UC3901 Datasheet | Unitrode

Isolated Feedback Generator UC1901 UC2901 UC3901 Features - An Amplitude-Modulation System for Transformer Coupling an Isolated Feedback Error Signal - Low-Cost Alternative to Optical Couplers - Internal 1% Reference and Error Amplifier - Internal Carrier Oscillator Usable to 5MHz - Modulator Synchronizable to an External Clock - Loop Status Monitor DESCRIPTION The UC1901 family is designed to solve many of the problems associated with closing a feedback control loop across a voltage isolation boundary. As a stable and reliable alternative to an optical coupler, these devices feature an amplitude modulation system which allows a loop error signal to be coupled with a small RF transformer or capacitor. The programmable, high-frequency oscillator within the UC1901 series permits the use of smaller, less expensive transformers which can readily be built to meet the isolation requirements of today's line-operated power systems. As an alternative to RF operation, the external clock input to these devices allows synchronization to a system clock or to the switching frequency of a SMPS. An additional feature is a status monitoring circuit which provides an activelow output when the sensed error voltage is within ±10% of the reference. The DRIVERA output, DRIVERB output, and STATUS output are disabled until the input supply has reached a sufficient level to allow proper operation of the device. Since these devices can also be used as a DC driver for optical couplers, the benefits of 4.5 to 40V supply operation, a 1% accurate reference, and a high gain general purpose amplifier offer advantages even though an AC system may not be desired. UC1901 SIMPLIFIED SCHEMATICNovember S µµ SLUS279A - November 1998 - Revised January 2010 µ...