Electric power conversion systems – Current conversion – With voltage multiplication means
Reexamination Certificate
2002-06-25
2003-12-02
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
With voltage multiplication means
C307S110000
Reexamination Certificate
active
06657876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switched-capacitor-type stabilized power supply device.
2. Description of the Prior Art
A conventional switched-capacitor-type stabilized power supply device will be described with reference to FIG.
7
. An input terminal IN is connected to the positive side of a capacitor C
2
and to the input side of a voltage step-up circuit
12
. The negative side of the capacitor C
2
is grounded.
The voltage step-up circuit
12
is provided with a capacitor C
1
and switching devices SW
11
to SW
14
. The node between one end of the switching device SW
12
and one end of the switching device SW
13
is connected to the input side of the voltage step-up circuit
12
. The other end of the switching device SW
12
is connected to one end of the switching device SW
11
, and the other end of the switching device SW
11
is connected to the output side of the voltage step-up circuit
12
. The other end of the switching device SW
13
is connected to one end of the switching device SW
14
, and the other end of the switching device SW
14
is grounded. One end of the capacitor C
1
is connected to the node between the switching devices SW
11
and SW
12
, and the other end of the capacitor C
1
is connected to the node between the switching devices SW
13
and SW
14
.
The output side of the voltage step-up circuit
12
is connected to one end of a resistor R
1
, to one end of a capacitor C
3
, and to an output terminal OUT. The other end of the capacitor C
3
is grounded. The other end of the resistor R
1
is grounded through a resistor R
2
.
The node between the resistors R
1
and R
2
is connected to the non-inverting input terminal of a comparator
3
. Connected to the inverting input terminal of the comparator
3
is the positive side of a constant voltage source
4
that output a reference voltage V
ref1
. The negative side of the constant voltage source
4
is grounded. The output terminal of the comparator
3
is connected to a control circuit
5
, which is connected to the control terminals of the switching devices SW
11
to SW
14
. The comparator
3
is of the type that exhibits hysteresis.
Now, the operation of the conventional switched-capacitor-type stabilized power supply device configured as described above will be described. A direct-current power source (not shown) is connected to the input terminal IN so that an input voltage V
in
is applied to the input terminal IN. The control circuit
5
turns on and off the switching devices SW
11
to SW
14
according to the level of the output signal S
1
of the comparator
3
, which will be described later. The control circuit
5
incorporates an oscillator, and evaluates the level of the output signal S
1
of the comparator
3
every period T.
When the output signal S
1
of the comparator
3
is at a low level, the control circuit
5
performs alternately, by switching every period T, charge control operation in which it keeps the switching devices SW
12
and SW
14
on and the switching devices SW
11
and SW
13
off and discharge control operation in which it keeps the switching devices SW
12
and SW
14
off and the switching devices SW
11
and SW
13
on.
On the other hand, when the output signal S
1
of the comparator
3
is at a high level, the control circuit
5
, rather than switching between the two types of control operation every period T, performs only charge control operation in which it keeps the switching devices SW
12
and SW
14
on and the switching devices SW
11
and SW
13
off.
As a result of the control circuit
5
performing charge control operation, the capacitor C
1
of the voltage step-up circuit
12
is charged, and its charge voltage reaches V
in
. During this charge period, an output current flows from the output terminal OUT to a load (not shown) connected to the output terminal OUT, and therefore the capacitor C
3
discharges, and the output voltage V
o
lowers.
On the other hand, as a result of the control circuit
5
performing discharge control operation, the negative side of the capacitor C
1
is connected to the input terminal IN, and thus the potential at the negative side of the capacitor C
1
, which was equal to zero when the control circuit
5
was performing charge control operation, becomes equal to V
in
. Accordingly, the potential at the positive side of the capacitor C
1
, which was equal to V
in
when the control circuit
5
was performing charge control operation, becomes equal to 2×V
in
. In this way, during the discharge period, a voltage stepped up by a factor of 2 is fed to the capacitor C
3
, and thus the output voltage V
o
increases.
The resistors R
1
and R
2
serve as a voltage detecting means for detecting the output voltage V
o
, outputting a division voltage V
a
of the output voltage V
o
to the comparator
3
. The comparator
3
compares the division voltage V
a
of the output voltage V
o
with the reference voltage V
ref1
and, when the division voltage V
a
of the output voltage V
o
is higher than or equal to the reference voltage V
ref1
, turns the output signal S
1
to a high level.
Since the comparator
3
is of the type that exhibits hysteresis, once it turns the output signal S
1
to a high level, it keeps the output signal S
1
at a high level even when the division voltage V
a
of the output voltage V
o
becomes lower than the reference voltage V
ref1
. When the output voltage V
o
becomes so low that the division voltage V
a
of the output voltage V
o
is lower than V
ref1′
(<V
ref1
), the comparator
3
turns the output signal S
1
from a high level to a low level.
As a result of the operation described above, the division voltage V
a
of the output voltage V
o
is kept in the range from V
ref1′
to V
ref1
and the output voltage V
o
is thereby stabilized within a predetermined range, so that the output voltage V
o
is kept substantially equal to the set output voltage V
o
*.
In the conventional switched-capacitor-type stabilized power supply device shown in
FIG. 7
, the voltage step-up circuit
12
employs a 2× voltage step-up circuit that steps up the input voltage by a factor of 2. It is possible, however, to realize voltage step-up circuits of various voltage step-up factors, such as 1.5× and 3×, by varying the combination of switching devices and capacitors used in them.
A battery is generally used as a direct-current power source for supplying electric power to a switched-capacitor-type stabilized power supply device. To extend the life of the battery, it is essential that the switched-capacitor-type stabilized power supply device operate stably until the battery voltage falls considerably low, and that it operate with as high power conversion efficiency as possible. In recent years, in particular, switched-capacitor-type stabilized power supply devices have been increasingly used as power sources for driving blue or white LEDs used as backlights for liquid crystal displays incorporated in cellular phones. This trend has been increasing the demand for switched-capacitor-type stabilized power supply devices that permit extended battery lives.
To permit a switched-capacitor-type stabilized power supply device to operate stably until the battery power falls considerably low, it needs to be provided with a voltage step-up circuit with a high voltage step-up factor.
However, inconveniently, increasing the voltage step-up factor of the voltage step-up circuit increases the difference between the voltage stepped-up by the voltage step-up circuit when the battery voltage is still high and the set output voltage Vo*, and thus lowers power conversion efficiency. For example, in the case of the conventional switched-capacitor-type stabilized power supply device having a 2× voltage step-up circuit shown in
FIG. 7
, its power conversion efficiency &eegr;[%] is approximated as (100×V
o
)/(2×V
in
), and thus, when, for example, V
o
=V
in
, the power conversion efficiency &eegr; is 50%. Moreover, where the voltage step-up c
Harness & Dickey & Pierce P.L.C.
Riley Shawn
Sharp Kabushiki Kaisha
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