Packaged in SO-8 or PDIP-7, the NCP1217 represents an enhanced version of the NCP1203 controller. Due to its high drive capability, the NCP1217 driver, large gate charge MOSFET, together with internal slope compensation and built-in overvoltage protection ease the design of modern AC/DC adapters. The NCP1217 provides a true replacement for UC384X based designs. Internally constructed to operate at different fixed frequencies (65-100-133 kHz), the controller features a high voltage start-up FET, ensuring a clean, lossless start-up sequence. Its current-mode control topology provides an excellent audio input sensitivity and inherent pulse-by-pulse control. Internal slope compensation easily prevents subharmonic oscillations from continuously occurring conduction mode designs. When the current setpoint falls below a given value, eg: output power demand decreases, the IC automatically enters a so-called skip cycle mode and provides excellent efficiency at light load conditions. Since this occurs at a user-adjustable low peak current, there is no acoustic noise. The NCP1217 features efficient protection circuits: 1) In the presence of an overcurrent condition, the output pulses are disabled and the device enters a safe burst mode to attempt restart. Once the default is gone, the device automatically recovers. 2) If an external signal (such as a temperature sensor) pulls pin 1 above 3.2 V, the output pulse stops immediately and the NCP1217 remains locked in this position. A reset occurs when VCC to ground collapses, such as when the user unplugs the power supply.