Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-06-03
2004-02-03
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000, C363S021020
Reexamination Certificate
active
06687137
ABSTRACT:
TECHNICAL FIELD
This invention relates to a switching power supply circuit which can be incorporated as a power supply in various electronic apparatus.
BACKGROUND ART
A switching power supply circuit which adopts a switching converter in the form of, for example, a flyback converter or a forward converter is widely known. Since switching converters of the types mentioned use a signal of a rectangular waveform as a signal for a switching operation, they have a limitation to suppression of switching noise. It is also known that the switching converters have a limitation to augmentation in power conversion efficiency from their operation characteristics.
Thus, various switching power supply circuits which employ various converters of the resonance type have been proposed by the assignee of the present application. A converter of the resonance type is advantageous in that a high power conversion efficiency can be obtained readily and low noise is realized because the switching operation waveform is a sine waveform. It is advantageous also in that it can be formed from a comparatively small number of parts.
FIG. 10
shows an example of a switching power supply circuit. The switching power supply circuit shown in
FIG. 10
includes a rectifier smoothing circuit for rectifying and smoothing the commercial ac power supply AC. The rectifier smoothing circuit is formed as a voltage multiplying rectifier circuit composed of a pair of rectifier diodes Di
1
and Di
2
and a pair of smoothing capacitors Ci
1
and Ci
2
. The voltage multiplying rectifier circuit produces, for example, where an dc input voltage equal to a peak value of an ac input voltage VAC is represented by Ei, a dc input voltage 2Ei approximately equal to twice the dc input voltage Ei.
The reason why a voltage multiplying rectifier circuit is adopted as a rectifier smoothing circuit in this manner is that it is intended to satisfy the condition of a comparatively heavy load that the ac input voltage is AC 100 V and the maximum load power is 150 W or more.
The switching converter of the voltage resonance type shown in
FIG. 10
has a self-excited construction including a single switching element Q
1
. In this instance, the switching element Q
1
may be a high voltage withstanding bipolar transistor (BJT: junction transistor). The base of the switching element Q
1
is connected to the positive electrode side of the smoothing capacitor Ci
1
(rectified smoothed voltage 2Ei) through a starting resistor RS so that the base current upon starting may be obtained from the rectifier smoothing line. Further, a resonance circuit for self-excited oscillation driving is connected between the base of the switching element Q
1
and the primary side ground and is formed from a series connection circuit including an inductor LB, a detection driving winding NB, a resonance capacitor CB, and a base current limiting resistor RB.
A clamp diode DD is interposed between the base of the switching element Q
1
and the negative electrode (primary side ground) of the smoothing capacitors Ci and forms a path for damper current which flows when the switching element Q
1
is off The collector of the switching element Q
1
is connected to an end of a primary winding N
1
of an insulating converter transformer PIT, and the emitter of the switching element Q
1
is grounded.
A parallel resonance capacitor Cr is connected in parallel between the collector and the emitter of the switching element Q
1
. The parallel resonance capacitor Cr forms, based on a capacitance of the parallel resonance capacitor Cr itself and a combined inductance (L
1
+Lc) obtained from a series connection of a leakage inductance L
1
of the primary winding N
1
side of an orthogonal insulating converter transformer PRT which is hereinafter described and an inductor Lc of a choking coil PCC, a primary side parallel resonance circuit of the voltage resonance type converter. Although detailed description is omitted here, when the switching element Q
1
is off, an operation of the voltage resonance type is obtained by an action of the parallel resonance circuit which causes the voltage Vcr across the parallel resonance capacitor Cr to actually exhibit a sine pulse wave.
The choking coil PCC has a transformer coupling construction of the inductor Lc and the detection driving winding NB. The detection driving winding NB excites an alternating voltage corresponding to a switching period in response to a switching output transmitted from the primary winding N
1
of the orthogonal insulating converter transformer PRT to the inductor Lc.
The orthogonal insulating converter transformer PRT has a function of transmitting a switching output of the switching element Q
1
to the secondary side thereof and performing constant voltage control of the secondary side output thereof The orthogonal insulating converter transformer PRT includes, for example, as shown in
FIG. 11
, a three dimensional core
200
which is formed such that two double channel-shaped cores
201
and
202
each having four magnetic legs are joined to each other at the ends of the magnetic legs thereof. The primary winding N
1
and a secondary winding N
2
are wound in the same winding direction around two predetermined ones of the magnetic legs of the three dimensional core
200
and a control winding NC is wound around two predetermined ones of the magnetic legs of the three dimensional core
200
such that the winding direction thereof is orthogonal to the primary winding N
1
and the secondary winding N
2
, whereby the orthogonal insulating converter transformer PRT is formed as a saturable reactor. In this instance, the opposing faces of the opposing legs of the double channel-shaped cores
201
and
202
are joined together and have no gap formed therebetween. Referring back to
FIG. 10
, one end of the primary winding N
1
of the orthogonal insulating converter transformer PRT is connected to the collector of the switching element Q
1
, and the other end of the primary winding N
1
is connected to the positive side of the smoothing capacitors Ci (rectified smoothed voltage 2Ei) through a series connection of the inductor Lc of the choking coil PCC as shown in FIG.
10
.
On the secondary side of the orthogonal insulating converter transformer PRT, an alternating voltage induced by the primary winding N
1
appears in the secondary winding N
2
. In this instance, as a secondary side parallel resonance capacitor C
2
is connected in parallel to the secondary winding N
2
, a parallel resonance circuit is formed from a leakage inductance L
2
of the secondary winding N
2
and a capacitance of the secondary side parallel resonance capacitor C
2
. The alternating voltage induced in the secondary winding N
2
is converted into a resonance voltage by the parallel resonance circuit. In short, a voltage resonance operation is obtained on the secondary side.
In the parallel resonance circuit on the secondary side formed in such a manner as described above, center taps are provided for the secondary winding N
2
, and rectifier diodes D
01
, D
02
, D
03
and D
04
and smoothing capacitors C
01
and C
02
are connected in such a manner as shown in
FIG. 10
to provide two full-wave rectifier circuits including a full-wave rectifier circuit including rectifier diodes D
01
and D
02
and smoothing capacitor C
01
and another full-wave rectifier circuit including rectifier diodes D
03
and D
04
and smoothing capacitor C
02
.
The full-wave rectifier circuit composed of the rectifier diodes D
01
and D
02
and smoothing capacitor C
01
receives a resonance voltage supplied from the secondary side parallel resonance circuit and produces a dc output voltage E
01
. The full-wave rectifier circuit composed of the rectifier diodes D
03
and D
04
and smoothing capacitor C
02
similarly receives the resonance voltage supplied from the secondary side parallel resonance circuit and produces a dc output voltage E
02
. It is to be noted that, in this instance, the dc output voltage E
01
and the dc output voltage E
02
are inputted also to a co
Frommer William S.
Frommer & Lawrence & Haug LLP
Han Jessica
Sony Corporation
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