What ratio for inductances in "LLC resonant converter"?

[eem2am]

Hello,

I have to do LED Driver from 370VDC Bus.

It is two series strings of LEDs, 100V and 0.5Amps for each string.

I wish to do LLC resonant converter to give me 180V from the 370VDC.

I will then switch the 180V with two buck LED drivers to give the 100V and 0.5A for each LED string.

I have read the two articles on LLC
https://www.fairchildsemi.com/onlineseminars/LLCresonantConverter.pdf
https://www.fairchildsemi.com/an/AN/AN-4151.pdf

....i am wondering what to make the ratio of Lr to Lm?
(Lr = resoant inductor
(Lm = magnetising inductor of transformer

Also, at what point does a "series LC resonant converter" become an "LLC resonant converter"......there seems to be essentially no difference between them

 

[chuckey]

"Also, at what point does a "series LC resonant converter" become an "LLC resonant converter"......there seems to be essentially no difference between them" . With the series LC circuit the transformer is part of the resonant circuit. With LLC, the leakage inductance and the C are the resonant components, the transformer is then fed by them, (even though the first L {leakage inductance} is actually part of the transformers construction)?
Frank

 

[eem2am]

thanks but are you sure?

i thought with LLC, the leakage , cap AND magnetising inductance are all part of the resonating circuit?

 

[inventor(y)]

Perhaps this app note from on semi might have the answer to your questions.

https://www.onsemi.com/pub_link/Collateral/AND8311-D.PDF