Electrical transmission or interconnection systems – Capacitor – Parallel-charge – series-discharge
Reexamination Certificate
2002-12-10
2004-07-06
Riley, Shawn (Department: 2838)
Electrical transmission or interconnection systems
Capacitor
Parallel-charge, series-discharge
Reexamination Certificate
active
06759766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply apparatus for driving a capacitive load, and more particularly, to a power supply apparatus capable of generating a high voltage without transformers. This power supply apparatus can be suitably used to supply a bias voltage of a high voltage level to a charger for charging a photoconductor member or a developing unit for developing a toner image on a photoconductor member. The present invention is also concerned with a power supply apparatus suitable for a driving unit of an inkjet recording apparatus, particularly, of a type equipped with piezoelectric elements supplied with drive signals for ejecting liquid link.
2. Description of the Related Art
Conventionally, the following is known as an electrophotographic image forming apparatus to which the power supply apparatus of the above-mentioned type is applied (hereinafter referred to as first conventional art for convenience' sake).
A conventional electrophotographic image forming apparatus is shown in FIG.
1
. The surface of a photoconductor drum
100
is evenly charged at a given voltage by a primary charger
101
. Then, an image is formed on the surface of the photoconductor drum
100
by exposure, so that an electrostatic latent image corresponding to the exposed image can be formed thereon. The electrostatic latent image formed on the photoconductor drum is developed by a developing unit
102
, this resulting in a toner image. The toner image formed on the photoconductor drum
100
is transferred onto a transfer sheet by charging of an image transfer charger
106
. The transfer sheet on which the toner image has been formed is separated from the photoconductor drum
100
by charging of a separator charger
108
. Then, the image forming process ends with the step of fixing the toner image on the transfer sheet by a fixing unit (not shown).
For example, a color image forming apparatus equipped with four developing units used to sequentially form toner images of four colors on the photoconductor drum while the drum makes four turns is required to develop the toner image of color of interest without disturbing the previously developed toner image(s) of color(s). From this viewpoint, a high-voltage power supply apparatus is used which supplies, during development, one of the four developing units with a DC development bias voltage with an AC voltage necessary for enabling excellent development being superimposed thereon, while supplying the three remaining developing units with a DC voltage that prevents toner from being deposited on the photoconductor drum.
This type of high-voltage power supply apparatus is disclosed in, for example, Japanese Unexamined Patent Publication No. 8-65893, and is now illustrated in FIG.
15
. The high-voltage power supply apparatus is equipped with four high-voltage power supply parts
110
-
113
respectively associated with four developing units
102
-
105
. Each of the parts
110
-
113
has an identical configuration, and is made up of an AC voltage generator
114
that generates an AC voltage, and a DC voltage generator
115
that generates a DC voltage. The AC voltage generator
114
has a stepup transformer T for AC, having a primary winding to which an AC switching controller
116
is connected. The controller
116
turns on and off the voltage applied across the primary winding of the transformer T, so that a high AC voltage can develop across the secondary winding of the transformer T. The high voltage power supply part
111
is equipped with a voltage monitor
117
and an over current monitor
118
in order to achieve a constant-voltage output and over-current protection. The monitors
117
and
118
monitor the output voltage and the output current respectively for on/off control of the voltage applied to the primary winding of the transformer T by means of the AC switching controller
116
. Thereby, the output voltage is maintained at the fixed voltage and over current is prevented from flowing in the circuit.
The DC voltage generator
115
includes a DC switching controller
119
coupled with the primary winding of another transformer T for DC. The controller
119
turns on/off a voltage applied to the transformer T, so that a high voltage can be developed across the secondary winding thereof. This high voltage is rectified by a rectifying circuit
120
composed of, for example, diodes, the resultant high DC voltage being output via a DC output controller
121
.
In the above-mentioned high-voltage power supply apparatus, the AC voltage and DC voltage respectively generated by the AC voltage generator
114
and DC voltage generator
115
of each of the high-voltage power supply parts
110
-
113
are superimposed and the resultant bias voltages are then applied to the developing units
102
-
105
.
However, the above-mentioned conventional high-voltage power supply apparatus has disadvantages resulting from the following. The apparatus is equipped with the four high-voltage power supply parts
110
-
113
respectively associated with the developing units
102
-
105
. The developing units
102
-
105
are supplied with the bias voltages at the respective timings as follows. One of the developing units
102
-
105
subjected to development is supplied with the DC bias voltage with the AC voltage being superimposed thereon, while the three remaining developing units are supplied with only the DC voltage. Therefore, each of the high-voltage power supply parts
110
-
113
must be equipped with the respective transformers, namely, the AC-use transformer and DC-use transformer. Further, the apparatus is needed to have the high-voltage power supply parts
110
-
113
equal in number to the developing units, which act as loads. This needs a large capacity of the power supply apparatus and increases the cost.
There are proposals directed to downsizing and cost reduction of the power supply apparatus due to miniaturization and an increased number of functions of the image forming apparatus, see, for example, Japanese Unexamined Patent Publication Nos. 8-65893, 7-287620 and 8-194551.
According to Japanese Unexamined Patent Publication No. 8-65893, as shown in
FIG. 16
, the input lines of the primary windings of stepup transformers T
1
-T
4
respectively associated with developing units
4
a
-
4
d
serving as loads can be turned on/off independently. This arrangement makes it possible to supply a DC bias voltage with an AC voltage being superimposed thereon to the loads
4
a
-
4
d
at the different timings. Further, switching means SW
1
-SW
4
are provided on the primary sides of the transformers T
1
-T
4
, so that the switching means SQ
1
-SW
4
can be formed by switching elements of a relatively low breakdown voltage. In
FIG. 16
, a reference numeral
1
indicates a photoconductor drum
1
, and
11
-
14
indicate high-voltage power supply units. Reference numerals
15
-
18
indicate ac voltage generating units, and
19
-
22
indicate DC voltage generating units.
According to Japanese Unexamined Patent Publication No. 7-287620, as shown in
FIG. 17
, two switching elements
1
and
2
connected between a high-voltage DC power source
8
and ground are alternately driven, so that a high AC voltage having a rectangular waveform can be generated at a node where the elements
1
and
2
are connected in series. Further, the circuit shown in
FIG. 17
allows a high DC voltage to be superimposed on the AC voltage.
Japanese Unexamined Patent Publication No. 8-194551 proposes a power supply apparatus capable of generating a DC output voltage depending on the ambient temperature. The proposed circuit does not use any transformer but employs a charge pump and a Cockcroft-Walton circuit for boosting the DC voltage. This circuit configuration enables miniaturization of the power supply apparatus.
Although the apparatus disclosed in Japanese Unexamined Patent Publication No. 8-65893 employs a smaller number of transformers, there is a limit on miniaturization because it still uses the transformers. The cir
Hiratsuka Masashi
Kondoh Yoshinao
Takahashi Kunihiro
Fuji 'Xerox Co., Ltd.
Riley Shawn
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