JP2007295722A - High-tension power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of an image failure by controlling a drive frequency of a piezoelectric transformer so as not to exceed a resonance frequency, even if electric power more than the capacity of the piezoelectric transformer is required by an unexpected situation. <P>SOLUTION: In a high-tension power supply device, a sub-CPU 205 outputs pulses that drive the piezoelectric transformer 101. The sub-CPU 205 operates within the frequency range including the resonance frequency of the piezoelectric transformer, and variably controls the drive frequency of the piezoelectric transformer based on a signal from a main CPU 207. The sub-CPU 205 is structured with a one-chip microcomputer, and measures the resonance frequency of the piezoelectric transformer or a frequency that maximizes an output voltage in advance. By performing the control so as not to exceed the resonance frequency, the problem above can be solved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high voltage power supply device applied to an image forming apparatus using an electrophotographic process.

  In a conventionally known electrophotographic image forming apparatus, when a direct transfer method is employed in which a recording sheet is brought into contact with a photosensitive member for transfer, a roller-like conductive rubber is provided on a metal shaft for a transfer member. A wound transfer roller is used. Then, it is driven to rotate according to the process speed of the photoreceptor. Further, a DC bias voltage is used as a voltage applied to the transfer member, and a current of about 10 μA is usually supplied in order to perform good transfer using the transfer roller.

  In order to generate a high voltage required for image formation as described above, a winding type electromagnetic transformer has been conventionally used. However, the electromagnetic transformer is composed of a copper wire, a bobbin, and a magnetic core. When used in an image forming apparatus having the above specifications, the output current value is about 10 μA. The leakage current had to be reduced to the maximum. For this reason, it is necessary to insulate the windings of the transformer by a mold or the like, and a larger transformer is required compared to the supplied power, which hinders the miniaturization and weight reduction of the high-voltage power supply device.

  Therefore, in order to compensate for these drawbacks, it has been studied to generate a high voltage by using a thin and light high-power piezoelectric transformer. That is, by using a piezoelectric transformer made of a ceramic material, it is possible to generate a high voltage with an efficiency higher than that of an electromagnetic transformer. In addition, the piezoelectric transformer can be separated from the primary and secondary electrodes, so there is no need to mold for special insulation, and the high-voltage generator can be made compact and lightweight. (See Patent Documents 1 and 2).

  Here, FIG. 9 shows a circuit diagram of a conventional example of a piezoelectric transformer type high voltage power source for performing constant voltage control.

  Reference numeral 110 denotes a voltage controlled oscillator (hereinafter referred to as VCO). The VCO 110 of this conventional example has a CR oscillation circuit as a basic configuration and has the following configuration. That is, the comparator 131 which is a comparison element, and the charge / discharge operation connected to the inverting input terminal (− terminal) of the comparator 131 include the capacitor 130 and the resistance element 136. Furthermore, it has resistance elements 132 and 133 and a diode 137 for generating a charge threshold voltage and a discharge threshold voltage, which are connected to a non-inverting input terminal (+ terminal) of the comparator 131 and switch between charge and discharge. An emitter follower circuit composed of a transistor 138 and resistance elements 139, 140, and 141 is connected in parallel with the resistance element 136 so that the charging current to the capacitor 130 is variable. As a result, the oscillation frequency can be controlled in accordance with the output voltage from the operational amplifier 109. The transistor 135 and the resistor 142 increase the rise time of the output terminal of the comparator 131. Further, the diode 134 is a protection diode for the transistor 138.

  As other components, 101 is a piezoelectric transformer (piezoelectric ceramic transformer), 102 and 103 are rectifier diodes, 104 is a high-voltage capacitor for smoothing, 105, 106, 107, and 108 are resistors, 111 is a transistor, and 112 is an inductor. 113 is a capacitor and 114 is a resistor.

  Next, the operation of the conventional piezoelectric transformer type high voltage power supply will be described.

