The MAX5019/MAX5020 integrate all the building blocks necessary for implementing DC-DC fixed-frequency power supplies. Either primary- or secondaryside regulation may be used to implement isolated or nonisolated power supplies. These devices are currentmode controllers with an integrated high-voltage startup circuit suitable for telecom/industrial voltage range power supplies. Current-mode control with leadingedge blanking simplifies control-loop design and internal ramp compensation circuitry stabilizes the current loop when operating at duty cycles above 50% (MAX5019). The MAX5019 allows 85% operating duty cycle and can be used to implement flyback converters whereas the MAX5020 limits the operating duty cycle to less than 50% and can be used in single-ended forward converters. A high-voltage startup circuit allows these devices to draw power directly from the 18V to 110V input supply during startup. The switching frequency is internally trimmed to 275kHz 10%, thus reducing magnetics and filter component costs. The MAX5019/MAX5020 are available in 8-pin SO packages.