- Chip bead
- Common mode chokes
- 3-terminal filter
Inductors are passive devices, available in a wide variety of models and designs. Even if you pay a great deal of money, you won't find the ideal coil which fulfills all requirements. When selecting the right coil, you need to know what application you are going to use it for. Do you need to filter a data line or the main power supply? Is differential signaling involved? Are differential or common mode interferences the problem? The right inductor cannot be selected until you know exactly what it is needed for.
The simplest form of inductor is a piece of wire with inductance in a line undesirable in most cases and regarded as parasitic. The inductance of a wire varies in length and diameter. There are different options available to ensure that there is no need to install interminably long wires for high inductance values. The wires are wound in a coil to reduce the size of components, producing what is known as an air-core coil. If this is not adequate, the air is replaced by a coil core. This core determines inductance to a large extent based on its magnetization characteristics (hysteresis curve).
Inductance can be explained as follows: a coil has an inductance of 1 henry if a voltage of 1 V produces a current of 1 A after 1 sec.
If a capacitor is charged, for instance, it initially has low impedance and then gradually high impedance, i.e. a great deal of current flows initially, but stops once the capacitor is fully charged. A coil acts in completely the opposite way. Initially, only a little current flows, which increases over time. When the coil core reaches saturation level, it is limited by the ohmic resistance in the coil wire. As ohmic resistance is normally very low, this current can be very high and cause permanent damage to the coil.