Designing Embedded Hardware, 2nd Edition

Inductors

Inductors are passive components that are essentially coils of conductive wire. The schematic symbol for an inductor is shown in Figure 4-38. Inductance is measured in Henries, with an equation symbol "L" and a unit symbol "H."

Figure 4-38. Schematic symbol for an inductor

The voltage across an inductor changes the current flow through it, measured with the following relation:

   V = L * dI / dt

Whereas applying a current to a capacitor caused the voltage to build across it, the opposite is true for an inductor. Applying a voltage across it builds current flow through it, and the resulting energy is stored in the inductor as a magnetic field. When the applied voltage is removed, the field collapses and returns the stored energy as a voltage spike.

Figure 4-39 shows a series R-L circuit.

Figure 4-39. Series R-L circuit

The voltage across the resistor (V_R) and the voltage across the inductor (V_L) are shown in Figure 4-40. When a voltage is applied at V_IN, the voltage across the resistor is initially small, whereas the voltage across the inductor is large. As the current flow through the inductor builds, the voltage across the resistor increases, while the voltage across the inductor diminishes accordingly.

Figure 4-40. Series R-L response to a step input

Figure 4-41 shows a series ...