  First, a high-voltage output control signal (hereinafter referred to as Vcont), which is an analog signal output from controller means (not shown), is input to the inverting input terminal (− terminal) of the operational amplifier 109 via the resistor 114. On the other hand, a voltage obtained by dividing the output voltage (hereinafter referred to as Vout) by the resistors 105, 106, and 107 is input to the non-inverting input terminal (+ terminal) of the operational amplifier 109 through the protective resistor 108. The operational amplifier 109 outputs a voltage from the output terminal so that the voltage value of Vcont input to the inverting input terminal (− terminal) is equal to the divided voltage obtained by dividing Vout by the resistors 105, 106, and 107. The output terminal of the operational amplifier 109 is connected to the VCO 110. The VCO 110 switches the transistor 111 at a frequency corresponding to the output voltage of the operational amplifier 109 and supplies power to the primary side of the piezoelectric transformer 101. The piezoelectric transformer 101 vibrates in accordance with the drive pulse supplied to the primary side, and generates an alternating voltage amplified at a step-up ratio corresponding to the size of the piezoelectric transformer 101 on the secondary side. The generated AC voltage is rectified and smoothed to a positive voltage by the diodes 102 and 103 and the high voltage capacitor 104 and supplied to a transfer roller (not shown) as a load.

  Next, FIG. 3 shows the relationship between the drive frequency of the piezoelectric transformer 101 and the output voltage when a voltage is supplied to a predetermined load. In general, the characteristics of the piezoelectric transformer have such a shape that the output voltage becomes maximum at the resonance frequency f0 as shown in FIG.

  Usually, the output voltage of the piezoelectric transformer is controlled by changing the frequency of the drive pulse between the maximum frequency fH and the resonance frequency f0.

JP-A-11-206113 JP-A-11-252905

  As described above, in the piezoelectric transformer type high voltage power supply described in the conventional example, the output power is controlled by changing the frequency of the driving pulse of the piezoelectric transformer between the maximum frequency fH and the resonance frequency f0.

  However, due to unforeseen circumstances such as the conveyance of the recording paper being delayed, if the large voltage required for the transfer to the recording paper is set even though there is no recording paper, the following problems Occurs. That is, there is a problem that even if the recording paper arrives after that, the output power necessary for image formation cannot be secured, and image defects continue to occur.

  FIG. 11 is a diagram showing the relationship between the drive frequency of the piezoelectric transformer and the output voltage when there is recording paper and when there is no recording paper. fL is the lowest frequency operable with the VCO 110, and fH is the highest frequency operable with the VCO 110.

Here, the operation when the conveyance of the recording paper is delayed will be described.
(1) A control means (not shown) raises Vcont to 4.5 V in order to set Vout to 3 kV at a predetermined timing.
(2) The operational amplifier 109 lowers the output voltage until the divided voltage of Vcont and Vout becomes the same, and lowers the operating frequency of the VCO 110. Since there is no recording paper, the operating frequency and Vout of the VCO 110 change following the broken line in FIG.
(3) However, when there is no recording paper, since the piezoelectric transformer 101 can output only Vout up to 2.7 kV, the operating frequency of the VCO 110 changes to a lower frequency side than the resonance frequency f0. Once the operating frequency of the VCO 110 changes to a lower frequency side than the resonance frequency f0, Vout decreases, so the VCO 110 continues to operate at the lowest operating frequency fL, and Vout becomes EfLb.
(4) After that, even if the recording paper arrives, Vout rises to EfLa shown in FIG. 10, but does not reach 3 kV set by Vcont, so the VCO 110 continues to operate at the lowest operating frequency fL. Since EfLa cannot secure a transfer current necessary for good transfer, an image defect occurs. The image defect continues to occur until Vcont is set to a set voltage equal to or lower than a value corresponding to EfLa.

  In order to prevent uneven charging of the photoconductor, a technique is employed in which the current flowing from the transfer roller to the photoconductor is kept within a predetermined range regardless of the presence or absence of recording paper. In other words, a predetermined voltage is applied to the transfer roller even between recording sheets (between sheets) in continuous image formation. In this case, once the operating frequency of the VCO changes to a lower frequency side than the resonance frequency f0, image defects continue to occur until continuous image formation is completed and the transfer bias is turned off.

