JP6828372B2 - Power supply and image forming equipment - Google Patents

Description

The present disclosure relates to a power supply device and an image forming device, and more particularly to a power supply device and an image forming device capable of outputting a plurality of voltages at the same time.

Power supply devices capable of outputting voltages of different magnitudes are widespread. The power supply device is composed of, for example, a primary winding to which an AC voltage is applied and a secondary winding that generates a voltage by mutual induction of the primary windings.

Regarding the power supply device, it is possible to output a voltage of a different magnitude. Japanese Patent Application Laid-Open No. 2008-61332 (Patent Document 1) outputs the voltage from the secondary winding by changing the frequency of the AC voltage applied to the primary winding. The power supply device for changing the voltage is disclosed. Japanese Unexamined Patent Publication No. 09-325655 (Patent Document 2) discloses a high-voltage power supply device capable of outputting AC voltage and DC voltage. Japanese Unexamined Patent Publication No. 04-325873 (Patent Document 3) discloses a power supply device capable of individually controlling a plurality of voltage output circuits.

Japanese Unexamined Patent Publication No. 2008-61332. Japanese Unexamined Patent Publication No. 09-325655 Japanese Unexamined Patent Publication No. 04-325873

When a voltage obtained by superimposing AC voltages of different frequencies (hereinafter, also referred to as "superimposed voltage") is applied to the primary winding, an AC voltage corresponding to the superposed voltage is generated in the secondary winding due to mutual induction of the primary windings. .. It is desired to separate the AC voltage generated in this way into AC voltages having different frequencies. Patent Documents 1 to 3 do not disclose applying a superposed voltage to the primary winding.

Even if the AC voltage generated in the secondary winding can be separated into AC voltages of different frequencies, the AC voltage of one frequency and the AC voltage of another frequency may interfere with each other and fluctuate from the ideal voltage. is there.

In particular, it is mounted on an image forming apparatus having a monochrome printing mode in which an image is formed only in black and a color printing mode in which an image is formed using a plurality of colors including black (for example, yellow, magenta, cyan, and black). In the case of a power supply that outputs a voltage corresponding to each color, fluctuations from the ideal voltage cause problems. Specifically, when executing monochrome mode, the AC voltage of the frequency corresponding to other colors (for example, yellow, magenta, cyan) fluctuates due to the interference with the AC voltage of the frequency corresponding to black. It is possible. In this case, so-called toner fog occurs in which toner of a color that is not originally printed is printed.

The present disclosure has been made to solve the above-mentioned problems, and an object in a certain aspect is a primary winding to which a voltage obtained by superimposing an AC voltage of a frequency corresponding to each of a plurality of colors is applied. It is an object of the present invention to provide a power supply device and an image forming apparatus capable of extracting a voltage corresponding to each color from the above and suppressing the formation of other colors when forming an image of only a specific color.

According to a certain aspect, a power supply device mounted on an image forming apparatus having a first mode in which an image is formed using a first color and a second mode in which an image is formed using at least the first color and the second color. Is a control unit for generating a first superimposed voltage in which an AC voltage of a first frequency corresponding to a first color and an AC voltage of a second frequency corresponding to a second color are superimposed, and a first superimposed voltage is used. It includes the applied primary winding and the secondary winding that is mutually induced and coupled to the primary winding, and outputs the first output voltage of the first frequency and the second output voltage of the second frequency generated in the secondary winding. A voltage output unit for converting the second output voltage, a first conversion unit for converting the second output voltage to the first DC voltage, and a first reverse bias voltage for canceling the first DC voltage when the first mode is executed. It includes a reverse bias voltage generation unit to be generated, and a first adder for outputting a second superposed voltage obtained by superimposing a first reverse bias voltage and a first DC voltage.

Preferably, the first reverse bias voltage has the opposite polarity to the first DC voltage. The absolute value of the first reverse bias voltage is the absolute value of the first direct-current voltage or more when executing the first mode.

Preferably, the absolute value of the first reverse bias voltage is greater than the absolute value of the first DC voltage when the first mode is executed. The control unit adjusts the AC voltage of the second frequency so that the second superimposed voltage becomes the target voltage.

Preferably, the reverse bias voltage generation unit includes a voltage detection unit for detecting the magnitude of the first DC voltage and an adjustment unit for adjusting the magnitude of the first reverse bias voltage according to the detection result by the voltage detection unit. And include.

Preferably, the reverse bias voltage generator generates a first reverse bias voltage from the first output voltage.

Preferably, in the second mode, the image forming apparatus uses the third color in addition to the first color and the second color to form an image. The control unit further superimposes the AC voltage of the third frequency corresponding to the third color on the first superposed voltage. The voltage output unit outputs the third output voltage of the third frequency generated in the secondary winding. The power supply device further includes a second conversion unit for converting the third output voltage into a second DC voltage and outputting the voltage.

At this time, the reverse bias voltage generation unit generates a second reverse bias voltage for canceling the second DC voltage when the first mode is executed. The power supply device further includes a second adder that outputs a third superimposed voltage obtained by superimposing a second reverse bias voltage and a second DC voltage.

