Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1996-07-18
1997-12-30
Berhane, Adolf
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
363 97, H02M 3335
Patent
active
057037655
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a flyback converter.
Such a flyback converter is already known from the book by Joachim Wustehube: "Schaltnetzteile: Grundlagen, Entwurf, Schaltungsbeispiele expert-verlag 1979, pages 87 to 91.
Conventional flyback converters have a transformer which absorbs energy during the time in which a power switch, which is located in the main circuit on the primary side, is switched on and emits energy to the main circuit on the secondary side at least during the part of the phase in which the power switch is switched off.
The output voltage of the flyback converter is a DC voltage whose magnitude is a fraction of the amplitude of the pulsed voltage on the secondary side. The control range of the power switch is frequently limited to a duty ratio of 0.5.
Furthermore, the reference elements which can be used as regulators are known from the book "Motorola Linear and Interface Integrated Circuits", 2nd Edition, 1988, pages 5-17 to 5-24. Such reference elements have a reference-ground voltage connection, an actual value input and a control voltage output.
The output voltage of a flyback converter can be regulated at a constant value with the aid of a regulating arrangement. However, difficulties can arise in this case when it is intended to produce a comparatively low output voltage with the aid of the flyback converter. If the regulating output voltage emitted from the flyback converter is not sufficient to be used as the auxiliary voltage for the regulating arrangement, then the required auxiliary voltage must be produced in addition to the regulated output voltage.
If the flyback converter, per se, has no suitable output circuit, then such an auxiliary voltage can be produced by means of a winding which is additionally fitted on the transformer core. This requires a transformer with increased complexity in terms of windings, and an increased requirement for winding space which, furthermore, can also lead to thermal problems in the case of the transformer.
Another option is to use an auxiliary voltage of another existing converter as the auxiliary voltage. However, when two converters are coupled in such a manner, difficulties can arise in terms of the constancy of the auxiliary voltage when the current of the additional converter is limited, or in the time sequencing of the running up of the auxiliary voltage and output voltage of the flyback converter.
SUMMARY OF THE INVENTION
The object of the invention is thus to design a flyback converter having a regulated output voltage in such a manner that the auxiliary voltage is produced with little complexity in the flyback converter itself.
Considerations in the context of the invention have shown that a square-wave voltage is available on the rectifier diode of the main circuit on the output side, the amplitude of the square-wave voltage in the case of a flyback converter of conventional design is approximately double the regulated DC output voltage and that, taking account of the comparatively low current load on the auxiliary voltage source, an auxiliary voltage which is required for a regulating arrangement can be obtained from this square-wave voltage with the aid of an auxiliary circuit.
In general terms the present invention is a flyback converter having an electronic switch which is connected in series with a primary winding of a transformer in a main circuit on the primary side and can be controlled by a control device. On the secondary side it has a main circuit which is connected to a secondary winding of the transformer. It contains a first diode in a series path and an energy-storage capacitor in a subsequent parallel path, connected in parallel with the output in the transformer. It has a regulating arrangement which is connected to an output of the flyback converter and is supplied with an auxiliary voltage. The duty ratio of the control voltage which controls the electronic switch is limited to a predetermined upper limit. The input of an auxiliary circuit is connected tot he rectifier diode of the
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patent: 4868729 (1989-09-01), Suzuki
patent: 4996638 (1991-02-01), Orr
patent: 5173847 (1992-12-01), Suzuki
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patent: 5301095 (1994-04-01), Teramoto et al.
patent: 5479087 (1995-12-01), Wright
patent: 5508904 (1996-04-01), Hara
Patent Abstracts of Japan, "Auxiliary Power Circuit for Switching Regulator", Toyoda Masashi, vol. 13, no. 117, JP63287364, Mar. 22, 1989
Berhane Adolf
Siemens Aktiengesellschaft
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