An ideal inductor would have zero capacitance and zero resistance.
The Figure below shows a graph of inductive reactance versus frequency . Inductive reactance increases linearly with frequency.
Figure: Inductive reactance vs frequency (ideal inductor)
A real inductor can be modeled by the following elements:
- a series inductor
- a series resistor or : The resistance of the inductor winding measured using DC current. The resistance in a component due to the length and diameter of the winding wire used. It represents the DC copper loss (due to DC resistance) of the wire.
- a parallel capacitor or : It is the distributed capacitance between the turns of the wire and is derived from the Self Resonant Frequency ().
- a parallel resistor : It represents the magnetic core loss of the inductor core.
The figure below shows a real-life impedance vs frequency graph.
Figure: Inductive reactance vs frequency (real inductor)
Self-Resonant Frequency (SRF) or in Hz: This is the frequency at which the inductance of the inductor resonates with the inductor’s distributed capacitance . Increasing or lowers . Decreasing or raises .
- the inductor will act as a pure resistor,
- the input impedance is at its peak,
- the Quality factor of the inductor is zero,
- the reactance of the inductor is zero,
- the capacitance is given by
At frequencies below the reactance is inductive and increases as the frequency increases.
At frequencies above the reactance is capacitive and decreases as the frequency increases.