This part is a kind of semiconductor called UC3843B.

Function of this product has HIGH PERFORMANCE CURRENT MODE CONTROLLERS.

Manufacturers : UTC

Image and pinout :

Some of the text within the PDF file :

UNISONIC TECHNOLOGIES CO., LTD UC3842B/3843B LINEAR INTEGRATED CIRCUIT HIGH PERFORMANCE CURRENT MODE CONTROLLERS  DESCRIPTION The UTC UC3842B/3843B are specifically designed for off-line and dc-to-dc converter applications offering the designer a cost-effective solution with minimal external components. The UC3842B has UVLO thresholds 16V (on) and 10V(off), ideally suited for off-line converters. The UC3843B is tailored for lower voltage applications having UVLO thresholds of 8.4V(on) and 7.6V(off).  FEATURES * Trimmed oscillator for precise frequency control * Oscillator frequency guaranteed at 250kHz * Current mode operation to 500kHz * Automatic feed forward compensation * Latching PWM for cycle-by-cycle current limiting * Internally trimmed reference with undervoltage lock [ ... ]

UC3843B PDF Datasheet Download