Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-06-30
2003-02-11
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S080000
Reexamination Certificate
active
06519163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to power supply units, and more particularly, to a power supply unit for a DC-DC conversion.
2. Description of the Related Art
FIG. 1
is a schematic circuit diagram of a conventional power supply unit. A power supply unit
1
is an AC adapter converting an AC input supplied from an AC power supply
2
connected thereto into a DC voltage, which is supplied to a load
3
.
The power supply unit
1
includes a fuse
4
, a rectifier circuit
5
on a primary side, a capacitor C
1
, a transformer
6
, a transistor Q
1
, a control circuit
7
, a rectifier circuit
8
on a secondary side, and an output voltage detecting circuit
9
.
The fuse
4
is blown to cut off the supply of current when an overcurrent flows from the AC power supply
2
into the power supply unit
1
. The rectifier circuit
5
on the primary side is a bridge rectifier circuit including four diodes, and rectifies an alternating current supplied from the AC power supply
2
. The current rectified by the rectifier circuit
5
on the primary side is supplied to one end of a primary winding L
1
of the transformer
6
. The transistor Q
1
is connected to another end of the primary winding L
1
thereof.
The transistor Q
1
is a field-effect transistor, which includes a drain connected to the other end of the primary winding L
1
, a source connected to a wiring line
16
on the negative-potential side of a circuit on the primary side, and a gate connected to the control circuit
7
. The control circuit
7
controls a DC output voltage by switching ON/OFF the transistor Q
1
by controlling the gate potential of the transistor Q
1
.
The control circuit
7
supplies the gate of the transistor Q
1
with a switching pulse having a predetermined frequency, in accordance with which the transistor Q
1
is switched ON/OFF. A pulsed current flows through the primary winding L
1
by the ON/OFF switching operation of the transistor Q
1
.
The transformer
6
includes the primary winding L
1
and a secondary winding L
2
, and generates a voltage in the secondary winding L
2
in accordance with the current flowing through the primary winding L
1
. The above generated voltage depends on the ratio of the number of turns on the primary winding L
1
to that of turns on the secondary winding L
2
.
The voltage generated in the secondary winding L
2
is supplied to the rectifier circuit
8
on the secondary side, which includes a diode D
1
and a capacitor C
2
. The diode D
1
performs a half-wave rectification on an alternating current generated in the secondary winding L
2
, and the capacitor C
2
absorbs the pulsation of the rectified voltage. The voltage rectified by the rectifier circuit
8
on the secondary side is supplied to the load
3
as an output voltage.
The output voltage detecting circuit
9
, which includes resistors R
1
through R
4
, a photo-coupler
10
, and a shunt regulator
11
, detects the output voltage supplied to the load
3
. The resistors R
1
through R
3
divide the output voltage, and a divided voltage is applied to the input terminal of the shunt regulator
11
.
FIG. 2
is a circuit diagram of the shunt regulator
11
. The shunt regulator
11
compares a voltage C
ont
of the connecting point of the resistor R
2
with the resistor R
3
and a reference voltage V
ref
generated inside the shunt regulator
11
, and outputs a voltage based on the result of the comparison. The shunt regulator
11
includes a Zener diode
12
, a differential amplifier
13
, and an NPN transistor
14
. The Zener diode
12
generates the reference voltage V
ref
. The differential amplifier
13
compares the reference voltage V
ref
generated by the Zener diode
12
and the voltage C
ont
of the connecting point of the resistor R
2
with the resistor R
3
, and supplies a current to the base of the NPN transistor
14
in accordance with the voltage difference therebetween. The NPN transistor
14
, which is controlled by an output signal of the differential amplifier
13
, includes a collector connected to the photo-coupler
10
and an emitter connected to the lower potential side of the load
3
.
The differential amplifier
13
increases/decreases the base potential of the NPN transistor
14
as the potential of the connecting point of the resistor R
2
with the resistor R
3
increases/decreases.
The shunt regulator
11
draws more/less current from the photo-coupler
10
as the potential of the connecting point of the resistor R
2
with the resistor R
3
increases/decreases, that is, the load
3
consumes less/more current.
The photo-coupler
10
includes a light-emitting diode D
2
and a phototransistor Q
2
disposed to face the light-emitting diode D
2
. The light-emitting diode D
2
is connected to the shunt regulator
11
. The light-emitting diode D
2
emits more/less amount of light as the shunt regulator
11
draws more/less current.
The phototransistor Q
2
, which includes a collector connected to a wiring line
15
on the positive-potential side of the circuit on the primary side, and an emitter connected to the control circuit
7
, controls a current flowing from the emitter in accordance with the amount of light emitted from the light-emitting diode D
2
.
The control circuit
7
, which is connected to the emitter of the phototransistor Q
2
of the photo-coupler
10
, supplies the switching pulse to the gate of the transistor Q
1
in accordance with the current flowing from the emitter of the phototransistor Q
2
.
The transistor Q
1
is switched ON/OFF by the switching pulse supplied from the control circuit
7
. The transformer
6
transmits an electric power from the primary winding L
1
to the secondary winding L
2
in accordance with the ON/OFF switching operation of the transistor Q
1
.
The control circuit
7
is connected to the wiring line
15
on the positive-potential side of the circuit on the primary side, and thus is constantly supplied with a driving current so as to be in an ever-driven state.
When the current consumed in the load
3
is reduced, the output voltage between outputs terminals T
out
1
and T
out
2
starts to rise. Then, the potential of the connecting point of the resistor R
2
with the resistor R
3
also starts to rise, thus resulting in an increase in the current which the shunt regulator
11
draws. In accordance with this increase in the current, the light-emitting diode D
2
of the photo-coupler
10
emits more amount of light, and more current flows from the emitter of the phototransistor Q
2
into the control circuit
7
.
The control circuit
7
then controls the switching pulse supplied to the gate of the transistor Q
1
so that the transistor Q
1
is ON for a shorter period of time, thus reducing the electric power transmitted from the primary winding L
1
of the transformer
6
to the secondary winding L
2
thereof. Then, the output voltage between the output terminals T
out
1
and T
out
2
is controlled to become lower to keep a constant value.
On the other hand, when the current consumed in the load
3
is increased, the output voltage between outputs terminals T
out
1
and T
out
2
starts to lower. Then, the potential of the connecting point of the resistor R
2
with the resistor R
3
also starts to lower, thus resulting in a decrease in the current which the shunt regulator
11
draws. In accordance with this decrease in the current, the light-emitting diode D
2
of the photo-coupler
10
emits less amount of light, and less current flows from the emitter of the phototransistor Q
2
into the control circuit
7
.
The control circuit
7
then controls the switching pulse supplied to the gate of the transistor Q
1
so that the transistor Q
1
is ON for a longer period of time, thus increasing the electric power transmitted from the primary winding L
1
of the transformer
6
to the secondary winding L
2
thereof. Then, the output voltage between the output terminals T
out
1
and T
out
2
is controlled to become higher to keep a constant value.
However, according to the conventional power supply un
Fushihara Yasunobu
Katayama Takayuki
Kawano Seiji
Yoshimoto Takayuki
Han Jessica
Ladas & Parry
Mitsumi Electric Co. Ltd.
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