SNVSB79A November 2018 – July 2019 LM25180
The 24-V output is DC stacked on top of the 5-V output as they share a common return connection. This enables lower secondary-to-secondary leakage inductance for better cross regulation and also reduced rectifier diode reverse voltage stress. Choose a primary-secondary turns ratio for the effective 19-V secondary based on an approximate 60% max duty cycle at minimum input voltage using Equation 38.
Set the turns ratio of the transformer secondary windings using Equation 39. The transformer turns ratio for both outputs is thus specified as 1 : 1.5 : 0.4.
Select a magnetizing inductance based on the minimum off-time constraint using Equation 40. Choose a value of 30 µH with a saturation current of minimum 2 A for this application.