What is the correct way of externally powering STM32F407G-DISC

[EDağl.1]

I know it's a bizarre question to ask but after having some research, I have to make sure knowing the proper way.

In the manual,

5V can also be used as input power supplies e.g. when the USB connector is not connected to the PC. 

But in my applications, I have to output out of 5V pin at the same time and i couldn't make it work properly. I also tried to supply input power from VDD pin. For the VDD pin, 5V makes LD1 goes orange and red. 3.3V makes it only blink red in a time interval.

I think that without the USB cable, STM32 should be supplied from VDD pin for 3.3 volts while 5V pins are being used for external power supply. I'd be so appreciated to hear some ideas.

Thank you in advance.

[RomainR.]

Hello @EDağl.1 (Community Member)

Did you updated the STLink of your F4 Discovery with the latest firmware ?

5V pins can be used as:

• 5V Output source when USB STLink is connected
• 5V Input source when USB STLink is not connected.

STM32F4-Discovery board can be powered with external 3.3V supply applied JP1 Idd.

You must remove the jumper and apply 3.3V voltage to JP1 (the pin near the Idd label side).

Then you can connect the USB STLink after applying 3.3V on JP1 to debug the device. The LD1 activity return to normal color.

Best Regards,

Romain,

[Tesla DeLorean]

Using the ST-LINK USB connector with a "charger" and having firmware version on the ST-LINK that doesn't clamp the STM32F4 in reset, or remove NRST solder bridge.

Review the schematic, seem to recall multiple diodes to allow alternate power options, MCU itself runs at around 3V as I recall.