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Inductance: Magnetic Fields and Energy Storage 🧲

An inductor is essentially a coil of wire — simple in construction, powerful in behavior.
When current flows through it, a magnetic field builds up around the coil.

👉 The big idea: an inductor stores energy in its magnetic field and hates sudden changes in current.

Try to stop the current suddenly, and the inductor fights back by generating a high voltage spike.

Inductance (L)​

Inductance measures how strongly an inductor resists changes in current.

L=N×ΦIL = \frac{N \times \Phi}{I}

Where:

  • L = Inductance (Henries)
  • N = Number of turns of wire
  • Φ = Magnetic flux (Webers)
  • I = Current (Amperes)
note

More turns, more flux, or a better magnetic core → higher inductance.

Common Inductance Units​

The Henry (H) is quite large for everyday circuits.

  • 1 Henry → Rare, bulky inductors
  • Millihenry (mH) = 10⁻³ H
  • Microhenry (µH) = 10⁻⁶ H
  • Nanohenry (nH) = 10⁻⁹ H
tip
  • Power electronics → µH to mH
  • RF / high-speed signals → nH
  • Motors & chokes → mH and above

Key Inductor Behavior​

Inductors behave very differently from capacitors:

  • Resist changes in current
  • At t = 0 → behaves like an open circuit
  • At t → ∞ → behaves like a short circuit
  • Generates large voltage spikes when current is interrupted
important

⚠️ Inductors don’t oppose current — they oppose changes in current.

Energy Stored in an Inductor​

Energy stored in an inductor is:

E=12×L×I2E = \frac{1}{2} \times L \times I^2

Example​

  • L = 10 mH
  • I = 2 A

E=0.5×0.01×4=0.02 JoulesE = 0.5 \times 0.01 \times 4 = 0.02 \text{ Joules}

note

Just like capacitors, current matters more — doubling current increases stored energy by 4×.

Where Inductors Are Used​

Inductors are everywhere in power and motion systems:

  • Switching power supplies (buck / boost converters)
  • Noise filtering on power lines
  • Energy transfer in motor drives
  • Current smoothing and surge protection

Dangerous Inductor Behavior ⚠️​

When you suddenly open a switch:

  • Current wants to keep flowing
  • The magnetic field collapses rapidly
  • A huge voltage spike is generated
  • Semiconductors, relays, or MCUs can be destroyed
warning

This effect is called inductive kickback — and it’s brutal if ignored.

Flyback Diode Protection 🛡️​

To protect your circuit:

  • Place a diode across the inductive load
  • The diode provides an alternate path for current
  • Energy is safely dissipated instead of creating a spike
tip

Rule of thumb:

  • Any relay, solenoid, motor, or coil → add a flyback diode
  • No exceptions.

Key Takeaway​

Inductors:

  • Store energy magnetically
  • Smooth and control current
  • Enable efficient power conversion
  • Can destroy circuits if mishandled

Respect the inductor — it always gets the last word. 😄