U.S. patent application number 13/951746 was filed with the patent office on 2014-02-06 for power supply apparatus, image forming apparatus, and integrated circuit.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Taro Minobe.
Application Number | 20140036546 13/951746 |
Document ID | / |
Family ID | 48906130 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140036546 |
Kind Code |
A1 |
Minobe; Taro |
February 6, 2014 |
POWER SUPPLY APPARATUS, IMAGE FORMING APPARATUS, AND INTEGRATED
CIRCUIT
Abstract
The power supply apparatus is configured to detect the output
voltage of a piezoelectric transformer and controls the frequency
of a pulse signal to drive the piezoelectric transformer based on
the detected output voltage and a preset target voltage so as to
perform feedback control of the output voltage of the piezoelectric
transformer, the gain when performing the feedback control is
switched in accordance with the target voltage.
Inventors: |
Minobe; Taro; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
48906130 |
Appl. No.: |
13/951746 |
Filed: |
July 26, 2013 |
Current U.S.
Class: |
363/21.02 ;
399/88 |
Current CPC
Class: |
H02M 3/33507 20130101;
H02M 7/217 20130101; H01L 41/107 20130101; G03G 15/80 20130101 |
Class at
Publication: |
363/21.02 ;
399/88 |
International
Class: |
G03G 15/00 20060101
G03G015/00; H02M 3/335 20060101 H02M003/335 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2012 |
JP |
2012-171146 |
Jun 17, 2013 |
JP |
2013-126546 |
Claims
1. A power supply apparatus comprising: a piezoelectric
transformer; a signal generation unit configured to generate a
signal to drive the piezoelectric transformer; a detection unit
configured to detect an output voltage of the piezoelectric
transformer; and a frequency determination unit configured to
determine a frequency of the signal from the signal generation unit
by a feed back control based on a feedback signal corresponding to
the output voltage detected by the detection unit and a target
voltage signal corresponding to a target voltage, wherein the
frequency determination unit is configured to determine the
frequency of the signal based on a gain of the feedback signal
switched in correspondence with the target voltage signal.
2. A power supply apparatus according to claim 1, wherein the
frequency determination unit includes a digital counter circuit
configured to generate a pulse signal to drive the piezoelectric
transformer.
3. A power supply apparatus according to claim 1, further
comprising a memory unit configured to store a table in which gains
each associated with each target voltage signal in the feedback
control are stored, wherein the frequency determination unit is
configured to refer to the table stored in the memory unit, and to
switch to one gain among the gains each associated with each target
voltage.
4. A power supply apparatus according to claim 1, wherein the
feedback signal is a converted signal that is digitally converted
from the output voltage detected by the detection unit, and the
frequency determination unit is configured to perform the feedback
control based on a difference between a preset target voltage
signal corresponding to a preset target voltage and the converted
signal.
5. A power supply apparatus according to claim 1, further
comprising an output unit configured to output a difference between
the output voltage detected by the detection unit and the preset
target voltage, wherein the frequency determination unit is
configured to perform the feedback control based on a value of a
signal obtained by digitally converting the difference output by
the output unit.
6. A power supply apparatus according to claim 1, wherein the gain
is a setting value of a control parameter used to perform PID
control.
7. An image forming apparatus comprising: an image forming unit;
and a power supply apparatus for supplying a high voltage to the
image forming unit, the power supply apparatus comprising: a
piezoelectric transformer; a signal generation unit configured to
generate a signal to drive the piezoelectric transformer; a
detection unit configured to detect an output voltage of the
piezoelectric transformer; and a frequency determination unit
configured to determine a frequency of the signal from the signal
generation unit by a feed back control based on a feedback signal
corresponding to the output voltage detected by the detection unit
and a target voltage signal corresponding to a target voltage,
wherein the frequency determination unit determines the frequency
of the signal based on a gain of the feedback signal switched in
correspondence with the target voltage signal.
8. An image forming apparatus according to claim 7, wherein the
image forming unit includes a charging unit configured to charge an
image bearing member, a developing unit configured to develop a
latent image formed on the image bearing member, and a transfer
unit configured to transfer an image formed on the image bearing
member.
9. An integrated circuit for controlling an operation of a power
supply apparatus including a piezoelectric transformer, comprising:
a signal generation unit configured to generate a signal to drive
the piezoelectric transformer; and a frequency determination unit
configured to determine a frequency of the signal from the signal
generation unit by a feed back control based on a feedback signal
corresponding to an output voltage of the piezoelectric transformer
and a target voltage signal corresponding to a target voltage,
wherein the frequency determination unit is configured to determine
the frequency of the signal based on a gain of the feedback signal
switched in correspondence with the target voltage signal.
10. An integrated circuit according to claim 9, wherein the
frequency determination unit includes a digital counter circuit
configured to generate a pulse signal to drive the piezoelectric
transformer.
