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Development => Other Hardware Development => Topic started by: PetrOsipov on Feb 27, 2019, 12:38 pm

Title: STM32F103 - on a 1S LiPo (3.7V)
Post by: PetrOsipov on Feb 27, 2019, 12:38 pm
I got a question - I am considering to try using STM32F103 board in my project except of an Arduino Pro Mini. It needs 3.3V (or 5V over supply).

I would be operating it on RC plane, and I want to hook it to the FPV camera battery, which is a 3.7V LiPo from old Smartphone. All extension modules (NEO-6M GPS, HC-12 433Mhz Comm, and GY-91 Gyro/Compass/Pressure) have 3-5 V in specification, so should work. Can the STM32 handle the 3.7V safely, over the 3.3 port? Or could it be fed to 5V IN?
 
Title: Re: STM32F103 - on a 1S LiPo (3.7V)
Post by: PaulS on Feb 27, 2019, 01:18 pm
Quote
Or could it be fed to 5V IN?
No, you can't put 3.7V into the 5V IN, and expect to get 3.3V out.

You could use a zener diode between the + side and the 3.3V pin, to get about a 0.4V voltage drop.
Title: Re: STM32F103 - on a 1S LiPo (3.7V)
Post by: PetrOsipov on Feb 27, 2019, 03:09 pm
Well, according to schematics it uses RT9193-33 regulator behind the 5V input, but as I understand, it would need at least 4.3V input... Dropping in a Zener is a good idea, but might be problematic due to non-constant discharge voltage.


I would probably need to use the main battery of my plane (6.6V 2S LiFePo4), and a stepdown voltage regulator... Or maybe get a 1S LiFePo4 cell instead of LiPo - it gives quite exactly 3.3V over 95% of discharge.
Title: Re: STM32F103 - on a 1S LiPo (3.7V)
Post by: PaulS on Feb 27, 2019, 03:15 pm
Quote
I would probably need to use the main battery of my plane (6.6V 2S LiFePo4), and a stepdown voltage regulator.
You can feed the 6.6V directly to the microcontroller. It's voltage regulator can take 6.6V.

Quote
Or maybe get a 1S LiFePo4 cell instead of LiPo - it gives quite exactly 3.3V over 95% of discharge.
Always a possibility, if weight isn't a problem.
Title: Re: STM32F103 - on a 1S LiPo (3.7V)
Post by: PetrOsipov on Feb 28, 2019, 10:18 am
I think I found a solution for my problem - I could use a Step up/down automatic voltage stabilizer, which converts 3-15V to a fixed 3.3V (called S09 module on Aliexpress). 0.6A max current should be more then enough for my purpose here. Just ordered a pair of these, to see how they work.