Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-07-09
2002-05-28
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021030, C363S097000
Reexamination Certificate
active
06396717
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply circuit having a power factor improving function.
FIGS. 10 and 11
are circuit diagrams showing different examples of a power factor improving circuit in a switching power supply circuit.
FIG. 11
shows only the section of a power factor improving circuit.
FIG. 10
shows a power factor improving circuit
20
a
of a capacitive coupling type using capacitor voltage division.
The power supply circuit is formed by providing a self-excited voltage resonance type switching converter with the power factor improving circuit
20
a
for improving the power factor.
The power supply circuit shown in the figure is provided with a bridge rectifier circuit Di for subjecting a commercial alternating-current power AC to full-wave rectification.
An output rectified by the bridge rectifier circuit Di is stored in a smoothing capacitor Ci via the power factor improving circuit
20
a
, whereby a rectified and smoothed voltage Ei is obtained across the smoothing capacitor Ci.
For description of the voltage resonance type converter, reference is to be made to embodiments of the present invention.
A parallel resonant capacitor Cr is connected to a collector of a switching device Q
1
. Capacitance of the parallel resonant capacitor Cr and leakage inductance L
1
on the primary winding N
1
side of an isolating converter transformer PIT form a primary-side parallel resonant circuit of the voltage resonance type converter. During the off period of the switching device Q
1
, a voltage across the resonant capacitor Cr practically forms a sinusoidal pulse waveform as a result of the effect of the parallel resonant circuit, and thus a voltage resonance type operation is obtained.
The power factor improving circuit
20
a
has a choke coil Ls and a fast recovery type diode D
1
connected in series with each other and inserted between a positive output terminal of the bridge rectifier circuit Di and a positive terminal of the smoothing capacitor Ci. A filter capacitor CN is provided in parallel with the series connection circuit of the choke coil Ls and the fast recovery type diode D
1
, thereby forming a normal-mode low-pass filter in conjunction with the choke coil Ls.
A parallel resonant capacitor C
10
is provided in parallel with the fast recovery type diode D
1
. The parallel resonant capacitor C
10
forms a series resonant circuit in conjunction with the choke coil Ls. The series resonant circuit thereby has an effect of controlling increase in the rectified and smoothed voltage Ei at light load.
The parallel resonant capacitor Cr is connected to the power factor improving circuit
20
a
at a node that connects the choke coil Ls, an anode of the fast recovery type diode D
1
, and the parallel resonant capacitor C
10
with each other, so that a switching output obtained in the primary-side parallel resonant circuit is fed back to the power factor improving circuit
20
a.
Thus, with the configuration of the power factor improving circuit
20
a
shown in the figure, the switching output obtained in the primary-side parallel resonant circuit is fed back to the rectified current path via the capacitive coupling of the parallel resonant capacitor Cr.
Since the parallel resonant capacitor Cr is connected to the anode of the fast recovery type diode D
1
in the power factor improving circuit
20
a
, the parallel resonant capacitor Cr and the parallel resonant capacitor C
10
are in a state of being connected in series with each other. Specifically, a voltage resonance pulse voltage appearing as a voltage across the parallel resonant capacitor Cr is divided by a capacitance ratio between the parallel resonant capacitor Cr and the parallel resonant capacitor C
10
. The voltage is fed back to the smoothing capacitor Ci via the parallel resonant capacitor C
10
connected in parallel with the fast recovery type diode D
1
, and thus a circuit system of a voltage feedback type is formed.
This circuit configuration divides a primary-side voltage resonance-pulse voltage Vcp=600 V, for example, into voltages in a ratio of about 3:1 by means of the primary-side parallel resonant capacitors Cr and C
10
, and then feeds back a high-frequency sinusoidal pulse voltage of 150 V.
At times near a positive and a negative peak of an alternating-current input voltage VAC, the fast recovery type diode D
1
conducts, and the smoothing capacitor Ci is charged with a steep pulse charging current from the alternating-current input power supply AC.
At other than the times near the positive and negative peaks of the alternating-current input voltage VAC, the fast recovery type diode D
1
is allowed to repeat switching operation by the pulse voltage being fed back. During the off period of the fast recovery type diode D
1
, a parallel resonance current caused by the parallel resonant capacitor Cr, the inductance LS, and the capacitor CN flows. During the on period of the fast recovery type diode D
1
, a high-frequency charging current flows from the alternating-current input power supply AC to the smoothing capacitor Ci via the inductance LS.
This operation increases the conduction angle of an alternating input current IAC, thereby making it possible to improve the power factor.
FIG. 11
shows a power factor improving circuit
20
b
of a diode coupling type using a tertiary winding system.
The power factor improving circuit
20
b
has a choke coil LS and a Schottky diode D
1
s connected in series with each other and inserted between the positive output terminal of the bridge rectifier circuit Di and the positive terminal of the smoothing capacitor Ci.
A filter capacitor CN is inserted in parallel with the series connection of the choke coil LS and the Schottky diode D
1
s, thereby forming a normal-mode low-pass filter in conjunction with the choke coil LS.
A tertiary winding N
3
of an isolating converter transformer PIT is connected via a series resonant capacitor C
3
to a node that connects an anode of the Schottky diode D
1
s and the choke coil LS with each other, whereby the switching output voltage obtained in the primary-side parallel resonant circuit is fed back to the power factor improving circuit
20
b.
In this case, around peaks of the absolute value of the alternating-current input voltage VAC, the Schottky diode D
1
s conducts, and a charging current I
1
flows from the alternating-current input power supply AC to the smoothing capacitor Ci via the choke coil LS and the Schottky diode D
1
s. At the same time, a voltage resonance pulse voltage of the tertiary winding N
3
is fed back to a series circuit of the series resonant capacitor C
3
and the Schottky diode D
1
s for switching operation of the Schottky diode D
1
s. Thereby, a flowing range of the alternating input current IAC is extended, and thus the power factor is improved.
When the absolute value of the alternating-current input voltage VAC is lowered, the Schottky diode D
1
s becomes nonconductive, and the voltage resonance pulse voltage of the tertiary winding N
3
is turned into a series resonance voltage by a series circuit of the series resonant capacitor C
3
, the choke coil LS, and the filter capacitor CN.
The two circuit examples are shown above, and the configuration of
FIG. 11
has the higher AC/DC power conversion efficiency &eegr;AC/DC. Characteristics of the AC/DC power conversion efficiency &eegr;AC/DC and the power factor PF in this case are shown in
FIGS. 12 and 13
.
FIG. 12
shows characteristics of the power factor PF and the AC/DC power conversion efficiency &eegr;AC/DC when the load power Po is varied from 40 W to 200 W.
FIG. 13
shows characteristics of variations in the power factor PF and the AC/DC power conversion efficiency &eegr;AC/DC when the alternating-current input voltage VAC is varied from 80 V to 260 V.
As is understood from the figures, it is possible to maintain a power factor PF of 0.7 or more and achieve an AC/DC power conversion efficiency &eegr;AC/DC of 90% or more over wide ranges of the load power and the alternating-current inp
Berhane Adolf Deneke
Maioli Jay H.
Sony Corporation
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