Laptop power supply 20V

The new Lenovo laptop I bought comes with an AC to 20V DC
external power converter.  Why such a high DC voltage?  I would
expect that most of the circuitry in there operates on 5V or even
3.3V.  While they may still need 12V to power disk drive motors
or something, is there anything at all that operates on anything
close to 20V?

"David Harmon"
>
> The new Lenovo laptop I bought comes with an AC to 20V DC
> external power converter.  Why such a high DC voltage?

** The PSU is also a battery charger and needs to have a voltage high enough 
to do that job. For a standard 14.8V Li-ion pack, the peak charging voltage 
is about 17V -  so having 3V more available allows the regulator circuitry 
to work.

> I would expect that most of the circuitry in there operates on 5V or even
> 3.3V.  While they may still need 12V to power disk drive motors
> or something, is there anything at all that operates on anything
> close to 20V?

** The internal 14.8V battery.


   ...   Phil

On Fri, 23 Nov 2012 21:55:11 -0800, David Harmon <source@netcom.com>
wrote:

>The new Lenovo laptop I bought comes with an AC to 20V DC
>external power converter.  Why such a high DC voltage?  I would
>expect that most of the circuitry in there operates on 5V or even
>3.3V.  While they may still need 12V to power disk drive motors
>or something, is there anything at all that operates on anything
>close to 20V?

The battery charger.

David Harmon a expos� le 24/11/2012 :
> The new Lenovo laptop I bought comes with an AC to 20V DC
> external power converter.  Why such a high DC voltage?  I would
> expect that most of the circuitry in there operates on 5V or even
> 3.3V.  While they may still need 12V to power disk drive motors
> or something, is there anything at all that operates on anything
> close to 20V?

Hello,

Furthermore I think the screen CFL through an inverter or the screen 
LEDs TBC

With kind regards