Lot's of little appliances can be charged straight from a USB port
these days. However carrying a PC with you all the time isn't very
practical, and laptops need to be plugged in to mains if they're to
last long enough to charge anything. That's where the travel charger
comes in! A small pocket sized device which runs from 2 - 4V, in other
words two 1.5V batteries. Easy to take with you anywhere no matter how
desolate the location, just remember to bring batteries. ;-)
Similar to the Minty Boost, except it
uses a more common PWM chip (at least in my neck of the woods), the LM3578.
It's just a boost converter which boosts the battery voltage up
to a regulated 5V. The support components were more less just taken
from the datasheet.
They take care of feedback compensation, oscillation frequency and
voltage regulation. The load regulation is good, IIRC it only dropped
from 5.05V to 4.95V when sourcing 250mA. Even when the battery voltage
dropped to 1.80V (the LM3578 is rated for 2V minimum) the output was
still 4.45V while charging my ipod. The chip did get warm however, so
use fresh batteries. According the Minty Boost site by selecting either
pull up or down resistors the charging current can be changed between
100mA and 250mA. See the bottom of the page. Don't forget to check the USB port pin-out. Next summer I'll have to make some kind of mini-generator for hard-core survivalists.
I do not take responsibility for any injury, death, hurt ego, or other
forms of personal damage which may result from recreating these
experiments. Projects are merely presented as a source of inspiration,
and should only be conducted by responsible individuals, or under the
supervision of responsible individuals. It is your own life, so proceed
at your own risk! All projects are for noncommercial use only.