Worklog XboxPSU

ttsgeb

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The xbox has some mildly odd power requirements. It uses the same 20 pin Molex MiniFit Jr connector that an ATX PSU output, however the pinout is completely different.
1590500534133.png

As it stands, the typical solution is to use a PicoPSU, a small ATX PSU, a modify it to work with the original xbox. PicoPSUs can be had for around $15, the power supplies for them can be had for around $10. It's a very inexpensive solution. Traditionally when this is done, the Power OK and Power On lines are ignored, the PSU is set to always on, and the wires are run all catywumpus to get to where they need to go. While this solution works, it's definitely a hack, and I believe we can do better.

So what are the xbox's actual power requirements?
While I haven't actually cut up a power supply and tried to get the xbox to full load while measuring the current draw, I have a V1.1 PSU here that handily has the power requirements right on the label.
Max Output Power: 96W
DC Output:
+5V -- 13.2A
+3.3V -- 4.8A
+12V --1.2A
+3VSB -- 0.045A
I hope it's safe to assume that further revisions of the xbox had similar or lower power draw. Regardless, this seems like a good starting point.

So, how do I plan to accomplish this?
With 4x LM2678 Regulators from Texas Instruments.
http://www.ti.com/product/LM2678
Why 4 regulators for 3 voltages?
The LM2678 is a 5A regulator. I need 13.2A on the 5V line. Having looked at the specs for the PicoPSUs that seem to work just fine, they're rated for 8A on the 5V line. This leads me to believe that 10A should suffice, so I'll need two regulators for 5V.
I'll also need a 12V regulator, as I plan to run this off of an easily obtainable laptop power supply rather than needing to source an 8A 12V supply.
I will also be designing a smaller footprint alternative that runs off of 12v for when space is of the highest concern. I'll likely also break down the xbox's power requirements even further at some point to see if I can't design a PSU that allows for aggressive trimming, but that's much further down the road.
 

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ttsgeb

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upload_2020-4-25_4-29-42.png

I've designed the first iteration of the 24v board, it's 60*32mm. Now that it's done, I don't like it for a variety of reasons. I'm going to try again, putting the low profile components on the backside of the board and the tall components on the topside of it. Maybe I'll be able to squish it down a bit more in the process.
 

ttsgeb

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upload_2020-4-25_8-3-11.png

There, that's a little better.
27.5*49.25 mm
 
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ttsgeb

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Oh, hey, I worked on this a bit.
I ditched the 12v regulator and changed it to 12v in. I also had to source different inductors, which are sadly larger, so the whole board got a couple of mm wider in the process.
1590232703855.png

26.5mm*57.2mm

I think I'm gonna actually order this one, and see if it works.
 

ttsgeb

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I found a couple of errors with the design, such as multiple components trying to take up the same space, and fixed them. I also actually bothered to do trace width calculations and discovered that I was way off, so that's been remedied as well. I'm going to sleep on the design revisions, and look over everything with fresh eyes tomorrow. If everything checks out, I'll order the parts and we'll see if this nonsense actually works.
 

ttsgeb

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I slept on it, and I'm really not happy with the plan to use multiple switching regs in parallel to get the amount of current I need on the 5v line. So... I'm starting over with a controller and a pair of MOSFETs for the 5v line in hopes that what I build is going to be a bit less likely to literally explode in my face.
 

ttsgeb

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1590721661710.png

I've gotten the new schematic thrown together, next up is assigning footprints to everything and laying out the board.
I'm definitely considering a PCB assembly service for this one, that's something like 35 components, most of them 0603, and I really don't want to have to put it together.

Update: I've gotten the 5v Circuit laid out
1590739417580.png

11*40mm

Update 2: The whole thing is laid out now.
1590749259862.png

20.5mm*56.5mm, or slightly smaller than the cutout in the xbox motherboard for the fan.
 
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ttsgeb

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Well, I just ordered everything I need for the first build. $76. I really hope this works.

Future boards will be under $30/each if this design works out, but that's with me assembling them, so there's quite a bit of time involved there.
 
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