Abstract: A drive circuit for a switching power supply includes a driving element (11, 12) for generating a drive signal (SD), and a transformer (15) for outputting the drive signal input via a capacitive element to a primary winding (15a) thereof (14), to a main switching element (21) from a secondary winding (15b) thereof. The drive circuit (3) is constructed such that breakage of the main switching element (21) can be prevented while permitting an increase in the range of switching control. The drive circuit (3) is characterized by comprising an inductive element (16) having an inductance value smaller than at least a value of an excitation inductance of the primary winding (15a) and allowing series resonance to be produced between the capacitive element (14) and the inductive element (16).

Abstract: A rectifying and smoothing circuit (3) which includes a first inductor connected between one end (2b1) of an output winding of a transformer (2) and a low potential-side output portion (16b), a second inductor connected between the other end (2b2) of the output winding and the low potential-side output portion, a first rectifying element (11) connected between the one end of the output winding and a high potential-side output portion (16a), and a second rectifying element (12) connected between the other end of the output winding and the high potential-side output portion, and which generates a DC voltage (V0) by rectifying and smoothing a bipolar voltage (VS) induced across the output winding, has a construction permitting reduction of the size and manufacturing costs thereof and enhancement of smoothing effects.

Abstract: The present invention provides an inductor having a small core loss at a high frequency. The inductor includes a transformer that has a core formed of a base core and a cover core, and a conductive plate sandwiched between the base core and the cover core, as well as a conductive plate sandwiched between the base core and the cover core. The base core is composed of a Mn--Zn ferrite with a mean grain size of 5 .mu.m or less. The transformer has a small core loss at a high frequency band without a decrease in power transmission efficiency.