Inductor Calculator

Understanding Inductors

An inductor is a passive electronic component that stores energy in a magnetic field when current flows through it. Inductance (L), measured in henrys (H), quantifies how much voltage the component generates in opposition to changes in current: V = L × dI/dt. This property, known as self-inductance, is the magnetic analog of capacitance. While a capacitor resists voltage changes, an inductor resists current changes. Together, they form the foundation of all analog signal processing and power conversion circuits.

This calculator provides four modes: calculating energy stored (E = ½LI²) for a given inductance and current, series and parallel combination totals, and the RL time constant (τ = L/R) that determines how quickly current builds or decays in an inductor-resistor circuit.

Energy Storage in Inductors

The energy stored in an inductor's magnetic field is E = ½LI². Unlike capacitors where energy depends on voltage squared, inductor energy depends on current squared. This stored magnetic energy is the operating principle of switching power supplies: during one phase, the inductor stores energy from the input; during another phase, it releases energy to the output at a different voltage. Boost converters, buck converters, and flyback transformers all rely on this cycle.

Series and Parallel Combinations

Inductors combine like resistors: in series, inductances add (L_total = L₁ + L₂ + ...), and in parallel, the reciprocals add (1/L_total = 1/L₁ + 1/L₂ + ...). These formulas assume no magnetic coupling between inductors. If inductors are close enough for their magnetic fields to interact (mutual inductance), the formulas must be modified. Transformers deliberately exploit mutual inductance between coupled coils.

RL Time Constant and Transient Response

In an RL circuit, the time constant τ = L/R determines the exponential rate of current change. After one time constant, current reaches 63.2% of its final value; after three, 95%; after five, 99.3%. This transient behavior is critical in relay driving circuits (where voltage spikes occur at turn-off), motor control, and filter design. A snubber diode is typically placed across an inductor to safely dissipate stored energy when the circuit is interrupted, preventing damaging voltage spikes.

Frequently Asked Questions

What is inductance?

Inductance (L) in henrys measures opposition to current changes. V = L dI/dt. More turns, larger area, and magnetic cores increase inductance.

How much energy does an inductor store?

E = ½LI². Energy is stored in the magnetic field and depends on current squared. Released when current decreases.

How do inductors combine in series and parallel?

Series: L_t = L₁ + L₂. Parallel: 1/L_t = 1/L₁ + 1/L₂. Same behavior as resistors (assuming no mutual coupling).

What is the RL time constant?

τ = L/R. After 1τ current reaches 63.2% of final value, 3τ reaches 95%, 5τ reaches 99.3%. Determines transient response speed.

What are common inductor applications?

Switching power supplies, RF tuning, transformers, EMI filters, motors/generators, and chokes for blocking high-frequency noise.