SNVSB79B November 2018 – May 2020 LM25180
Set the turns ratio of the transformer secondary windings using Equation 32, where NS1 and NS2 are the number of secondary turns for the respective outputs.
Choose a primary-secondary turns ratio of 1 : 1 for the 15-V output based on an approximate 60% duty cycle at minimum input voltage using Equation 33. The transformer turns ratio for both outputs is thus specified as 1 : 1 : 0.52.
Select a magnetizing inductance based on the minimum off-time constraint using Equation 34. Choose a value of 30 µH and a saturation current of 2 A for this application.
Find the maximum output current for a given turns ratio, assuming the outputs are symmetrically loaded, using Equation 35.