Linear power supply vs SMPS (losses in transformer)

Question

We know that, in a power supply, there are always losses taking place.

If we have a linear power supply, the major source of loss is the core loss in the transformer.

But in an SMPS, where we have a very high frequency voltage passing through the transformer, there are two main sources of loss

1. the switching element, usually a Mosfet of a power transistor and
2. the losses in the transformer.

To reduce the losses in the switching element, in this case being the Mosfet, there are two types of mosfet's : Trench type and Lateral type.

Now, coming back to the losses in the transformer, how do we calculate the different losses in the transformer, for a particular power supply (Linear power supply and SMPS).

Also, what are the different losses taking place in the transformer, when it is connected to a linear power supply, and when it is connected to an SMPS.

Also, how do we overcome these losses.

I read at a few different places stating two different things, being :

1. The core losses and the eddy current losses in a transformer are proportional to the frequency of the incoming wave, i.e., the core losses are directly proportional to the frequency, and the eddy current losses are directly proportional to the square of the frequency of the incoming frequency.
2. Another site states that, even though we can see that, from the equation of eddy current losses, that it is directly proportional to the square of the frequency of the incoming wave, but, it actually depends on the supply voltage.

So, what are the actual factors affecting the losses in a transformer, when we are connecting it to a linear power supply as compared to when it is connected to an SMPS.

Also, how do we decide about the trade off between the losses of the two systems, so as to select a particular supply for a particular application, considering the major factors, such as cost efficiency and and the efficiency of the system, given that the size is not an issue.

(NOTE : the SMPS in the above question is an Isolated toplogy, hence the transformer.)

Also, what are the different methods that can be used to isolate the supply, other than a transformer, if there is any better option.

Also, other than mosfet's and power transistors, (if any) is there any other switching device that can be used to provide switching to the SMPS. (which may have more or less switching losses).

Answer 1

If you want a truly optimized converter and/or compare different topologies directly, this is one way how it is done:

In an overall system optimization, you are taking into account losses of all relevant components, especially power semiconductors and inductors and transformers. You start with a topology, then calculate losses, size and cost estimate (BOM) of the whole converter for a given parameter set (e.g. switching frequency, transformer core material, power semiconductor...). You loop through a large number of parameter sets, sort out designs which don't fit the specs, and look for the best compromise in e.g. cost vs. efficiency ("Pareto optimization").

It is complex and time-consuming. Getting the right models is not trivial, and one has to find a compromise between model accurracy and model complexity. You would have to employ a circuit simulator and an inductor/transformer design tool.

Here is one typical converter optimization example: Google Little Box Challenge, see Fig. 10 for the general procedure and Fig. 12 for typical results.

If you want to compare different topologies (referring to your question), you have to run the system optimization procedure for the different topologies, with different semiconductors, different transformer core materials, and so on, and compare the best solutions directly.