  The operation lower limit frequency of the VCO is set higher than the assumed resonance frequency f0, and the operation frequency of the VCO 110 is controlled to be higher than the set frequency. As a result, it is possible to prevent the operating frequency from changing to a lower frequency side than the resonance frequency f0. However, the actual resonance frequency f0 varies greatly from one piezoelectric transformer to another. For this reason, the following problems arise when trying to avoid the change of the operating frequency to the lower frequency side than f0 for all the piezoelectric transformers. In other words, a piezoelectric transformer having a resonance frequency f0 on a lower side than other piezoelectric transformers causes a problem that a desired voltage cannot be output if the above-described lower limit frequency of the VCO is used. In order to avoid this, it is necessary to individually set the VCO operating lower limit frequency with a variable resistor or the like for each piezoelectric transformer. For example, the resistors 132 and 133 in FIG. 9 must be replaced with variable resistors. However, in a high-voltage power supply apparatus in an apparatus having a large number of piezoelectric transformers such as an image forming apparatus, adjusting all variable resistances, particularly manual adjustment, is a very complicated operation. For this reason, there has been a problem that a great amount of adjustment time is required.

  The present invention solves the above problems, and an object of the present invention is to provide a high-voltage power supply apparatus that eliminates the need to manually adjust the operating lower limit frequency for each piezoelectric transformer. Further, the object of the present invention is to prevent the occurrence of image defects by preventing the control range of the piezoelectric transformer, that is, the drive frequency from exceeding the resonance frequency, even when power exceeding the capacity of the piezoelectric transformer is required due to unforeseen circumstances. An object of the present invention is to provide a high-voltage power supply device that can be used.

  The present invention is a high-voltage power supply apparatus that generates a high voltage to be supplied to at least one of a charging bias, a developing bias, and a transfer bias used in an electrophotographic image forming apparatus, and that corresponds to the frequency of a driving pulse. A piezoelectric transformer for outputting a high voltage, a driving pulse generating means for generating the driving pulse, a frequency control means for controlling the frequency of the driving pulse generated by the driving pulse generating means, and an output voltage of the piezoelectric transformer are detected. Voltage detecting means, and the frequency control means sequentially increases or decreases the frequency of the driving pulse generated by the driving pulse generating means step by step, and the voltage value obtained by the voltage detecting means exceeds the peak. Is detected, the frequency one step before the peak is set as the operation lower limit frequency, and the image The frequency of the drive pulse generated by said drive pulse generating means during operation of the forming device and controls over the operation limit frequency.

  According to the high-voltage power supply device of the present invention, the piezoelectric transformer can be used without manually adjusting the driving frequency range of the piezoelectric transformer for each piezoelectric transformer, even when used in an apparatus having a large output load fluctuation such as an image forming apparatus. It becomes possible to prevent control from becoming impossible. Further, without increasing the cost, it is possible to prevent the occurrence of image defects by preventing the controllable range of the piezoelectric transformer, that is, the drive frequency from exceeding the resonance frequency, thereby preventing the occurrence of image defects.

Example 1
The first embodiment of the present invention will be described below.
FIG. 2 is a configuration diagram of the color laser printer of this embodiment.

  401 is a color laser printer, 402 is a deck for storing the recording paper 32, 403 is a deck paper presence / absence sensor for detecting the presence / absence of the recording paper 32 in the deck 402, and 404 is a pickup roller for feeding out the recording paper 32 from the deck 402. Reference numeral 405 denotes a deck paper feed roller that conveys the recording paper 32 fed by the pickup roller 404, and reference numeral 406 denotes a retard roller that forms a pair with the deck paper feed roller 405 and prevents double feeding of the recording paper 32. A registration roller pair 407 that synchronously conveys the recording paper 32 and a pre-registration sensor 408 that detects the conveyance state of the recording paper 32 to the registration roller pair are disposed downstream of the deck paper feed roller 405.

