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Fez Cerberus - Powering from ATX Power Supply?


#1

Hi,

Has anyone powered a Gadgeteer board from an ATX power supply?

I have an ATX Power Supply that I just removed last night and I want to use it to power a Fez Cerberus board that I have. I was thinking that I could pull power from one of the 5v lines to the board, the problem is how should I connect to the Cerberus? Can I just cut one of the 10 cables and supply 5v on pin 2 and gnd on pin 10 (assuming the pin out information I found for gadgeteer is correct). OR should I just buy the USB Client DP Module and use the barrel connector? I would like to keep the cost down and if I can just use a Gadgeteer cable that I already have that would be great.

Cheers!


#2

This would work just fine, just make sure that the voltage you connect is indeed the 5v line :slight_smile:


#3

Actually, no it’s not going to work the way you state, or without some effort.

A Cerberus is a 3v3 device and needs 3v3 supplied to it. You can either do that directly with a 3v3 input, or you can do that with a 5v input into a client SP or DP module that have a 5v-to-3v3 regulator on it. So you can use a 3v3 output from the ATX supply if yours has one, and this will be fine. Or you can use a 5v into the USB connection on the Client SP, or you can use it into a barrel connector on a Client DP.


#4

@ Brett - I am asking out of pure ignorance, but the Client DP barrel jack says 7v - 30v input, will 5v work if connected to the barrel jack?


#5

Looking again, yes Brett is always right :wink: add an extra 7833 and this should work…

[EDIT] and skip the DP module


#6

@ Brett - Thank you for catching that. I will pull from the 3.3v pin.


#7

You’re right, it won’t work “to spec” but it would most likely work. The 5v input would be lowered by the regulator by perhaps 1v, so the “5v output” would now be say 4v, which is input into the 3v3 regulator, and will produce 3v3 output or perhaps slightly lower… probably still in tolerance for the uC. So if you want to use the barrel jack, (I would strongly recommend thinking seriously about doing this because you then can’t mis-wire it or something), AND you wanted to use the 5v supply from the DP module for downstream devices (a module connected to the mainboard) then it’d be easiest to use one of the 12v outputs from the ATX PSU.


#8

Don’t forget that an ATX PS needs a load on the 5v rail to properly power the 12v rail. The simplest solution is to wire a 10Ohm 10W resistor between 5v and Ground. From experience, I recommend a heatsink/heatshield for the resistor, it will get warm.


#9

Even if it works. It’s a waste of energy I think. These power supplies don’t work that optimal for very low powers I think.
And as Gregg mentioned, you most likely have to waste a minimum of power so the power supply does not shut down.
Some of the latest Intel CPU’s ran into the problem to consume less power than the ATX spec has defined as a minimum , so some power save functions in the bios needed to be disabled to make it working :wall: