Abstract: In a converter which is usable as a kind of DC--DC converter and which comprises a transformer for processing an exciting current into an excited current under influence of an inductance value of the transformer, the inductance value is controlled in compliance with a value of the exciting current. The exciting current is controlled by a current control circuit with reference to the excited current so that exciting current is intermittently supplied to the transformer. While the exciting current is absent during intermittent supply to the transformer, the transformer produces the excited current.

Abstract: A voltage-resonant DC-DC forward converter is provided with a snubber circuit in its secondary circuit. The snubber circuit comprises a series connection of a first capacitor and a first diode connected to both ends of the secondary winding of the main transformer to make up a loop of a secondary resonance circuit which allows a secondary resonance current to flow in the forward direction of the first diode, the forward direction being so directed that the first diode blocks the secondary resonance current from flowing at least while the second winding supplies a current to the smoothing circuit through a second diode for rectifying the secondary current. The converter is further provided with a regulation circuit for regulating the output voltage of the converter. The circuit has a transistor for controlling switching of the output current which varies linearly with time.

Abstract: According to this invention, a converter includes a voltage transformer, a switching transistor, a resistor, a control transistor, and a control circuit. The voltage transformer has a primary winding, a secondary winding, and a control winding. The switching transistor is connected in series with the primary winding. The resistor is connected between the switching transistor and one terminal of an input power source. The control transistor has a base connected to a connection point between the resistor and the switching transistor and a collector connected to a control electrode of the switching transistor. The control circuit controls the control transistor on the basis of a control voltage extracted from the control winding.