Housed in a SOIC-7 or PDIP-7 package, the NCP1217 represents the second generation of NCP1203-based controllers. Thanks to its high drive capability, NCP1217 drives large gate-charge MOSFETs, which together with internal ramp compensation and built-in over voltage protection, ease the design of modern AC/DC adapters. NCP1217 offers a true alternative to UC384X-based designs.With an internal structure operating at different fixed frequencies (65, 100, 133kHz), the controller features a high-voltage start-up FET, which ensures a clean and loss less startup sequence. Its current-mode control topology provides an excellent input audio-susceptibility and inherent pulse-by-pulse control. Internal ramp compensation easily prevents subharmonic oscillations from taking place in continuous conduction mode designs.When the current setpoint falls below a given value, e.g. the output power demand diminishes, the IC automatically enters the so-called skip cycle mode and provides excellent efficiency at light loads. Because this occurs at a user adjustable low peak current, no acoustic noise takes place.The NCP1217 features two efficient protective circuitries: 1) in presence of an over-current condition, the output pulses are disabled and the device enters a safe burst mode, trying to re-start. Once the default has gone, the device auto-recovers. 2) if an external signal (e.g. a temperature sensor) pulls pin1 above 3.2V, output pulses are immediately stopped and the NCP1217 stays latched in this position. Reset occurs when the VCCcollapses to ground, e.g. the user un-plugs the power supply.