Looking for 2nd opinion: +12v & +5v only, no need for AT/ATX or neg rails

**Gibson99** · 08-19-2004, 07:57 PM

well i tried to search, but terms like that are being blocked as "common used words" or it actually interprets the NOT as an operand, not a regular word.

anyway here's what i've got: a SBC mainboard that, instead of an AT or ATX power connector, has a connector identical to the one you'd see on the back of a cdrom or hdd. yup - it actually only needs +5v to run, but you get better quality sound if you give it +12v as well. so at home i'm testing it with an old 45W AT power supply, with the AT leads just dangling. for the car i want to go the direct DC-DC route for space and efficiency, but i'm not sure what's out there, and would like to build my own p/s instead of shucking out $150+ for a p/s that (imho) just has more parts to break and aren't needed.

I was thinking of getting the ITPS and feeding my +12v rail for my HD, CDROM and mobo directly from the ITPS, and then making some sort of regulator or transformer to drop the regulated +12v down to regulated +5v for the mobo and drives.

so my question is, do you think i can do it this way? i can switch it all externally with relays and switches, and can do a fake UPS no sweat (got 4 serial ports to play with!) what would you recommend as a way to drop the 12 down to 5 in a way that won't overload anything?

**rando** · 08-20-2004, 12:17 AM

12V: TI PT5071
5V: TI PT6653D

Or

Just build the +12 and +5v portions of Mastero's Sproggy (MK3.5, MK4, or MK4.5).

It doesn't get much easier.

**Mastero** · 08-20-2004, 04:08 AM

Email me and i can design you what you require ... it shall be small and you shall have a full kit to build your own ....

Mastero

**rando** · 08-20-2004, 09:40 AM

Having Mastero design a kit for you is quite possibly an even easier solution.

I stand corrected.

**Gibson99** · 08-20-2004, 09:08 PM

cool, thanks mastero. i'll email you in a little bit once i come up with my requirements. it probably wouldn't be hard to put the relays onboard, which would not only make the install smaller (very important in a mazda mx5!), it would be simpler to install, too.

after reading more and more on the forums, it sounds like the istp (or whatever) will not work for me, since most people say it doesn't survive engine cranking, and doesn't run (most of the time) with the engine off. but the sproggy DOES. and that's what i want.

thanks again mastero.

**Rob Withey** · 08-21-2004, 04:23 AM

Look on my site (Hardware page). I have exactly the same situation, and built a 5v/12v power supply specifically for the em586. Based around a PT5071 and a PT6625, the entire power supply sits over the motherboard keeping your system footprint down.

These regulators even have a switch-on pin that removes the need for relays on the input.

**Gibson99** · 08-21-2004, 08:49 PM

Originally Posted by Rob Withey

Look on my site (Hardware page). I have exactly the same situation, and built a 5v/12v power supply specifically for the em586. Based around a PT5071 and a PT6625, the entire power supply sits over the motherboard keeping your system footprint down.

These regulators even have a switch-on pin that removes the need for relays on the input.

so you have the voltage from your car going straight to your powersupply with no external regulation? very interesting indeed. however, i will be hanging a lot more hardware off mine than what you're running - a big 3.5" hdd, a cdrom, pcmcia wifi, usb touchscreen, and eventually GPS (likely also usb). plus my cpu, though an amd, is running at 300 mhz - more juice.

**Rob Withey** · 08-22-2004, 05:33 AM

Originally Posted by Gibson99

so you have the voltage from your car going straight to your powersupply with no external regulation?

Correct.

Originally Posted by Gibson99

very interesting indeed. however, i will be hanging a lot more hardware off mine than what you're running - a big 3.5" hdd, a cdrom, pcmcia wifi, usb touchscreen, and eventually GPS (likely also usb). plus my cpu, though an amd, is running at 300 mhz - more juice.

The power supply on my site should be good for 5A at 5V and 1.5A at 12V. You may need some heatsinks/forced airflow. I have a heatsink on and a fan sitting right over the 5V regulator.

**Gibson99** · 08-22-2004, 12:11 PM

well after doing a little more searching and reading, i think the carnetix is what i need... except i will need to mod the cnx to also have a 5v rail. i think i can just build the 5v side of rob's mk2 p/s, which would be fed from the 12v output of the cnx. and conveniently, the cnx has an unused wire on its 6 pin output - the white one. i can probably put the +5v out into this wire. i wonder if it'll all fit inside the cnx casing... <evil grin>

**rando** · 08-22-2004, 12:17 PM

The carnetix is a good choice for a high power 12V regulator.

Rob's 5V supply (PT66xx based) can be fed directly from your battery...just like the carnetix. There is no advantage in powering it from the Carnetix. In fact, you'd just be wasting a good chunk of your Carnetix output in doing so. Rob's supply has a turn-on wire that can be fed from the carnetix so that they come on/off together.