11. An integrated circuit according to claim 9, further comprising
a memory unit configured to store a table in which gains each
associated with each target voltage signal in the feedback control
are stored, wherein the frequency determination unit is configured
to refer to the table stored in the memory unit, and to switch to
one gain among the gains each associated with each target
voltage.
12. An integrated circuit according to claim 9, wherein the
feedback signal is a converted signal that is digitally converted
from the output voltage of the piezoelectric transformer, and the
frequency determination unit is configured to perform the feedback
control based on a difference between a preset target voltage
signal corresponding to a preset target voltage and the converted
signal.
13. An integrated circuit according to claim 9, further comprising
an output unit configured to output a difference between the output
voltage of the piezoelectric transformer and the preset target
voltage, wherein the frequency determination unit is configured to
perform the feedback control based on a value of a signal obtained
by digitally converting the difference output by the output
unit.
14. An integrated circuit according to claim 9, wherein the gain is
a setting value of a control parameter used to perform PID control.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a power supply apparatus,
an image forming apparatus, and an integrated circuit and, more
particularly, to a high-voltage power supply using a piezoelectric
transformer.
[0003] 2. Description of the Related Art
[0004] Conventionally, an image forming apparatus using an
electrophotographic method such as a copying machine, a printer, or
a facsimile apparatus has been known. The image forming apparatus
using the electrophotographic method includes a developing member
that develops a latent image formed on an image bearing member
using toner serving as a developing material, a charging member
that uniformly charges the image bearing member, and a transfer
member that transfers the toner image formed on the image bearing
member to a recording material. A high voltage is applied to the
developing member, the charging member, and the transfer member,
thereby performing image formation. From the viewpoint of reducing
the size and weight of a high-voltage power supply apparatus
serving as a high-voltage power supply for outputting a high
voltage to the plurality of members, there has been proposed
generating a high voltage using a thin and lightweight high-power
piezoelectric transformer (for example, Japanese Patent Application
Laid-Open No. 2011-250549). A power supply apparatus using a
piezoelectric transformer made of a ceramic can generate a high
voltage at an efficiency higher than an electromagnetic transformer
and also increase the distance between the electrode on the primary
side and that on the secondary side. In addition, since special
molding for insulation is unnecessary, the image forming apparatus
can be made compact and lightweight.
[0005] FIG. 5A is a schematic view of a conventional high-voltage
power supply apparatus using a piezoelectric transformer. Note that
the same reference numerals as in a high-voltage power supply
apparatus to be described later in the embodiments denote the same
parts, and a detailed description thereof will be made in the
embodiments. Since a piezoelectric transformer 101 generally has a
characteristic with tails extending so that the output voltage is
maximized at a resonance frequency FO, as shown in FIG. 5B, voltage
control using a frequency is possible. The graph of FIG. 5B plots
the driving frequency (Hz) of the piezoelectric transformer 101
along the abscissa and the output voltage (V) along the ordinate.
Note that as the feature of the relationship between the frequency
and the output voltage, the output voltage is maximized at the
resonance frequency FO and lowers as the frequency becomes higher
or lower than the resonance frequency FO. In the high-voltage power
supply apparatus described in Japanese Patent Application Laid-Open
No. 2011-250549, a frequency generation block 2015 first outputs a
pulse signal of a frequency Fmax much higher than the resonance
frequency FO. After that, the frequency of the piezoelectric
transformer 101 is changed between the frequency Fmax and the
resonance frequency FO, thereby controlling the output voltage.
That is, the output voltage of the piezoelectric transformer 101
can be increased by changing the frequency from the higher side to
the lower side. Hence, a high voltage control unit 201 raises or
lowers the frequency of the pulse signal of the frequency
generation block 2015, thereby controlling the voltage of an output
terminal Vout to the target voltage.
[0006] However, the conventional digital control circuit
arrangement has the following problem because the frequency
generation block 2015 uses a general digital counter circuit (for
example, Japanese Patent Application Laid-Open No. 2009-038892). A
control calculation block 2014 executes calculation using a
predetermined formula based on a difference calculation result from
a difference calculation block 2013, and outputs the preset value
to the frequency generation block 2015 that is a digital counter
circuit at the subsequent stage. The frequency generation block
2015 formed from the digital counter circuit generates a pulse
signal in accordance with the input preset value. That is, the
frequency generation block 2015 is configured to raise or lower the
frequency of the pulse signal in accordance with the preset value.
