The LT1103 Offline Switching Regulator is designed for high input voltage applications using an external FET switch whose source is driven by the open collector output of the LT1103. The LT1103 is optimized for 15W to 100W applications. For higher power applications or additional switch current flexibility, the LT1105 is available and its totem pole output drives the gate of an external FET. Unique design of the LT1103/LT1105 eliminates the need for an optocoupler while still providing 1% load and line regulation in a magnetic flux-sensed converter. This significantly simplifies the design of offline power supplies and reduces the number of components which must cross the isolation barrier to one, the transformer.