Linear Tech's LT8315 high voltage flyback converter with integrated 630 V / 300 mA switch needs no opto-isolator for regulation. It samples the output voltage from the isolated flyback waveform appearing across a third winding on the transformer. Its quasi-resonant boundary mode operation improves load regulation, reduces transformer size, and maintains high efficiency. At start-up, the LT8315 charges its INTV_CC capacitor via a current source attached to the DRAIN pin. The current source turns off and the device draws its power from a third winding on the transformer during normal operation. It operates from a wide range of input supply voltages and can deliver up to 15 W of power. The LT8315 is available in a thermally enhanced 20-pin TSSOP package with four pins removed for high-voltage spacing.