high power and then needing few watts is mutually exclusive. If you have a Type-A device, it must not draw more than 0.5W without negotiating. \$\endgroup\$
    – Justme
    Nov 29, 2023 at 12:47
  • \$\begingroup\$ Yes, I'd like to connect the usb-c to the smartphone (and use it as power source), on the other side (eventually cutting the cable and soldering directly the power line) I'll connect the device (to act as sink) \$\endgroup\$
    – Paa
    Nov 29, 2023 at 12:54
  • \$\begingroup\$ Afaik not every Phone can actively drive it's USB-port. Some newer Phones do support USB-PD, though. What model is your Phone? \$\endgroup\$
    – S_G
    Nov 29, 2023 at 12:57
  • \$\begingroup\$ I's a Samsung phone, but I had similar problems using a Samsung phone charger (with usb-c output) \$\endgroup\$
    – Paa
    Nov 29, 2023 at 13:03
  • \$\begingroup\$ You have to ask for power with the USB OTG protocol. \$\endgroup\$
    – Jeroen3
    Nov 29, 2023 at 13:10

1 Answer 1


In order to get 5v out of USB-C — with no data negotiation — you have to pull the cc1 and cc2 leads low, through 5.1k resistors iirc. I just did a PCB like this, and it worked.

  • 2
    \$\begingroup\$ This is correct, but you don't have access to CC lines if you chop an Type-C to Type-A adapter half in the middle. The resistors are already embedded in the Type-C plug, assuming it was a correct type adapter with a Type-A receptacle, and if the adapter had a Type-A plug, it is a wrong type of adapter anyway with wrong resistors. So this does not really answer the asked question. \$\endgroup\$
    – Justme
    Nov 29, 2023 at 14:09

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