This LT3758 schematic shows a non-isolated flyback converter that operates from a 36V to 72V input voltage and provides a 12V output with 1.2A of current. The high input voltage can be applied directly the IC, without requiring a series resistor or bias voltage. This is due to the LT3758 being able to accept input voltages up to 100V. An isolated flyback can be accommodated with the addition of an optocoupler and the LT4430 optocoupler driver.