AN993 Datasheet, PDF (23/27 Pages) STMicroelectronics – Electronic ballast with PFC using L6574 and L6561

AN993
Figure 21. Operating transfer function
Vlamp
Vin
Design tips
freq
f = f(L,C,rr) fmin
AM01329v1
If one of these conditions is not verified, the evaluation process has to be redone changing
the initial hypothesis (frequencies or assumption on the Cb ripple). If everything concords,
the values found can be used and a preliminary stage of design can be concluded. Further
experiments may be required and the initial assumptions may need to be verified to correctly
set the components and frequency values, and if necessary another evaluation process
reiterated with better assumptions.
The following flow chart can help the iteration process.
Figure 22. Iterative process
DATA:
operating lamp elec.characteristic
HVB
HYPOTHESIS:
fmin
Cb
L evaluation
DATA:
ignition and preheating lamp elec.characteristic
HYPOTHESIS:
fpre
C evaluation
Transfer preheating funct.
OK
Transfer operating funct.
OK
check on board
OK
AM01330v1
Doc ID 5656 Rev 10
23/27