How power works in pc

[Guest]

When we switch on a PC, how/what way the power moves from one component to another? please suggest me the components in order.
Regards
MB

 

[Herr_Koos]

Each component has its own power connector, so... All at the same time?

Seriously though, why would you need to know this?

 

[Guest]

Hi Herr,

My is friend is doing a course on mother board, he raised this question to know the power activities in PC. Please advise

 

[ghnader hsmithot]

Well what do you need to know specifically?Nothing wrong with a question or two.
Below are some basics.
http://www.howstuffworks.com/power-supply.htm

Any Other questions just ask.

 

[jsc]

Herr_Koos is pretty much, but not quite, correct. Everything plugged directly into the PSU is going to power up at the same time. Unfortunately, the CPU and memory are not plugged directly in to the PSU. They both get their power from motherboard power regulators. So they are going to follow the rest of the system by a few milliseconds.

Even then, although the CPU has power applied to it, it will not boot until it receives a control signal from the PSU called something like "PowerOK" (pin 8, gray wire). This goes to 5 volts after the PSU outputs have stabilized. This usually takes 200 - 300 milliseconds.

This signal removes a hardware reset, enabling the CPU to boot.

 

[hunter315]

Most components in the system are directly connected to their power source, like Hard drives, and Optical drives with their power connector. On a modern system a CPU gets all its power from the 4/8 pin connector near it, that goes to its voltage regulation circuitry(all the capacitors, ICs and chokes around the CPU). The 24 pin motherboard connector feeds a variety of things, it feeds 75W to any PCI-E connector, some power for the ram, and power for the chipset and any other onboard components, the power is send through traces on the motherboard, if you find one that you can see the traces on the power ones tend to be much fatter than the signal traces making them easier to find and follow.

As for how the PSU knows when to turn on, the green wire on the 24 pin main connector is held up to +5V by the power supply when the system is off, it has a very low current rating and really only serves as a signal wire, when the system is turned on the motherboard shorts this wire to ground dropping the voltage of this wire inside the power supply indicating it needs to power up all the systems.



Thats simplified power distribution, if you want more complex Hardware Secrets has a couple of good articles about the VRMs near the CPU, the anatomy of a power supply, and a few other power related ones.

 

[gomarcool]

Herr_Koos is pretty much, but not quite, correct. Everything plugged directly into the PSU is going to power up at the same time. Unfortunately, the CPU and memory are not plugged directly in to the PSU. They both get their power from motherboard power regulators. So they are going to follow the rest of the system by a few milliseconds.

Even then, although the CPU has power applied to it, it will not boot until it receives a control signal from the PSU called something like "PowerOK" (pin 8, gray wire). This goes to 5 volts after the PSU outputs have stabilized. This usually takes 200 - 300 milliseconds.

This signal removes a hardware reset, enabling the CPU to boot.

Trying to get clear on the voltage on the gray pin. Mine goes to 4.00 volts and computer does not boot. I get
three long beeps sometimes other times various beeps. AIM bios. The other voltages are within spec.