Alternatively, the difference between the third frequency and the first frequency is larger than the difference between the second frequency and the first frequency, and the reverse bias voltage having the opposite polarity to the second DC voltage is not superimposed on the second DC voltage.

Preferably, the voltage output unit has a first filter for passing the AC component of the first frequency among the AC components of the voltage generated in the secondary winding and outputting the AC component as the first output voltage. Among the AC components of the voltage generated in the secondary winding, it includes a second filter for passing the AC component of the second frequency and outputting the AC component as the second output voltage.

Preferably, the voltage output unit is mutual-inductively coupled to the primary winding as a secondary winding, and is mutual-inductively coupled to the primary winding for generating the first output voltage and the primary winding. Includes a secondary secondary winding for generating two output voltages.

According to another aspect, the image forming apparatus includes the power supply device described above.

In a certain aspect, when the voltage corresponding to each color is extracted from the primary winding to which a voltage obtained by superimposing an AC voltage of a frequency corresponding to each of a plurality of colors is applied, and when image formation of only a specific color is performed, another It is possible to suppress the formation of color.

It is a figure which shows an example of the internal structure of the image forming apparatus which concerns on Embodiment 1. FIG. It is a block diagram which shows the main hardware composition of the image forming apparatus which concerns on Embodiment 1. FIG. It is a figure which shows an example of the circuit structure of the power supply device of the 1st reference example. It is a figure which shows the transformer of the 1st reference example. It is a figure which shows the transmission characteristic of the transformer shown in FIG. It is a figure which shows the appearance of the transformer shown in FIG. It is a disassembled view of the transformer shown in FIG. It is a figure which shows an example of the circuit structure of the power supply device of the 2nd reference example. It is a figure which shows the transmission characteristic of a transformer when the resonance frequency fluctuates. It is a figure which shows an example of the circuit structure of the power supply device which concerns on Embodiment 1. FIG. It is a figure which shows the circuit structure of the reverse bias generation circuit. It is a figure which shows an example of the primary transfer voltage for yellow, magenta, and cyan when a monochrome print mode is set. It is a figure which shows an example of the circuit structure of the power supply device which concerns on Embodiment 2. It is a figure which shows an example of the circuit structure of the power supply device which concerns on Embodiment 3. It is a block diagram which shows the internal structure of the reverse bias generation unit. It is a figure which shows the circuit structure of the generation circuit provided in the reverse bias generation unit. It is a figure which shows an example of the circuit structure of the power supply device which concerns on Embodiment 4. FIG.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following description, the same parts and components are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of these will not be repeated. In addition, each embodiment and each modification described below may be selectively combined as appropriate.

<Embodiment 1>
[Internal configuration of image forming apparatus]
The image forming apparatus 100 equipped with the power supply apparatus 50 will be described with reference to FIG. FIG. 1 is a diagram showing an example of the internal structure of the image forming apparatus 100.

FIG. 1 shows an image forming apparatus 100 as a color printer. Hereinafter, the image forming apparatus 100 as a color printer will be described, but the image forming apparatus 100 is not limited to the color printer. For example, the image forming apparatus 100 may be a multifunction device (MFP: Multi-Functional Peripheral).

The image forming apparatus 100 has a monochrome printing mode in which an image is formed using only black, and a color printing mode in which an image is formed using yellow, magenta, cyan, and black.

The image forming apparatus 100 includes an image forming unit 1Y, 1M, 1C, 1K, an intermediate transfer belt 30, a primary transfer roller 31, a secondary transfer roller 33, a cassette 37, a driven roller 38, and a drive roller 39. The timing roller 40, the fixing device 43, and the power supply device 50 are included.

The image forming units 1Y, 1M, 1C, and 1K are arranged in order along the intermediate transfer belt 30. The image forming unit 1Y receives the toner supply from the toner bottle 15Y and forms a yellow (Y) toner image. The image forming unit 1M receives the toner supply from the toner bottle 15M and forms a toner image of magenta (M). The image forming unit 1C receives the toner supply from the toner bottle 15C and forms a toner image of cyan (C). The image forming unit 1K receives the toner supply from the toner bottle 15K and forms a black (BK) toner image.

The image forming units 1Y, 1M, 1C, and 1K are arranged along the intermediate transfer belt 30 in the order of rotation of the intermediate transfer belt 30, respectively. The image forming units 1Y, 1M, 1C, and 1K each include a photoconductor 10, a charging device 11, an exposure device 12, a developing device 13, and a cleaning device 17, respectively.

The charging device 11 uniformly charges the surface of the photoconductor 10. The exposure device 12 irradiates the photoconductor 10 with laser light in response to a control signal from the main body control device 70, which will be described later, and exposes the surface of the photoconductor 10 according to the input image pattern. As a result, an electrostatic latent image corresponding to the input image is formed on the photoconductor 10.

