FLYBACK TRANSFORMER

PURPOSE:To obtain a high quality flyback transformer, by constituting a hole part which is not opened outward, in a gap spacer or the abutting part of part cores, and forming leakage magnetic flux which leaks outward. CONSTITUTION:When an alternating current is made to flow in the primary coil of an winding 3, magnetic flux lines 9 forming closed loop are generated in a circuit constituted of an U-shaped part cores 2a, 2b and a gap spacer 6. Said magnetic flux lines 9 alternate with the same period as the current flowing through the primary coil. In the state that the gap spacer is not inserted, the reluctance of the magnetic flux lines 9 is determined by the dimension of a gap 5. When the spacer 6 is inserted, the relutance is given by formula I where mu1 is the permeability of the U-shaped part core, mu2 is the permeability of the gap spacer, and S2 is the sectional area of the gap spacer vertical to the magnetic path. When the number of turns of the primary coil is N1, and an alternating current I is made to flow through said coil, the generated magnetic flux PHI and the average magnetic flux density B are shown by formula II. Thereby the magnetic saturation of a flyback transformer 1 can be prevented.