ICE3BR0365 Datasheet, PDF (13/16 Pages) Infineon Technologies AG – Design Guide for Off-line Fixed Frequency DCM Flyback Converter

DCM Flyback
Design Note DN 2013-01
V1.0 January 2013
STEP 4:
Flyback reflected voltage (VR) and the Max VDS MOSFET voltage stress: For a 650V MOSFET on
ICE3BR0665 CoolSET, VR is chosen at 75V Assuming 30% leakage spike the expected maximum VDS is equal
to:
STEP 5:
Determining Dmax based on Vreflected and Vinmin:
STEP 6:
Calculating primary inductance and primary peak current:
STEP 7:
Choosing the proper core type and size: Using the table outline on Step 7, we can use EE20/10/6
ferriite core for this 25W power level
Core: EE20/10/6 Ferroxcube/TDK
Cross Sectionl Are, Ae=32mm2
Core Material: 3C96/Ferroxcube, TP4A/TDK
Bobbin:E20/10/6 coil former, 8 pins
STEP 8:
Determining minimum primary turns:
STEP 9:
Determine the number of turns for the secondary main output (Ns) and other auxiliary turns (Naux):
Note: Round off non integer secondary value to the next integer value, in this case Ns =11. Using this setup
(Np/Ns=65/11) VR is decreased a bit, we can used this value or increase the primary turns to get the same VR as
assumed. In this case we will adjust Np to 66 turns to maintain the same VR. Even turns is also desirable on the
primary for low leakage split primary winding construction, with the same turns in each section.
An auxiliary winding, Naux, on the primary is needed for the VCC supply. For ICE3BR4765 an internal HV startup is
used to supply the initial bias before Vaux kicks in. We set Vaux at 15V to be above 11.2V max turnoff voltage.
STEP 10: Determining the wire size for each output windings: The RMS current on each winding is calculated
using Equation 11-13:
From Table 6 we can use: AWG 29-Primary, AWG22-Secondary, AWG 34-Auxiliary winding*
13