AN2450 datasheet(24/35 Pages) STMICROELECTRONICS

24 / 35 page

Design procedure

AN2450

24/35

DocID12784 Rev 6

–

Step 3 - calculate the maximum normalized operating frequency (according to the

definition):

Equation 57

–

Step 4 - calculate the effective load resistance reflected at transformer primary

side, from Equation 14 on page 7 and Equation 17 on page 7:

Equation 58

–

Step 5 - impose that the converter operates at maximum frequency at zero load

and maximum input voltage, calculating the inductance ratio from Equation 38 on

page 15:

Equation 59

–

Step 6 - calculate the max Q value to work in the ZVS operating region at

minimum input voltage and full load condition, from Equation 37 on page 15 and

Equation 46 on page 18:

Equation 60

–

Step 7 - calculate the max Q value to work in the ZVS operating region at no-load

condition and maximum input voltage, applying Equation 50 on page 18:

Equation 61

–

Step 8 - choose the max quality factor for ZVS in the whole operating range, such

that:

Equation 62

fnmax

fmax

-----------

Rac



------n

2Vout

Pout

--------------



1Mmin

–

Mmin

----------------------

fnmax

–

--------------------------



Mmax

--------------





---

Mmax

–

--------------------------

Qmax 95



Qzvs1

Qzvs2



---

f

nmax

 1

f

nmax



–

--------------------------------------------

RacCzvs

----------------------

Qzvs min Qzvs1 Qzvs2

}



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