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Grand Central M4 Express Power Supply Selection Circuit
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Grand Central M4 Express Power Supply Selection Circuit

by Aakash_Dey on Thu May 19, 2022 3:00 am

Hi,

I have gone through the schematic for Grand Central M4 Express using SAMD51. I want to know the functionality of the USB CONNECTION & SELECTION and POWER SUPPLY SELECTION circuit.
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USB Part_Grand Central M4.png
USB Part_Grand Central M4 Schematic
USB Part_Grand Central M4.png (107.03 KiB) Viewed 139 times
)
I have measured the voltage as different points of this circuit at different conditions as attached in excel format.
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USB Part_Grand Central M4 Test.png
USB Part_Grand Central M4 Test
USB Part_Grand Central M4 Test.png (29.77 KiB) Viewed 139 times
)

Could you please explain why the MOSFET (TR1) Based circuit is used and what is its functionality?

Aakash_Dey
 
Posts: 2
Joined: Thu May 19, 2022 2:39 am

Re: Grand Central M4 Express Power Supply Selection Circuit

by dastels on Thu May 19, 2022 8:23 am

The purpose is to disconnect the USB's 5v from the board when the barrel connector is being used to power the board (and the power switch is "on").

Dave

dastels
 
Posts: 10114
Joined: Tue Oct 20, 2015 3:22 pm

Re: Grand Central M4 Express Power Supply Selection Circuit

by Aakash_Dey on Fri May 20, 2022 2:39 am

Ok, I understood. But, when Only USB is connected to the PC, the USB itself is powering to the whole circuit. Is the circuit functionality is correct in this case? Or else, the circuit should not be powered up when only USB is connected to the PC i.e. DC jack is not connected?

Aakash_Dey
 
Posts: 2
Joined: Thu May 19, 2022 2:39 am

Re: Grand Central M4 Express Power Supply Selection Circuit

by dastels on Fri May 20, 2022 9:55 am

With Vin not present (no voltage from the barrel connector and/or the switch is off) to turn off the FET it conducts because there is 5v from the USB.

I think of it as a one-way door into a room. If Vin is in the room, it puts a chair under the doorknob to prevent anyone coming it. If Vin isn't there, there's no chair, and nothing to prevent someone (5v from USB) from pushing their way into the room.

Dave

dastels
 
Posts: 10114
Joined: Tue Oct 20, 2015 3:22 pm

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