Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-03-20
2001-02-06
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S098000
Reexamination Certificate
active
06185111
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switching power supply apparatus for supplying a stabilized DC voltage to industrial and consumer-oriented electronic apparatuses.
BACKGROUND OF THE INVENTION
In recent years, switching power supply apparatuses have been required to be more compact, efficient and reliable as electronic apparatuses in which switching power supply apparatuses become less expensive, more compact, higher in performance and more energy-efficient. A switching power supply apparatus basically comprises an inverter that turns on and off an input DC voltage at a high frequency to covert it into a high-frequency AC voltage, a transformer for converting AC currents and voltages and for keeping insulation between input and output, and a rectifying and smoothing circuit for converting an alternating current into a direct current. The output voltage is regulated by changing the on/off ratios of the switching devices in the switching sections of the inverter section. Since the transformer is driven at a high frequency, it can be made compact. In addition, the transformer has an extremely low loss because of on/off operation. For these reasons, the switching power supply apparatus is characterized to be made compact and highly efficient.
However, in reality, there is no ideal switching device. In a semiconductor switch used in a switching section or a rectifying circuit, an on-voltage occurs due to the resistance of the semiconductor switch at its on-period, thereby causing a loss. Since a high-speed on/off characteristic is usually required for a rectifying and smoothing circuit in particular, high-speed diodes are used for the circuit. However, the high-speed diode has the disadvantage of requiring a particularly high on-voltage, thereby reducing efficiency. In recent years, MOS FETs have been improved greatly in performance, and attempts have been made to improve their efficiency by using such MOS FETs as rectifying devices and by carrying out synchronous rectification described below.
Half-bridge-type and full-bridge-type circuits have been used for high-power switching power supply apparatuses.
FIG. 6
shows a circuit diagram of a conventional example of a switching power supply apparatus comprising a combination of a full-bridge converter and synchronous rectifying devices. Referring to
FIG. 6
, the voltage value of an input DC power supply
1
is assumed to be “Vin”. A series circuit comprising a first switching section
69
and a second switching section
70
is connected across input terminals
2
a
and
2
b
. A series circuit comprising a third switching section
71
and a fourth switching section
72
is also connected across the input terminals
2
a
and
2
b
. A transformer
73
has a primary winding
73
a
, a first secondary winding
73
b
, a second secondary winding
73
c
, a first driving winding
73
d
and a second driving winding
73
e
. The ratio of the number of turns of the above-mentioned five windings is represented by N:1:1:N′:N′ (N is a positive number). One terminal of the primary winding
73
a
is connected to the connection point of the first switching section
69
and the second switching section
70
, and the other terminal is connected to the connection point of the third switching section
71
and the fourth switching section
72
.
The cathode of a first rectifying diode
74
and the cathode of a second rectifying diode
75
are connected to each other, and their anodes are connected to the first secondary winding
73
b
and the second secondary winding
73
c
of the transformer
73
, respectively. A fifth switching section
76
is connected in parallel with the first rectifying diode
74
, thereby forming a synchronous rectifying circuit. By connecting the fifth switching section
76
, i.e., a switching device, the on-voltage of which is lower than that of the first rectifying diode
74
, in parallel with the first rectifying diode
74
, the loss in this configuration can be made lower than that in the case when only the rectifying diode
74
is used. The fifth switching section
76
operates so as to turn on only when a positive voltage generates at the first driving winding
73
d
of the transformer
73
. A sixth switching section
77
is connected in parallel with the second rectifying diode
75
. The sixth switching section
77
and the second rectifying diode
75
operate so that the sixth switching section
77
turns on only when a positive voltage generates at the second driving winding
73
e
of the transformer
73
. This forms a synchronous rectifying circuit.
An inductance device
16
is connected in series with a smoothing capacitor
17
. One terminal of this series circuit is connected to the connection point of the first secondary winding
73
b
and the second secondary winding
73
c
, and the other terminal is connected to the connection point of the first rectifying diode
74
and the second rectifying diode
75
. Output terminals
18
a
and
18
b
are connected across both terminals of the smoothing capacitor
17
. A load
19
is connected across the output terminals
18
a
and
18
b
, and consumes electric power. A PWM circuit
20
detects a voltage “Vout” across the output terminals
18
a
and
18
b
, and generates a PWM signal that controls the voltage constant. A distribution circuit
21
distributes the signal supplied from the PWM circuit
20
to two channels. A first high side driving circuit
78
and a second high side driving circuit
81
are each formed of a semiconductor device or a driving transformer, and generate on/off signals for turning on/off the first switching section
69
and the third switching section
71
, respectively depending on the output of the distribution circuit
21
. “High side” refers to the positive side of the input DC power supply
1
.
A first driving circuit
80
and a second driving circuit
79
generate on/off signals for turning on/off the second switching section
70
and the fourth switching section
72
, respectively depending on the output of the distribution circuit
21
. Since the first high side driving circuit
78
and the second driving circuit
79
have a common input, the first switching section
69
and the fourth switching section
72
turn on/off simultaneously.
In the same way, since the second high side driving circuit
81
and the first driving circuit
80
have a common input, the second switching section
70
and the third switching section
71
turn on/off simultaneously. A third driving circuit
82
generates an on/off signal so that the fifth switching section
76
turns on when a positive voltage generates at the first driving winding
73
d
of the transformer
73
. In the same way, a fourth driving circuit
83
generates an on/off signal so that the sixth switching section
77
turns on when a positive voltage generates at the second driving winding
73
e
of the transformer
73
.
The operation of the switching power supply apparatus configured as described above will be described below referring to
FIG. 7
a
to
FIG. 7
j
.
FIG. 7
a
to
FIG. 7
j
show the waveforms of the signals, voltages and currents at relevant parts.
FIG. 7
a
shows the on/off signals G
1
and G
4
of the first and fourth switching sections
69
and
72
, respectively.
FIG. 7
b
shows the on/off signals G
2
and G
3
of the second and third switching sections
70
and
71
, respectively.
FIG. 7C
shows the current Ip flowing through the primary winding
73
a
of the transformer
73
.
FIG. 7
d
shows the voltage Vp applied to the primary winding
73
a
of the transformer
73
.
FIG. 7
e
shows the voltage Vsr
1
generated at the first driving winding
73
d
of the transformer
73
.
FIG. 7
f
shows the voltage Vsr
2
generated at the second driving winding
73
e
of the transformer
73
.
FIG. 7
g
shows the current Isr
1
flowing through the fifth switching section
76
.
FIG. 7
h
shows the current Isr
2
flowing through the sixth switching section
77
.
FIG. 7
i
shows the current Ir
1
flowing through the first rectifying diode
74
.
FIG. 7
j
Akin Gump Strauss Hauer & Feld L.L.P.
Matsushita Electric - Industrial Co., Ltd.
Nguyen Matthew
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