As recent electronic units become compact, highly efficient, and inexpensive, power supply units are also required to be compact, highly efficient, and inexpensive.  Patent Document 1 below discloses two inductors that share part of a magnetic loop to reduce their costs.  In Patent Document 1, a single core member is used to provide two inductors that are magnetically independent of each other. 
Patent Document 2 below discloses a resonant reactor and a smoothing reactor that are structured by forming a plurality of windings around a plurality of closed magnetic paths.  The resonant reactor disclosed in Patent Document 2 is magnetically coupled with the smoothing reactor to reduce current flowing in the smoothing reactor. 
Patent Document 3 below discloses a choke coil having a single closed magnetic path around which two windings are formed.  The technology disclosed in Patent Document 3 provides a compact, inexpensive choke coil that can easily obtain a predetermined inductance or a choke coil having a nonlinear inductance by providing a narrow magnetic path on a magnetic member that forms a closed magnetic path. 
Non-patent Document 1 below discloses an insulated DC-DC converter that uses a tapped inductor-type filter.  The DC-DC converter disclosed in Non-patent Document 1 is highly efficient: it reduces circulating current flowing in a transformer while a smoothing inductor releases energy. 
Patent Document 1: Japanese Patent Laid-open No.  Hei 8(1996)-298219
Patent Document 2: Japanese Patent Laid-open No.  2005-176540
Patent Document 3: Japanese Patent Laid-open No.  2001-319817
Non-patent Document 1: The Institute of Electronics, Information, and Communication Engineers (IEICE), Energy Engineering in Electronics and Communications (EE), Vol 1.  102, No.  475 (20021018) pp.  73-78