The calculations use the equations seen on pages 2 & 3 of AN-4151 by Fairchildsemi.com AN-4151 is prob the best beginner guide to LLC design. with LLC, it behaves just like a "standard transformer" when operated on load at the upper resonant frequency. ie Vs/Vp = Ns/Np. Remember that if you do half bridge LLC, then you vin is actually your input bus volts divided by 2. The lower resonant frequency is that frequency below which you must not go. Or else severe reverse recovery ensues. Also, you need to plot Vout vs freq for your design...locate the peak of this curve, you must not operate to the left of peak...ie no lower in freq. You will enjoy the LLC most if you are lucky enough to have a fixed vin and vout....because then you can get very low off and on sw losses. |
LLC with integrated transformer needs an airgap to set Lp for resonant operation. This has nothing to do with flyback.2. Do LLC transformers have an air gap? If so, why are the windings coupled together in the same direction? (dots on the winding). FlyBack stores energy. And I don't see how to collect it because the diodes on the secondary side are directed towards conduction.
Very good of you to go through derivation....to design LLC, you dont have to do that.
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