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From: Larry DeMers (cray.com!demers)
Date: Wed Oct 02 1996 - 11:46:57 EDT
I have done some research into the problem of powering the laptop from
the ship's batteries. The temptation to design a use-specific circuit
and to package it for sale was strong, but then my research proves this to
be unnecessary, as there are numerous sources for circuits that will work
very well in the application that we have in mind.
A DC to DC converter takes 12vdc (actually 9-18VDC) and applies a switching
technique to arrive at a regulated 12 VDC output capable of providing up to
5A to the load. The source that I am looking at right now is Polytron
Devices Inc. (201-345-5885)
They offer full input/output isolation; 86% efficiency; short circuit
protection; over current protection; epoxy encapsulation; 6 sided shielding
against RFI.
Specs:
Voltage Accuracy +/- 1%
Line Regulation +/- .1%
Load Regulation +/- .5%
Ripple/Noise +/- 50 mVp-p
I would however, add a dual pi output filters to the output. This is to
smooth out the ripple content due to the switching circuitry. This is a
simple five component circuit, which can be built in place (without a
printed circuit board). It consists of 4 capacitors and an inductor.
Sample prices are below: Contact me for more info or to answer questions.
OUTPUT
CURRENT MODEL SIZE
WATTAGE (MA) NUMBER (in.) PRICE
------- ------- -------------- ---------- -------
25W 2100 KW25-12S12 2.9 X 2.7 $99.00
40W 3400 KW49-12S12 3.9 X 2.8 $104.00
60W 5000 KW60-12S12 3.5 X 5.5 $159.00
Regards,
Larry DeMers Cray Research Inc/SGI
S/V DeLaMer Dev. Circuits & Components Lab
Cape Dory 30 Sailing Lake Superior
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