ESP8266 Community Forum

- Thu Apr 11, 2019 8:21 pm #81699 Seems like this should be straightforward, but can't find definitive answer online! I want to step down the voltage from a 3.7 volt LiPo battery to use with a NodeMCU board (3.3 volts). I've been told I can use two resistors in series, but can't find what size resistors to use! Also keep reading about buck converters... why use $6 buck converter when I can use two resistors for pennies?

If this is a dufus newbie question I apologize... please educate me!

[RichardS]

- Thu Apr 11, 2019 9:40 pm #81700 Can not do it that way, only works if the device you connect it to draws near zero current.

Due to the fact the your so close to the 3.3V from the 3.7V you could use a diode and drop 0.4V across it, a diode can pass the current required.

1N4001 or 1N4007 drop 0.4 - 0.5V at 250mA this is almost perfect. Costs $0.05

The capacitor in the image below is not really needed.

https://electronics.stackexchange.com/q ... to-esp8266

RichardS

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- Fri Apr 12, 2019 1:27 am #81705 with a freshly charged LiPo he is close to 4.2V for a relevant amount of time. This is - even with the drop over one diode - over the max. of the esp8266.
Why not suggest a sound solution like a low drop voltage regulator?
Costs maybe 50c but is a safe and sound solution.
Good ones even just pass the voltage( with nominal drop) if input is below 3.3V

- Fri Apr 12, 2019 3:30 am #81716 Agreed LDO is best choice for LIPO powering.

Don't use a 117 type. They still have a fairly high dropout and also draw significant standby current.

I use XC6203E332 which can be got for about 0.2 UKP in volumes of 10. They have a low quiescent current and the low drop out means they will power the ESP over the full range of battery voltage; 4.2V fully charged down to 3.3V when the battery is exhausted. Note the E in the part number. This means there is no current limiter built in which is good for this application.