Hello,

I have this Question ,

as we know , Most notebooks power adapters are 19.5V output.

While the CPU and GPU works on 12V and the SSD works on 5V . , so the motherboard should have two DC to DC power converters ,

one from 19.5V to 12V for CPU and GPU

and another From 19.5v to 5V for SSD nd harddrives.

mainly the notebook will never need 19.5 V .. so why dont they choose 12V Power supplies for notebooks in General and use 19.5 V power supplies ?

Why bother making two DC to DC inverters instead of just one ?

in case of 12V power supply , they already have 12V ready and just need a DC to DC converter to get the 5V for SSD.

keep in mind that internal desktop power supplies never outputs 19.5 V , it just outputs 12V and 5 V and 3.3 V ... now imagine this power supply external (lol) the place is not a big deal isnt it ?

so back to the main Q , Why all External power supplies used for PC outputs 19.5V and not 12V like in the internal ones ? it makes no sense.

 

The 19.5V is to charge the battery and also to power the device for mains use.

 

Why all External power supplies used for PC outputs 19.5V and not 12V like in the internal ones ? it makes no sense.

It makes sense to the engineers who design them.

Part of it has to do with the battery management and related power draws that will quite often create a moderate voltage drop between the power supply and the actual internal power management systems.
At full processing and related power draw plus while having a drained battery pulling its maximum power the internal power management system may only be seeing ~15 - 16 volts in the laptop due to power supply droop and line losses which would barely put its actual internal input voltage high enough to handle things.

 

The 19.5V is to charge the battery and also to power the device for mains use.

An Olivetti laptop brick I had was primary side voltage sensed and the regulation was bad enough to directly charge nickel chemistry batteries - I'm not entirely certain that wasn't what they were doing.