Display device comprising transformer comprising core having structure related with coupling factor of inductor

A display device comprising a transformer, the transformer comprising:

• a first core including a first surface and a protrusion protruding from the first surface along a direction which the first surface faces, wherein a cross-section of the protrusion perpendicular to the direction has a first area;
• a first inductor sub-assembly including a first bobbin including a first opening corresponding to the first area, to be in contact with an outer circumference of the protrusion of the first core, and an inductor wound around the first bobbin;
• a second core including a second surface facing and being spaced apart from a first surface of the first core, and a protrusion protruding from the second surface along a direction which the second surface faces, wherein a cross-section of the protrusion perpendicular to the direction which the second surface faces has a second area different from the first area;
• and
• a second inductor sub-assembly including a second bobbin having a second opening corresponding to the second area, to be in contact with an outer circumference of the protrusion of the second core, and an inductor wound around the second bobbin;
• and
• a third inductor sub-assembly including a third bobbin having a third opening corresponding to an outer circumference of the first inductor sub-assembly, and an inductor wound around the third bobbin, wherein the third inductor sub-assembly is in contact with at least a portion of the outer circumference of the first inductor sub-assembly.