Electric power conversion systems – Current conversion – With voltage division by storage type impedance
Reexamination Certificate
2002-09-16
2004-02-17
Nguyen, Matthew V. (Department: 2838)
Electric power conversion systems
Current conversion
With voltage division by storage type impedance
Reexamination Certificate
active
06693808
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a DC—DC converter suitable for a power supply circuit, specifically to a DC—DC converter with an improved efficiency.
Video equipments in recent years such as a camcorder, a digital still camera (DSC) and a mobile phone with DSC use charge-coupled devices (CCDs) to capture an image. A power supply circuit that provides both positive and negative high voltages (over 10 volts) and high current (several milliamperes) is required in order to drive the CCDs. A switching regulator is used for that purpose today.
The switching regulator can generates the high voltages with high performance, i.e. with high power efficiency. However it has a drawback to generates a harmonic noise when switching a current, and therefore the power supply has to be used with a noise shield. Another drawback with the switching regulator is a difficulty in reducing the size of the equipment, since it requires a coil as an external part.
Switched capacitor type DC—DC converters have been proposed in order to overcome the drawbacks mentioned above. An example of the DC—DC converters of the kind is reported in the Journal of Institute of Electronics, Information and Communication Engineers (C-2 Vol.J81-C-2 No.7 pp. 600-612, July 1998).
FIG.
9
and
FIG. 10
are circuit diagrams of a switched capacitor type DC—DC converter of the prior art. A voltage source
10
provides a supply voltage Vdd. Each of the capacitors C
1
, C
2
and C
3
composes each stage of the DC—DC Converter. Each of switches
11
,
12
and
13
is connected between the power supply Vdd and one end of each of the capacitors respectively, and each of switches
21
,
22
and
23
is connected between a ground (0V) and the other end of each of the capacitors respectively.
A switch
30
is disposed between the power supply Vdd and a ground (0V) side end of the capacitor C
1
. A switch
31
is disposed between a Vdd side end of the capacitor C
1
and a ground (0V) side end of the second stage capacitor C
2
. A switch
32
is disposed between a Vdd side end of the capacitor C
2
and a ground (0V) side end of the third stage capacitor C
3
. A switch
33
is disposed between a Vdd side end of the capacitor C
3
and an output terminal
40
. Cout is an output capacitor. A current load
50
is connected to the output terminal
40
. Operation of this three-stage DC—DC converter will be described hereafter.
The switches
11
-
13
and
21
-
23
are turned ON, and the switches
30
-
33
are turned OFF, as shown in FIG.
9
. The capacitors C
1
-C
3
are connected in parallel between the power supply Vdd and the ground (0V). Each of voltages V
1
-V
3
of each of the respective capacitors C
1
-C
3
is charged to Vdd. Given that an output current from the output terminal
40
is Iout, a charging current to each of the capacitors is 2 Iout.
Next, as shown in
FIG. 10
, the switches
11
-
13
and the switches
21
-
23
are turned OFF, and the switches
30
-
33
are turned ON. Then the capacitors C
1
-C
3
are connected in series with each other while they are disconnected from the power supply Vdd and the ground (0V), and discharging takes place. The voltage V
1
is boosted to 2 Vdd, the voltage V
2
is boosted to 3 Vdd and the voltage V
3
(=Vout) is boosted to 4 Vdd, due to a capacity coupling effect. Given that the output current from the output terminal
40
is Iout, a current from the power supply Vdd to the capacitor C
1
is 2 Iout.
As described above, the switched capacitor type DC—DC converter generates as high voltage as 4 Vdd from the output terminal
40
when provided with the power supply voltage of Vdd.
A theoretical efficiency &eegr; of a DC—DC converter is defined as output power/input power. Assuming that duration of a status of FIG.
9
and duration of a status of
FIG. 10
are equal, and neglecting all voltage loss due to the switches and other factors,
Input power=4×2 Iout/2×Vdd=Iout×4 Vdd
Output power=Iout×4 Vdd
Therefore the theoretical efficiency &eegr; is 100%.
In general, n-stage switched capacitor type DC—DC converter provides an output voltage of (n+1) Vdd.
However the conventional switched capacitor type DC—DC converter provides a boosted voltage in increments of Vdd only. When the switched capacitor type DC—DC converter is used as a power supply circuit, a step-down voltage adjustment is made by a regulator in order to adjust the output voltage to a desired voltage. A drawback of this method is a decline in the efficiency of the power supply circuit, especially when the discrepancy between the desired voltage and the output voltage of the DC—DC converter of (n+1) Vdd is large.
SUMMARY OF THE INVENTION
An objective of this invention is to improve the efficiency of a power supply circuit by providing a DC—DC converter capable of generating a boosted voltage in increments of less than a supply voltage of Vdd, for instance, 1.5 Vdd, 2.5 Vdd or 3.5 Vdd.
The DC—DC converter of this invention comprises a plurality of stages, each of which has a first capacitor, a first switch to connect the capacitor to a power supply to charge the capacitor and a second switch to connect the capacitor to a capacitor in a next stage. At least one of the stages has a plurality of second capacitors, a third switch to connect the second capacitors in series and a fourth switch to connect the capacitors in parallel.
Since the second capacitors are connected in series during charging, each of the second capacitors is charged to a divided voltage (0.5 Vdd when two capacitors are disposed, for instance). And then the divided voltage is transferred to the next stage by a capacity coupling, as the second capacitors are connected in parallel during discharging. By doing so, it is made possible to generate an output voltage in increments of less than the supply voltage Vdd, for example, 1.5 Vdd, 2.5 Vdd or 3.5 Vdd.
Also it is possible to prevent deterioration in the efficiency of the DC—DC converter by turning OFF the second, third and fourth switches when the first switches make switching so that a reverse current is prevented.
REFERENCES:
patent: 4531106 (1985-07-01), Ganesan
patent: 6198645 (2001-03-01), Kotowski et al.
patent: 6304007 (2001-10-01), Yu
Fish & Richardson P.C.
Nguyen Matthew V.
Sanyo Electric Co,. Ltd.
LandOfFree
Control method of DC-DC converter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control method of DC-DC converter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control method of DC-DC converter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3338801