This part is a kind of semiconductor called HY3845.

Function of this product has (HY3842 / HY3845) PWM controller.

Manufacturers : Hooyi

Image and pinout :

Some of the text within the PDF file :

HY3842/43/44/45 DESCRIPTION The HY3842D-N/3843D-N/3844D-N/3845D-N, are fixed frequency current mode PWM controller. They are specially designed for OFF−Line and DC to DC converter applications with a minimal external components. Internally implemented circuits include a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET. Protection circuitry includes built under voltage lockout and current limiting. The HY3842D-N, HY3844D-N, have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the HY3843D-N/3845D- N are 8.4V (on) and 7.6V (off). The HY 3842D-N, HY3843D-N, can operate within 100% duty cycle. [ ... ]

HY3845 PDF Datasheet Download