Working principle HF transformer

[Peter_1]

Anyone noticed yet the High Frequency transformers - sometimes called switch mode HF transformers - you see on the PCB's of nowadays electronic equipment?

This is one and

This is a type you often see in AC's

In every decent AC, you will find some of these.

Sometimes a 2 kW transformer is crunched in a housing of only 2 inch high on a footprint of only 3 x 2 inch and it weighs almost nothing compared to a normal transformer.
A normal 2 kW transformer is a real heavy peace of copper and iron

Does anyone know of a link of the working principle?

[NH3LVR]

Sounds like one our friend Star882 could answer!
Not my area of expertise, but here goes.
I copied this from the link below.
http://mrtmag.com/mag/radio_switching_vs_linear/
The basic technology behind switching transformers is: As the rate of change of the magnetic field increases in the transformer (i.e., increase in switch frequency), the transformer can be made smaller with smaller cores and wires to produce the same output power. Lighter core materials such as ferrite can be used instead of laminated iron. The resulting transformer assembly becomes much smaller and lighter than its linear counterpart.