Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-07-10
2002-07-02
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021170, C363S040000
Reexamination Certificate
active
06414856
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of power supplies, and in particular, to a method and apparatus directed to a multiple output power converter with higher precision on matching output voltages.
BACKGROUND OF THE INVENTION
Power converters are employed in a wide variety of electronic systems, including personal computers, cable modems, disk drives, calculators, televisions, test-equipment, and hi-fi equipment. A power converter, also called a power supply, is a device for the conversion of available power with one set of characteristics to another set of characteristics. A power converter may be used to produce a regulated (or controlled) output voltage from an unregulated input voltage. The regulated output voltage may have a magnitude and possibly a polarity that differs from the input voltage. For example, a 120 V ac utility voltage may be rectified or converted to produce a dc voltage of about 170 V. A dc—dc converter may then be employed to reduce the voltage to a regulated 5 V.
Because of its circuit simplicity and relative low cost, a flyback type of converter has become a favored topology for high-voltage power supplies such as televisions and computer monitors. The flyback converter topology also finds wide appeal in switching power supplies in the 50-100 watt power range.
An example of a conventional two-output flyback converter (
100
) is shown in FIG.
1
. As shown in the figure, the conventional two-output flyback converter (
100
) includes a primary transformer winding (L
11
), a switch device (SW
11
), a secondary transformer winding (L
12
), a tertiary transformer winding (L
13
), a primary output diode (D
11
), a secondary output diode (D
12
), a primary output capacitor (C
11
), and a secondary output capacitor (C
12
).
In
FIG. 1
, the primary transformer winding (L
11
) is connected between nodes N
101
and N
104
. The switching device (SW
11
) is connected between node N
104
and a circuit ground potential (GND). The secondary transformer winding (L
12
) is connected between node N
102
and a circuit ground potential (GND). The primary output diode (D
11
) is connected between node N
102
and node N
103
. The primary output capacitor (C
11
) is connected between node N
103
and a circuit ground potential (GND). The tertiary transformer winding (L
13
) is connected between node N
105
and node N
107
. The secondary output diode (D
12
) is connected between node N
105
and node N
106
. Node N
106
is connected to a circuit ground potential (GND). The secondary output capacitor (C
12
) is connected between node N
107
and node N
106
. A core (F
11
), such as a ferrite core, is located between the primary transformer winding (L
11
), the secondary transformer winding (L
12
), and the tertiary transformer winding (L
13
).
Although the transformer windings (L
11
-L
13
) and the core (F
11
) appear similar to a transformer, it is more descriptively referred to as a “three winding inductor.” Unlike an ideal transformer, the current does not flow simultaneously in the first and second (or third) windings of the conventional two-output flyback converter (
100
). Instead, the flyback converter's magnetizing inductance assumes the role of an inductor and a magnetizing current is switched between the primary transformer winding (L
11
), the secondary transformer winding (L
12
) and the tertiary transformer winding (L
13
), during the flyback's operation.
In operation, an input voltage (Vin) is coupled to node N
101
, and the flyback converter (
100
) provides a primary output voltage (Vo
11
) and a secondary output voltage (Vo
12
) at nodes N
103
and N
107
respectively. The primary (Vo
11
) and secondary (Vo
12
) output voltages are coupled to a primary and secondary load (not shown). The flyback converter has two operating modes corresponding to the operation of the switching device (SW
11
).
During the first mode of operation of the flyback converter (
100
), the switching device (SW
11
) is closed (the “on” period). The winding polarity of the transformer ensures that the output diodes (D
11
) and (D
12
) are reverse-biased so that no transformer secondary current flows through the secondary transformer winding (L
12
). The primary transformer winding (L
11
) functions as an inductor, connected through node N
101
to the input voltage (Vin) and producing a primary current. The primary current rises linearly in the primary transformer winding (L
11
) during this period. The transformer is designed to have a high inductance so that energy is stored in the magnetic field. The output capacitors (C
11
) and (C
12
) act as reservoirs (having been charged during the “off” periods) maintaining the voltages across the loads (not shown).
In the second mode of operation (the “off” period), the switch circuit (SW
11
) is opened and the primary current ceases to flow in the primary transformer winding (L
11
). The magnetizing current is then referred to the secondary transformer winding (L
12
) and the output diodes (D
11
) and (D
12
) now become forward biased. Thus, energy stored in the magnetic field of the converter during the “on” period of the switching device (SW
11
) is transferred to the output loads (not shown) creating the first and secondary output voltages (Vo
11
and Vo
12
).
SUMMARY OF THE INVENTION
The present invention is directed to provide a method and apparatus that produces high precision output voltage matching in a multiple output power converter. In a conventional multiple output power converter, such as a flyback converter, poor output voltage precision often is a result of the non-ideal characteristics of the components used in the circuit. The present invention minimizes the effects of the non-ideal characteristics of the components by the incorporation of transfer capacitance circuits. As a result, the output voltages are closer together in their magnitudes, resulting in higher precision in matching output voltage.
In accordance with one embodiment of the present invention, an apparatus is directed to producing multiple output signals from an input signal. The apparatus includes inductive windings, transfer capacitance circuits, rectifier capacitance circuits, output capacitance circuit, and a switching circuit. In the apparatus, a first inductive winding is magnetically coupled to a second inductive windings. A first transfer capacitance circuit is coupled to the first and second inductive winding. A first rectifier circuit is coupled to the second inductive winding and a first output terminal. A first output capacitance circuit is coupled to the first output terminal and a circuit ground potential. A second transfer capacitance circuit is coupled to the first inductive winding and a third inductive winding. A second rectifier circuit is coupled to the third inductive winding and the circuit ground potential. Additionally, a second output capacitance circuit is coupled to the second output terminal and the circuit ground potential. In the apparatus, the first and second transfer capacitance circuits store energy in response to the input signal when the switching circuit is in a closed position. The first and second transfer capacitance circuits transfer energy through the first and second output terminals respectively when the switching circuit is in an open position. One of the multiple output signals is associated with the first output terminal and a second of the multiple output signals is associated with the second output terminal. The output signals associated with the first and second output terminals have substantially the same magnitude. Moreover, the first, second, and third inductive windings may be wound on a common core.
The apparatus above can be extended by further including at least one additional circuit that is arranged to provide an additional one of the multiple output signals. Each of the additional circuits includes an additional inductive winding, an additional transfer capacitance circuit that is coupled to the first inductive winding and the additional inductive winding, and an addi
Ambatipudi Ravindra
Hartman Mark
Hertzberg Brett A.
National Semiconductor Corporation
Vu Bao Q.
LandOfFree
Method and apparatus for multiple output converter with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for multiple output converter with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for multiple output converter with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2831833