Motherboard Design Process - Page 8

..:: Inductors ::..

Another of the more common, and larger, components found on modern motherboards is that of an inductor. The type of inductor that is commonly used on a motherboard is what is known as a “torodial” inductor. There are several different types of inductors, however the main implementation is “torodial” inductors due to their high level of inductance for the amount of physical space that they require. Physically speaking, an inductor looks like nothing more than a donut-shaped object, surrounded in a long coil of copper wire. In essence, that is indeed all that a torodial inductor is. Inductors store energy in a magnetic field, and are passive devices. When inductors are placed into a series or parallel circuit with capacitors, they can be used to smooth out the incoming AC current to provide pure DC, and can serve as a core component of an oscillator.

The total inductance is directly proportional to the number of turns, or coils, that the inductor posses. The level of inductance also depends on the core material that is used, which is typically a ferromagnetic substance such as powdered iron, or laminated iron. Inductors can also utilize dielectrics such as glass, wood, plastic, or even air depending on the inductance needed. Air core inductors provide the least inductance, while the ferromagnetic cores provide the most, sometimes in the order of 500 to 1000+ times the inductance of an air core. The last important factor for inductance is shape. As was previously stated, there are several different types of inductor, all with their won pros and cons. Due to their shape, torodial inductors can offer much higher inductance than could a solenoidal inductor.

..:: Inductors - Physical Background ::..

Inductance is typically illustrated by the idea of a wound wire resisting any change in the electric current flowing through it. Stated in other words, inductance is the property of a circuit to store energy in an electromagnetic field. Inductance can be quite a difficult idea to grasp as it is based upon several ideas dealing with electromagnetic fields and Law’s such as electromagnetic flux, Ampere’s Law, Faraday’s Law, and Lenz’s Law. When Faraday’s Law is applied to an inductor, it states that a changing current through the inductor will produce a backwards electromotive force that opposes the change. This is also known as self-inductance.

This idea of self-inductance is useful in describing the uses of inductors as this property allows for absorption of sudden changes in current, similar to how capacitors are used to absorb sudden changes in potential. When there is a steady current flowing through an inductor, there will be no backwards electromotive force. In reality, inductors will never pure inductances due to inherent resistance and capacitance between the coil wires. The torodial inductors that are used in motherboard applications are used because they have little resistance in the coil itself. These inductors produces lines of electromagnetic force inward towards the center, and therefore do not need any exterior shielding to prevent it from interfering with operation of nearby circuits. Even though the inductors on motherboards are often placed very close to each other, there is virtually no interaction between them.

Inductors also go by another name on occasions where they are used to smooth out varying or pulsating forms of current. When inductors are used in this situation, they are referred to as choke coils. The term “choke” coil is used because the effect the inductor has in choking out variations in the current. Choke coils are typically found in audio and power frequency applications.