Air Core Transformer & Ferrite Core Transformer

Question

What is the differnce between a transformer having ferrite core and another transformer without any core (air core transformer).How these two affects the output power and leakage flux??

Answer 1

The main reasons ferrite cores are used are: -

• They contain the magnetic field better than air preventing coupling to other circuits
• Higher value inductances can be made with much less copper - trading off copper loss with core loss gives the designer more options.
• Coupling of two or more windings is more effective (should this be required)
• Ferrite solutions (when applicable) are usually physically smaller than air.

The main reasons ferrite cores are not used are: -

• Permeability drifts with temperature hence air cored inductors are more stable in some applications
• Air cores don't saturate and produce 3rd order harmonics like ferrite. Useful, unless you are designing a saturable reactor of course.
• For tuned circuits in the VHF and above, ferrites are too lossy in some applications.

These are the main pros and cons.

Answer 2

Consider the two scenarios.

Without a core, the magnetic field strength is determined by #loops and the current (And many other factors - shape, design, resistance, but we're assuming they're identical for both transformers)

With a ferromagnetic core (Like e.g. Ferrite), applying a magnetic field will induce magnetism in the core, which will increase the magnetic field strength, which will induce magnetism in the core, which will...

As such, you can get a higher field strength from the same current with a ferromagnetic core.