Sphere478 wrote on 2022-06-06, 21:23:

Maybe I’m wrong, but I could have sworn that there was like a half volt give or take drop passing through any transistor or diode. Because of forwarding losses

There is, a diode or a bjt will have a drop of about 0.6v-ish (I've found that a big ish)
A mosfet has a drop because it's not like a relay but a fully switched on mos should behave as a resistor.

(from what I've read anyway, haven't messed around with mosfets enough myself to say for sure)

EDIT:
Mosfet spec sheets mention a voltage drop across a diode, the diode is there to protect the mosfet from reverse current.
As far as I can see earlier mosfets didn't have the diode baked into them but engineers added a diode to the circuit.

REPOST

Hello.

About the idea of pumping the 3.3v from the ATX psu to the CPU IO and then to the step down converter for CPU vcore.
As I mentioned in the thread about the ATX pico, I was thinking that the 3.3v line should be controlled by a mosfet. The logic being that the 5v power good line of the PSU goes high once the power rails are stable. It would be nice to have the cpu get power once the psu rails are stable and not before.

So I was looking into the topic and spec sheets and I came up with parts and a potential circuit.

2 p-channels in parallel to help cut the resistance and spread any heat HSU60P02.
Resistors to pull them high thus keeping the mosfet off, protection diode for any reverse current.
Then an 2n7000 n-channel mosfet that is switched on by the 5v power good signal that should pull the gates of the p-channels to ground thus sending power to the CPU.

What do you think?

I never made a circuit with a mosfet before so I could very easily be missing something important. It's nice to actually feel like I'm starting to understand mosfets, so even if the circuit is a waste, may have learned something from it at least.

Note: error cap position is reversed

Hey Calamity, got something for ya.

took it to 6 layer, moved the traces to the 3.3v layer in the middle and made it all hold even more current by opening up the 12, 5v, and ground planes as well I doubled up the traces on the 3.3v layers. 3.3v is on the inner layer with ground planes separating all power layers.

I even added LEDs for -12v, and 3.3v

also solved all but one of the DRCs

more pics

Note: error cap position is reversed

version 0.7

for some reason I didn't think 6 layer was that much more expensive on jlcpcb. they want 94$ to make 5. Such a shame this one is better.

Might see if I can collapse the design back into a 4 layer pcb.

Is the user supposed to solder a wire to the side of the PCB for the 3.3v?

Also 94$ for 5 of these boards is a tad pricey 😂

CalamityLime wrote on 2022-06-15, 01:36:

Is the user supposed to solder a wire to the side of the PCB for the 3.3v?

Also 94$ for 5 of these boards is a tad pricey 😂

see next post

I also kinda made this update also to compliment the socket 1/2/3 tweaker

Re: Socket 1/2/3 Tweaker (Alpha)

I honestly had no idea they were gonna charge that much crazy.. 🤣

Note: error cap position is reversed

phew.... that was a lot of work...

Not only was I able to get it onto 4 layers. The current doesn't seem to have suffered, and! it now has fan headers!

outer ones are 12v, inner ones are 5v

layers

Hello!

I think the fan heads run the risk of being in the way. At least on my AT boards they would interfere with the ram slots.
Besides that, judging by a previous photo of a more assembled unit, the connectors for the AT side have little fangs that go around back and I think you'll have to move the outermost fan headers inwards for those.

Also I looked the Power good lines on my boards and the trace looks about half a mm thick. So if you need to slim your PG trace, you can trim it a good bit.

At first I was wondering what you were going with the 2 -12 volt lines, at a glance it looked like you connected two traces together with a via by mistake, but I see what you were up to.

About the regulator,
If you're struggling with space you can put in a smaller regulator. I took a look on lcsc and found this that still looks easy to solder by hand.Link to LCSC Might give yourself more breathing room. Or even switch out the filter caps for smaller ones, like 0805's

Have you assembled the units you ordered yet?

Or maybe even switch to a 79l05 in a TO-92 form factor. According to Necrowares video on the voltage blaster you need about 10ma for a sound card.
79l05 in a to-92 can deliver 100ma.

I know that it doesn't have the same reassurance as the 7905 but it would go with the pico vibe of this.

Updated above post check it out now, lemme know if you see any errors.

Eh, no reason not to keep the big fet methinks. (you could install the smaller one where the big one goes if you want)

My thought was that the user could install the fan headers if they wanted. it's kinda a free feature.

Looks good.
I was just suggesting the smaller regulator since it might give you room for a 3.3v header or a power on button or something like that.
Up to you what you want to use.

CalamityLime wrote on 2022-06-16, 01:18:

Looks good.
I was just suggesting the smaller regulator since it might give you room for a 3.3v header or a power on button or something like that.
Up to you what you want to use.

Not bad ideas 😀

I don’t mind the connector at the edge.

I was pondering making a little jut out there though and making it work with a 0.250” spade quick connect. Might be a better way. But I can’t find a footprint for one. I suppose I can make a footprint based on the data sheet though

I thought about putting a pad down low next to the AT connector but didn’t want to tempt fate making it larger down there for clearance reasons.

most people won't use the 3.3v tap unless they are trying to add 3.3v to pci or trying to power the tweaker I'd imagine. so making it unassuming on the edge should be fine.

btw:
The pico psu adapter and the socket 1/2/3 tweaker shown with the 3.3v pads near each other where a wire can go between. I kinda figure these two can kinda go together as a pair for 3.3v cpus in old 5v platforms. Maybe put a coupler on the wire should you wish to seperate.

there is also the pci 3.3v adapter which can use the 3.3v Re: Adding 3.3v to pci

V0.6 prototype arrived. Albeit late 🤣 as I’ve already ordered the 0.8 version 🤣.

👍

Ooooo

Got around to making a Github and put my original designs in a repository so they don't get lost. Feel free to branch the design and so forth. 😀
https://github.com/wiretap-retro/PICO-AT-Power-Adapter

wiretap wrote on 2022-09-09, 21:05:

Got around to making a Github and put my original designs in a repository so they don't get lost. Feel free to branch the design and so forth. 😀
https://github.com/wiretap-retro/PICO-AT-Power-Adapter

You may do as you like with my modification as well 😀