A transformer (1, 1A to 1H) comprising: a main core (1, 1A to 1C) shaped as a loop; characterized in that the transformer (1, 1A to 1H) further comprises: a first winding wound around the main core (1, 1A to 1C) in a first section of the loop of the main core (1, 1A to 1C); a second winding wound around the main core (1, 1A to 1C) in a second section of the loop of the main core (1, 1A to 1C), the second section being separated from the first section; at least one first bypass core provided along the first section of the main core (1, 1A to 1C) and outside the first winding; a third winding wound around the main core (1, 1A to 1C) and the first bypass core in the first section of the main core (1, 1A to 1C); at least one second bypass core provided along the second section of the main core (1, 1A to 1C) and outside the second winding; a fourth winding wound around the main core (1, 1A to 1C) and the in the second section of the main core (1, 1A to 1C); and at least one gap formed in the main core (1, 1A to 1C) so as to intersect the loop of the main core (1, 1A to 1C), at a position separated from both the first and second sections (A1, A2) of the main core (1, 1A to 1C). a main core (1, 1A to 1C) shaped as a loop; characterized in that the transformer (1, 1A to 1H) further comprises: a first winding wound around the main core (1, 1A to 1C) in a first section of the loop of the main core (1, 1A to 1C); a second winding wound around the main core (1, 1A to 1C) in a second section of the loop of the main core (1, 1A to 1C), the second section being separated from the first section; at least one first bypass core provided along the first section of the main core (1, 1A to 1C) and outside the first winding; a third winding wound around the main core (1, 1A to 1C) and the first bypass core in the first section of the main core (1, 1A to 1C); at least one second bypass core provided along the second section of the main core (1, 1A to 1C) and outside the second winding; a fourth winding wound around the main core (1, 1A to 1C) and the in the second section of the main core (1, 1A to 1C); and at least one gap formed in the main core (1, 1A to 1C) so as to intersect the loop of the main core (1, 1A to 1C), at a position separated from both the first and second sections (A1, A2) of the main core (1, 1A to 1C). a first winding wound around the main core (1, 1A to 1C) in a first section of the loop of the main core (1, 1A to 1C); a second winding wound around the main core (1, 1A to 1C) in a second section of the loop of the main core (1, 1A to 1C), the second section being separated from the first section; at least one first bypass core provided along the first section of the main core (1, 1A to 1C) and outside the first winding; a third winding wound around the main core (1, 1A to 1C) and the first bypass core in the first section of the main core (1, 1A to 1C); at least one second bypass core provided along the second section of the main core (1, 1A to 1C) and outside the second winding; a fourth winding wound around the main core (1, 1A to 1C) and the in the second section of the main core (1, 1A to 1C); and at least one gap formed in the main core (1, 1A to 1C) so as to intersect the loop of the main core (1, 1A to 1C), at a position separated from both the first and second sections (A1, A2) of the main core (1, 1A to 1C).