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NCP1249: PWM Controller Featuring Peak Power Excursion and HV Startup

The NCP1249 is a highly integrated high-voltage PWM controller capable of delivering a rugged and high performance offline power supply with extremely low no-load consumption. With a supply range up to 30 V, the controller hosts a jittered 65-kHz switching circuitry operated in peak current mode control. When the power on the secondary side starts to decrease, the controller automatically folds back its switching frequency down to a minimum level of 26 kHz. As the power further goes down, the part enters skip cycle while freezing the peak current setpoint.To help build rugged converters, the controller features several key protective features: an internal brown-out, a non-dissipative Over Power Protection for a constant maximum output current regardless of the input voltage and two latched over voltage protection inputs - either through a dedicated pin or via the Vcc input.The controller architecture is arranged to authorize a transient peak power excursion when the peak current hits the limit. At this point, the switching frequency is increased from 65 kHz to 130 kHz until the peak requirement disappears. The timer duration is then modulated as the converter crosses a peak power excursion mode (long) or undergoes a short circuit (short). Similar to NCP1255 & NCP1254 with integrated HV Startup NCP1249 has Active ON (A&B) and Active OFF (C&D) versions.

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