News Column

"Dc-Dc Converter with Lc Resonance Circuit" in Patent Application Approval Process

June 26, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Yonezawa, Yu (Sagamihara, JP); NAKASHIMA, YOSHIYASU (Kawasaki, JP), filed on February 11, 2014, was made available online on June 12, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to Fujitsu Limited.

The following quote was obtained by the news editors from the background information supplied by the inventors: "A typical forward-type DC-DC converter includes a switch circuit that alternately switches on and off an electric current flowing through the primary side of a transformer in a predetermined cycle. In response to the repeatedly alternating on-state and off-state of the primary-side current, an electric current appearing on the secondary side alternates between an on-state and an off-state. The secondary-side current that alternates between the on-state and the off-state is rectified by a rectifying circuit, and is then smoothed by a capacitor and an inductor, thereby generating an output having an approximately constant current and voltage.

"In the DC-DC converter having the configuration described above, an electric current flowing through the transformer is of a rectangular wave form, which exhibits a sudden change at the edges thereof so as to include high frequency components. The higher the operating frequency, the greater the loss in the core of the transformer is.

"It is thus not preferable to use an electric current having a rectangular wave shape.

"A DC-DC converter disclosed in None-Patent Document 1 utilizes an LC resonance circuit to generate an electric current having a sinusoidal wave form whose frequency is equal to the resonance frequency. An electric current having a wave form synthesized from this sinusoidal-wave-form current is then supplied to the transformer. The fact that a sinusoidal wave has only one frequency component without having higher frequency components ensures that loss in the transformer is small, thereby allowing an efficient DC-DC converter to be provided.

"However, the DC-DC converter disclosed in None-Patent Document 1 does not use PWM (pulse-width modulation) control to adjust the output voltage thereof, but changes the switching frequency on the primary side of the transformer to adjust the output voltage thereof. Such a configuration involves the use of a VCO (voltage-controlled oscillator) or the like, which results in a cost increase. Further, a small load connected to the output means that the switching frequency is to be increased. In such a case, the wave form input into the transformer ends up having a shape distorted from a sinusoidal wave form, which results in an increase in the loss in the transformer.

"A DC-DC converter disclosed in Patent Document 1 utilizes an LC resonance circuit to generate an electric current having a sinusoidal wave form whose frequency is equal to the resonance frequency, thereby reducing switching loss occurring in transistors. In such a DC-DC converter, the sinusoidal wave form of electric current input into the transformer cannot be maintained under certain conditions of switching timing, which may cause an increase in the loss in the transformer. [Patent Document 1] Japanese Laid-open Patent Publication No. 03-060367 [None-Patent Document 1] 'Green Electronics No. 1, Designing of Highly Efficient, Low-Noise Power Supply Circuit', p. 55, CQ Publishing Co., Ltd., Apr. 1, 2010"

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "According to an aspect of the embodiment, a DC-DC converter includes a capacitor configured to be charged for a predetermined period by an external voltage, an inductor configured to constitute an LC resonance circuit together with the capacitor, a closed-loop current path configured to release energy accumulated in the capacitor after the predetermined period to cause a current flowing in the LC resonance circuit to oscillate, a transformer configured to receive a current flowing in the closed-loop current path, and a rectifying circuit situated on an output side of the transformer.

"According to another aspect, a DC-DC conversion method includes charging a capacitor with an external voltage for a predetermined period, releasing energy accumulated in the capacitor after the predetermined period to cause a current to flow and oscillate in a closed-loop current path inclusive of an LC resonance circuit that includes the capacitor and an inductor, supplying the current flowing in the closed-loop current path to a transformer, and rectifying an output of the transformer.

"An information apparatus includes a DC-DC converter, a CPU; and a memory device, wherein the DC-DC converter includes a capacitor configured to be charged for a predetermined period by an external voltage, an inductor configured to constitute an LC resonance circuit together with the capacitor, a closed-loop current path configured to release energy accumulated in the capacitor after the predetermined period to cause a current flowing in the LC resonance circuit to oscillate, a transformer configured to receive a current flowing in the closed-loop current path, and a rectifying circuit situated on an output side of the transformer.

"The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

"FIG. 1 is a drawing illustrating an example of the configuration of a DC-DC converter according to an embodiment;

"FIG. 2 is a drawing illustrating the operation of the DC-DC converter illustrated in FIG. 1;

"FIG. 3 is a drawing illustrating a more specific example of the configuration of the DC-DC converter illustrated in FIG. 1;

"FIG. 4 is a drawing illustrating switch conditions and current flows in a given operating state of the DC-DC converter illustrated in FIG. 3;

"FIG. 5 is a drawing illustrating switch conditions and current flows in a given operating state of the DC-DC converter illustrated in FIG. 3;

"FIG. 6 is a drawing illustrating switch conditions and current flows in a given operating state of the DC-DC converter illustrated in FIG. 3;

"FIG. 7 is a drawing illustrating control signals and currents relating to the operations of the DC-DC converter illustrated in FIG. 4 through FIG. 6;

"FIG. 8 is a drawing illustrating a variation of the DC-DC converter illustrated in FIG. 3;

"FIG. 9 is a drawing illustrating examples of wave forms when the pulse width of SW1 is calculated based on a duty ratio and an interval T, and SW2 and SW3 are set equal to the inverse of SW1;

"FIG. 10 is a drawing for explaining the time at which a switch circuit is turned off;

"FIG. 11 is a drawing illustrating the configuration for controlling the time at which the switch circuit is turned off;

"FIG. 12 is a waveform diagram illustrating an example of the operation of the DC-DC converter illustrated in FIG. 11;

"FIG. 13 is a drawing illustrating a variation of the DC-DC converter illustrated in FIG. 3;

"FIG. 14 is a diagram illustrating an example of the operation of the DC-DC converter illustrated in FIG. 13;

"FIG. 15 is a drawing illustrating a variation of the DC-DC converter illustrated in FIG. 3; and

"FIG. 16 is a drawing illustrating an example of the configuration of an information apparatus."

URL and more information on this patent application, see: Yonezawa, Yu; NAKASHIMA, YOSHIYASU. Dc-Dc Converter with Lc Resonance Circuit. Filed February 11, 2014 and posted June 12, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4184&p=84&f=G&l=50&d=PG01&S1=20140605.PD.&OS=PD/20140605&RS=PD/20140605

Keywords for this news article include: Fujitsu Limited.

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Source: Politics & Government Week


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