Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-04-14
2001-05-08
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021160, C363S021020, C363S021030, C363S089000, C363S127000
Reexamination Certificate
active
06229717
ABSTRACT:
OBJECT OF THE INVENTION
The present invention relates to a switched power supply converter that comprises a switching element on the primary side, which serves for supervising the transfer of energy between the input and the output of the converter. The switching action of the switching element is done at zero voltage through the control of the duty cycle of an auxiliary switching element.
The switched power supply converter is of special, but not exclusive, application in distributed power supply systems in which there is a requirement for switched power supply converters with low power and voltage, that are mounted on printed circuit boards as one more electronic component thereof and, consequently, high density integration and reduced size are necessary.
STATE OF THE ART
A zero voltage switched power supply converter has been described in the U.S. Pat. No. 5,594,629 by R. L. Steigerwald, incorporated in the present patent application by reference.
The switched converter comprises a transformer in which one end of a primary winding is connected to a first terminal of the first switching element, a second terminal of the first switching element is connected to one end of a direct current power source and its other end is connected to the other end of the primary winding, a storage capacitor is connected in parallel with the previously described series combination, making up the primary side of the converter.
Likewise, a secondary winding is connected in series with a second switching element for maintaining a constant output voltage, forming the secondary side of the converter.
A switching signal is applied to the control terminal of the first switching element for controlling its switching action (non-conducting or conducting), so that its switching action takes place at zero voltage. That is, when the second switching element stops conduction and the first switching element is still in a non-conducting state, the resonance circuit formed by a parasitic capacitance of the first switching element and a magnetising inductance of the transformer reduces to zero the voltage across the first and second terminal of the first switching element.
The period for the resonance circuit to bring to zero the voltage between the first and second terminal of the first switching element is fixed.
Nevertheless, the operation mode of the aforementioned switched converter does not guarantee switching at zero voltage for a broad range of input voltages, due to the fact that both the conducting period and the non-conducting period of the first switching element is a function of the input voltage and load conditions, and as the resonance circuit is made up of passive elements it is not possible to vary the period that it requires for bringing the voltage to zero; consequently, the first switching element is switched at a voltage other than zero whereby the efficiency of the converter is impaired.
Thus, there exists a need to develop a zero voltage switched converter which accepts a broad range of input voltages and guarantees, for all of them, switching at zero voltage of the switching element of the primary side, all of the foregoing acting to boost the performance of the converter and, therefore, of the power distribution system.
CHARACTERIZATION OF THE INVENTION
To overcome the problems mentioned above, a zero voltage switched power supply converter is proposed so that the voltage in a first switching element connected in series with a primary winding of a transformer reaches the value zero before the start of a new conducting period of the first switching element.
The power supply converter is connected to a power source and comprises a transformer which has a primary winding connected in series with the first switching element, a secondary winding connected in series with a second switching element and a series combination of a storage capacitor and a third switching element connected in parallel with the second switching element.
The operation of the power supply converter is such that during any non-conducting period of the first switching element, and once the second switching element is in the conduction state, the third switching element also starts a conducting period. This conducting period continues after the second switching element turns off, that is, begins its next non-conducting period; the third switching element being turned off before the start of the next conducting period of the first switching element.
In brief, two periods of resonance are established, the first is an active resonance period which begins at the start of the non-conducting period of the second switching element and concludes at the start of the nonconducting period of the third switching element.
At the moment in which both the second switching element and the third switching element cease, respectively, to conduct, the second resonance period begins, this being a period of natural or free resonance and the duration of which is predetermined.
However, the active resonance period is variable in duration and is a function of the duty cycle of the third switching element and of the duty cycle of the first switching element, that is, of the voltage of the power source and of its load.
In this manner, it is assured that the switching of the first switching element takes place always at zero voltage, independently of the power source voltage and of the load.
REFERENCES:
patent: 4809148 (1989-02-01), Barn
patent: 5434768 (1995-07-01), Jitaru et al.
patent: 5594629 (1997-01-01), Steigerwald
patent: 5781420 (1998-07-01), Xia et al.
patent: 5973939 (1999-10-01), Tan
patent: 5986899 (1999-11-01), Xia et al.
patent: 6002597 (1999-12-01), Rozman
patent: 6061253 (2000-05-01), Igarashi et al.
Alvarez Barcia Lourdes
Corral Blanco Juan Antonio
Rascon Martinez Miguel
Alcatel
Riley Shawn
Sughrue Mion Zinn Macpeak & Seas, PLLC
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