Llc resonant converter

AC-DC Power Converters
1

I am working on an LLC resonant converter design,
Lm=490µH,
Lr=90µH

image
image989×369 45.5 KB

My next step is to design the transformer.Could someone explain:

  1. What type of transformer is typically used after the resonant tank circuit in an LLC converter (UCC256404)?
  2. How are the transformer specifications determined (core type, turns ratio, winding details)?
  3. Are there any standard guidelines or reference methods for calculating turns, core selection, and wire sizing for LLC resonant converter transformers?

My smps is about 240W ,10A, 24V dc output and 240V AC input.

Any detailed explanation or reference material would be greatly appreciated.

Regards.

2

Hi @royal.animator69,

Thank you for posting to the MPS Technical Forum. Are you using an MPS LLC resonant converter for this application? Some of our LLC controllers such as the HR1002A come with excel calculation sheets that you can use to size your transformer for that specific application.

3

Yes @Isabella.FAE , I am using that tool but I have encountered a few issues:

In the above schematic, there is no resonant capacitor (Cr) and (Lm) shown.

Should this capacitor be placed in series or in parallel within the resonant tank?

I also need to design an auxiliary winding for the LLC converter like the schematic.

How should I calculate the number of turns and design parameters for this auxiliary winding?

Are there specific guidelines to ensure proper voltage levels and isolation for auxiliary supplies?

Any detailed explanation, design formulas, or reference material would be greatly appreciated.

Regards

4

Hi @royal.animator69,

The resonant capacitor is placed in series with the resonant inductor Lr. The applications section of our LLCs’ datasheets also provide formulas for calculating some of the parameters including the transformer turns ratio and core size, and the values for Lr, Cr, and Lm based on the optimal operation of the specific converter.

For more generalized information about LLC converters, we have some informational pages such as the Understanding LLC Operation and Designing LLC Converters pages that go into more detail about the working principles of LLC converters.