Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-10-25
2002-09-17
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021020, C363S021120, C363S019000
Reexamination Certificate
active
06452817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power supply circuit equipped to various types of electronic equipment as a power source.
2. Description of the Related Art
There has been widely known a switching power supply circuit using a switching converter of such a type as a fly-back converter or a forward converter. These switching converters are restricted in reduction of switching noises because the switching operation waveform thereof is a rectangular waveform. Further, it has been found that restrictions are imposed on improvements of the power transform efficiency from the viewpoint of the performance characteristics.
Therefore, various types of switching power supply circuits each based on a resonance type converter were previously proposed by the applicant of this application. The resonance type converter can easily achieve a high power transform efficiency, and also it can reduce the noises because the switching operation waveform is a sine wave. Further, there is a merit that it can be constructed by a relatively small number of parts.
FIG. 7
is a circuit diagram showing a conventional switching power supply circuit, which can be constructed on the basis of the invention previously-proposed by the applicant of this application. As the basic construction of the power supply circuit shown in
FIG. 7
, it is equipped with a voltage resonance type converter as a primary switching converter.
In the power supply circuit shown in
FIG. 7
, a rectified smoothened voltage Ei corresponding to the level which is once as high as an alternating input voltage VAC is generated from a commercial alternating power source (alternating input voltage VAC) by a bridge rectifying circuit Di and a smoothing capacitor Ci.
At the primary side of the power supply circuit thus constructed, a self-exciting type construction is shown as a voltage resonance type converter circuit for performing a single-end operation by a single-stone switching element Q
1
. In this case, a bipolar transistor (BJT; junction type transistor) having high resistance to voltage is adopted for the switching element Q
1
.
The base of the switching element Q
1
is connected to the positive polarity side of the smoothing capacitor Ci (rectified smoothened voltage Ei) through a starting resistor (RS), and the base current at the starting time is achieved from the rectifying and smoothing line.
A drive winding NB comprising one turn 1T of winding at the primary side of the insulating converter transformer PIT, and a series resonance circuit for self-exciting driving operation which comprises a series circuit of an inductor LB, a resonance capacitor CB and a base current limiting resistor RB are connected across the base of the switching element Q
1
and the earth at the primary side. A switching frequency fs for switching on/off the switching element Q
1
is generated by the self-exciting circuit.
A route for clamp current flowing when the switching element Q
1
is in off-state is formed by a clamp diode DD
1
inserted between the base of the switching element Q
1
and the negative polarity (the earth at the primary side) of the smoothing capacitor Ci. Further, the collector of the switching element Q
1
is connected to the winding-start edge portion of the primary winding N
1
of the insulating converter transformer PIT, and the emitter thereof is connected to the earth.
A parallel resonance capacitor Cr is connected between the collector and emitter of the switching element Q
1
in parallel to the switching element Q
1
. In this case, the primary parallel resonance circuit of the voltage resonance type converter is also formed by the capacitance of the parallel resonance capacitor cr itself and a leakage inductance L
1
at the primary winding N
1
side of the insulating converter transformer PIT.
The insulating converter transformer PIT is provided to transmit the switching output of the switching converter achieved at the primary side to the secondary side.
The insulating converter transformer PIT is provided with an EE type core comprising ferrite E type cores CR
1
, CR
2
as shown in FIG.
8
. In the insulating converter transformer PIT, divided bobbins B are used, and the primary winding N
1
and the secondary winding N
2
both of which are litz wires are wounded around the divided areas as shown in FIG.
8
. Here, the primary winding N
1
and the secondary winding N
2
are wound in the same winding direction.
A gap G is formed for a center magnetic leg of the EE type core as shown in FIG.
8
. The leakage inductance in the insulating converter transformer PIT is determined by the gap length of the gap G, and loose coupling based on a required coupling coefficient is achieved. The coupling coefficient k at this time is set to k≈0.85 so that the loose coupling state is achieved, and thus the saturation state is hardly achieved. The gap G can be formed by making the center magnetic leg of the E-type cores CR
1
, CR
2
shorter than two outer magnetic legs, and the gap length in this case is set to about 1 mm.
For the mutual inductance M between the inductance L
1
of the primary winding N
1
and the inductance L
2
of the secondary winding N
2
, the operation of the insulating converter transformer PIT may be selectively set to a +M operation mode (additive polarity mode: forward operation) or a −M operation mode (subtractive polarity mode: fly-back operation) in accordance with the connection relationship between the polarity (winding direction) of the primary winding N
1
, the secondary winding N
2
and the rectifying diode D
0
.
For example, assuming that the polarities (winding directions) of the primary winding N
1
and the secondary winding N
2
are the same, the mutual inductance is set to +M if the circuit is equivalent to the circuit shown in
FIG. 9A
, and the mutual inductance is set to −M if the circuit is equivalent to the circuit shown in FIG.
9
B.
As shown in
FIG. 7
, the winding-start edge portion of the primary winding N
1
of the insulating converter transformer PIT is connected to the collector of the main switching element Q
1
, and the winding-end edge portion is connected to the line of the rectified smoothened voltage Ei.
Further, the winding-start edge portion of the secondary winding N
2
is connected to the earth at the secondary side, and the winding-end edge portion is connected to the positive-polarity terminal of the smoothing capacitor C
01
through the rectifying diode D
01
.
In such a connection style, the additive polarity connection is carried out between the primary winding N
1
and the secondary winding N
2
of the insulating converter transformer PIT, and this corresponds to the equivalent circuit shown in FIG.
9
A.
The switching output of the main switching element Q
1
forming the primary voltage resonance type converter is transmitted to the primary winding N
1
of the insulating converter transformer PIT having the above construction, and further transmitted to the secondary winding N
2
while it is excited.
In this case, at the secondary side of the insulating converter transformer PIT, the secondary parallel resonance capacitor C
2
is connected to the secondary winding N
2
in parallel as shown in the figure, so that the secondary parallel resonance circuit is formed together with the leakage inductance L
2
of the secondary winding N
2
.
A half-wave rectifying circuit comprising the rectifying diode D
01
and the smoothing capacitor C
01
is connected to the secondary parallel resonance circuit in the connection style shown in the figure, thereby outputting the secondary DC output voltage E
01
.
In the power supply circuit thus constructed, the primary side is equipped with the parallel resonance circuit for setting the switching operation to the voltage resonance type, and the secondary side is equipped with the parallel resonance circuit for achieving the voltage resonance operation. In this specification, the switching converter that operates while it is equipped with the resonance circu
Frommer William S.
Frommer & Lawrence & Haug LLP
Riley Shawn
Sony Corporation
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