🧲 Inductors in Real Life — Practical Design and Selection

An inductor is simply a coil of wire. When current flows through it, a magnetic field is created around the coil.

The key behavior:

• Inductors oppose changes in current
• Faster current change → stronger opposition

This opposition is called inductive reactance, and it depends on frequency.

Unit: Henry (H)
Common values:

• $$\mu H$$ (microhenry)
• $$mH$$ (millihenry)

The inductance value determines how strongly an inductor resists current change.

• Small $$L$$ → weak opposition
• Large $$L$$ → strong opposition

Inductance depends on:

• Number of turns
• Coil geometry
• Core material

Like capacitors, inductors come in standard values, chosen during circuit design.

Unlike capacitors, inductors rely heavily on core material.

Core Types and Behavior

Ferrite cores dominate modern power electronics due to their efficiency at high frequencies.

Real inductors are not lossless.

Main loss mechanisms:

1. DC Resistance (DCR) — wire resistance
2. Skin effect — current crowds outer conductor at high frequency
3. Core losses — hysteresis and eddy currents

Copper loss:
$$
P_{copper} = I^2 \times R
$$

Core loss increases rapidly with frequency and flux density.

Magnetic cores have a saturation limit.

When current exceeds the saturation current:

• Inductance collapses
• Current spikes
• Heat rises rapidly

This is a common cause of SMPS failure.

👉 Always select:
$$
I_{sat} \ge 1.5 \times I_{max}
$$

Inductor impedance increases with frequency:

• Low frequency → almost short circuit
• High frequency → blocks current

This makes inductors perfect for:

• Low-pass filters
• Noise suppression
• Chokes

However, parasitic capacitance causes self-resonance, beyond which the inductor stops behaving ideally.

The Q factor measures how efficient an inductor is.

Definition:
$$
Q = \frac{X_L}{R}
$$

• High Q → low loss, sharp resonance
• Low Q → high loss, damping

Used heavily in:

• RF circuits
• Tuned filters
• Oscillators

• Choke Coils: Noise suppression
• Filter Inductors: Power smoothing
• RF Inductors: High-Q, low loss
• Power Inductors: High current, SMPS use

Each type is optimized for specific current, frequency, and loss constraints.

Inductors introduce practical challenges:

• EMI radiation
• Noise pickup
• Voltage spikes during switching

Inductive kickback voltage:
$$
V = L \frac{dI}{dt}
$$

This is why:

• Flyback diodes
• Snubbers
• TVS diodes

are essential with inductive loads.