Featured Articles
Announcing Pi
Technical Specifications
Raspberry Pi FAQs
Win a Pi
Raspberry Pi Wishlist
Actions
Forum Thread Details
  • Replies 18 replies
  • Subscribers 671 subscribers
  • Views 3415 views
  • Users 0 members are here
Related

Raspberry Pi 2 "5 V Power Supply" Notes

Former Member

Some time ago, I ordered and received the RPi 2,.  ordered and imaged a new SD card and found the board not booting.

 

Having been using a RPi 1 with power supply, monitor, mouse and keyboard and never seen any problems starting,. I expected

the new board also to boot with the new SD card and the rest of the hardware.

 

After spending quite some time with changing to another RPi 2 board ( exchange )  different SD cards, I had the conclude that

my problem most likely had to do with the the power supply.

 

All the used SD cards and hardware  did work with The RPi 1.

 

Up to this point both boards did not work while the RP1 1 never failed to boot.

 

The power supply I was using provided about 5.4 V measured on the miniature USB connector on the board. Changing start sequence

had no effect, 110 Volt first, USB switching with Power Supply already powered up. No variations in the board voltage were noticed.

during the start-up.

 

The power supply ( Chinese switching ) had a relative thin output power cord ( by closer inspection )

 

Finally, by using an home built power supply with adjustable output voltage and the heavier gauge output power cord, I got both computer

board to work with all the SD cards I had required in the previous process.

 

Not having an oscilloscope available, I was not able to look for any non wanted effects at the time of switching on the RPi 2.

My final conclusion is that the RP1 2 is much more sensitive to possible voltage changes than the RPi 1 during start-up and booting

With the adjustable 5 V power, I experienced no problems running between 4.5 and 5.5 V input to the board.

 

Wished I had known this a little earlier....!

 

Rein Smit

Parents

  • I ordered one of those "5.25 volt" power supplies from Adafruit and unfortunately it spits out 5.35V according to my multimeter.  I'm worried that at very low currents 5.35V could damage something.  So the new supply is sitting in a box until I can check the image Raspberry Pi 2  schematics image and see which components are hooked up to that 5V power input.  (Yes, jamesh, we really do need schematics.)

     

    I'll pick up a Schottky diode next time I order some parts and get a 0.2V drop.

     

    For now, I've been able to run a RasPi 2, keyboard, mouse, and Papilio DUO with a 700 mA supply.  With Ethernet plugged in, too! image

  • in reply to johnbeetem

    Hi John, there's obviously not a lot on that board and really nothing I can see that uses the 5V directly it all goes via the DCDC. The USB may be a different kettle of fish, so the juice coming out of there maybe a bit hot for some things, there again most USB devices are pretty robust and probably regulate down to their own 3.3V supplies any way.

Reply
  • in reply to johnbeetem

    Hi John, there's obviously not a lot on that board and really nothing I can see that uses the 5V directly it all goes via the DCDC. The USB may be a different kettle of fish, so the juice coming out of there maybe a bit hot for some things, there again most USB devices are pretty robust and probably regulate down to their own 3.3V supplies any way.

Children
  • in reply to Problemchild

    The +5V is used to supply power for USB, HDMI, the GPIO connector (and anything connected to it of course) and is connected to the VDD_BAT1 - VDD_BAT4

    and VDDBAT2 inputs on the BCM2835 SoC.

     

    All of the old 74xx(x) series and their variations (LS, ALS, S, F) are +-10%. The 54xx(x) series (these are miltary grade versions of the 74) are +-5%. I

    also found some old PLDs (16L8 etc.) that are +-5%. There are probably more. I have noticed that more of the modern 5V ICs are +-5%. The absolute

    maximum voltage ratings usually allow for up to 6V but in the long run this will probably affect reliability.