5 V power supply Olimexino-32U4

Started by JeanFrancois, October 21, 2021, 06:48:15 pm

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JeanFrancois

Good evening,

I'd like to power the board from a 5V power supply which Olimex provides in the accessories. After looking at the schematics and getting to how this would work, I found out the simple solution.

Could you please check, comment or provide a better way, or approve on this ?

- Power supply through conn.1 pins 3/4 (5V/GND)
- Equivalent to USB 5V supply except it does not power back to the usb cable (reverse on FET1), otherwise similar to powering through USB.

Thanks for your view on this question,

Regards

Jean-François Simon

LubOlimex

Don't power the board from power pins of CON1, there is risk of short-circuit if you ever use USB or external power supply at the same time. The voltage wires you see there 5V and 3V3 - are meant as output. These were not designed as inputs.

If you put 5V at CON1 and have USB attached at the same time - there would be short circuit.

To modify this behavior for the inputs you would need to alter the hardware.

My advice is to power the board from the power jack. If you don't have compatible jack, consider this:

https://www.olimex.com/Products/Components/Cables/PWR-CABLE/

Technical support and documentation manager at Olimex

JeanFrancois

Hello Lub,

Well could you please precise the meaning of FET1 ? I can't get it.
Thanks for you advices on supply. I'll heck it next week with the client.

See you & regards

Jean-François

LubOlimex

In the hardware design of Olimexino-32u4, FET1 is meant to allow for switching between USB power supply and external power supply (which had already been lowered to 5V by voltage regulator VR1).
Technical support and documentation manager at Olimex

JeanFrancois

Good morning Lub and team,

I meant the details:

FET1 seems plugges backward, it connects +5V to +5V_USB through S->D when driven or +5V_USB to +5V through its diode.

Thus I am wondering why not a simple diode instead of FET1, and why does it seems backward connected ?

I remind having seen somewhere in the Olimex forum or documentation a mention about reverse connected FET, but can't find it back.

Can you please remind me why this design ?

Thank you

Regards

Jean-François Simon

LubOlimex

Well for example diode has power loses.
Technical support and documentation manager at Olimex