Update: 30 September, 2023
This document introduces UCC3884, a high-performance current mode PWM controller designed for single-ended switch mode power supplies. The chip implements a frequency foldback scheme that decreases the oscillator frequency as the output voltage falls below a programmed value. This technique decreases the average output current sourced into a low impedance load, which can occur during an output short circuit or overload condition. Excessive short circuit current is more prevalent in high frequency converters where the propagation delay and switch turn-off time forces a minimum attainable duty cycle. An accurate volt-second clamp limits the duty cycle during line or load transient conditions which could otherwise saturate the transformer. The volt-second clamp may also be used with an external overvoltage protection circuit to handle fault conditions such as current sense disconnect or current transformer saturation. The frequency foldback, volt-second clamp, cycle-by-cycle current limit, and overcurrent shutdown functions ensure that the power supply is always in a safe state under various fault conditions.
File format: PDF
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MD5 Checksum: F860DCE09B70FE7B1760140E046F6025
Publication date: 01 August, 2012
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PDF Link: Unitrode Products UCC1884 UCC2884 UCC3884 handbook PDF