Inductors

An inductor is an electrical device that stores energy in the form of a magnetic field when current flows through it. Typically made from a coiled wire, it resists sudden changes in current and operates based on the principle of electromagnetic induction.

Key Features:

1. Magnetic Field Creation:

• • When current passes through a wire, it generates a magnetic field around the wire. An inductor enhances this effect by coiling the wire to concentrate the magnetic field.

2. Inductance (L):

• • Inductance is a measure of an inductor’s ability to store energy in its magnetic field. The SI unit of inductance is Henry(H). The more turns in the coil and the larger the coil’s core, the higher the inductance.

3. Energy Storage capability of Inductor:

• • An inductor can be thought of as a device that temporarily stores energy, but not in the form of electric charge (as capacitors do), rather in the form of a magnetic field. When current flows through the inductor, it builds a magnetic field around its coil. The energy is stored in this magnetic field, and when the current is interrupted, the collapsing magnetic field releases this energy back into the circuit.
  • The energy stored in an inductor is proportional to the square of the current flowing through it. It can be calculated by the formula:

Where,    E = Energy in Joule

           L = Inductance in Henry

                     I = Current in Ampere

4. Opposition to Current Changes:

• • Inductors oppose changes in the current flowing through them. When the current changes, the inductor generates a voltage (called back EMF) that resists the change. This property makes inductors useful in filtering and smoothing applications in circuits.
  • Lenz’s Law states that the direction of induced EMF always opposes the change that produced it. Therefore, inductance is the tendency of a coil to resist sudden changes in current.

5. Induced Voltage:

Where,    V = Voltage across the inductor

                    L = Inductance

                               dl/dt  = Rate of change of current

6. Time Constant in RL Circuit:

In an RL circuit (Resistor & Inductor based circuit), the time constant (𝜏) determines how quickly the current changes:

     Where,         𝜏 = Time Constant

                    L = Inductance

                    R = Resistance in Ohms.

Factors Affecting Inductance:

• Number of Turns: More turns in the coil increase inductance.
• Core Material: Magnetic cores (such as iron or ferrite) increase inductance.
• Coil Area: A larger cross-sectional area enhances the magnetic field, increasing inductance.
• Length of Coil: A shorter coil length (for the same number of turns) results in higher inductance.

Types of Inductors:

Inductors come in various types, each designed for specific applications based on their structure and materials. Most common types of inductors are listed below:

(i) Air-Core Inductors:

These inductors use air as the core material, meaning there is no solid core inside the coil.

• • Advantages: They don’t suffer from core losses (such as hysteresis and eddy currents) and are ideal for high-frequency applications.
  • Applications: Used in RF (radio frequency) circuits, high-frequency filters, and oscillators.

(ii) Iron-Core Inductors:

These inductors have an iron core inside the coil to increase the inductance.

• • Advantages: The iron core enhances the magnetic field, increasing inductance for a smaller coil.
  • Applications: Used in low-frequency applications such as audio equipment, power transformers, and AC power circuits.

(iii) Ferrite-Core Inductors:

These inductors use ferrite, a ceramic-like material with high magnetic permeability, as the core.

• • Advantages: Ferrite cores reduce energy losses and are excellent for high-frequency applications. They offer a good balance between high inductance and low core losses.
  • Applications: Commonly found in switch-mode power supplies, filters, and RF applications.

(iv) Toroidal Inductors:

Toroidal inductors have a donut-shaped core (typically made from ferrite or powdered iron) around which the coil is wound.

• • Advantages: Their shape reduces electromagnetic interference (EMI) because the magnetic field is largely confined within the core.
  • Applications: Used in power supplies, transformers, and noise suppression circuits.

(v) Laminated-Core Inductors:

These inductors use laminated layers of iron or steel as the core to reduce eddy current losses.

• • Advantages: The laminated core helps minimize energy loss, making them efficient for handling large currents at low frequencies.
  • Applications: Common in transformers, motors, and industrial power systems.

(vi) Variable Inductors:

These inductors have adjustable cores, allowing the inductance to be changed by moving the core or altering the number of coil turns.

• • Advantages: Their adjustability makes them useful for tuning circuits.
  • Applications: Used in radios, oscillators, and signal processing circuits where precise control of inductance is needed.

(vii) Multilayer Inductors:

Multilayer inductors consist of multiple layers of coils stacked together, often built on a ceramic base.

• • Advantages: They are compact and provide high inductance values in a small package.
  • Applications: Common in surface-mount technology (SMT) for compact electronics like smartphones, laptops, and other portable devices.

(viii) Choke Inductors:

These are inductors specifically designed to block or “choke” certain frequencies while allowing others to pass.

• • Advantages: They are excellent for filtering unwanted signals.
  • Applications: Used in power supplies, audio circuits, and EMI suppression.