For this reason, when frequency control is performed for the
piezoelectric transformer 101 that exhibits a nonlinear
characteristic as shown in FIG. 5B as the relationship between the
frequency and the output voltage, the relationship between the
preset value and the output voltage is represented by a nonlinear
characteristic as shown in FIG. 5C. More specifically, when the
piezoelectric transformer 101 is controlled near the resonance
frequency FO, the output voltage exhibits a steep characteristic
with respect to the frequency. Hence, the output voltage exhibits a
steep characteristic with respect to the preset value. On the other
hand, when the piezoelectric transformer 101 is controlled at a
frequency much higher than the resonance frequency FO, the output
voltage exhibits a moderate characteristic with respect to the
frequency. Hence, the output voltage exhibits a moderate
characteristic with respect to the preset value. For these reasons,
when the frequency generation block 2015 formed from a digital
counter circuit performs frequency control of the piezoelectric
transformer 101, the preset value (abscissa) and the output voltage
(ordinate) have a nonlinear relationship, as shown in FIG. 5C.
[0007] If the high-voltage power supply apparatus using the
piezoelectric transformer 101 is used to output a low voltage, the
difference calculation result of the difference calculation block
2013 becomes small, and the amount of increase in the preset value
of the control calculation block 2014 also becomes small. Hence,
the preset value is increased many times until the target voltage,
resulting in a long rise time. To solve this problem, the rise time
can be shortened by switching the control gain in accordance with
the voltage of the output terminal Vout, like a high-voltage power
supply apparatus described in, for example, Japanese Patent
Application Laid-Open No. 2007-189880. However, the system of an
engine controller 501 becomes complex with this technique. More
specifically, in the high voltage control unit 201, the number of
operations of sequentially storing the voltage of the output
terminal Vout in an output voltage register 2022 of a memory unit
2011 and transmitting the information of the output voltage
register 2022 to a CPU 301 increases. In the CPU 301, the number of
operations of determining the control gain based on the
sequentially transmitted information of the output voltage register
2022 and storing the gain in the memory unit 2011 increases. For
this reason, the system for controlling the high-voltage power
supply apparatus becomes complex, resulting in, for example,
increases in the development cost and the cost of the engine
controller 501. Additionally, in, for example, the high-voltage
power supply apparatus described in Japanese Patent Application
Laid-Open No. 2007-189880, if the output of the piezoelectric
transformer 101 changes due to an instantaneous load variation or
the like during the image forming operation, and the control gain
switches, it may be impossible to obtain a stable output voltage.
This may lead to a degradation in quality of a formed image.
[0008] Such speeding up of the image forming operation and the
influence on image quality sufficiently meet the requirements for
the performance of the conventional image forming apparatus.
However, recent image forming apparatuses particularly need to
attain high quality and speeding up. There is also a demand for
quickly outputting the target voltage even when the target voltage
is low in the high-voltage power supply apparatus employing the
piezoelectric transformer. To cope with this, it is necessary to
stabilize the output voltage and quickly output the target voltage
when controlling the voltage in a wide range.
SUMMARY OF THE INVENTION
[0009] In order to solve the above-described problem, the present
invention enables to stably obtain the output of a power supply
apparatus and shorten the rise time until the target voltage in a
power supply apparatus using a piezoelectric transformer.
[0010] (1) The present invention provides a power supply apparatus
including a piezoelectric transformer, a signal generation unit
configured to generate a signal to drive the piezoelectric
transformer, a detection unit configured to detect an output
voltage of the piezoelectric transformer, and a frequency
determination unit configured to determine a frequency of the
signal from the signal generation unit by a feed back control based
on a feedback signal corresponding to the output voltage detected
by the detection unit and a target voltage signal corresponding to
a target voltage, wherein the frequency determination unit
determines the frequency of the signal based on a gain of the
feedback signal switched in correspondence with the target voltage
signal.
[0011] (2) The present invention also provides an image forming
apparatus comprising an image forming unit, and a power supply
configured to supply a high voltage to the image forming unit,
wherein the power supply includes a piezoelectric transformer, a
signal generation unit configured to generate a signal to drive the
piezoelectric transformer, a detection unit configured to detect an
output voltage of the piezoelectric transformer, and a frequency
determination unit configured to determine a frequency of the
signal from the signal generation unit by a feed back control based
on a feedback signal corresponding to the output voltage detected
by the detection unit and a target voltage signal corresponding to
a target voltage, wherein the frequency determination unit
determines the frequency of the signal based on a gain of the
feedback signal switched in correspondence with the target voltage
signal.
[0012] (3) The present invention also provides an integrated
circuit for controlling an operation of a power supply apparatus
including a piezoelectric transformer, including a signal
generation unit configured to generate a signal to drive the
piezoelectric transformer, and a frequency determination unit
configured to determine a frequency of the signal from the signal
generation unit by a feed back control based on a feedback signal
corresponding to an output voltage of the piezoelectric transformer
and a target voltage signal corresponding to a target voltage,
wherein the frequency determination unit determines the frequency
of the signal based on a gain of the feedback signal switched in
correspondence with the target voltage signal.
