This part is a kind of semiconductor called UC3843B.

Function of this product has (UC3842B - UC3845B) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER.

Manufacturers : ST Microelectronics

Image and pinout :

Some of the text within the PDF file :

® UC2842B/3B/4B/5B UC3842B/3B/4B/5B HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER . . . . . . . . . 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 LOCKOUT HIGH CURRENT TOTEM POLE OUTPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS LOW START-UP AND OPERATING CURRENT Minidip SO8 DESCRIPTION TheUC384xB family ofcontrolICs providesthe necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under volta [ ... ]

UC3843B PDF Datasheet Download