Sony Corporation

Masayuki Yasumura

Ichiro Mitamura

There is provided a switching power supply circuit which may include a rectifying and smoothing section for converting an alternating input voltage from an alternating-current power supply into a primary side direct-current voltage; a converter section for converting the primary side direct-current voltage from the rectifying and smoothing section into an alternating voltage and further converting the alternating voltage into a secondary side direct-current voltage; and a power factor improving section for improving a power factor.

Switching power supply circuit

In the switching power supply circuit disclosed in the present invention, the DC voltage is supplied to the primary winding in the converter transformer and the AC voltage is generated. First and second series resonant circuit are formed, and the resonant frequency of the first and second series resonant circuits are set to be substantially equal to each other. A parallel resonant circuit is formed, and the resonant frequency of the parallel resonant circuit is set higher than the resonant frequencies of the first and second series resonant circuits. The secondary winding includes first and second secondary windings so that currents are extracted from the first and second secondary windings, respectively, and a ratio of the number of turns of the first secondary winding to that of the second secondary winding is defined so that magnitudes of the currents are substantially equal to each other.

A voltage resonant converter is provided with a secondary side parallel resonant circuit, and an isolated converter transformer PIT is set in a state of loose coupling at a coupling coefficient k=about 0.7 or lower. Thus a steep unimodal characteristic is obtained as a constant-voltage control characteristic to reduce a control range of switching frequency which range is necessary for stabilization. A primary side parallel resonance frequency foand a secondary side parallel resonance frequency foare set so as to obtain favorable power conversion efficiency characteristics.

A wide-range compatible switching power supply circuit employs switching frequency varying control and allows enhancement of its AC to DC power conversion efficiency when a large AC input voltage is used. A coupled resonant circuit employing electromagnetic coupling by an isolation converter transformer is formed by providing a series resonant circuit both on the primary side and on the secondary side of the transformer. In order to achieve a unimodal output characteristic in the coupled resonant circuit, the length of a gap formed in a core of the isolation converter transformer is set to about 2.0 mm, and a coupling coefficient is set to about 0.8 or less. Thus, the switching frequency variable control range can be narrowed, which allows a wide-range compatible configuration. In addition, resonant frequencies of primary-side and secondary-side resonant circuits are set so that a requisite phase shift arises between a primary-side series resonant current and a secondary-side rectified current at least when an AC input voltage is 100 V and the load power is the maximum load power. Thus, the AC to DC power conversion efficiency when the AC input voltage VAC is 230 V can be enhanced.

The present invention may provide a switching power supply circuit for converting primary side direct-current voltage to secondary side direct-current voltage. The switching power supply circuit may include a choke coil, a converter transformer; a switching element, a primary side series resonant capacitor, a primary side parallel resonant capacitor, an oscillating and driving circuit, a secondary side rectifier circuit, and a control circuit. Resonance frequency of the primary side first series resonant circuit may be set at a frequency substantially twice resonance frequency of the primary side second series resonant circuit. Resonance frequency of the primary side parallel resonant circuit may be set at a frequency substantially equal to or higher than 1.5 times the resonance frequency of the primary side first series resonant circuit.

The present invention provides a voltage resonant converter that achieves ZVS over the entire allowable load range. A switching power supply circuit includes a class-E resonant converter as its primary-side switching converter that is supplied with a DC input voltage arising from the rectification and smoothing of a commercial AC voltage by a rectifier circuit (including a smoothing capacitor Ci). A choke coil of a primary-side series resonant circuit in the class-E switching converter is used as a primary winding Nin an isolation converter transformer PIT. The total coupling coefficient between the primary side and secondary side is set to about 0.65 by the coupling coefficient of the isolation converter transformer PIT itself and equivalent parallel connection between a choke coil Land the primary winding N. The resonant frequency foof a primary-side parallel resonant circuit and the resonant frequency foof the primary-side series resonant circuit are set to almost the same value of about 60 kHz.

Enhancement of the power conversion efficiency and reduction of switching noise of a power supply circuit are achieved. The power supply circuit includes, on the primary side, a composite resonance type converter formed from a current resonance type converter and a partial voltage resonance circuit in combination, and is configured so as to produce a plurality of secondary side DC output voltages. A particular one of the plural secondary side DC output voltages is controlled to a constant voltage by variably controlling the switching frequency of a primary side switching converter. Each of the remaining secondary side DC output voltages is controlled to a constant voltage by adjusting the level of control current to be supplied to a controlling winding of a control transformer in response to the level of the secondary side DC output voltage to adjust the inductance of a controlling winding of the control transformer inserted in a rectification current path.

An abnormal operation in which a current flows through a switching device before the end of an off period of the switching device at medium load is eliminated by setting the coupling coefficient of an isolated converter transformer to about 0.7 or lower. A primary side parallel resonance frequency and a secondary side series resonance frequency are set so as to obtain favorable power conversion efficiency characteristics.

