Key Engineering Takeaways
- •An inductor is a coil of insulated wire that stores energy in a magnetic field whenever current passes through it.
- •Inductance (L) is measured in Henrys (H), millihenrys (mH), and microhenrys (µH).
- •Lenz's Law: Inductors resist any change in current. When current starts, inductors oppose the increase; when current stops, they create a high-voltage spike (Back-EMF) to keep current flowing.
- •Transformers transfer AC electrical energy between two isolated coils via mutual magnetic induction: Vp/Vs = Np/Ns.
- •Inductors are the vital active components in high-efficiency DC-DC Buck and Boost switching power regulators.
Prerequisites
- • Magnetic fields and AC/DC basics
Required Hardware / Tools
- • Toroid / Drum Core Inductor (100µH - 10mH)
- • Step-Down Mains Transformer
- • Multimeter
What is an Inductor & Electromagnetic Induction
When electric current passes through any conductor, it generates a concentric **magnetic field** around the wire.
By coiling the wire tightly into loops (often around an iron, ferrite, or air core), the magnetic field lines concentrate into a powerful unified magnetic flux. This component is called an **Inductor** (or Choke / Coil).
Unlike a capacitor (which stores energy in an *electrostatic field* and opposes changes in *voltage*), an inductor stores energy in a **magnetic field** and **opposes changes in current**.
Lenz's Law & Back-EMF Voltage Spikes
According to **Faraday's Law of Induction** and **Lenz's Law**, when current flowing through an inductor changes, the collapsing or expanding magnetic field induces a counter-voltage:
$$V = -L \frac{di}{dt}$$
If you have a $12\,\text{V}$ DC motor or relay drawing $1\,\text{A}$ and you suddenly open the switch in $1\,\mu\text{s}$ ($dt = 10^{-6}\text{s}$):
$$V = -(0.05\,\text{H}) \times \frac{-1.0\,\text{A}}{10^{-6}\text{s}} = +50{,}000\,\text{Volts!}$$
This massive instantaneous **Back-EMF spike** will produce a visible blue electrical spark across mechanical switches or vaporize driving transistors unless snubbed with a diode.
How Transformers Work: Step-Up & Step-Down Winding Ratios
A **Transformer** places two independent inductor coils (**Primary** and **Secondary**) around a shared iron core.
When AC current flows through the primary coil, its alternating magnetic flux couples through the core and induces an AC voltage in the secondary coil:
$$\frac{V_{\text{primary}}}{V_{\text{secondary}}} = \frac{N_{\text{primary}}}{N_{\text{secondary}}} = \frac{I_{\text{secondary}}}{I_{\text{primary}}}$$
- **Step-Down Transformer**: $N_p = 1000$ turns, $N_s = 100$ turns $\to$ Steps $230\,\text{V}$ AC down to $23\,\text{V}$ AC.
- **Step-Up Transformer**: More secondary turns $\to$ Boosts voltage higher.
Frequently Asked Questions
Do inductors work with DC current?
For constant steady-state DC, once the magnetic field stabilizes, an inductor acts like a simple piece of copper wire (near-zero resistance). It only exhibits inductive reactance when current is turning on, turning off, or oscillating (AC/PWM).
Tags:#Basic Electronics#Inductor#Transformer#Electromagnetism#Back-EMF#Magnetic Field#Henry