  An electrostatic attraction transfer belt (hereinafter referred to as ETB) 409 is disposed downstream of the registration roller pair 407. On the ETB 409, a color image composed of toner images of four colors of Y (yellow), M (magenta), C (cyan), and B (black) is formed as follows. That is, an image formed by an image forming unit including process cartridges 410 (Y, M, C, B) for four colors Y, M, C, and B and a scanner unit 420 (Y, M, C, B) is formed. Then, the images are sequentially superposed by the transfer rollers 430 (Y, M, C, B). As a result, a color image is formed and transferred onto the recording paper 32. The recording paper 32 on which the color image is formed is conveyed downstream. A fixing unit is provided downstream, and the toner image transferred onto the recording paper 32 is thermally fixed. The fixing unit includes a pair of a fixing roller 433 and a pressure roller 434 each having a heater 432 for heating therein, and a pair of fixing paper discharge rollers 435 for conveying the recording paper 32 from the fixing roller. Further, a fixing paper discharge sensor 436 for detecting the conveyance state of the recording paper from the fixing unit is provided.

  Each scanner unit 420 includes a laser unit 421, a polygon mirror 422, a scanner motor 423, and an imaging lens group 424. The laser unit 421 emits laser light modulated based on each image signal sent from the video controller 440. The polygon mirror 422 and the scanner motor 423 scan the laser light from each laser unit 421 on each photosensitive drum 305. Each process cartridge 410 includes a photosensitive drum 305, a charging roller 303 and a developing roller 302, and a toner storage container 411 necessary for a known electrophotographic process, and is configured to be detachable from the laser printer 401 main body. Yes. Further, when the video controller 440 receives image data sent from an external device 441 such as a host computer, the video controller 440 develops the image data into bitmap data and generates an image signal for image formation.

  Reference numeral 201 denotes a DC controller which is a control unit of the laser printer 401. The DC controller 201 includes a one-chip microcomputer (hereinafter referred to as a main CPU) 207 having a RAM 207a, a ROM 207b, a timer 207c, a digital input / output port 207d, and a D / A port 207e. The ROM 207b stores the control procedure of the main CPU shown in FIG. Furthermore, the DC controller 201 includes a nonvolatile memory device (EEPROM) 208, various input / output control circuits (not shown), and the like. Reference numeral 202 denotes a high voltage power supply (piezoelectric transformer type high voltage power supply device). The high-voltage power supply 202 has a charging high-voltage power supply (not shown) and a development high-voltage power supply (not shown) corresponding to each process cartridge 410 (Y, M, C, B). Further, the high voltage power source 202 has a transfer high voltage power source using a piezoelectric transformer capable of outputting a high voltage corresponding to each transfer roller 430 (Y, M, C, B). Reference numeral 205 denotes a one-chip microcomputer (hereinafter referred to as a sub CPU) that controls the high-voltage power supply 202. The sub CPU 205 performs serial communication with the main CPU 207 and controls the output voltage of each high-voltage power supply by changing the frequency of the output pulse. The serial communication uses three general communication lines, outputs a clock (CLC) and a command (CMD) from the main CPU 207, and outputs a status (STS) from the sub CPU 205.

  Next, the configuration of the piezoelectric transformer type high voltage power source of this embodiment will be described.

  FIG. 1 shows a circuit diagram of a piezoelectric transformer type high-voltage power supply in the present embodiment.

  The same components as those of the conventional example are denoted by the same symbols, and the description thereof is omitted.

  The difference from the circuit diagram of the conventional example is that the sub CPU 205 outputs a drive pulse for driving the piezoelectric transformer instead of the VCO. The sub CPU 205 constitutes drive pulse generation means. The main CPU 207 that controls the sub CPU 205 constitutes frequency control means for controlling the frequency of drive pulses generated by the sub CPU 205.

  Next, the operation of the high-voltage power supply circuit in this embodiment will be described with reference to FIGS.