A switching power supply circuit which can achieve enhancement of the power conversion efficiency is disclosed. In a composite resonance converter wherein a current resonance type converter constructed on the primary side and a primary side partial voltage resonance circuit are combined, a primary side DC input rectification circuit is formed from a full-wave rectification circuit. Further, a gap G of the core of an insulating converter transformer (PIT) is set to 2.0 mm to set the coupling coefficient of the primary winding (N) and the secondary winding (N) to approximately 0.81 of a loose coupling state. Further, the numbers of turns of the primary winding (N) and the secondary winding (N) are selected so that the induced voltage per one turn of the secondary winding (N) is 2 V or less. With the configuration, if the leakage inductance (L) of the primary winding (N) and the leakage inductance (L) of the secondary winding (N) are increased, then reduction of the primary side current (I) in a light load condition can be achieved and the switching output current (IQ), (IQ) can be reduced.

A switching power supply circuit includes a plurality of switching converters, each including a partial resonance voltage circuit combined with a current resonance type switching converter using a half-bridge connection system. For changeover control, a rectification circuit serves as a voltage doubler rectification circuit at an AC voltage less than or equal to 150V, but serves as a full-wave rectification circuit at an AC voltage greater than or equal to 150V. The voltage output of the converters is fed back to a rectification current path by a power factor improving transformer, the rectification current being interrupted by means of a rectification diode to expand the conduction angle of the AC input current. A DC switch circuit in the rectification current path is switched between on and off conditions in response to the input of a predetermined starting signal to control the starting order of the secondary side DC output voltage.

A secondary side series resonant circuit formed by at least one secondary winding and a secondary side series resonant capacitor is provided together with a secondary side series resonant circuit forming a current resonant converter, whereby a coupling type resonant circuit is formed by magnetic coupling of an isolated converter transformer. For this coupling type resonant circuit to obtain a unimodal characteristic, a gap G formed in a core of the isolated converter transformer PIT is set to about 2.4 mm, and a coupling coefficient k is set to k=0.65 or lower. Thereby, the variable control range of switching frequency can be reduced, and a wide range-ready configuration can be realized. Also, since the variable control range of the switching frequency can be thus reduced, cross regulation of secondary side direct-current output voltage &#x2212;Eo can be improved.

Resonant converter with outputs of different polarities

The invention aims at putting a single ended resonance type converter capable of obtaining a ZVS operation over an overall corresponding load region to practical use. A switching power supply circuit includes a primary side switching converter of a class-E resonance type, and a choke coil of a primary side series resonance circuit of the class-E resonance type converter is used as a primary winding of an insulating converter transformer. With this structure, a choke coil winding to be inserted into an input line of a DC input voltage is arranged between a positive-polarity end portion of a smoothing capacitor, and a node between the primary winding and a primary side series resonance capacitor. Thus, a resonance pulse voltage generated in the choke coil winding is superimposed on an AC voltage in the primary winding. Also, a primary series resonance current is caused to separately flow through the choke coil winding.

In a switching power supply circuit including a primary side rectifying and smoothing circuit, a switching element, a converter transformer, a secondary side rectifying and smoothing circuit, and a switching element controlling section, a first primary side series resonant circuit is formed by a choke coil and a primary side series resonant capacitor, a second primary side series resonant circuit is formed by a leakage inductance occurring in a primary winding and the primary side series resonant capacitor, and a secondary side series resonant circuit is formed by a leakage inductance occurring in a secondary winding and a secondary side series resonant capacitor.

A switching power supply circuit is disclosed which can achieve a high power conversion efficiency and besides achieve reduction of the circuit scale and the cost by simplification in circuit configuration. The switching power supply circuit includes a synchronous rectification circuit of the winding voltage detection system on the secondary side of a resonance converter. The coupling coefficient of an insulating converter transformer or the induced voltage level per one turn of the secondary winding is set so that the magnetic flux density of the insulating converter transformer may be lower than a fixed level thereby to maintain the secondary side rectification current in a continuous mode even in a heavy load condition. An inductor is inserted in series in a path along which rectification current is to be supplied to a secondary side smoothing capacitor so that reverse current appearing on the rectification current is suppressed by counter electromotive force generated in the inductor to further reduce the reactive power. A dc superposition characteristic of the inductor is set so that abnormal oscillation in a very light load condition (for example, 12.5 W or less) is prevented.

A switching power supply circuit includes a switching element, a converter transformer, a secondary-side rectifying and smoothing circuit, a switching element control unit, a choke coil, a primary-side series resonant circuit, a primary-side parallel resonant circuit, and a series circuit. The switching element implements switching for a direct-current (DC) voltage to convert the voltage into an alternating-current (AC) voltage. The choke coil is supplied with the voltage and is connected to one winding end of the primary winding and one terminal of the switching element. The primary-side series resonant circuit connects a primary-side series resonant capacitor, having a resonant frequency dominated by a leakage inductance. The primary-side parallel resonant circuit connects a primary-side parallel resonant capacitor in parallel to the switching element, having a resonant frequency. The series circuit is formed of a clamp capacitor and an auxiliary switch element which conducts in a non-conducting period of the switching element.

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Kanagawa, Japan

Masayuki Yasumura