This document describes how the NCP 1216A controller can be used to design a DC/DC single−ended forward converter suitable for telecommunication applications. The requirements for the converter are as follows: − Input voltage range from 36 V to 72 VDC − Continuous output power greater than 30 W for a 12 V output voltage − Small PCB dimensions − Efficiency greater then 85% − Input to output isolation voltage of 1500 V The NCP1216A controller is an attractive solution for this application, due to the following features: • 50% Maximum Duty Cycle Operation Forward converters usually limit the maximum duty cycle to 50%. Since the voltage reset is constrained to be equal to the input voltage (1:1 reset ratio), it is not desirable to exceed 50% DC to avoid saturating the transformer core. • No Auxiliary Winding Operation The DSS (Dynamic Self−Supply) function allows the NCP1216A derive power directly from the HV line without having to supply VCC either from the secondary output inductance (creepage distance and isolation issues) or via an auxiliary winding delivering a variable voltage of N x Vin. • 500 mA Peak Current Capability The NCP1216A can drive a MOSFET directly without any additional driver stage. If the selected MOSFET gate charge would overload the DSS capability, then an auxiliary winding could be used solely to supply the driver pulses.