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PSUs 101: A Detailed Look Into Power Supplies

Inductors And Transformers


An inductor, or induction coil, stores electrical energy in a magnetic field. Inductors are used in many electronics and they play an especially important role in PSUs. An inductor is simply a coil of wire wrapped around a core (composed of iron, ferrite or simply air). Depending on their usage they have several names: coils, chokes, solenoids, etc.

So how do inductors work? The whole concept is very simple: when a current passes through an inductor, a magnetic field is created around the wire. Every change in current affects the magnetic field, which in turn induces voltage across the inductor. That voltage creates a current flow opposite of the initial current. This property is known as inductance (L) and it's measured in henries, which is a quite large unit of measure usually documented in millihenries (mH) or microhenries (μH).

Here are some interesting facts about inductors:

  • They store electrical energy in magnetic fields.
  • They act as an open circuit at first when DC (direct current) is applied to them, but after a while they freely allow it to pass.
  • They oppose current changes.


Now, let us take a quick look at transformers. Typically, inductors are shielded so their magnetic fields do not interact with other components in the same circuit. However, if we place two unshielded inductors side-by-side and feed one of them with AC (alternating current), then its magnetic field induces a voltage not only in the current inductor, but also in the other inductor. The process of inducing voltage in the second inductor is called mutual inductance. So if you pass current in one inductor you create voltage in the inductor near it.

A transformer is nothing more than two inductors, or coils, wound around the same core material in a way that mutual inductance is at a maximum level. The coil that lets the current pass is called a primary coil and the coil that is induced with voltage is called a secondary coil. A transformer can electrically isolate two circuits and also step voltages up or down.

Aris Mpitziopoulos
Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.