View Full Version : Power Supply for mini ITX
lonnie
10-30-2002, 08:36 AM
Something that you guys can keep an eye out for is a DC - DC converter to take 12V to 30V and provide the signals that the mini ITX motherboards require. They are low power, and would make very inexpensive, yet ideal Multi Board Computer (MBC) units.
The basics can be had for under $100 but they lack a power source, and the 110VAC ATX supplies are a pain to run as POE. :wink:
Anonymous
11-11-2002, 06:43 PM
Although dc on POE is handy, using 110VAC as the POE current might not be so bad. Instead of 12 V, you're running 120, so the current is MUCH smaller, meaning less losses ...
Theoretically, it's perfect :)
lonnie
11-11-2002, 07:48 PM
Whoa ---- don't even want to venture into that territory. That can be lethal. A shot from 12V goes largely un-noticed and 24V is a slight tingle. 110VAC will make your arm jerk very violently and it will make your heart change its pattern.
Now just to be safe - 24V is lethal as heck, with the right conditions. The good news is that those conditions are pretty extreme and typically would not ever occur.
That is why most Electrical Codes have very few stipulations for 12V. It is considered to be pretty safe.
georgew
11-12-2002, 06:09 PM
If you don't want to g to 120v, you can use 48v. 48v is safe to contact though it will wake you up if you touch it. NEC lists 48v systems as safe to work on while live using uninsulated tools. 48v nominal means as much as 60v, and that will get your current levels down as long as you have an efficient power supply, some sort of high-quality switcher.
One of the things I have done in a past life was design and build power supplies. There are a fair number of low-cost single-chip solutions for dc-dc power conversions. Most require some sort of inductor, but you can usually get those from the chip maker. I think National Semiconductor had some good ones, and they were good about selling parts in prototyping kits and it is easy enough to buy small quanities of them (after you get your prototype to work) from distributors like Digikey, Allied, Pioneer and others. You can build a DC-DC power supply on about 1 or 2 square inches of circuit board. For about $200 you can have several boards professionally made that have 25 to 100 power supplies
etched onto them. You cut them apart with tin snips, solder the parts to the board, and use nylon posts, or some other good quality mounting method to fix them into your radio. Don't use hot glue or double sticky tape, as the heat from the power supply may soften the adhesive.
Some of the power supply chips are pretty good, producing a solid output voltage over a wide range of supply voltages... this is handy is you have a battery backup that slowly drops in voltage during power outtages.
This is also the advantage of building DC-DC converters... you can run directly off of a battery, then use a fairly ordinary battery charger to keep the battery charged. This is how telecom companies run their power.
George
texas instruments has the nifty little things calls isr's (integrated supply regulators) They will send you a few samples NEXT DAY AIR! if you request them from their website. I used them to build a completly functional (-12v, -5v, -3.3v, +3.3v, +5v, +12v) ATX power supply for my computer, from a single 7 - 16v dc input(for use in a car) with a breadboard, some caps, some relays and these little thingys and it all fit in a regular atx case. They're extremely efficient also, the inductors are built in. They're just wonderful :) And it didn't cost me a dime. I am using them now to add POE to some non-POE devices (eg. linksys wap11) Here is the link to them:
http://focus.ti.com/docs/prod/productlist.jhtml?familyId=462&templateId=2
ginovilla
11-21-2002, 09:38 PM
why just buy the mini itx case, it comes with a dc-dc adapter...for $65 you get case,dc-dc adpter amd ac-dc adapter..
Gino
TheBarron
12-21-2002, 09:58 PM
dkii: So how about putting your schematic online and posting a link to it?
ginovilla: The $65 case you're referring to.. You have a URL?
Sure.. I'll have to draw them up, didn't use any schematics, and I never perfected the ATX on/off feature, but everything else worked fine, I was able to post an asus p3b-f motherboard with a celeron 533, a fujutsu 10gb hd, 256mb ram, an 8x cdrom, and a netcard in it and it appeared to be stable, got window2000 installed and was downloading updates before my battery died. So as I was waiting for the battery to charge back up, I ran across the soekris units, and haven't put anymore time into it. I'll see if I can't draw up a board design and some schematics for it.