  FIG. 3 is a diagram showing the characteristics of the output voltage (Vout) with respect to the drive frequency of the piezoelectric transformer 101. As shown in the figure, the shape is such that the output voltage becomes maximum at the resonance frequency f0. fL is the lowest frequency at which the resonance frequency f0 fluctuates due to variations in the piezoelectric transformer 101, and fH is the highest frequency at which the sub CPU 205 can generate a pulse. The frequency range of the pulses generated by the sub CPU 205 is a range in which the highest includes fH and the lowest includes the frequency fL.

  FIG. 4 is a flowchart showing a control procedure of the main CPU 207 for measuring the resonance frequency f0 in the present embodiment. The trigger for executing this process may be executed by an operator before shipment from the factory, or may be executed by a serviceman when the user replaces the high-voltage board due to a failure or the like.

  First, the measurement operation mode of the resonance frequency f0 is set by a key operation on an operation panel (not shown).

  The color laser printer 401 drives the photosensitive drum 305, the charging roller 303, the developing roller 302, and the ETB 409 by respective driving motors (not shown). Then, an initial charging bias and developing bias are applied to the charging roller 303 and the developing roller 302 of each color so as not to consume useless toner. The frequency (Fout) of the driving pulse of the piezoelectric transformer for the charging bias is 180 kHz (about −1 kV), and that for the developing bias is 170 kHz (about 300 V). First, characteristic measurement is started from the Y charging bias.

  The counter t is set to 0 (S101). Fout (t), that is, Fout (0) is set to fH (200 kHz) [kHz] (S102). A value of Vsns (t) as a detected value of the output voltage Vout (obtained by dividing Vout) is read by the sub CPU 205 and stored in the RAM 207a (S103). The value of Vout at this time is transmitted by serial communication and stored in the RAM 207a. If the value of Vout is equal to or greater than the value measured last time, the counter t is incremented by 1 (S105), Fout is set to Fout (t) = Fout (t−1) −0.1 kHz (S106), and the process returns to S103. If the value of Vsns (t) is smaller than the previously measured value in S104 (S104), the previous Fout (t−1) is recognized as the resonance frequency f0, and Fout (t− The value of 1) is stored in the EEPROM 208 (S107). The power supply of the main body is turned off, and the measurement operation ends.

  Thereafter, the characteristics of the charging bias, the developing bias, and the transfer bias are measured in the same manner for each bias of each color.

  With such a configuration and operation, Fout which is the resonance frequency f0 of each bias is stored in the EEPROM 208, and the value of the drive frequency Fout is equal to or higher than the resonance frequency f0 (in the normal operation region of FIG. 3) during normal printing operation. Fout is controlled so as to have a frequency of

  Therefore, the piezoelectric transformer can be controlled in a frequency range higher than the resonance frequency inherent in each actual piezoelectric transformer, and the piezoelectric transformer can be prevented from becoming uncontrollable.

  The communication method between the main CPU and the sub CPU in this embodiment is an example of a commonly used three-wire serial communication. However, as long as communication is possible between the main CPU and the sub CPU, Other methods may be used. For example, parallel communication using a bus or a two-wire system using a common command and status can be used.

(Example 2)
In the first embodiment, the sub CPU 205 outputs drive pulses to the piezoelectric transformer. In this embodiment, the main CPU 207 outputs a drive pulse.

  In this embodiment, the sub CPU 205 is deleted from FIG.

  FIG. 5 shows a circuit diagram of the piezoelectric transformer type high voltage power source in the present embodiment.

  The same configurations as those of the conventional example and the first embodiment are denoted by the same reference symbols, and description thereof is omitted.

  The difference from the first embodiment is that a pulse is output from the port P1 of the main CPU 207 without using the sub CPU 205, and the high voltage output detection signal Vsns is input to the analog input port (AIN) of the main CPU. It is. Of course, the main CPU 207 uses a high-performance CPU. For example, H8S / 2282F (manufactured by Hitachi, Ltd.) or M16C / 62T is suitable.

