Understanding Inductors

An inductor is an electronic component that stores energy in a magnetic field when electric current flows through it. Made from a coil of wire, often wound around a core material, inductors oppose changes in current flow - a property called inductance. They are essential in power supplies, filters, radio circuits, and countless other applications.

Objectives

• Understand how inductors store energy in magnetic fields
• Apply Faraday's Law and Lenz's Law to inductor behavior
• Calculate inductance in series and parallel configurations
• Work with RL time constants for circuit analysis
• Identify different types of inductors and their applications
• Understand back-EMF and implement proper protection circuits
• Safely handle inductors and inductive loads

Key Takeaways

• Inductors store energy in magnetic fields (E = ½LI²)
• V = L × di/dt - voltage opposes changes in current
• Current through an inductor cannot change instantaneously
• Series inductors add; parallel inductors combine reciprocally
• RL time constant is τ = L/R (note: L/R, not L×R)
• Inductors pass DC but increasingly block higher frequencies
• Back-EMF is dangerous - always use protection circuits with inductive loads
• Core material determines frequency range and saturation characteristics

Theory

Inductors in Series

Series inductors add directly (like resistors), assuming no magnetic coupling between them.

L_total = L1 + L2 + L3 + ... + Ln

Inductors in Parallel

Parallel inductors combine like parallel resistors (reciprocal sum), assuming no coupling.

1/L_total = 1/L1 + 1/L2 + 1/L3 + ... + 1/Ln

Applications

• Switching Power Supplies: Store and release energy each switching cycle (buck, boost, flyback converters)
• EMI/RFI Filtering: Chokes block high-frequency noise while passing DC power
• LC Filters: Combined with capacitors for frequency-selective filtering
• RF Circuits: LC tanks for oscillators, tuned circuits for radio receivers
• Transformers: Coupled inductors for voltage transformation and isolation
• Current Limiting: Ballasts for fluorescent lights, inrush current limiters
• Energy Storage: Temporary energy storage in welders, pulsed power systems
• Sensors: Inductive proximity sensors, metal detectors, LVDT position sensors

Practice Problems

Problem 1: A 10mH inductor has current changing at 500 A/s. What voltage is induced?

Problem 2: How much energy is stored in a 100mH inductor carrying 2A?

Problem 3: Three inductors (10µH, 22µH, 47µH) are in series. What is total inductance?

Problem 4: Two 100µH inductors are in parallel. What is the equivalent inductance?

Problem 5: A 50mH inductor is in series with 100Ω. What is the time constant?

Problem 6: What is the inductive reactance of a 100µH inductor at 1 MHz?