Motherboard Design Process - Page 5

..:: Processor Power Delivery - Component Background ::..

The topic of processor power delivery is one that brings about several misconceptions, and misunderstandings. Before I delve into the control aspects of the power delivery scheme for the processor, I’m going to quickly go over a few points to explain what the various components are, and what they are responsible for when it comes to the power delivery for the processor. First off, if you take a look at the image above, you’ll notice the line of small capacitors along the edge of the heatsink retention mechanism. There are also two light green “hoops” with a coil of wire wrapped around them, these being inductors. When these two electrical components are placed in a circuit and current travels though, you create an oscillator.

Several of you may, or may not be familiar with what an oscillator is, rather only have heard the term used and have an estimated understanding. In order for something to oscillate, the energy the system uses must be converted back and forth between two forms. Let’s take a weight attached to a spring hanging from some surface as an example. When you attach the weight to the spring and let it settle, the spring will extend down to a point where it reaches equilibrium. In this instance, it is where both types of energy are themselves equal to zero. If the weight is stretched lower from this point and let go, the system will no longer be in equilibrium and will begin to oscillate. When the weight is stretched, potential energy is added to the system, yet the kinetic energy remains zero because the weight is not yet in motion. When the weight is released, the energy of the system changes from completely potential to completely kinetic. Thus, we have created an oscillation. This same process must apply to a system of capacitors and inductors as well in order for it to create an oscillation. But how?

The two forms of energy involved in the example above were kinetic and potential. In a situation involving a capacitor and inductor, the energy of the system is stored in an electrostatic field and magnetic field. Capacitors store energy in an electrostatic field, while inductors store energy in a magnetic field. As you can now probably understand, in order for a system of a capacitor and inductor to create an oscillation, something has to happen in order to switch back and forth between the two forms of energy. To explain this, let’s first take a look at exactly how each of these devices themselves works, and how they store the energy needed for operation.

The way that a capacitor works and stores energy is rather simple. You see, inside the capacitor there are two metal plates called conductors that are separated by a dielectric. This dielectric can be anything from air to something along the lines of a ceramic substance. I won’t get too into it, but depending on the dielectric used to separate the two plates of a capacitor, the capacitance can vary greatly depending on the dielectric constant. When a capacitor is placed in a circuit, and charge is allowed to flow, as the current flows through the capacitor, the two plates within attain equal but opposite charges. Thus, an electrostatic field has been formed, and energy stored. The process is a little more involved of course, but you only need a basic understanding of the process.

The way that an inductor stores energy is just as involved as a capacitor, so I’ll only be giving you a cursory explanation for those who aren’t math or physics buffs. To put it plainly, an inductor is nothing more than a copper wire that is coiled around some material called the “core.” As with capacitors, the “core” material can greatly effect the overall inductance. The type of inductors that are readily seen on motherboards are what are referred to as “torodial” inductors. For those who aren’t up on their shapes terminology, this name comes about because the core of the inductor is in the general shape of a torus. The other important aspects that determine the capacity of the inductor are the length of the coil, the number of coils / how tightly packed the coils are, and the cross-sectional area of the coil. As a current begins to flow into this coil, a magnetic field begins to build up and temporarily the coil actually restricts current flow. Once the magnetic field has been completely built, current is then able to flow normally through the coil. When an inductor is placed in a circuit, and the circuit opened after it has been charged, the device in the circuit that is using the electrical energy will continue to work as the magnetic field slowly collapses and gives off the energy that has been stored.

Now that we have a generalized idea as to how each of these devices stores energy, let’s examine how they act when placed in a closed circuit together. Let’s say for example, that we have a capacitor that has been fully charged and we initially place it into the circuit. As soon as this happens, the capacitor will begin to discharge and the current will begin to flow around the circuit. As the current moves through the circuit, it will then come to the inductor where the magnetic field will begin to form. When the capacitor has been fully discharged, and the magnetic field built, the field will then immediately begin to collapse as the inductor will try to keep current flowing through the circuit. As the field collapses, the energy will then begin to recharge the capacitor and the process will repeat itself until the system runs out of energy due to resistance, unless of course periodically energy is added to the circuit to keep it at a given level. Thus, we have created an oscillator, an imperative factor in the power delivery for the processor.