[0013] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A is a view showing a section of an image forming
apparatus according to the first and second embodiments.
[0015] FIG. 1B is a block diagram showing the constituent blocks of
the image forming apparatus indicating an application example of a
high-voltage power supply apparatus according to the first and
second embodiments.
[0016] FIG. 2 is a block diagram showing the circuit arrangement of
the high-voltage power supply apparatus according to the first
embodiment.
[0017] FIG. 3A is a block diagram showing the arrangement of a
frequency generator block according to the first embodiment.
[0018] FIG. 3B is a view showing a table used to set a control gain
parameter group.
[0019] FIG. 4A is a block diagram showing a modification of the
circuit arrangement of the high-voltage power supply apparatus
according to the first embodiment.
[0020] FIG. 4B is a block diagram showing the circuit arrangement
of the high-voltage power supply apparatus according to the second
embodiment.
[0021] FIG. 5A is a block diagram showing the circuit arrangement
of a conventional high-voltage power supply apparatus.
[0022] FIG. 5B is a graph showing the driving frequency vs. output
voltage characteristic of a piezoelectric transformer.
[0023] FIG. 5C is a graph showing the relationship between a preset
value and the output voltage.
DESCRIPTION OF THE EMBODIMENTS
[0024] Preferred embodiments of the present invention will now be
described in detail in accordance with the accompanying
drawings.
[0025] The arrangement and operation of the present invention will
now be described. Note that the embodiments to be described below
are not intended to limit the technical scope of the present
invention, but are merely examples. The embodiments of the present
invention will be described below in detail with reference to the
accompanying drawings.
First Embodiment
[0026] Image Forming Apparatus
[0027] An image forming apparatus according to the first embodiment
will be described. In this embodiment, an example will be explained
in which a high-voltage power supply apparatus is applied to a
color laser printer serving as an image forming apparatus. FIG. 1A
is a schematic sectional view of the color laser printer serving as
the image forming apparatus according to this embodiment. A laser
beam printer 10 includes a pickup roller 12 that picks up a
recording sheet 11 (recording medium) stored in a tray (not shown),
and sheet feeding rollers 13 that convey the recording sheet 11
picked up by the pickup roller 12. A secondary transfer unit 26 and
an intermediate transfer belt 24 are provided downstream of the
sheet feeding rollers 13 in the conveyance direction of the
recording sheet 11. The secondary transfer unit 26 transfers a
toner image (developing material image) transferred to the
intermediate transfer belt 24 to the recording sheet 11 fed by the
sheet feeding rollers 13 so as to form a color image. The toner
image is formed by an image forming unit.
[0028] The image forming unit includes photosensitive drums 21a to
21d each serving as an image bearing member on which an
electrostatic latent image is formed, and charging units 22a to 22d
that uniformly charge the photosensitive drums 21a to 21d,
respectively. The image forming unit also includes developing units
23a to 23d that develop the electrostatic latent images formed on
the photosensitive drums 21a to 21d by toners, and primary transfer
units 25a to 25d that transfer the toner images developed on the
photosensitive drums 21a to 21d to the intermediate transfer belt
24. Note that suffixes a to d in the image forming unit represent,
for example, yellow, magenta, cyan, and black, and will be omitted
hereinafter except when necessary. A fixing unit 27 that
incorporates a heater and a pressure roller to thermally fix the
toner images transferred to the recording sheet 11 is provided
downstream in the conveyance direction of the recording sheet 11.
Note that the image forming apparatus including the power supply
apparatus of this embodiment is not limited to the image forming
apparatus having the above-described arrangement.
[0029] High-Voltage Power Supply Apparatus and Loads
[0030] FIG. 1B is a block diagram showing the constituent blocks of
a plurality of high-voltage power supply apparatuses provided in
the laser beam printer 10, and a charging unit 22, a developing
unit 23, a primary transfer unit 25, and the secondary transfer
unit 26 that are loads to which high voltages are applied. Note
that the loads shown in FIG. 1B correspond to the image forming
apparatus having the arrangement shown in FIG. 1A. When the power
supply apparatus according to this embodiment is applied to an
image forming apparatus having another arrangement, the voltages
are applied to loads corresponding to the image forming
apparatus.
