Introduction

The inductive solutions section of Bourns University will to give you a comfortable understanding of what makes these components work.

We'll begin with a single, straight wire with a resistor in it. If a wire is connected to a battery, current begins to flow at a constant rate from one terminal of the battery, through the wire and resistor, to the other terminal of the battery. (Figure 8.1) This is known as DIRECT CURRENT (DC). The current maintains the same level until the battery weakens.

DC Current from Battery Figure 8.1	AC Current from Outlet Figure 8.2

Now, let us connect the wire with the resistor to an outlet in a typical home. (Figure 8.2 - Only an example- please do not try at home.) The current coming out of this outlet is constantly changing from a high, positive value to a high, negative value and back again in a sine wave. This is known as ALTERNATING CURRENT (AC). (Figure 8.3)

AC vs DC Waveform Figure 8.3

Changing current passing through a wire creates a magnetic field. (Figure 8.4) This current can be alternating between positive and negative, or it can be increasing or decreasing from an existing value. Constant current (DC) will not create a magnetic field. We refer to Figure 3 for the following explanation of what happens to a wire as AC current is passed through it.

Wire with Magnetic Field Figure 8.4

At point "A" the current is at its highest negative value. As it increases along the slope "B," the changing value of current creates a magnetic field around the wire. As it reaches the highest positive value at "C," the current begins to change value in the opposite direction. The existing field collapses and a magnetic field is built in the opposite direction as current continues to change along the slope "D." Current continues to change value until we reach "E" and the cycle begins again.

In brief, a magnetic field is created only when the value of the current is changing. The field increases in one direction when the value of the current increases in a positive direction. It increases in the opposite direction when the value of the current increases in a negative direction. (Figure 8.5) A field will not be created by constant, unchanging current (DC).

1) Current begins to flow	2) Current reaches maximum
1) Current begins to flow in opposite direction	2) Current reaches maximum flow in opposite direction
Field Created by Alternating Current Figure 8.5

In a straight wire the field surrounding the wire is weak. However, if we wind the wire around a core (usually a metallic material), the lines of the field overlap and are concentrated into a much stronger magnetic field. (Figure 8.6) This coil with the strong magnetic field is an INDUCTOR.

Coil showing lines of magnetic field (Coil on left; cross-section through coil on right) Figure 8.6

The strength of this magnetic field is measured in Henries. (Joseph Henry was an American scientist who discovered principles of electromagnetism.) An inductor with the strength of one Henry is quite large. The applications in which Bourns' inductive products are used do not require such an intense field. The inductance of Bourns' products is measured in nanohenries (nH = 1/1,000,000,000 Henry), microhenries (uH = 1/1,000,000 Henry), and millihenries (mH = 1/1,000 Henry).