LLC Converter Qmax and M value

DC-DC Power Converters
1

Hello Guys
I design the llc boost converter but I do not understand Qmax and M values what value should I choose? Can I just choose those values depending on my gain at an input-output voltage or should I also think of the switching frequency of the MOSFET?
When I looked at some application notes they are chance Qmax values 0.3-0.5.
Thanks!

2

Hi,
I am no expert but your Qmax depends of how much u need boost voltage to nominal when your input is to low (it’s done via resonant circuit)

Qmax=(sqrt(Lr/Cr))/Rac

Rac it’s a impedance of your load in primary side of transormer.
Rac=(8/(PI^2))*(Np/Ns)^2 * ((Vout^2)/Po,max)

Po,max= maximum of output power
Np number turns of primary side
Ns number turns of secondary side
Lr inductance of rezonant coil
Lm inductance of magnetaizing coil

M it’s ratio Lr(resonant coil) and Lm (magnetization coil) it’s
M=(Lr+Lm)/Lr
approximately u need take this value in 6

I hope this will be helpful
Online you can take a lot of white papers to make LLC

Karol C.

3

Hello @aydin.berkay.ee ,

We have some great articles that explain how the LLC converter works. We also have a great LLC Design Tool that will aid in your design when provided system specs.
Understanding LLC Operation (Part I): Power Switches and Resonant Tank | Article | MPS (monolithicpower.com)
Understanding LLC Operation (Part II): What to Consider in LLC Converter Design | Article | MPS (monolithicpower.com)
LLC Design Tool | Monolithic Power Systems
Hope this helps!

Regards,
Jonathan