Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-11-07
2001-11-13
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S019000, C363S097000
Reexamination Certificate
active
06317337
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply circuit for use as a power supply for various electronic devices.
Switching power supply circuits that are widely known in the prior art employing a switching converter such as a flyback converter or a forward converter. These switching converters suffer a limitation on the suppression of switching noise because the switching waveform is rectangular. It is also known that their operating characteristics pose a limitation on efforts to increase the power conversion efficiency.
The applicant of the present application has proposed various switching power supply circuits that employ various resonant converters. The resonant converters are capable of easily achieving a high power conversion efficiency and are subject to low noise because the switching waveform becomes sinusoidal. The resonant converters are also advantageous in that they can be constructed of a relatively small number of parts.
FIG. 10
of the accompanying drawings shows an embodiment of a switching power supply circuit based on an invention proposed by the applicant.
The switching power supply circuit shown in
FIG. 10
is capable of a maximum load power of 150 W or higher in a commercial power supply system of AC 100 V available in Japan and the U.S.A.
The switching power supply circuit shown in
FIG. 10
has a voltage doubler rectifying circuit comprising rectifying diodes Di
1
, Di
2
and smoothing capacitors Ci
1
, Ci
2
as a rectifying and smoothing circuit for rectifying and smoothing a commercial AC power supply AC. The voltage doubler rectifying circuit generates a DC input voltage 2Ei which is about twice a DC input voltage Ei that corresponds to the peak value of the AC power supply AC. If the AC input voltage VAC of the AC power supply AC is VAC=144 V, for example, then the DC input voltage 2Ei is about 400 V.
The voltage doubler rectifying circuit is used as the rectifying and smoothing circuit in order to meet the relatively high load condition of the maximum load power of 150 W or higher in the commercial power supply system of AC 100 V. Stated otherwise, since the DC input voltage is about twice the ordinary DC input voltage, the amount of a current flowing into a switching converter in a following stage is suppressed to keep the components of the switching power supply circuit reliable.
A rush current limiting resistor Ri is inserted in a rectifying current path of the voltage doubler rectifying circuit for suppressing a rush current which flows into smoothing capacitors when the power supply is turned on.
In
FIG. 10
, tne switching power supply circuit includes a self-excited voltage-resonant switching converter including a switching element Q
1
which comprises a high-withstand-voltage bipolar transistor (BJT: junction transistor).
The switching element Q
1
has a base connected to the positive terminal of the smoothing capacitor Ci
1
(the rectified and smoothed voltage 2Ei) via a starting resistor RS, so that a base current will be produced from the rectifying and smoothing line when the switching power supply circuit starts to operate. A resonant circuit for self-excited oscillation, which comprises a series-connected circuit of an inductor LB, a detecting drive winding NB, a resonant capacitor CB, and a base current limiting resistor RB, is connected between the base of the switching element Q
1
and primary-side ground.
A clamping diode DD inserted between the base of the switching element Q
1
and the negative terminal of the smoothing capacitor C
1
(primary-side ground) forms a path of a damper current which flows when the switching element Q
1
is turned off. The switching element Q
1
has a collector connected to a terminal of a primary winding N
1
of a crossed insulated converter transformer PIT. The emitter of the switching element Q
1
is connected to the ground.
A parallel resonant capacitor Cr is connected parallel between the collector and emitter of the switching element Q
1
. The capacitance of the parallel resonant capacitor Cr, and the combined inductance (L
1
+Lc) obtained by a series-connected circuit of the leakage inductance L
1
of the primary winding N
1
of the crossed insulated converter transformer PRT and the inductor Lc of a choke coil PCC jointly make up a primary-side parallel resonant circuit of the voltage-resonant converter. Although not described in detail here, when the switching element Q
1
is turned off, the parallel resonant circuit causes a voltage Vcr across the resonant capacitor Cr to have a sine-wave pulse waveform, resulting in voltage-resonant operation.
The choke coil PCC has the inductor Lc and the detecting drive winding NB connected to each other as a transformer. The detecting drive winding NB induces an alternating voltage corresponding to a switching period due to a switching output transmitted from the primary winding N
1
of the crossed insulated converter transformer PRT to the inductor Lc.
The crossed insulated converter transformer PRT has a function to transmit the switching output of the switching element Q
1
to a secondary side thereof and also to perform constant-voltage control on the secondary-side output.
As shown in
FIG. 11
of the accompanying drawings, for example, the crossed insulated converter transformer PRT comprises a three-dimensional core
200
having two double-C-shaped cores
201
,
202
each with four magnetic legs, the magnetic legs of the double-C-shaped cores
201
,
202
being connected at ends thereof to each other. The insulated converter transformer PRT has a primary winding N
1
and a secondary winding N
2
which are wound around two magnetic legs of the three-dimensional core
200
in one direction, and a control winding NC wound around two magnetic legs of the three-dimensional core
200
perpendicularly to the primary winding N
1
and the secondary winding N
2
. The crossed insulated converter transformer PRT is thus constructed as a saturable reactor. The mating ends of the magnetic legs of the double-C-shaped cores
201
,
202
are joined to each other with no gap defined therebetween.
The primary winding N
1
of the crossed insulated converter transformer PRT has a terminal connected to the collector of the switching element Q
1
and another terminal connected to the positive terminal of the smoothing capacitor C
1
(the rectified and smoothed voltage 2Ei) via the series-connected inductor Lc of the choke coil PCC.
An alternating voltage is induced across the secondary winding N
2
of the crossed insulated converter transformer PRT by the primary winding N
1
thereof. A secondary-side parallel resonant capacitor C
2
is connected parallel to the secondary winding N
2
, and the leakage inductance L
2
of the secondary winding N
2
and the capacitance of the secondary-side parallel resonant capacitor C
2
jointly make up a parallel resonant circuit, which causes the alternating voltage to be induced as a resonant voltage across the secondary winding N
2
, thereby providing voltage resonant operation on the secondary side.
To the parallel resonant circuit on the secondary side, there are connected rectifying diodes D
01
, D
02
, D
03
, D
04
and smoothing capacitors C
01
, C
02
as shown via central taps of the secondary winding N
2
. The rectifying diodes D
01
, D
02
and the smoothing capacitor C
01
make up a full-wave rectification circuit, and the rectifying diodes D
03
, D
04
and the smoothing capacitor C
02
make up another full-wave rectification circuit.
The full-wave rectification circuit which is constructed of the rectifying diodes D
01
, D
02
and the smoothing capacitor C
01
is supplied with the resonant voltage from the parallel resonant circuit on the secondary side and generates a DC output voltage E
01
. The full-wave rectification circuit which is constructed of the rectifying diodes D
03
, D
04
and the smoothing capacitor C
02
is supplied with the resonant voltage from the parallel resonant circuit on the secondary side and generates a DC output voltage E
02
.
The DC output volta
Frommer William S.
Frommer Lawrence & Haug LLP.
Kessler Gordon
Laxton Gary L.
Sony Corporation
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