This part is a kind of semiconductor called KA3842.

Function of this product has Linear Integrated Circuit(CURRENT-MODE PWM CONTROLLER).

Manufacturers : Wing Shing Computer Components

Image and pinout :

Some of the text within the PDF file :

Linear Integrated Circuit CURRENT−MODE PWM CONTROLLER The KA3842A KA3842AM are fixe frequency current-mode PWM controller. They are specially designed for OFF−Line and DC−to−DC converter applications with minimal external components. These integrated circuits feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totempole output ideally suited for driving a power MOSFET. Protection circuity includes built under−voltage lockout and current limiting. The KA3842A,KA3842AM have UVLO thresholds of 16 V(on) and 10 V (off). The KA3842A ,KA384AM can operate within 100% duty cycle The KA3842A has been proven in applications using the same external components as Motorola's [ ... ]

KA3842 PDF Datasheet Download