This part is a kind of semiconductor called UC3843.

Function of this product has (UC3842 - UC3845) CURRENTMODE PWM CONTROLLER.

Manufacturers : STMicroelectronics

Image and pinout :

Some of the text within the PDF file :

® UC2842/3/4/5 UC3842/3/4/5 CURRENT MODE PWM CONTROLLER . . . . . . . . . . . OPTIMIZED FOR OFF-LINE AND DC TO DC CONVERTERS LOW START-UP CURRENT (< 1 mA) AUTOMATIC FEED FORWARD COMPENSATION PULSE-BY-PULSE CURRENT LIMITING ENHANCED LOAD RESPONSE CHARACTERISTICS UNDER-VOLTAGE LOCKOUT WITH HYSTERESIS DOUBLE PULSE SUPPRESSION HIGH CURRENT TOTEM POLE OUTPUT INTERNALLY TRIMMED BANDGAP REFERENCE 500 KHz OPERATION LOW RO ERROR AMP Minidip SO14 DESCRIPTION TheUC3842/3/4/5family of controlICs provides the necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal externalparts count.Internallyimplementedcircuits include undervoltagelockout featuring start-up current less than 1 mA, a precision reference trimmed for ac [ ... ]

UC3843 PDF Datasheet Download