External power supplies and DC to DC converters for powered  parts - Page 1
Forum section: electronics / beginners

author: Horizons
author_rank: Newbie
timestamp: September 11, 2017, 10:02:41 am
content: Hello,Part one :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 GPUand 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.Part Two :Graphic Cards power ..As we all know , most mid range to high end Graphics cards needs more power , and they come either with a 6 pins 12 v plug or 8pins 12V plugs for more power it needs (150 watts to 250 watts)My question is : If I use an external power supply of 12v outputs and plugged it into the Graphic cards direclty , would it work ? or is it better to use the 19.5V notebook external power supply and add a DC to DC converter from 19.5 to 12V and then plug it into the card?and in case the 12V works , does it need some kind of Board to make that 12V inline with the card voltage specs ? for more stabe 12V ? or is it Standardized and it will be within specs ?some cards like the GTX 1070 needs 150 watts 12V input , and some like the 1080 , 180 Watts , and the 1080 Ti 250 watts.I can find 150 watts external power with 12V output , but sadly anything more than this outputs 19.5 and needs DC to DC board ... example the DELL Notebooks power supply of 330 watts outputs 19.5 volts ...Part Three :some ATX power supplies come modular , and my question is : lets say I use just one 12V plug and ignore the other plugs , can I use the whole wattage from that single plug ? or is there a limitation of each plug watt?They say it is single Rail (meaning watt is not divided between Vi) but I am concerned about the plug wattage and the wires if they can stand it or not.Example : I need to power a graphics card of 300 watts .. and I use an ATX power supply with single rail of 350 watts ... the power supply has the motherboard connectors that I will not use , and has only one PCIe 6 pin plug for card .. but since I am not using it for mother board , can I use one port for the whole 300 watts or do I need to take 12 V from the Motherboard plug ?I can use thicker wires for 300 watts , if the plug on the power supply can stand 300 watts ..more over , on the PCB of the power supply itself , does it stand 300 watts since it is a single rail or must also be divided between plugs ?Thanks for your replies .

author: jeroen79
author_rank: Frequent Contributor
timestamp: September 12, 2017, 01:49:41 am
content: Notebooks run on batteries and 19,5 volts is just a few convenient volts higher than 4 fully charged Li-Ion cells in series.You could possibly power a GPU from a separate power supply as long as it uses the same ground.I'm not to sure if it'll take 19,5V.An ATX power supply will have a sticker on the side detailing what current and power can be taken from each rail individually and the power supply as a whole.