[0031] An engine controller 501 includes a CPU 301, and high
voltage control units 201a to 201d. To perform the respective
processes of image formation, it is necessary to apply
predetermined high voltages from the high-voltage power supply
apparatus to the charging unit 22, the developing unit 23, the
primary transfer unit 25, and the secondary transfer unit 26. The
high voltage control unit 201a causes a voltage detection circuit
108a (see FIG. 2 to be described later, and the same shall apply
hereinafter) to detect a high voltage applied to the charging unit
22, and controls a booster circuit 114a to make the detected
voltage equal to a target voltage set by the CPU 301. The high
voltage control unit 201b causes a voltage detection circuit 108b
to detect a high voltage applied to the developing unit 23, and
controls a booster circuit 114b to make the detected voltage equal
to a target voltage set by the CPU 301. The high voltage control
unit 201c causes a voltage detection circuit 108c to detect a high
voltage applied to the primary transfer unit 25, and controls a
booster circuit 114c to make the detected voltage equal to a target
voltage set by the CPU 301. The high voltage control unit 201d
causes a voltage detection circuit 108d to detect a high voltage
applied to the secondary transfer unit 26, and controls a booster
circuit 114d to make the detected voltage equal to a target voltage
set by the CPU 301.
[0032] Arrangement of High-Voltage Power Supply Apparatus
[0033] The arrangement of the high-voltage power supply apparatus
according to this embodiment will be described in detail. As a
characteristic feature of this embodiment, in the high-voltage
power supply apparatus using a piezoelectric transformer 101, the
control gain is switched in accordance with the target voltage.
FIG. 2 is a block diagram showing the high-voltage power supply
apparatus according to this embodiment. The high-voltage power
supply apparatus incudes a booster circuit 114, a voltage detection
circuit 108 (detection means), and the engine controller 501. The
booster circuit 114 corresponds to the booster circuits 114a to
114d described with reference to FIG. 1B, and the voltage detection
circuit 108 corresponds to the voltage detection circuits 108a to
108d also described with reference to FIG. 1B. The booster circuit
114 includes the piezoelectric transformer 101, rectifier diodes
102 and 103, a rectifier capacitor 104, a field effect transistor
111, a voltage resonance inductor 112, and a voltage resonance
capacitor 113. The field effect transistor 111 performs a switching
operation based on a pulse signal supplied from a high voltage
control unit 201 to be described later. An LC resonance circuit
formed from the inductor 112 and the capacitor 113 amplifies the
pulse signal. The piezoelectric transformer 101 vibrates in
accordance with the pulse signal supplied to its primary-side
terminal, and generates, at its secondary-side terminal, an AC
voltage amplified at a boost ratio corresponding to the size of the
piezoelectric transformer 101.
[0034] A rectifying circuit is connected to the subsequent stage of
the piezoelectric transformer 101. That is, the secondary-side
terminal of the piezoelectric transformer 101 is connected to the
cathode terminal of the diode 102 and the anode terminal of the
diode 103. One terminal of the capacitor 104 is connected to the
cathode terminal of the diode 103 and also to an output terminal
Vout. The other terminal of the capacitor 104 is connected to the
anode terminal of the diode 102 and also grounded. The diodes 102
and 103 and the capacitor 104 form a rectifying circuit. Hence, the
AC voltage output from the secondary-side terminal of the
piezoelectric transformer 101 is rectified and smoothed to a
positive voltage by the rectifying circuit and supplied from the
output terminal Vout to the load (not shown).
[0035] The voltage detection circuit 108 includes resistors 105,
106, and 107. The voltage of the output terminal Vout is divided by
the voltage detection circuit 108, and the divided voltage is input
to an A/D converter 2012 of the high voltage control unit 201 to be
described later.
[0036] The engine controller 501 includes the high voltage control
unit 201 (control means), the CPU 301, and a clock generation unit
401. The high voltage control unit 201 corresponds to the high
voltage control units 201a to 201d described with reference to FIG.
1B, and performs constant voltage control of the voltage of the
output terminal Vout. The CPU 301 sets the target voltage in the
high voltage control unit 201. The clock generation unit 401
supplies a clock to the high voltage control unit 201 and the CPU
301.
[0037] Control Operation of High-Voltage Power Supply Apparatus
[0038] The control operation of the high-voltage power supply
apparatus shown in FIG. 2 will be described next. The high voltage
control unit 201 includes a memory unit 2011 (memory means) that is
a volatile memory, the A/D converter 2012, a difference calculation
block 2013, a control calculation block 2014, and a frequency
generation block 2015 using a digital counter circuit. The memory
unit 2011 includes a target value setting block 2021, an output
voltage register 2022, and a gain setting register 2023. The
high-voltage power supply apparatus according to this embodiment is
different from the conventional high-voltage power supply apparatus
shown in FIG. 5A in that the memory unit 2011 includes the gain
setting register 2023.
[0039] The output of the output terminal Vout input to the A/D
converter 2012 is digitally converted and stored in the output
voltage register 2022 of the memory unit 2011. The target voltage
is stored from the CPU 301 in the target value setting block 2021
and the gain setting register 2023 of the memory unit 2011. The
difference calculation block 2013 calculates the difference between
the values stored in the output voltage register 2022 and the
target value setting block 2021, and outputs it to the control
calculation block 2014.
