A transformer and a manufacturing method thereof are provided. The transformer includes a bottom structure, a top structure, and a middle structure. The bottom structure includes a bottom circuit layer embedded in a bottom insulating layer. The top structure is disposed over the bottom structure and includes a top circuit layer embedded in a top insulating layer. The middle structure is disposed between the bottom structure and the top structure and includes an insulating layer, ring-shaped metal layers, and conductive pillars. The ring-shaped metal layers are stacked in a first direction in the insulating layer. The conductive pillars are disposed in the insulating layer and on an inner side and an outer side of the stacked ring-shaped metal layers. The insulating layer electrically isolates the conductive pillars from the ring-shaped metal layers. The top circuit layer and the bottom circuit layer are electrically connected through the conductive pillars.

A transformer structure is provided. The transformer structure includes a core unit, a first winding, and a second winding. The first winding is disposed on the core unit and has a first low segment, a first high segment, and a first connecting portion connected between the first low segment and the first high segment. The second winding is accommodated in a gap formed between the first low segment and the first high segment.

A transformer includes a core having a center leg portion extending in a first direction, a side leg portion extending in the first direction and provided away from the center leg portion in a second direction, and a coupling portion connecting the center leg portion to the side leg portion, a primary winding wound around the center leg portion, a secondary winding wound around the center leg portion, and a path core forming a magnetic path, extending in the second direction, and being provided between the primary winding and the secondary winding. A gap is formed in the path core and located, as viewed in the first direction, between an inner edge of the primary winding and an outer edge of the primary winding in the second direction.

A transformer includes a core having a center leg portion extending in a first direction, a side leg portion extending in the first direction and provided away from the center leg portion in a second direction, and a coupling portion connecting the center leg portion to the side leg portion, a primary winding wound around the center leg portion, a secondary winding wound around the center leg portion, and a path core forming a magnetic path, extending in the second direction, and being provided between the primary winding and the secondary winding. A gap is formed in the path core and located, as viewed in the first direction, between an inner edge of the primary winding and an outer edge of the primary winding in the second direction.