  The characteristic measurement processing procedure by the main CPU 207 may be the same as that of the first embodiment.

  With such a configuration, the substrate area of the high-voltage power supply can be reduced. In addition, communication processing is unnecessary, and malfunctions due to poor communication can be avoided.

(Example 3)
In this embodiment, a drive pulse for a piezoelectric transformer is generated by an application specific integrated circuit (hereinafter referred to as ASIC), and is controlled by a main CPU.

  FIG. 6 shows a circuit diagram of the piezoelectric transformer type high voltage power source in the present embodiment.

  The same configurations as those of the conventional example and the first embodiment are denoted by the same reference symbols, and description thereof is omitted.

  The difference from the first embodiment is that an ASIC is mounted instead of the sub CPU.

  Further, the control is performed by the main CPU 207, and the high voltage detection signal Vsns is input to the analog input port (AIN) of the main CPU 207.

  The characteristic measurement processing procedure may be the same as in the first embodiment.

  FIG. 7 is an internal block diagram of the ASIC. A serial register 701 is input by serial communication and converts it into a 12-bit parallel signal. 702 converts a 12-bit parallel signal into 8-bit data and 4-bit address data, and selects an output destination. That is, there are 16 high-voltage outputs, and one of the output units (703a to 703u) of each line is selected. Each output unit detects that the output to be set by the data select 704a is selected, and performs digital-to-analog conversion by the DA converter 705a. The analog output signal is input to the VCO 706a, and the VCO 706a outputs a pulse (Fout) at a set frequency. The specific circuit of the VCO 706a is the same as the conventional example.

  In this embodiment, there are 16 high-voltage outputs, and each data selection (704b to 704u) 8-bit digital-analog conversion (DAC) (705b to 705u), VCO (110b to 110u), pulse output (Fout1 to Fout16) It has. By adopting such a configuration, the cost can be reduced as compared with the case of using a sub CPU.

Example 4
In this embodiment, an ASIC is installed in a DC controller, a piezoelectric transformer drive pulse is generated, and control is performed by a main CPU.

  FIG. 8 shows a circuit diagram of the piezoelectric transformer type high voltage power source in the present embodiment.

  The same components as those of the conventional example and the first to third embodiments are denoted by the same reference numerals, and the description thereof is omitted.

  The difference from the third embodiment is that the ASIC 290 is mounted on the DC controller 201. The ASIC 290 and the main CPU 207 perform bus communication at a speed higher than that of serial communication.

  Further, the control is performed by the main CPU 207 as in the third embodiment, and the high voltage detection value Vsns is input to the analog input port (AIN) of the main CPU 207.

  The internal block diagram of the ASIC has a configuration in which the 12-bit serial register 701 in FIG. 7 is deleted. Because it is bus communication, serial-parallel conversion is not required.

  The characteristic measurement processing procedure may be the same as in the first embodiment.

  By mounting the ASIC 290 on the DC controller 207 as in the present embodiment, there is an advantage that the stepping motor control and the function as an expansion port can be provided.

(Example 5)
In the first to fourth embodiments, the resonance frequency fo or the frequency corresponding to the maximum operating voltage is stored in the storage unit at a predetermined timing. In this embodiment, characteristic measurement is performed at the time of initial operation immediately after power-on. The configuration is the same as in the first to fourth embodiments. Further, the processing procedure is the same as that described in the description of FIG. 5 of the first embodiment, and its start is programmed to be at the start of the initial operation. That is, the execution timing is automatically executed, not by key operation on the operation panel. Since it is executed every time the power is turned on, it is possible to cope with temperature changes due to the environment around the color laser printer and changes over time (changes in fo) as durability progresses, and the effect of reducing the storage area of the EEPROM is there.

  In the first to fifth embodiments, the description has been given of the configuration in which the output voltage is increased by changing the driving frequency of the piezoelectric transformer from the high frequency side to the low frequency side. However, the output voltage may be increased by changing the drive frequency from the low frequency side to the high frequency side.

