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Topic: Arduino Due 5V pin outputs more than 5V (Read 590 times) previous topic - next topic

yaoyaoh

Hi,
When my Arduino due is powered with 12V DC adapter, the 5V pin outputs 7.2V. I also tested some other voltage supplies, as shown below.

DC supp -> 5V pin output

12V -> 7.2V

9V -> 7.2V

7.5V -> 6.2V

6V -> 5V


I tested many boards and found that most of them is like that. However, there are actually several boards that output 5V no matter the supply voltages.
When I powered them with USB cable, all the boards are normal (5V).

Is there anyone has this situation? I do not believe that many of my boards are broken?!


thanks.

WattsThat

Where and how are you connecting your voltmeter? A photograph would be best to show us what you're doing.
Vacuum tube guy in a solid state world

yaoyaoh

Where and how are you connecting your voltmeter? A photograph would be best to show us what you're doing.
I just measured the 5V pin (next to 3.3V pin, RESET and IOREF pin). The reason why I need 5V is to power an external DAC which needs exact 5 volt.

slipstick

No. A meter always needs TWO connections. One is on the 5V pin. Where is the other one?

Steve

yaoyaoh

No. A meter always needs TWO connections. One is on the 5V pin. Where is the other one?

Steve
Of course, the other one is GND next to it.

WattsThat

#5
Dec 14, 2018, 07:39 pm Last Edit: Dec 14, 2018, 07:39 pm by WattsThat
Hi,
When my Arduino due is powered with 12V DC adapter, the 5V pin outputs 7.2V. I also tested some other voltage supplies, as shown below.

DC supp -> 5V pin output

12V -> 7.2V

9V -> 7.2V

7.5V -> 6.2V

6V -> 5V


I tested many boards and found that most of them is like that. However, there are actually several boards that output 5V no matter the supply voltages.
When I powered them with USB cable, all the boards are normal (5V).

Is there anyone has this situation? I do not believe that many of my boards are broken?!


thanks.
Are you certain your 12 volt adapter is actually DC and not AC?

As for the other voltages you list, it's all pointless since you do not explain what and how you're measuring things.

We cannot SEE what you're doing, we only know what you TELL us, which isn't much.  
Vacuum tube guy in a solid state world

outsider

#6
Dec 14, 2018, 08:20 pm Last Edit: Dec 14, 2018, 08:21 pm by outsider
Your PS may only be rectified and filtered AC, not regulated. What voltage does it read, with no load, on the DC AND AC meter settings?

Wawa

Some DMMs display a higher voltage if the battery goes flat.
Do you have a low battery warning on the LCD?

The reason why I need 5V is to power an external DAC which needs exact 5 volt.
The Due uses a switching (buck) 5volt supply when on external power.
Seems a bad idea to power a DAC from a potentially dirty supply.
Make sure the DAC doesn't mind the 3.3volt logic.
Leo..

hammy

Check your meter is reading correctly against a voltage which you know.
Something is wrong because your processors would be dead with those voltages.
As said it's possible your 12v supply is not a steady voltage but has an AC component.

yaoyaoh

Some DMMs display a higher voltage if the battery goes flat.
Do you have a low battery warning on the LCD?
The Due uses a switching (buck) 5volt supply when on external power.
Seems a bad idea to power a DAC from a potentially dirty supply.
Make sure the DAC doesn't mind the 3.3volt logic.
Leo..
The DMMs is normal. I measured the 3.3V pin; it is always 3.3V.
I actually need a 5V range Analog signal. I am using this DAC:  https://learn.adafruit.com/mcp4725-12-bit-dac-tutorial?view=all

yaoyaoh

hey guys,
this problem is so wired. I am sure my voltage supply is 12V DC (basically, it is a normal wall adapter), and my voltmeter is also working correctly (always read 3.3V on 3.3V pin).
If you have a due on hand, please test if the 5V pin is outputting 5V when the board is only powered by an external 12V DC adapter.
I also noticed that the 5V on Due is regulated from Vin with a chip LM2734Y. Anyone knows more about that chip? thanks.

Wawa

As said, the DUE uses a switching 5volt supply.
LM2734 datasheet here.
Output voltage is set by R11,R12 on the DUE schematic.
10k:52.3k calculates to 0.8volt, wich is the FB reference of the chip.
I doubt anything is wrong there. Check that 5volt rail with a second DMM, or with a scope if it's 'clean'.
Leo..

ard_newbie

#12
Dec 15, 2018, 05:45 am Last Edit: Dec 15, 2018, 05:52 am by ard_newbie
If you measure more than 5 volts between any 5V pin and any Gnd pin, providing you power the board thru the jack with a 7V to 12V DC, then your board has an issue with the voltage regulator, ask a refund to your board reseller.

https://arduino.stackexchange.com/questions/12476/arduino-due-and-vin-3-3v-and-5v-power-inputs

Some thoughts about the currents/voltages you will find on a DUE:

Voltage regulator used for 3.3v rail limits the current and allows the maximum of 800ma if external power source is being used. If you draw more current the voltage regulators get heated and temporarily switch off the supply until cooled. However if you power due using USB the USB interface limits the current and allows the maximum of 500ma. If you try to draw more current you might damage the USB port or make it temporarily unavailable. In case of digital out pins you are not supposed to draw more than 130ma, I recommend 100ma.

In case the board is connected with a USB cable , either on the programming port or the Native USB port and you connect a battery pack thru the jack, then the board will be powered by the battery pack and the regulator allows the maximum of 800 mA.

https://www.arduino.cc/en/Hacking/PinMappingSAM3X



yaoyaoh

Thanks guys.
As 'ard_newbie' said, there must be an issue with the voltage regulator. Anyway, I just returned the bad boards (actually more than 50% of them were bad) and get some new ones which work just fine.
Hope this will help someone. Thanks again.

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