I wonder if any body knows about the typical current derived from power supply of a regular desktop computer(PC). I know it supplies different voltages and for each, motherboard or peripherals may absorb different currents...
Posted on 2010-05-17 21:29:50 by logicman112
Posted on 2010-05-17 22:02:20 by SpooK
Are you literally looking for current, as opposed to power/wattage?

If so, you can get a rough idea of the current by dividing the wattage by the voltage. However, when it comes to inductors and capacitors, both of which you'll find in a power supply, the calculation is not as straight-forward as a purely resistor-based circuit.
Posted on 2010-05-17 22:08:05 by SpooK
thank you for the reply. My surprise is that CPU needs 130 Watt and the data-sheet of CPU mentions currents to 140 A! Does a power supply provide to 140 A in real?! 
Posted on 2010-05-17 22:17:39 by logicman112
Running 140 amps (watts / volts) of any significant voltage sounds like way too much for a nanometer-scaled CPU... I want to say that the CPU would simply start to melt from the sheer amount of heat generated.

140 watts (volts * current), however, sounds realistic for higher-end processors, as it would be around 12 amps at 12 volts.

In an idealistic calculation, a power supply with a maximum sustained rating of 500 watts could produce around 40 amps at 12 volts. At such a sustained capacity, you can probably double your computer as a space heater :lol:
Posted on 2010-05-18 00:02:10 by SpooK
140A in the CPU because of it's voltage of 1V.
the 12V from power supply is switched in a little SMPS near the CPU (capacitors, inductors, mosfets and diodes), to reach the value of 1V.
Posted on 2010-05-22 05:43:00 by edfed

Even at 1v, the cpu requires, and consumes, nothing like 140A.
Imagine how long your laptop battery would last if it was using 140 amps per hour!
I think a car battery produces about 100 amps per hour, for about 4 hours, to put that in perspective.

Posted on 2010-05-22 10:11:14 by Homer
Well, a quick Google search brought up the following:

The Intel Core 2 Duo processor requires a minumum of 8 Amps continuous and 13 Amps peak for 10ms on 12V2.

In which closely matches what I stated, in which is nothing more than basic electronic theory.

140A in the CPU because of it's voltage of 1V.
the 12V from power supply is switched in a little SMPS near the CPU (capacitors, inductors, mosfets and diodes), to reach the value of 1V.

I think you are confusing the "little SMPS near the CPU" for an AC transformer, when it is in fact closer to a basic DC voltage divider.
Posted on 2010-05-22 11:38:12 by SpooK
Battery life is specified at its nominal voltage. 70Ah @ 12V is equal to 840Ah @ 1V (minus the losses in the form of Joule-Lenz heat). Core 2 Duo voltage is ~1V and its rated maximum dissipated power varies from 65 to 100 W depending on the model. This means that a typical current is 65 - 100 A. I don't see any reason Why it would be something strange. Yes, the supply current is 8-13 A @ 12V. But that just means that it's 96 - 156 A @ 1V (minus the heat). And that's precisely what the specs for those CPUs say.
Dissipated current means NOTHING if you don't specify the voltage, because it's the POWER that matters.

Low impedance inside CPUs (and the resulting high current) is required for the gates to switch faster. That's why from one generation of CPUs to another you can see an increase in current and a decrease in voltage. GFX Cards on the slowest AGP operated at 3.3V and on the fastest one they operated at 0.8V and consumed more power than on the slowest one (therefore any currents in them were AT LEAST 4 times larger).

When we transfer electric power, we can transfer it in the form of high voltage / low current OR high current / low voltage.

It goes like this:

High voltage / low current pros: Low power losses due to heat, little skin effect and eddy currents in AC power supplies.
High voltage / low current cons: Unsafe for living beings.

Low voltage / high currents pros: Safe for living beings, allows to use very low impedances and thus decrease switching times
Low voltage / high currents cons: High losses in the form of heat, large skin effect and eddy currents in AC power supplies.

BTW: This also explains why the CPUs are so hot.
Posted on 2010-05-22 21:14:01 by ti_mo_n

Same stuff used on mobos. Many of the cpu pins are +Vdd and many are GND.
Transistor count gets doubled; but you can't make the parasitic capacitance be half of what it was, thus the only courses of action are to lower voltage and die-shrink (which lowers that parasitic cap.); and design ways to switch fewer transistors per cycle. (power drain happens only during switching, thanks to the parasitic capacitance - and only slightly to power the megaohm/gigaohm input impedance of each gate).
Mobile versions of cpus have designs to sacrifice some performance for battery-life;  all modern cpus have ACPI states C0..C3+;  
Laptops have a ~55Wh battery, which with active work you can drain in 30 mins, or for 10+ hours with less intensive tasks (short single UI interactions, effectively just the backlight and LCD drain the battery) .
Posted on 2010-05-27 10:29:17 by Ultrano