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My project supplies the NodeMCU with 3.3 V from a battery source via the 3.3 V input pin. I would also like to connect USB for power and programming and to feed a small battery charger from the Vu pin. Is there going to be a problem with the onboard regulator conflicting with my 3.3 V source?

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  • \$\begingroup\$ You have draw and show the setup. Please show the battery, on Baird regulator, USB input, battery input, Vu pin and proper connections. Common methods are to use diodes in series for both or a FET and a diode in front of the battery input.. what type of battery it is. Is it regulated? \$\endgroup\$
    – User323693
    Jan 2, 2020 at 11:56
  • \$\begingroup\$ Not at PC to draw setup, but 3.3v supplied from S7V8F3 step up/down 3.3v regulator fed from a 18650 battery. The Vu output from nodeMCU is going into a micro usb 1A 18650 battery charger board from eBay to keep the battery charged while connected via the usb port. I only want one usb port so I can combine charging and programming through the one port. \$\endgroup\$ Jan 2, 2020 at 12:26
  • \$\begingroup\$ Thanks for the answers so far. On reflection I'm going to switch to using the ESP12 module, and a FTDI Serial adaptor so I can separate the supplies with a battery to run the ESP and the charger to be fed from the FTDI Vcc output. \$\endgroup\$ Jan 3, 2020 at 17:03

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  • Connect a low drop Schottky diode in series with the battery positive pin before connecting it to node MCU power Pin. This will ensure that the on board regulator won't try to charge the battery. Disadvantage is that the final vorlage which will reach the node MCU will be battery voltage minus the diode drop.

  • You can also use a PFET as a reverse polarity protection instead of diode. Advantage is you will get a Vorlage drop in a few 10s of mV instead of a few 100s of mV drop.

  • Advantages of both the above approach: provides inherent Reverse polarity protection

  • Check the leakage current of Schottky diode. It might even kill your project if it is a battery operated device.

  • If you are planning to charge the battery via 5V pin on the MCU e make sure you will not be drawing more current from the USB port,else you can damage the computer Port.

  • Charging a battery from the USB port of computer isn't a good idea. For charging purpose can you may use a 5 V wall adapter (phone chargers?) Still, when you are trying to program and if the battery charging circuit isn't disconnected, it can atleast harm the PC port temporarily.

  • Also note that some PC USB ports won't even give more than 100 mA of current unless the slave device asks for it.

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