[0040] The control calculation block 2014 performs
proportional-integral-derivative(PID) control based on the
difference calculation result of the difference calculation block
2013, calculates a preset value that is a value to determine the
frequency of the pulse signal to be generated by the frequency
generation block 2015, and outputs the preset value to the
frequency generation block 2015. When the preset value for
frequency control input from the control calculation block 2014
becomes small, the frequency generation block 2015 raises the
frequency of the pulse signal. On the other hand, when the preset
value for frequency control input from the control calculation
block 2014 becomes large, the frequency generation block 2015
lowers the frequency of the pulse signal.
[0041] Frequency Generator Block
[0042] The arrangement and operation of the frequency generation
block 2015 will be described next in detail with reference to FIG.
3A. The frequency generation block 2015 includes an N-bit
programmable counter 20151, a 1-bit counter 20153, and an AND gate
20154.
[0043] The clock generation unit 401 supplies an input pulse (for
example, a clock of several MHz) to the N-bit programmable counter
20151 (to be referred to as the N-bit counter 20151 hereinafter).
The N-bit counter 20151 increments the count value by one every
time the input pulse goes high (to be referred to as H
hereinafter), thereby performing count. In addition, when the
above-described count value matches the preset value input from the
control calculation block 2014, the output of the N-bit counter
20151 is inverted, and the above-described count value is cleared
to zero (0). The output of the N-bit counter 20151 is output to the
1-bit counter 20153 to be described later. Note that when a
low-level (to be referred to as L hereinafter) signal serving as a
reset signal is input to a reset terminal RESET, the N-bit counter
20151 is reset, and the count value becomes zero (0). The reset
signal to be input to the N-bit counter 20151 is supplied from the
CPU 301.
[0044] The 1-bit counter 20153 inverts the output voltage every
time the output signal from the N-bit counter 20151 changes to the
H signal; it generates a pulse signal of a frequency corresponding
to the information of the preset value input via the N-bit counter
20151. Note that the 1-bit counter 20153 is reset when a reset
signal is input to the reset terminal RESET. The reset signal to be
input to the 1-bit counter 20153 is supplied from the CPU 301.
[0045] When the preset value input from the control calculation
block 2014 becomes small, the inversion period of the signal output
from the N-bit counter 20151 shortens. Hence, the frequency of the
pulse signal output from the frequency generation block 2015 rises.
On the other hand, when the preset value input from the control
calculation block 2014 becomes large, the inversion period of the
signal output from the N-bit counter 20151 lengthens. Hence, the
frequency of the pulse signal output from the frequency generation
block 2015 lowers.
[0046] The AND gate 20154 on/off-controls the output of the
high-voltage power supply apparatus in accordance with an ENABLE
signal output from the CPU 301. More specifically, when the ENABLE
signal is an L output, the AND gate 20154 outputs a pulse signal
corresponding to the output of the 1-bit counter 20153. On the
other hand, when the ENABLE signal is an H output, the output of
the AND gate 20154 is forcibly changed to an L signal, and the AND
gate 20154 outputs the L signal. Hence, since the pulse signal
output from the high voltage control unit 201 can be
on/off-controlled in accordance with the ENABLE signal output from
the CPU 301, the output of the high-voltage power supply apparatus
can be on/off-controlled.
[0047] Note that when changing the frequency of the piezoelectric
transformer 101 between a frequency Fmax and a resonance frequency
FO shown in FIG. 5B described above, the limit values Fmax and FO
are provided for the preset value of the control calculation block
2014. That is, when the preset value has reached the limit value
Fmax or FO, the calculation operation of PID control of the control
calculation block 2014 is stopped (the calculation result is held).
At this time, the limit values Fmax and FO can be stored in the
memory unit 2011, set by the CPU 301, or fixed.
[0048] Control Gain Switching Operation
[0049] An operation of switching the control gain in accordance
with the setting voltage value (target voltage value) in the
high-voltage power supply apparatus according to this embodiment
will be described. FIG. 3B is a view showing a table 800 used to
set the control gain in accordance with the setting voltage value
according to this embodiment. The table 800 is an example of a
lookup table that defines the correspondence between the setting
voltage value (Tgt[V]) of the high-voltage power supply apparatus
and the control gain parameter group (to be also referred to as a
gain or control gain hereinafter) of the control calculation block
2014. The table 800 that associates the high-voltage power supply
apparatus and the gain is stored in advance in the ROM included in
the CPU 301. Note that the control gain parameter group in the
table 800 includes the parameters of the gains of the proportional
(P term), integral (I term), and derivative (D term) of PID control
as an example of feedback control. That is, the control gain
parameter group includes the set values of control parameters for
performing PID control, which are optimized for each setting
voltage value in view of elements of the time delay in the
high-voltage power supply circuit and the A/D converter 2012 of the
high voltage control unit 201. The table 800 may define a relation
defining the correspondence between the setting voltage value of
the high-voltage power supply apparatus and the control gain
parameter group of the control calculation block 2014.
