Match the power stage design to the modulator curves by ensuring that the boundary conduction mode (BCM – boundary of operation between DCM and CCM) point coincides with the minimum bulk-capacitor voltage at minimum line, at rated output power. This choice results in DCM operation at all line voltages for all loads up to continuous rated load, and minimizes power loss and EMC impacts due to output rectifier reverse recovery during CCM operation. This design choice allows operation to extend into the CCM region of operation as required to deliver the transient peak load.
To achieve this design target, the required primary magnetizing inductance, LPRI is calculated from Equation 25. In this equation, the value of FSW(nom) is 60 kHz, taken from the modulator curve region P3 to P4, in Table 5. The value of VBULK(min) is the value that occurs with the actual used bulk capacitance of 127 μF.
This calculates a value of 257 μH. Round the value to 260 μH.