[ltp] car and airplance adapter

[Peter Stuge]

On Sun, Nov 07, 2004 at 08:14:00AM -0500, James Knott wrote:
> Peter Stuge wrote:
> >>(Check your AC adapter.)  BTW, anybody know how they raise the
> >>voltage for DC?
> >
> >Probably using a charge pump.
> >http://www.eecg.toronto.edu/~kphang/ece1371/chargepumps.pdf
> 
> Probably not.  Charge pumps put out approximate mulitples of the
> input voltage, not a minor increase as needed in notebook
> computers.  They also have poor voltage regulation.

I assumed it would be regulated down afterwards. But I guess that's
unneccessarily wasteful.


> Most power supplies convert DC to high frequency AC, which can then
> be stepped up (or down) with a transformer and then rectified.  The
> switching used to create the AC, can be modulated, for voltage
> regulation. Also the higher frequencies used, mean that the
> transformer can be a small ferrite toroid, which allows for a
> small, efficient package.

Indeed. I erroneously thought that most DC-DC-converters were charge
pumps rather than switched. It is obviously much better to have the
supply produce a voltage that is closer to the final output and only
regulate it moderately.

Thanks for correcting me! :)


//Peter