Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-12-06
2004-05-04
Bethane, Adolf (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06731521
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a switching power supply circuit which includes a circuit for improving the power factor.
Various power supply circuits wherein a resonance type converter is provided on the primary side have been proposed by the assignee of the present patent application.
FIG. 9
shows an example of a switching power supply circuit including a configuration for improving the power factor which is one of switching power supply circuits proposed by the assignee of the present patent application. The switching power supply circuit is suitable for conditions of the load power Po=200 W or more and the ac input voltage VAC=200 V type or conditions of the load power Po=150 W or less and the ac input voltage VAC=100 V type.
Referring to
FIG. 9
, the power supply circuit shown includes a common mode choke coil CMC and a filter capacitor CL connected in such a manner as seen in
FIG. 9
to a commercial ac power supply AC to form a filter for removing harmonics superposed on the commercial ac power supply AC.
A power choke coil PCH is inserted in series in one of a pair of lines of the commercial ac power supply AC. The power factor PF is improved to approximately 0.75 by the power choke coil PCH.
A full-wave rectification circuit including a bridge rectification circuit Di and a smoothing capacitor Ci connected in such a manner as shown in
FIG. 9
is formed for the commercial ac power supply AC. The full-wave rectification circuit rectifies and smoothes the commercial ac power supply AC to produce a rectified smoothed voltage Ei which appears across the smoothing capacitor Ci. The rectified smoothed voltage Ei has a level equal to the ac input voltage VAC and is inputted as a dc input voltage to a primary side switching converter of the following stage.
In this instance, a current resonance type separately excited converter is used as the switching converter which performs a switching operation with the above-mentioned dc input voltage inputted thereto. The current resonance type converter includes two switching elements Q
1
and Q
2
as seen in FIG.
9
.
In this instance, the switching elements Q
1
and Q
2
are formed from MOS-FETs and connected in such a manner as seen in
FIG. 9
to form a switching circuit of the half bridge coupling type.
Clamp diodes DD
1
and DD
2
are connected in such directions as seen in
FIG. 9
in parallel to the switching elements Q
1
and Q
2
, respectively.
A partial resonance capacitor Cp for partial voltage resonance is connected to the switching element Q
2
from between the switching elements Q
1
and Q
2
.
An isolation converter transformer PIT is provided to transmit a switching output of the primary side switching converter to the secondary side.
The isolation converter transformer PIT includes, for example, an EE type core shown in
FIG. 13. A
primary winding N
1
and a secondary winding N
2
are wound on a central magnetic leg of the EE type core of the isolation converter transformer PIT using a bobbin or the like such that an isolation condition from each other may be assured.
The central magnetic leg of the EE type core has a gap of, for example, approximately 1.5 mm to 2.0 mm formed therein so that a loose coupling state wherein the coupling coefficient k is approximately k=0.8 may be obtained between the primary winding N
1
and the secondary winding N
2
. This prevents occurrence of abnormal vibrations when an intermediate load is applied.
The primary winding N
1
of the isolation converter transformer PIT is connected at one end thereof to the drain of the switching element Q
1
and at the other end thereof to a source-drain node of the switching elements Q
1
and Q
2
through a series resonance capacitor C
1
. Through the connection just described, a switching output of the switching elements Q
1
and Q
2
is transmitted to the primary winding N
1
.
In the connection scheme described, the primary winding N
1
and the series resonance capacitor C
1
are connected in series, and thus, a primary side series resonance circuit is formed from the leakage inductance of the primary winding N
1
and the capacitance of the series resonance capacitor C
1
. The primary side series resonance circuit makes the switching operation of the switching elements Q
1
and Q
2
a switching operation of the current resonance type.
A full-wave rectification circuit formed from a bridge rectification circuit DBR and a smoothing capacitor C
0
is connected to the secondary winding N
2
of the isolation converter transformer PIT. A secondary side dc output voltage E
0
is obtained across the smoothing capacitor C
0
by the full-wave rectification circuit. The secondary side dc output voltage E
0
is supplied to a load not shown. Further, the secondary side dc output voltage E
0
is branched and supplied as a detection voltage also to an oscillation drive/control circuit
2
.
The oscillation drive/control circuit
2
may be formed typically from an IC for universal use and is provided to drive the switching elements Q
1
and Q
2
in accordance with separate excitation system to perform a switching operation.
Driving signals (voltages) are outputted from the oscillation drive/control circuit
2
to the gates of the switching elements Q
1
and Q
2
so that the switching elements Q
1
and Q
2
perform switching on/off alternately with a required switching frequency.
The oscillation drive/control circuit
2
operates to vary the frequency of the driving signals in response to the level of the secondary side dc output voltage E
0
inputted thereto. Consequently, the switching elements Q
1
and Q
2
are controlled so as to vary the switching frequency in response to the level of the secondary side dc output voltage E
0
.
When the switching frequency varies in this manner, the resonance impedance of the primary side dc resonance circuit varies, and also the energy to be transmitted from the primary side to the secondary side in the isolation converter transformer PIT varies. Therefore, also the level of the secondary side dc output voltage E
0
is variably controlled. In other words, the secondary side dc output voltage E
0
is varied by variably controlling the switching frequency thereby to achieve constant voltage control.
The power supply circuit shown in
FIG. 9
is suitable for conditions of the load power Po=200 W or more and the ac input voltage VAC=200 V type or conditions of the load power Po=150 W or less and the ac input voltage VAC=100 V type. In contrast, in order to satisfy conditions of the load power Po=200 W or more and the ac input voltage VAC=100 V type, the rectification circuit system for rectifying the commercial ac power supply AC to obtain the rectified smoothed voltage Ei (dc input voltage), the power supply circuit shown in
FIG. 9
is modified in such a manner as seen in
FIG. 10
, in which like reference characters to those of
FIG. 9
denote like elements.
Referring to
FIG. 10
, the power supply circuit shown includes, as a rectification circuit system for rectifying the commercial ac power supply AC, two rectification diodes D
13
and D
14
and two smoothing capacitors Ci
1
and Ci
2
. The elements mentioned are connected in such a manner as seen in
FIG. 10
so that the rectified smoothed voltage Ei (dc input voltage) obtained across the smoothing capacitors Ci
1
and Ci
2
connected in series has a level equal to twice that of the ac input voltage VAC. In other words, the rectification circuit system is formed as a double voltage rectification circuit.
It is known that, for example, where the dc input voltage is equal to twice the ac input voltage VAC in a comparatively low load condition that the load power Po is Po=200 W or more where the ac input voltage VAC is 100 V type, the peak current flowing through the switching elements in the succeeding stage increases and the power loss increases as much. Therefore, if the dc input voltage of the level equal to twice that of the ac input voltage VAC is obtained by the
Bethane Adolf
Maioli Jay H.
Sony Corporation
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