Electric power conversion systems – Current conversion – With voltage multiplication means
Reexamination Certificate
2002-02-06
2004-05-18
Sherry, Michael (Department: 2838)
Electric power conversion systems
Current conversion
With voltage multiplication means
C327S536000
Reexamination Certificate
active
06738271
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charge pump type DC/DC converter and a power supply apparatus for liquid crystal devices using the same.
As a conventional charge pump DC/DC converter (hereafter referred to as a first conventional apparatus), a double step-up complementary driving type shown in
FIG. 6
is known.
The first conventional apparatus is equipped with, as shown in
FIG. 6
, a double step-up first charge pump circuit
1
, a first driving circuit
2
that drives the first charge pump circuit
1
, a double step-up second charge pump circuit
3
, a second driving circuit
4
that drives the second charge pump circuit
3
, an oscillation circuit
5
that oscillates a signal to be provided to the first driving circuit
2
and the second driving circuit
4
, an input terminal
6
and an output terminal
7
.
The first charge pump circuit
1
is formed from MOS transistors Q
1
to Q
4
and a capacitor C
1
. Also, the second charge pump circuit
12
A is formed from switching MOS transistors Q
5
to Q
8
and a capacitor C
2
,
Next, operations of the first conventional apparatus having the structure described above are described with reference to FIG.
6
and
FIGS. 7A and 7B
.
In the first conventional apparatus, the first and second charge pump circuits
1
and
3
are placed in a state shown in
FIG. 7A
in a first period, and in a state shown in
FIG. 7B
in a second period. The operations in the first period and the second period are alternately repeated.
In other words, in the first period, in the first charge pump circuit
1
, only the MOS transistors Q
2
and Q
4
are turned on by the first driving circuit
2
, and the capacitor C
1
is charged with an input DC voltage Vin (see FIG.
7
A).
Also, in the same first period, in the second charge pump circuit
3
, only the MOS transistors Q
5
and Q
7
are turned on by the second driving circuit
4
, and a voltage in which a charged voltage of the capacitor C
2
in the second period in a previous round is added to an input DC voltage Vin becomes to be an output DC voltage Vout (see FIG.
7
A).
In contrast, in the second period, in the first charge pump circuit
1
, only the MOS transistors Q
1
and Q
3
are turned on by the first driving circuit
2
, and a voltage in which a charged voltage of the capacitor C
1
in the first period in a previous round is added to an input DC voltage Vin becomes to be an output DC voltage Vout (see FIG.
7
B).
Also, in the same second period, in the second charge pump circuit
3
, only the MOS transistors Q
6
and Q
8
are turned on by the second driving circuit
4
, and the capacitor C
2
is charged with an input DC voltage Vin (see FIG.
7
B).
Meanwhile, as a second example of a conventional charge pump DC/DC converter (hereafter referred to as a second conventional apparatus), a type shown in
FIG. 8
is known.
The second conventional apparatus is equipped with, as shown in
FIG. 8
, a charge pump circuit
11
, a driving circuit
12
that drives the charge pump circuit
11
, an oscillator
13
that oscillates a specified signal to be supplied to the driving circuit
12
, an input terminal
14
and an output terminal
15
.
The charge pump circuit
11
is formed from MOS transistors Q
11
to Q
14
, and a capacitor C
11
.
Next, operations of the second conventional apparatus having the structure described above are described with reference to FIG.
8
and
FIGS. 9A and 9B
.
In the second conventional apparatus, the charge pump circuit
11
is placed in a state shown in
FIG. 9A
in a first period, and in a state shown in
FIG. 9B
in a second period. The operations in the first period and the second period are alternately repeated.
More specifically, in the first period, in the first charge pump circuit
11
, only the MOS transistors Q
12
and Q
14
are turned on by the driving circuit
12
, and a capacitor C
11
is charged with an input DC voltage Vin (see FIG.
9
A).
On the other hand, in the second period, in the charge pump circuit
11
, only the MOS transistors Q
11
and Q
13
are turned on by the driving circuit
12
, and a voltage in which a charged voltage of the capacitor C
1
in the first period is added to an input DC voltage Vin becomes to be an output DC voltage Vout (see FIG.
9
B).
It is noted that the first conventional apparatus is a complementary driving type, which is effective in reducing output impedance or reducing output ripple, but has an increased current consumption compared to a non-complementary type. Also, there is a problem in that, when the complementary drive is always performed, its conversion efficiency at the time of a low load or no load may be lowered.
Also, in the second conventional apparatus, it is designed taking in account of its maximum load for continuous operation, its output impedance and current consumption remain the same even when the load or input voltage state changes. Consequently, its capacity becomes excessive and is wasted at the time of a light load. In addition, there are problems in that the second conventional apparatus has a greater output ripple compared to the first conventional apparatus of the complementary driving type, and reduction of its impedance is difficult.
Furthermore, in power supply apparatuses for liquid crystal devices using DC/DC converters, it is desired to eliminate wastes in the current consumption, and improve the power conversion efficiency while maintaining an optimized display on a liquid crystal display device.
BRIEF SUMMARY OF THE INVENTION
Accordingly, the present invention may provide a DC/DC converter that maintains a reduced output impedance, improves the efficiency in converting power at the time of a light load or no load, and realizes a higher power conversion efficiency.
The present invention may further provide a DC/DC converter that reduces current consumption at the time of a light load or no load to thereby eliminate wastes in the current consumption.
The present invention may still further provide a power supply apparatus for a liquid crystal device, which maintains an optimized display on a liquid crystal display apparatus, eliminate wastes in the current consumption and realizes a higher efficiency in power conversion.
A DC/DC converter according to one aspect of the present invention comprises:
two charge pump circuits each of which converts a DC input voltage into a given DC output voltage; and
two driving circuits driving the two charge pump circuits respectively,
wherein in a first mode, the two driving circuits complementarily drive the two charge pump circuits respectively, and the given output voltage is output from each of the two charge pump circuits, and
wherein in a second mode, one of the two driving circuits drives one of the two charge pump circuits, and the given output voltage is output from one of the two charge pump circuits and is not output from the other one of the two charge pump circuits.
In this aspect of the invention, two charge pump circuits are, for example, complementarily driven, and the driving of one of the charge pump circuits is controlled according to size of a load or the like. As a result, the low output impedance can be maintained and the efficiency in converting power at the time of a light load can be improved, whereby a higher power conversion efficiency can be realized.
A DC/DC converter according to another aspect of the present invention comprises:
a charge pump circuit which converts a DC input voltage into a given DC output voltage;
a driving circuit which drives the charge pump circuit;
an oscillation circuit which supplies an oscillation output to the driving circuit,
wherein the oscillation circuit varies a frequency of the oscillation output according to an operation mode.
In this aspect of the invention, the frequency of the drive signal for the charge pump circuit is varied according to size of a load or the like. As a result, the current consumption at the time of a low load can be reduced, and wastes in the current consumption can be eliminated.
A DC/DC converter according to a further aspect of the present i
Harness & Dickey & Pierce P.L.C.
Laxton Gary L.
Seiko Epson Corporation
Sherry Michael
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