Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-09-04
2004-12-07
Berhane, Adolf (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S041000
Reexamination Certificate
active
06829151
ABSTRACT:
The invention relates to a resonant converter, a regulation method for a resonant converter and a switched-mode power supply.
A switched converter operating as a DC voltage converter transforms an input side DC voltage into one or more output side DC voltages in that the input-side DC voltage is first chopped i.e. transformed into a switched AC voltage and with this switched AC voltage a resonant arrangement comprising at least one capacitor is fed, which capacitor comprises the primary side of a transformer. On the second side the transformer comprises one or more windings whose voltages are rectified to generate output DC voltages.
Known switched-mode power supplies comprise a power supply input circuit for connection to the electricity power grid, and a switched converter. The power supply input circuit renders an intermediate circuit DC voltage available with which the switched converter is fed. The intermediate circuit DC voltage is transformed into one or more output DC voltages by the converter.
Many circuits for switched converters are known. They are not only resonant converters but also circuits in which no resonant arrangement is used. Switched converters can be instrumental in manufacturing cost-effective small and light power supplies/switched-mode power supplies which may be used to advantage in consumer electronics such as set top boxes, satellite receivers, television sets, computer monitors, video recorders, compact audio sets and so on. For these applications are often necessary converters that generate a plurality of output voltages from one DC input voltage.
Usually, one of the output voltages is regulated to a set value. With state-of-the-art converters which produce a plurality of output voltages, with each of the output voltages being assigned a secondary winding of the transformer, a plurality of output voltages cannot be regulated independently of each other. In such circuits is provided a regulating device for only one of the output voltages. It is assumed then that the other voltages—which are linked with the one regulated voltage via the ratio of the number of windings—are “co-regulated” with the latter. However, with very different load on the individual outputs this is highly disadvantageous.
A known topology of a converter comprises the so-termed load resonant converter. In a known circuit for this converter a DC voltage-supplied half bridge is used as an inverter, which half bridge supplies power to a series combination of a resonant capacitor and the primary side of a transformer. The resonant capacitor together with the stray inductance of the transformer as well as further, also secondary-side inductances or capacitors forms a resonant arrangement. On the secondary side the load resonant converter has one or several secondary windings. In this manner a number of output DC voltages is supplied which are customarily filtered by at least one capacitive filter after rectification.
To regulate the output voltage of such a resonant converter it is known to change the drive of the inverter. The switches of the inverter are then controlled so that an AC voltage, in many cases a pulse width modulated voltage is generated having predefined parameters (for example frequency). By variation of the frequency of this voltage the magnitude of the output voltage can be regulated. The output voltage is then increased the closer the frequency comes to the resonant frequency of the resonant arrangement. For LLC converters, operation in the hypercritical area is customary i.e. the resonant arrangement is fed with a voltage whose frequency is higher than the resonant frequencies. During this operation the output voltage can be increased in that the frequency of the voltage is reduced. In known load resonant converters only one output voltage can be regulated directly. Further output voltages are coupled to the directly regulated output voltage via the ratio of the number of windings and are thus “co-regulated”.
The type of converter dominating in consumer electronics is the flyback converter. This is a non-resonant converter. On the primary side the inverter usually needs to have only one switching element. On each of its outputs the flyback converter provides one-way rectification. One of the outputs can be regulated directly. If a second output voltage is necessary in the flyback converter, which output voltage is to be regulated directly, it is known to connect a further converter referred to as step-down converter or buck converter to one of the outputs of the flyback converter, which step-down converter is fed with the output voltage of the first flyback converter and supplies the second output voltage with a separate regulation. Such a circuit comprising two converters is very costly, however.
A further extension of the flyback converter topology which renders two regulated output voltages available is the so-termed double forward flyback converter. A corresponding topology is described, for example, in IEEE-PESC 1988, p. 142: “A Complete Study of the Double Forward—Flyback Converter” by J. Sebastian et al. As with the flyback topology used as a basis here it is not a resonant arrangement, but the primary-side AC voltage that is generated via a simple switch and is directly fed to the primary side of the transformer. On the secondary side there are two secondary units each formed by a secondary winding of the transformer and a one-way rectifier element (diode). The secondary voltages supplied by them are capacitively filtered by one secondary unit and inductively by the other. In this way it is possible to regulate an (inductively filtered) output voltage via the duty cycle of the pulse width modulated voltage and the other (capacitively filtered) output voltage via the frequency of the pulse width modulated voltage. But this “hard switching” topology gives rise to considerable switching losses.
In modern consumer electronics appliances it is more and more often necessary to produce a plurality of supply voltages because there are outputs with a lower power consumption and outputs with a higher power consumption
It is an object of the invention to provide a resonant converter, a regulating method and a switched-mode power supply on at least two outputs of which, which outputs are arranged for delivering powers of different magnitudes, predefined voltages can be delivered.
This object is achieved by a resonant converter as claimed in claim
1
, a regulating method as claimed in claim
10
and a switched-mode power supply as claimed in claim
11
. Dependent claims relate to advantageous embodiments of the invention.
According to the invention a resonant topology is proposed i.e. a resonant arrangement is supplied with power by an inverter which comprises a series capacitor and the primary side of a transformer. Further, secondary-side elements may also form part of the resonant arrangement. In such a resonant topology the secondary voltages can be regulated via the frequency of the primary-side AC voltage. Via hypercritical operation there may be achieved with such a resonant converter that the resonant arrangement acts as an inductive load at the source, so that switching without losses (zero voltage switching) is possible.
According to the invention two types of secondary units are provided which have each at least one secondary winding of the transformer and at least one rectifier element. A first secondary unit (a first type of secondary units, respectively) and a second secondary unit (a second type of secondary units, respectively) are then oppositely oriented. The orientation is understood to mean the winding orientation in connection with the circuitry with the rectifier element. For example, two secondary units of opposite types can be distinguished in that the winding orientation on the shared transformer core is opposite with otherwise the same wiring. It is also possible in case of the same winding orientation of two secondary windings to distinguish the secondary unit of the first and the second type by respectively reversed wiring. Wiring is und
Duerbaum Thomas
Elferich Reinhold
Raets Hubert
Berhane Adolf
Halajian Dicran
Koninklijke Philips Electronics , N.V.
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