The peak-to-average primary current ratio in a DCM flyback is high relative to other topologies; however, at low power levels, this is not a serious drawback. On-state losses are minimal. Magnetics are small. Also, the transformer reset voltage is set by the minimum input voltage and remains fairly constant as the line voltage changes. As a result, a 600-V MOSFET proves adequate, even with ac inputs up to 300 V RMS. The DCM flyback converter, when operated under current-mode control, provides a natural input volt-second limit, which helps keep the drain voltage from getting out of control during line or load transient conditions. Also, today's power MOSFETs are able to withstand avalanche current many times greater than a low power circuit can typically deliver (see appendix A). As such, the MOSFET will serve as a clamp for the occasional spike which may result from a short circuit or extreme load transient. Cross regulation is fairly good, especially if leakage inductance between windings can be kept low.[1] In a universal-input application, meeting VDE input-to-output isolation requirements is essential. Depending on the end product, this can be as high as 3750-V RMS, primary to Document Number: 70581