[0050] (When Setting Voltage Value Is Low)
[0051] When frequency control of the piezoelectric transformer 101
is performed to obtain a low voltage, the frequency generation
block 2015 drives the piezoelectric transformer 101 in a region
where the output voltage with respect to the frequency is moderate
(see FIG. 5B). Hence, the output voltage exhibits a moderate
characteristic (see FIG. 5C) with respect to the preset value of
the control calculation block 2014. In this embodiment, the CPU 301
increases the gain of PID control of the control calculation block
2014 and largely changes the preset value of the control
calculation block 2014, thereby largely changing the frequency of
the pulse signal. That is, the CPU 301 sets the setting voltage
value and the control gain parameter group (in FIG. 3B, a parameter
group corresponding to G1) corresponding to the setting voltage
value in each of the target value setting block 2021 and the gain
setting register 2023 of the memory unit 2011.
[0052] G1 is a gain group optimized to obtain a low target voltage
lower than, for example, 1,000 V (Tgt<1000). In this embodiment,
it is set by the proportional (P term)=10, the integral (I term)=8
and the derivative (D term)=4. The PID control of the control
calculation block 2014 can largely change the preset value of the
control calculation block 2014 by changing the gains used in the
proportional (P term), integral (I term), and derivative (D term).
As a result, even when the piezoelectric transformer 101 is driven
in the region where the output voltage is moderate with respect to
the frequency, the preset value can largely be changed. It is
therefore possible to quickly output the target voltage.
[0053] (When Setting Voltage Value Is High)
[0054] Reversely, when frequency control of the piezoelectric
transformer 101 is performed to obtain a high voltage, the
frequency generation block 2015 drives the piezoelectric
transformer 101 in a region where the output voltage is steep with
respect to the frequency (see FIG. 5B). Hence, the output voltage
exhibits a steep characteristic (see FIG. 5C) with respect to the
preset value of the control calculation block 2014. In this
embodiment, the CPU 301 changes the gain of PID control of the
control calculation block 2014 and finely changes the preset value
of the control calculation block 2014, thereby finely changing the
frequency of the pulse signal. That is, the CPU 301 sets the
setting voltage value and the control gain parameter group (in FIG.
3B, a parameter group corresponding to G5) corresponding to the
setting voltage value in each of the target value setting block
2021 and the gain setting register 2023 of the memory unit
2011.
[0055] G5 is a gain group optimized to obtain a high target voltage
equal to or higher than, for example, 4,000 V (4000 Tgt). In this
embodiment, it is set by the proportional (P term)=6, the integral
(I term)=4 and the derivative (D term)=4. The PID control of the
control calculation block 2014 can change the preset value of the
control calculation block 2014 to be finer than terms in G1 by
changing the gains used in the proportional (P term), integral (I
term), and derivative (D term). As a result, even when the
piezoelectric transformer 101 is driven in the region where the
output voltage is steep with respect to the frequency, calculation
can be done using the conventional PID control gain. This makes it
possible to output the target voltage in a time equal to the
conventional rise time and also output a stable voltage without
overshoot.
[0056] As described above, according to the arrangement of this
embodiment, the gain of PID control is switched in accordance with
the setting voltage value. This allows the high-voltage power
supply apparatus using the piezoelectric transformer to quickly
output the target voltage even when outputting a low voltage.
Other Embodiments
[0057] Note that in the above-described explanation, the voltage of
the output terminal Vout is divided by the voltage detection
circuit 108, and the divided voltage is input to the A/D converter
2012 of the high voltage control unit 201. However, the embodiment
is not limited to the above-described case. For example, the
difference calculation block 2013 may be formed as an analog
circuit, as indicated by 125 in FIG. 4A. That is, reference numeral
125 denotes a differential amplification circuit including an
operational amplifier 120 and resistors 121, 122, 123, and 124,
which will be referred to as the differential amplification circuit
125 (output means) hereinafter. The voltage of the output terminal
Vout is divided by the voltage detection circuit 108, and the
divided voltage is input to the inverting input terminal
(-terminal) of the operational amplifier 120 via the resistor
121.
