Abstract: The current resonant converter according comprises a voltage converting transformer having a primary winding and a secondary winding, a switching circuit, disposed on the primary side of the transformer, for turning on and off a current supplied from an DC power to the transformer, a resonant circuit disposed adjacent to the transformer, a rectifying and smoothing circuit, disposed on the secondary side of the transformer, for supplying an output to a load, and a control circuit for controlling a switching frequency of the switching circuit, whereby the current resonant converter is operated in two modes, consisting of a first mode for prohibiting a DC current component from flowing in the primary winding and a second mode for allowing the DC current component to flow in the primary winding.

Abstract: A current resonance converter including a resonant circuit composed of an inductance Lr and a capacitor Cr, a switching element SW connected to the resonant circuit in series so as to turn on and off the resonant circuit, an oscillating circuit VCO for driving the switching element SW, a strobe pulse generating circuit SPG adapted to generate a strobe pulse after a predetermined period of time elapses from the time when the switching element SW is turned on, and a controlling circuit CTL serving to reduce an oscillation frequency derived from the voltage controlled oscillator VCO or stop oscillation of the same while the case where an electric current flows through the resonant circuit in the forward direction when a strobe pulse is generated is recognized as a case where the converter is loaded with an overload is disclosed. With this construction, the converter can be constructed in smaller dimensions with a lighter weight while assuring protection when the converter is loaded with an overload.

Abstract: A noise induced from a switching power supply source or the like is applied to a power line. The noise is classified into two kinds, one of them being normal mode noise appearing between power lines and the other one being common mode noise appearing between a power line and a ground line. Thus, a line filter is required to attenuate these noises.