The LT3748 is a high input voltage isolated flyback DC/DC controller that does not require an opto-isolator, third winding or signal transformer for feedback. The output voltage is sensed from the primary-side flyback signal, and is set with two external resistors and the transformer turns ratio. The LT3748 operates over a 5V to 100V input voltage range, drives an external N-channel power MOSFET and maintains better than ±5% overall regulation.