pros & cons of 12v-to-18v DC-to-DC converter for Cappucino PC

Here are some links to references for the above post:

Evolution Robotics ER1 Mini-book PC Project:
    http://www.evolution.com/community/projects/
    http://www.evolution.com/community/projects/MiniBookRobot.pdf

Cappucino PC website:
    http://www.cappuccinopc.com/cappuccinoez3.asp

Wouldn't ya know it ?!?!? Just a few minutes after I posted this thread, I
discovered that SaintSong is the actual manufacturer of the Cappucino PC. Of
course, I have emailed them my questions re 12vdc vs. 18 vdc.

Here is their website, FYI: http://www.saintsong.com.tw/index.html

(Oops. Posted this outside of the thread. My apologies.)

The question about " 12vdc or 18vdc input power "
12vdc or 18vdc can all be used, but 18vdc is a more suitable specification
as for Cappuccino, so we suggest you to use 18vdc better.
You are always welcome to contact us whenever you think it is needed.
Best regards,

SaintSong Customer center

I've been using LDO voltage regulators instead of the standard volt
regulators. I want to save on battery weight.
cya

I learn something new almost everytime I get a reponse on here! Hot dawg!

So using LDO regulators allow the battery to last a bit longer than standard
regulators, & therefore you can use a lighter weight battery, right ?

I found an article on LDO here, for those that are interested:
http://www.elecdesign.com/Articles/ArticleID/8530/8530.html

Hi!

This doesn't make much sense I'm afraid. First, the power loss on *any*
linear regulator is proportional to the voltage drop and the current. If
you're making 5V out of 9, and your current is 2A, than you will dissipate
(convert to heat on the regulator) (9-5)*2 = 8W. It doesn't matter if it is
an LDO or not. The only case an LDO can help is if your input and output
voltages are close. Every linear regulator has a minimal voltage drop that
it needs for proper operation. For LDOs this is lower. So, LDOs *can* be
used in applications where normal regulatros can't and in those applications
they are more efficient. But in any particular application where both could
be used, their efficiency is the same.

Second, if I understand this correctly the OP wants to make 18V out of 12V.
That is, the output is higher than the input. No linear regulator will do
that. You will need a (step-up) switching regulator.

My suggestion is to open up the case, find the power supply chip in the PC
and look up it's datasheet. Chances are it is used in it's standard
configuration and the datasheet will give you a good starting point to
figure out what it can handle and what it can't.

My guess is that your +12V line internal to the PC will not be kosher, but
the rest (+5V, +3.3V) are fine (can you measure them?). If that's the case,
than try to figure out what the 12V is used for. In this PC the hard-drive
and the CD-ROM look like laptop devices and hence are running from 5V
exclusively. Your RS232 transcievers might need +/-12V, but most likely they
don't. Again, find them and look up the datasheets. But even if they are,
they probably don't care much if the 12V is only 10 or so. That leaves the
CPU.

In Socket370 systems the CPU power supply is usually run from the 5V line,
but uses the 12V to generate the gate-voltage for the MOS-FETs. Again, find
the chip, and look up the datasheet. Also look up the datasheet for the
MOS-FETs. What you will most likely find is that the gate-source potential
on the upper-side MOS-FET for the CPU power should be 12-5=7V. If your 12V
line is below spec, let's say 10V, than your gate-potential will drop to 5V.
That's most likely OK though border-line. It will increase the
channel-resistance of the MOS-FET and will result in increased
heat-dissipation on it. You might not be able to run the fastest CPU on the
board full-speed, stable. Worst case you can burn out the FET and destroy
your motherboard (unless you know how to replace the demaged part). Note
however that there are socket370 systems where the CPU is powered from the
12V line. I honestly would doubt it in your case, but you never know until
you looked.

If you in some way can look up the max current specification on the 12V
line, you can make a pretty good guess at what the CPU power supply is
running from (provided that the HDD ad CDROM are indeed 5V only). If the
power supply can't supply more than 1A on the 12V rail, than your CPU is
powered from the 5V line for sure.

Regards,
Andras Tantos

Hi and thanks for the info!

1) What are you saying doesn't make much sense ? You mean the article on
LDOs ? Or doyou mean what I am trying to do ?

2) Are you using Socket370 as an example, or is it somehow related to the
Cappuccino system ?

Thanks again because it's all one big learning curve !
JCD

What doesn't make much sense is this: "I've been using LDO voltage
regulators instead of the standard volt regulators. I want to save on
battery weight." Unless you change the voltages in your system, moving from
standard to LDO regulators won't save you much.


From the website it looked to me that both Cappuccino systems are Socket370
ones. (one is a i810 and the other is a i815 based system). P-VI/Athlon and
higher power supplies usually use the 12V rail to generate the CPU voltage.

Regards,
Andras Tantos

Now *that* is some very valuable info to me! Thanks !