The LT3573 is an isolated monolithic flyback converter with an integrated 1.25A NPN transistor. It makes designing a flyback converter as easy as designing a buck converter. It significantly simplifies the design of a flyback converter by sensing the output voltage directly from the primary-side flyback waveform. The LT3573 operates over an input voltage range of 3V to 40V at output power levels up to 7 watts, and can be used in a wide variety of industrial, medical, datacom and automotive applications requiring isolated power. The LT3573 operates in Boundary Mode, which is a variable frequency current mode switching scheme, resulting in a total regulation band of ±3% over a wide input voltage range and output load current. Boundary Mode operation also permits the use of a smaller and less complex transformer when compared to equivalent continuous conduction mode designs. In many cases, standard, off-the-shelf transformers can be used. The output voltage is easily set with two external resistors. The LT3573 has additional features that include an on board LDO that allows a third winding to be used for higher efficiency in some designs, along with programmable soft start, undervoltage lockout, adjustable current limit, and output voltage temperature compensation. The LT3573 is available in a small thermally enhanced MSOP-16 package and 3mm x 3mm QFN-16, both of which are offered in extended and industrial temperature ranges from -40°C to 125°C.