This part is a kind of semiconductor called D2102.
Function of this product has 2SD2102.
Manufacturers : Hitachi Semiconductor
Image and pinout :
Some of the text within the PDF file :
2SD2102 Transient Thermal Resistance Thermal resistance θj-c (°C/W) 10 3 TC = 25°C 1.0 0.3 0.1 1m 10m 100m 1.0 10 100 1000 Time t (s) [ ... ]