Powering Beaglebone black through VDD_5V

I've made a power supply to power my BBB, but whenever I connect it
(to pins 5 & 1 of P9 connector for VDD & GND), the power led blinks
for some seconds and then it is off.

The output comes from a 7805CKCT, which can provide up to 1.5A.

It's a typical power supply from a rectifier + capacitors + regulator.

What does this "blinking" mean? any ideas of what is going wrong?

Regards
José L.

P.S. The board works perfectly plugging it to a computer via USB

I am not sure you can power it that way. I am a newbie to beaglebone black but checkout page 110 of 124.
Pin 5 of J9 is VDD_5V which is described as the following:

VDD_5V is the main power supply from the DC input jack. This voltage is not present when the board is powered via USB. The amount of current supplied by this rail is dependent upon the amount of current available. Based on the board design, this rail is limited to 1A per pin from the main board.

I believe it is an output from a regulator.

You are going to want to connect to TP5 - BAT, TP8 - GND, TP6 - SENSE

BBB_SRM.pdf (5.02 MB)

Looking at it some more it looks like you are only trying to power one of the three rails. The blinking might indicate it is missing the 3.3V rail and the SYS_5V rail.

Actually, VDD_5V is raw 5V power, connected directly to the DC power
jack. It is absolutely possible to power the BeagleBoard this way, and
I have several capes that do so and work just fine (the BeBoPr and K9)
powering the 'Bone via VDD_5V.

The LED behavior likely indicates something is going wrong with booting
the operating system. The easiest way to debug these issues is with a
serial port cable, so you can see what's happening. As a guess, you may
be tying some other pins (specifically the LCD_DATA lines) to circuitry
and messing up the AM335x boot process. By changing the values on these
signals at reset, you can determine if the CPU should boot from eMMC
flash, SD card, ethernet, USB, serial, etc., so messing this up can
easily result in a system that won't boot.

Double-check the LCD_DATA lines, and get a serial debug cable so you can
see what's going on.

I stand corrected … like I said I am a newbie to the BBB.

Respectfully,
Dan Metcalf

No worries...you're actually correct if we were talking about SYS_5V (on
P9 pins 7 and 8) instead of VDD_5V (P9 pins 5 and 6).

The SRM section you reference is a bit confusing, as it talks about
drawing power from that rail and not powering the board with it. I
almost always fall back to the schematic as the "primary source" for how
things work, and there's other sections in the SRM (6.1.2, page 42 and
8.6.2, page 110/111) that talk about powering the board with 5V via the
expansion connector.

Actually, VDD_5V is raw 5V power, connected directly to the DC power
jack. It is absolutely possible to power the BeagleBoard this way, and
I have several capes that do so and work just fine (the BeBoPr and K9)
powering the 'Bone via VDD_5V.

I see at http://elinux.org/Beagleboard:BeBoPr_Cape that 3.3v signals
are also used by this cape. I guess they're used as output after
powering through VDD_5V de board.

The LED behavior likely indicates something is going wrong with booting
the operating system. The easiest way to debug these issues is with a
serial port cable, so you can see what's happening. As a guess, you may
be tying some other pins (specifically the LCD_DATA lines) to circuitry
and messing up the AM335x boot process. By changing the values on these
signals at reset, you can determine if the CPU should boot from eMMC
flash, SD card, ethernet, USB, serial, etc., so messing this up can
easily result in a system that won't boot.

Nope, I'm connecting only GND and VDD_5V for testing, no other
connections are made to the board.

Double-check the LCD_DATA lines, and get a serial debug cable so you can
see what's going on.

I'll try to get a serial cable trying to see anything, but the board
powers down in 5 or 6 seconds (at least the power led does it), so I
don't think I'll have time to check it.

Thanks for your advices.

José L.

Do you have a multimeter or scope you can use to watch the voltage going to the board? I wonder if the regulator isn't supplying quite enough over time.

Zach

Yes, I have checked it and the voltage is correct.
There must be a lack of current problem. Feeding the regulator with a 9 volts battery, it works. If I plug the transformer with the diode bridge it blinks for some seconds and stays off.

José L.

In addition to the average value of 5V, the BeagleBone needs a stable 5V
value that doesn't have large swings away from the 'typical' 5V value or
the on-board power controller will go into under- or over- voltage
lock-out mode and the system will shut down.

Put a 'scope on your 5V and make sure it's clean.

I've seen with the scope a 30 mV peak-to-peak ripple, I didn't think
this could cause problem, but could this ripple be enough to enter in
lock-out mode?

This is an old thread, but I thought I’d add a solution. I found that the BBB would reset part way through booting when powering the BBB via the barrel connector or Vdd_5v pins. I needed to add a large capacitor. 10,000 uf did the job.

Thanks, I will try it. I am working with a Chinese mobile phone charger without problem, but I’d prefer to integrate the power supply in my own circuit.

José L.

I used a similar wall switcher 1.5A usb power supply, and found that it was fine to power via the mini usb socket, but when used for Vdd_5v it would fail to deliver enough power during boot. I’m not sure, but it seems the power management of the BBB allows it to draw a lot more current (for short spikes) form the Vdd_5v than from the USB. In either case, it draws under 400mA once booted, it’s just some instantaneous power demands during boot that cause reset. --Karl

I’m having power issues booting a BBBW, where did you solder in the capacitor?

Hello,

Just put the capacitor between 5v and ground anywhere.

–Karl