The LT3748 is a high input voltage isolated flyback DC/DC controller that significantly simplifies the design of an isolated DC/DC converter. No opto-isolator, third winding or signal transformer is required for feedback, since the output voltage is sensed from the primary-side flyback signal during the off time of the power switch. The LT3748 operates over a 5V to 100V input voltage range, drives an external N-channel power MOSFET and can deliver up to about 60W. The LT3748 operates in boundary mode, which is a variable frequency current mode control switching scheme, resulting in ±5% typical regulation over the full line, load and temperature range. Boundary mode also permits the use of a smaller transformer, compared to equivalent continuous conduction mode designs.