Ncp1027: 16 W, 12 Vdc Modem Power Supply

This design note presents a simple yet feature loaded 16 watt output, universal AC input adapter power supply for modems, hubs or similar applications. The circuit is a discontinuous mode (DCM) flyback converter topology designed around ON Semiconductor’s NCP1027 monolithic current mode controller with internal 700V MOSFET The output will provide up to 1.5 amps peak and will regulate at full output as low as 85 Vac input. The supply also includes an EMI input Filter as well as adjustable brown-out and power limit features. A very simple Zener Diode and Optocoupler feedback scheme is used that provides good output regulation with a minimum of components. The schematic of an optional resonant snubber is also shown which will improve the efficiency an additional two percentage points over the standard RCD snubber for the 120 Vac input range (see figure 2 and plots).
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Schematic for the 16 W, 12 V AC-DC modem adapter
Schematic for the 16 W, 12 V AC-DC modem adapter



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