Operational frequencies

AN2530

6/13

2

Operational frequencies

Figure 3 shows a gray area with a note "optional". This rectifying stage is not really

necessary as it was done for testing and measuring purposes.

More explanations and clarifications are provided as we go through this design.

Much of the basis for this application note was taken from another ST application note,

mainly AN1660 (ZVS resonant converter for consumer application using L6598 IC), which is

a 180 W ZVS resonant converter. As stated in AN1660 (ZVS resonant converter for

consumer application using L6598 IC) you must "choose" some operational parameters that

are recalculated after real component values have been chosen. Only your experience with

this kind of SMPS can guide you.

For this case the following values have been chosen:

●

●

●

to the driver's maximum operational frequency. Therefore, we leave the converter much

"room" to change its operational frequency (via the feedback) so the regulation does not

suffer because of a range that is too restrictive.

below:

Equation 1

Equation 2

Equation 3

Equation 4

Rf

min

1.41

F

min

C

f

•

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

91.56 K

Ω

=

=

(

∼100 kΩ)

Rf

start

1.41

F

start

F

min

–

() C

f

•

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

27.27 k

Ω

=

=

(

∼27 kΩ)

F

min

1.41

Rf

min

C

f

•

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

64.09 kHz

=

=

F

start

1.41

Rf

start

C

f

•

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

F

min

237.4 kHz

=

+

=