STM32F0 Discovery freezes when powered without connecting to a computer

Xinran Li · ‎2018-04-14

Posted on April 14, 2018 at 09:34

Hi all,

I am trying to use an external power supply to power the STM32f0 discovery board. I used a 7805cv to regulate a 12v DC to 5v. When I connect my 5v output to the board's 5v pin, it will start to function normally for about half a minute to a minute. Then all of a sudden everything will freeze, reset button no use, the only thing moving is the LD2 onboard LED flashing red as usual. I measured the 5v pin and 3v pin onboard, each says 5v and 3v, which seems about correct. If I disconnect the power and reconnect things will start to function normally again, for a minute or so before it freezes. Does anyone have a similar experience? What am I doing wrong? I also measure the 5v pin voltage when its powered by a USB cable, it's around 4.7v instead.

Thank you!

PS: I tried other boards, no difference. And, a

fter I connect the power, the board does not seem to be affected if I don't start to run the program by pressing reset. the problem appears after the program starts running.

UPDATE: I fixed the problem by dividing the 5v to 4.7v. But I still don't understand the reason behind it.

T J · ‎2018-04-15

Posted on April 16, 2018 at 03:06

when you connect the PC, the ground wire actually goes to earth on a wire outside your building.

having trouble without ground is indicative of a noisy power supply.

can you explain this better ?

UPDATE: I fixed the problem by dividing the 5v to 4.7v. But I still don't understand the reason behind it.

it sounds like your power supply is noisy.

how much capacitance do you have on the 12V rail ? at least 1000uF I would suggest.

and 100uF at the 5V end to be sure.