[0058] On the other hand, the setting voltage value (target voltage
value) set in the target value setting block 2021 by the CPU 301 is
output to a D/A converter 2016. The setting voltage value output
from the D/A converter 2016 is input to the noninverting input
terminal (+terminal) of the operational amplifier 120 via the
resistor 123. The operational amplifier 120 outputs the signal such
that the inverting input terminal and the noninverting input
terminal form a virtual short. The output of the operational
amplifier 120 is input to the control calculation block 2014 via
the A/D converter 2012. Hence, the differential amplification
circuit 125 can output the difference between the setting voltage
value and the voltage of the output terminal Vout, like the
difference calculation block 2013. The control calculation block
2014 outputs the preset value based on a value obtained by causing
the A/D converter 2012 to digitally convert the difference output
from the differential amplification circuit 125. Note that the same
reference numerals as in FIG. 2 denote the same parts in FIG. 4A,
and a description thereof will be omitted.
[0059] As described above, according to this embodiment, it is
possible to stably obtain the output of the power supply apparatus
and shorten the rise time until the target voltage in the power
supply apparatus using the piezoelectric transformer.
Second Embodiment
[0060] High-Voltage Power Supply Apparatus
[0061] The arrangement and operation according to the second
embodiment will be described in detail with reference to FIG. 4B.
In the first embodiment, the table 800 is stored in advance in the
ROM included in the CPU 301, and the CPU 301 sets the control gain
parameter group in the gain setting register 2023 of the memory
unit 2011. The second embodiment is different in that a table 800
(see FIG. 3B), which is stored in the CPU 301 in the first
embodiment, is stored in a memory unit 2011 of a high voltage
control unit 201. In this embodiment, a description of the same
parts as in the first embodiment will be omitted, and the
arrangement that stores the table 800 in the memory unit 2011 of
the high voltage control unit 201 and its operation will be
described in detail.
[0062] FIG. 4B is a block diagram showing a high-voltage power
supply apparatus according to this embodiment. A gain setting table
2017 stores the table 800 of the first embodiment. The gain setting
table 2017 is an example of a lookup table that defines the
correspondence between the setting voltage value (target voltage
value) and the PID control gain parameters of a control calculation
block 2014. Note that the PID control gain parameter group in the
table 800 is optimized for each setting voltage value, as in the
first embodiment. The table 800 may define a relation defining the
correspondence between the setting voltage value of the
high-voltage power supply apparatus and the control gain parameter
group of the control calculation block 2014, as in the first
embodiment.
[0063] The control calculation block 2014 can perform PID control
calculation using the control gain parameter group corresponding to
the setting voltage value from the gain setting table 2017. Hence,
as in the first embodiment, switching the control gain in
accordance with the setting voltage value makes it possible to
stably obtain the output of the high-voltage power supply apparatus
and quickly output the target voltage even when outputting a low
voltage.
[0064] When the table 800 is stored in the memory unit 2011 of the
high voltage control unit 201, as in this embodiment, the CPU 301
sets only the target voltage in the memory unit 2011 of the high
voltage control unit 201. For this reason, the number of registers
in the high voltage control unit 201 can be decreased. In addition,
control can be done without intervening the CPU 301.
[0065] Note that in this embodiment as well, the difference
calculation block 2013 may be changed to a differential
amplification circuit 125 formed from an analog circuit, as in the
first embodiment.
[0066] In the table 800 in the above-described first and second
embodiments, although the values G1, G2, G3, G4, and G5 in the
control gain parameter group of the table 800 satisfies the value
relationship within the range satisfying
G1>G2>G3>G4>G5, the present invention is not restricted
by this relationship term. For example, the impedance variation of
the member to which the high voltage power supply supplies a high
voltage can be considered as the values G1, G2, G3, G4, and G5 in
the table 800. That is, since the relationship between the
frequency and the output voltage shown in FIG. 5B varies according
to the impedance of the member, the output value of the high
voltage power supply can be stably obtained by detecting the
impedance of the member, considering the characteristic variation
between the frequency and the output voltage and optimizing the
values G1, G2, G3, G4, and G5 in the control gain parameter group
in the table 800.
[0067] In the above-described first and second embodiments, PID
control has been exemplified as the feedback control of the control
calculation block 2014. However, feedback control of any other form
is usable if the gain of the feedback control can be changed.
[0068] As described above, according to this embodiment, it is
possible to stably obtain the output of the power supply apparatus
and shorten the rise time until the target voltage in the power
supply apparatus using the piezoelectric transformer.
[0069] Note that the high voltage control unit 201 described in the
first and second embodiments may be formed as an integrated
circuit. For example, the high voltage control unit 201 can be
formed as, for example, an ASIC (Application Specific Integrated
Circuit). The integrated circuit can reduce the circuit scale of
the power supply apparatus, leading to size reduction of the
circuit board of the power supply apparatus.
[0070] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0071] This application claims the benefit of Japanese Patent
Application Nos. 2012-171146, filed Aug. 1, 2012, and 2013-126546,
filed Jun. 17, 2013 which are hereby incorporated by reference
herein in their entirety.
* * * * *