Switching power supply unit

A switching power supply unit operating in a current-continuous mode, comprising:

• a transformer including a primary winding, a secondary winding, a first drive winding, and a second drive winding;
• an inductor;
• an input power supply;
• a first switching circuit including a parallel circuit including a first switching element, a first diode, and a first capacitor;
• wherein
• the primary winding, the inductor, the input power supply, and the first switching circuit are connected in series;
• a capacitor;
• a second switching circuit including a parallel circuit including a second switching element, a second diode, and a second capacitor;
• wherein
• a first series circuit includes the primary winding and the inductor;
• a second series circuit includes the capacitor and the second switching circuit;
• the second series circuit is connected to the first series circuit in parallel;
• a rectifying and smoothing circuit which includes a rectifying element and which is connected to the secondary winding;
• and
• first and second switching control circuits for alternately turning on/off the first and second switching elements, with a period when both the first and second switching elements are turned off therebetween, the first switching control circuit being connected between the first drive winding and a control terminal of the first switching element and the second switching control circuit being connected between the second drive winding and a control terminal of the second switching element;
• wherein
• energy is stored in the primary winding and the inductor during an ON-period of the first switching element and the energy is emitted from the secondary winding during an OFF-period of the first switching element such that the first and second switching elements perform self-excited oscillation;
• the inductor and the capacitor define a resonant circuit which resonates during the OFF-period of the first switching element;
• the first switching control circuit includes a first ON-time control circuit in which a time constant is set such that the first switching element is turned off at a desired time after the first switching element is turned on;
• and
• the second switching control circuit includes a second ON-time control circuit in which a time constant is set such that the second switching element is turned off in order to interrupt a resonant current applied to a series circuit including the second switching element and the inductor after the second switching element is turned on and before the energy is completely emitted from the secondary winding.

A switching power supply unit operating in a current-continuous mode, comprising:

• a transformer including a primary winding, a secondary winding, a first drive winding, and a second drive winding;
• an inductor;
• an input power supply;
• a first switching circuit comprising a parallel circuit including a first switching element, a first diode, and a first capacitor;
• wherein
• the primary winding, the inductor, the input power supply, and the first switching circuit are connected in series;
• a capacitor;
• a second switching circuit comprising a parallel circuit including a second switching element, a second diode, and a second capacitor;
• wherein
• a series circuit includes the capacitor and the second switching circuit;
• the series circuit is connected to the first switching circuit in parallel;
• a rectifying and smoothing circuit which includes a rectifying element and which is connected to the secondary winding;
• and
• first and second switching control circuits for alternately turning on/off the first and second switching elements, with a period when both the first and second switching elements are turned off therebetween, the first switching control circuit being connected between the first drive winding and a control terminal of the first switching element and the second switching control circuit being connected between the second drive winding and a control terminal of the second switching element;
• wherein
• the primary winding, the inductor, the first switching circuit, and the input power supply are connected in series,
• energy is stored in the primary winding and the inductor during an ON-period of the first switching element and the energy is emitted from the secondary winding during an OFF-period of the first switching element such that the first and second switching elements perform self-excited oscillation;
• the inductor and the capacitor define a resonant circuit which resonates during the OFF-period of the first switching element;
• the first switching control circuit includes a first ON-time control circuit in which a time constant is set such that the first switching element is turned off at a desired time after the first switching element is turned on;
• and
• the second switching control circuit includes a second ON-time control circuit in which a time constant is set such that the second switching element is turned off in order to interrupt a resonant current applied to a series circuit including the second switching element and the inductor after the second switching element is turned on and before the energy is completely emitted from the secondary winding.

A switching power supply unit operating in a current-continuous mode, comprising:

• a transformer including a primary winding, a secondary winding, a first drive winding, and a second drive winding;
• an inductor;
• a capacitor;
• an input power supply;
• a first switching circuit including a parallel circuit including a first switching element, a first diode, and a first capacitor;
• a second switching circuit including a parallel circuit including a second switching element, a second diode, and a second capacitor;
• wherein
• the second switching circuit is connected in parallel to a series circuit including the primary winding, the inductor, and the capacitor;
• a rectifying and smoothing circuit which includes a rectifying element and which is connected to the secondary winding;
• and
• first and second switching control circuits for alternately turning on/off the first and second switching elements, with a period when both the first and second switching elements are turned off therebetween, the first switching control circuit being connected between the first drive winding and a control terminal of the first switching element and the second switching control circuit being connected between the second drive winding and a control terminal of the second switching element;
• wherein
• the primary winding, the inductor, the capacitor, the first switching circuit, and the input power supply are connected in series;
• energy is stored in the primary winding and the inductor during an ON-period of the first switching element and the energy is emitted from the secondary winding during an OFF-period of the first switching element such that the first and second switching elements perform self-excited oscillation;
• the inductor and the capacitor form a resonant circuit which resonates during the OFF-period of the first switching element;
• the first switching control circuit includes a first ON-time control circuit in which a time constant is set such that the first switching element is turned off at a desired time after the first switching element is turned on;
• and
• the second switching control circuit includes a second ON-time control circuit in which a time constant is set so that the second switching element is turned off in order to interrupt a resonant current applied to a series circuit including the second switching element and the inductor after the second switching element is turned on and before the energy is completely emitted from the secondary winding.