The core is of ferrite material, which has a high permeability. The coil may consist of a single-layer winding, a multilayer winding, or even several coils wound on the same toroid. (d) Schematic Symbol for Power Transformer ToroidĪ very common type of inductor is the toroid, a small doughnut-shaped coil, as shown in figure 4. Note the primary and secondary windings for transformers.įig.3: Transformers: (a) RF Transformer. Some typical transformer and their schematic symbols are shown in figure 3. TransformerĪnother popular type of inductor is the transformer, which can be used with power and audio frequencies as well as radio frequencies. Because of the high permeability of this kind of core, the inductance value can be made to vary over an appreciable range. The symbol for such a device is represented in figure 2 (c). Many RF coils have a ferrite slug or powered iron core inside the coil, which can be screwed in or out. No iron core is used at these frequencies.

(b) Schematic Symbol (c): Schematic Symbol for Coil with Adjustable Ferrite Core Typical radio frequency (RF) coils are shown in figure 2 (a), and the symbol is shown in figure 2 (b).įig.2: Radio Frequency Coil: (a) Typical RF Coil. Above the audio range (approximately 20 kHz), the losses in the core become too large to be practical. Inductors with iron cores are suitable for use only with a power line and audio frequencies. The two parallel lines beside the coil represent an iron core. You May Also Read: Inductor Questions and Answers A filter choke for a power supply is shown in figure 1 (a), and its symbol is shown in figure 1(b).įig.1: Iron Core Choke Coil: (a) Typical Choke.

High frequency inductor core