Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-02-04
2002-12-24
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000
Reexamination Certificate
active
06498734
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power supply unit used for electronic apparatus such as office automation equipment of various kinds. The invention also relates to an electronic apparatus using the same.
BACKGROUND OF THE INVENTION
A conventional power supply unit is shown in FIG.
12
.
As shown in
FIG. 12
, primary winding
2
p
of transformer
2
is connected to D.C. power supply
1
. The primary winding
2
p
is also connected with switching element
3
and forward controller
4
for controlling the switching element
3
. The forward controller
4
has forward control circuit
4
a
and voltage comparator
4
b
. Output terminal
9
is connected to secondary winding
2
s
of the transformer
2
through rectifier element
5
, choke coil
7
, and smoothing circuit
8
. Another rectifier element
6
, one end of which is grounded, is connected to a point of connection between the rectifier element
5
and the choke coil
7
. A structure described above is an example of so-called forward-type power supply unit. A supply of 24 volts, for instance, is obtained from the output terminal
9
.
In order to obtain another output from the above-described forward-type power supply unit, chopper power supply unit
12
is connected to a point of connection between the choke coil
7
and the smoothing circuit
8
through smoothing means comprised of choke coil
10
and capacitor
11
. A voltage of 5 volts, for instance, is output from output terminal
17
. This chopper power supply unit comprises switching element
13
, rectifier element
14
, choke coil
15
, smoothing circuit
16
, and chopper control circuit
18
.
In other words, electric power is supplied to the chopper power supply unit
12
from the point of connection between the choke coil
7
and the smoothing circuit
8
of the forward-type power supply unit through the smoothing circuit comprised of the choke coil
10
and the capacitor
11
. The chopper power supply unit
12
carries outs voltage conversion by chopping and controlling current that flows into the choke coil
15
with the switching element
13
. As a result, it can supply electric power of several amperes or more at 5 volts from the output terminal
17
.
As described above, the conventional power supply unit requires the choke coil
15
for converting voltage, and the choke coil
10
and the capacitor
11
for smoothing the voltage. That is, in order to make voltage-current conversion of the D.C. voltage efficiently, the chopper power supply unit
12
controls a conducting period of the switching element to regulate the current flowed to the choke coil
15
, and outputs the converted voltage to the output terminal
17
. The choke coil
15
is needed for this purpose.
Moreover, there occurs a ripple voltage in the output terminal
9
, because a switching cycle of the switching element
13
does not synchronize with the forward-type power supply. The choke coil
10
and the capacitor
11
are therefore necessary to prevent it. In order to satisfy the required characteristic, it is imperative for these choke coils
10
and
15
to be considerably large in size. This is one of the reasons that make difficult to downsize and lighten the power supply unit and electronic apparatuses using the same.
DISCLOSURE OF THE INVENTION
The present invention is devised in consideration of the foregoing aspect, and it aims to reduce size and weight of power supply unit and electronic apparatus.
To achieve the above object, a power supply unit of this invention comprises:
a transformer having a primary winding connected in series to a D.C. power supply;
a first switching element having a control terminal and connected in the series to the primary winding;
a first rectifier element connected in series to a secondary winding of the transformer;
a choke coil connected in series to the first rectifier element;
a second switching element connected in series to the choke coil;
a first smoothing circuit connected in series to the second switching element;
a control circuit being input with an output voltage of the first smoothing circuit, for controlling the first switching element;
a second rectifier element connected in parallel with the first rectifier element and the secondary winding;
a third switching element connected in series to the choke coil;
a second smoothing circuit connected in series to the third switching element; and
a divider control circuit having a first input terminal being input with any of an input voltage and an output voltage of the second smoothing circuit, for controlling a conducting period of the third switching element responsive to the voltage being input.
An electronic apparatus of this invention comprises the power supply unit described above, a load device (e.g. an actuator), and a controller for the load device, wherein the first smoothing circuit supplies electric power to the load device, and the second smoothing circuit supplies electric power to the controller for controlling the load device.
REFERENCES:
patent: 5508904 (1996-04-01), Hara
patent: 5619403 (1997-04-01), Ishikawa et al.
patent: 5640315 (1997-06-01), Hirano et al.
patent: 5973946 (1999-10-01), Yasumura
patent: 56-139075 (1981-10-01), None
patent: 59-110376 (1984-06-01), None
patent: 02-026382 (1990-02-01), None
Berhane Adolf Deneke
Matsushita Electric - Industrial Co., Ltd.
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