  In the first to fifth embodiments, the image forming apparatus is described with the configuration of a color laser printer. However, the image forming apparatus is not limited to a color laser printer, and may be a monochrome laser printer, a copying machine, or a fax machine.

  In the first to fourth embodiments, an EEPROM is taken as an example of the storage means. However, other nonvolatile storage devices or nonvolatile storage elements can be substituted, and needless to say, for example, a flash ROM or the like may be used.

  Furthermore, in Examples 1 to 5, although the resonance frequency f0 is stored in the storage unit, the value of Fout, which is the control frequency corresponding to the maximum operating voltage, may be stored. Further, the resonance frequency f0, the maximum operating frequency, etc. can be estimated, or the value of the control frequency Fout that can be calculated may be stored.

1 is a schematic circuit diagram of a printer equipped with a piezoelectric transformer type high voltage power supply in Embodiment 1. FIG. 1 is a configuration diagram of a color laser printer in Embodiment 1. FIG. FIG. 3 is a diagram illustrating characteristics of a driving frequency and an output voltage of a piezoelectric transformer in Example 1. FIG. 3 is a flowchart illustrating a resonance frequency measurement operation in the first embodiment. FIG. 5 is a schematic circuit diagram of a printer equipped with a piezoelectric transformer type high-voltage power supply in Example 2. FIG. 6 is a schematic circuit diagram of a printer equipped with a piezoelectric transformer type high-voltage power supply in Example 3. 6 is a block diagram of an integrated circuit (ASIC) in Examples 3 and 4. FIG. FIG. 9 is a schematic circuit diagram of a printer equipped with a piezoelectric transformer type high-voltage power supply in Example 4. It is a figure showing the drive frequency of a piezoelectric transformer and the characteristic of an output voltage in a prior art example. It is a figure explaining operation | movement of the high voltage power supply circuit in a prior art example. It is a figure showing the drive frequency of a piezoelectric transformer and the characteristic of an output voltage in a prior art example.

Explanation of symbols

101 Piezoelectric transformer (piezoelectric ceramic transformer)
102, 103, 135 Diode 104 High voltage capacitor 109, 504, 703, 803 Operational amplifier 110 Voltage controlled oscillator (VCO)
112 Inductor 201 DC Controller 202 High Voltage Power Supply (Piezoelectric Transformer High Voltage Power Supply Device)
205 Sub CPU (1-chip microcomputer)
207 Main CPU (1-chip microcomputer)
208 EEPROM (nonvolatile memory element)
290 ASIC (Application Specific Integrated Circuit)
401 color laser printer (image forming apparatus)

Claims (5)

A high-voltage power supply device that generates a high voltage supplied to at least one of a charging bias, a developing bias, and a transfer bias used in an electrophotographic image forming apparatus,
A piezoelectric transformer that outputs a high voltage corresponding to the frequency of the drive pulse; drive pulse generating means for generating the drive pulse; frequency control means for controlling the frequency of the drive pulse generated by the drive pulse generating means; Voltage detecting means for detecting the output voltage of the transformer,
When the frequency control means detects that the voltage value obtained by the voltage detection means exceeds the peak by gradually increasing or decreasing the frequency of the drive pulse generated by the drive pulse generation means step by step, A frequency one step before the peak is set as an operation lower limit frequency, and the frequency of the drive pulse generated by the drive pulse generation means during operation of the image forming apparatus is controlled to be equal to or higher than the operation lower limit frequency. High voltage power supply device.   2. The high-voltage power supply device according to claim 1, wherein the drive pulse generating means is constituted by a one-chip microcomputer.   2. The high-voltage power supply device according to claim 1, wherein the drive pulse generating means is constituted by an integrated circuit.   The high-voltage power supply device according to claim 1, wherein the drive pulse generation unit is provided in a control unit in the image forming apparatus. The high-voltage power supply apparatus according to claim 1, wherein the frequency control unit executes the setting operation of the operation lower limit frequency when the image forming apparatus is powered on.

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