Power supply

[simon]

Hello,

the current design demands to supply 12V and 5V. A desktop power-supply which is strong enough to power all chips, floppy, harddrive, ... is expensive. What about supplying 12V only and use a voltage regulator for the 5V? But a 7V drop is not very good. What about a step down converter? How to avoid annoying ripple noise?

Simon

[benchoff]

Heh. Just noticed there's an actual power supply thread.

How many amps do the 12 and 5V rails need? You're right that a 7805 (or whatever) would be very hot if it's pulling a lot of current, but I don't know if it will be possible to build a power supply for less expense than you can *buy* one.

That, and just about everyone who would buy this has an old ATX supply lying around.

[simon]

I actually didn't measure how much power is needed. The power-supply I use has 5A for the 5V and 2A for the 12V line.

Actually testing an ATX power-supply is on my to-do list. And I want to test adding an inline LC-filter. Well, I will have to order some coils to try out the filter.
If we go with a desktop power-supply as it is used with my prototype the price will drop for a single voltage output supply.

Simon

[benchoff]

Well, there's this: http://www.linear.com/product/LTC1775

but that would require multiple chips. Jesse over at Hackaday thinks this thing from Sparkfun https://www.sparkfun.com/products/317

would be a good idea, but seeing it can only supply 1.5 A, it might be better just to clean up an Mini ITX supply.

[simon]

Right, it needs some external parts and it is a step down converter. I really don't like the idea of having a step down converter right on the board. I fear a pontential ripple noise disturbing audio and video signals.
Maybe we should keep the currect design and let the user decide which suppy is the best? I would add a filter near the power-pug though.

Maybe I can measure how much ampere the board consumes, when I build a filter circuit.

Simon

[netwar]

why not build and external brick that fit the retro look(vic-20 esq) that is the power supply? or inside the case have a shield and a seprate board? just thoughts. I also have a good power supply from a cannablized rackmount server that i could copy and send you or give the schematics?

[simon]

An external brick would be nice. I would like to see a small standard PC power-supply as these are pretty cheap. If I could find one which is smaller than the standard bricks and preferably silent (passive cooling)...

I did not order needed parts yet because I don't want to submit an order just for a handful parts. Thus a PC power-supply is still untested.

Simon

[netwar]

I just got an idea why not see if a laptop power supply would work? like a cheap generic? mine for my laptop is
input 100-240v 2.0amps @60hz AC
output 20v 7.7amps DC
(this is a big brick like 9"x5"x1.5" but its for a tank of a laptop)
or again maybe i could clone the single sided server power supply and see how it runs? I think thats my weekend project time for hardware hacking
Before the server died i had converted it to passive with heatsinks so it already fits that requirement. I understand completely the bulk order thing, espically if this is going to be like a 100 lot buy then I'm assuming you'll use a Pick and Place machine at some factory(or have the joy of soldering all the boards by hand) and buy them on Reels/tubes.
-Michael

[lee]

Actually testing an ATX power-supply is on my to-do list.

I'd use an ATX supply because ..

I have a few.

Lee.

[netwar]

Hahaha nice.