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
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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
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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

October 31, 2021, 10:04:13 am #4 Last Edit: March 19, 2022, 04:56:05 pm by JeanFrancois
Good morning Lub and team,

I meant the details:

FET1 seems plugged 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

[Edit] The diode is symbolic, i was mislead, I also missed the fact it's a P channel mosfet. Got it clear now, that's the gate to select source from USB or Vin to the circuit based on which one is available. Also prevents feeding the Vin to back to USB if i properly understand the schematics.
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LubOlimex

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

JeanFrancois

hi,
Got is, both FETs are P mos used as switch gates for power supply "OR" from Vin (ext.), USB, or battery.

The source is selected and disconnecting the other channel eg. FET1 Overrides USB supply with Vin if available.

Jean-François
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