The developing device 13 applies a developing bias to the developing roller 14 while rotating the developing roller 14 to adhere toner to the surface of the developing roller 14. As a result, the toner is transferred from the developing roller 14 to the photoconductor 10, and the toner image corresponding to the electrostatic latent image is developed on the surface of the photoconductor 10.

The photoconductor 10 and the intermediate transfer belt 30 are in contact with each other at a portion where the primary transfer roller 31 is provided. The primary transfer roller 31 is configured to be rotatable. By applying a transfer voltage having the opposite polarity to the toner image to the primary transfer roller 31, the toner image is transferred from the photoconductor 10 to the intermediate transfer belt 30.

In the color printing mode, the yellow (Y) toner image, the magenta (M) toner image, the cyan (C) toner image, and the black (BK) toner image are superimposed in this order from the photoconductor 10 to the intermediate transfer belt. Transferred to 30. As a result, a color toner image is formed on the intermediate transfer belt 30. On the other hand, in the monochrome printing mode, the black (BK) toner image is transferred from the photoconductor 10 to the intermediate transfer belt 30.

The intermediate transfer belt 30 is stretched on the driven roller 38 and the driving roller 39. The drive roller 39 is rotationally driven by, for example, a motor (not shown). The intermediate transfer belt 30 and the driven roller 38 rotate in conjunction with the drive roller 39. As a result, the toner image on the intermediate transfer belt 30 is transferred to the secondary transfer roller 33.

The cleaning device 17 is in pressure contact with the photoconductor 10. The cleaning device 17 collects the toner remaining on the surface of the photoconductor 10 after the transfer of the toner image.

Paper S is set in the cassette 37. The paper S is fed from the cassette 37 one by one to the secondary transfer roller 33 along the transport path 41 by the timing roller 40. The secondary transfer roller 33 applies a transfer voltage having a polarity opposite to that of the toner image to the paper S being conveyed. As a result, the toner image is attracted from the intermediate transfer belt 30 to the secondary transfer roller 33, and the toner image on the intermediate transfer belt 30 is transferred to the paper S. The transfer timing of the paper S to the secondary transfer roller 33 is adjusted by the timing roller 40 according to the position of the toner image on the intermediate transfer belt 30. The timing roller 40 transfers the toner image on the intermediate transfer belt 30 to an appropriate position on the paper S.

The fixing device 43 pressurizes and heats the paper S passing through itself. As a result, the toner image formed on the paper S is fixed on the paper S. After that, the paper S is discharged to the tray 48.

The power supply device 50 supplies, for example, a voltage of a different magnitude to each device in the image forming apparatus 100. Details of the power supply device 50 will be described later.

[Hardware configuration of image forming apparatus]
An example of the hardware configuration of the image forming apparatus 100 will be described with reference to FIG. FIG. 2 is a block diagram showing a main hardware configuration of the image forming apparatus 100.

As shown in FIG. 2, the image forming apparatus 100 includes a power supply device 50, a main body control device 70, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a network interface 104, and an operation panel. The 107 and the storage device 120 are included.

The main body control device 70 is composed of, for example, at least one integrated circuit. An integrated circuit is composed of, for example, at least one CPU, at least one DSP, at least one ASIC (Application Specific Integrated Circuit), at least one FPGA (Field Programmable Gate Array), or a combination thereof.

Preferably, the main body control device 70 controls both the power supply device 50 and the image forming device 100. That is, the main body control device 70 is shared by the power supply device 50 and the image forming device 100. The main body control device 70 may be configured separately from the power supply device 50, or may be configured integrally with the power supply device 50. When the main body control device 70 is configured separately from the power supply device 50, the configuration of the power supply device 50 becomes simple.

The main body control device 70 selects either a monochrome printing mode or a color printing mode according to the information input to the operation panel 107, and controls the power supply device 50 and the image forming device 100 according to the selected mode. The main body control device 70 outputs a selection mode identification signal indicating the selected mode to the power supply device 50.

The main body control device 70 controls the operation of the image forming device 100 by executing the control program 122 of the power supply device 50 and the image forming device 100. For example, the main body control device 70 sets a target voltage value for the power supply device 50.

The main body control device 70 reads the control program 122 from the storage device 120 into the ROM 102 based on the reception of the execution command of the control program 122. The RAM 103 functions as a working memory and temporarily stores various data necessary for executing the control program 122.

An antenna (not shown) or the like is connected to the network interface 104. The image forming apparatus 100 exchanges data with an external communication device via an antenna. External communication devices include, for example, mobile communication terminals such as smartphones, servers, and the like. The image forming apparatus 100 may be configured so that the control program 122 can be downloaded from the server via the antenna.

The operation panel 107 is composed of a display and a touch panel. The display and the touch panel are overlapped with each other, and the operation panel 107 receives, for example, a printing operation or a scanning operation on the image forming apparatus 100.

The storage device 120 is a storage medium such as a hard disk or an external storage device. The storage device 120 stores the control program 122 and the like of the image forming device 100. The storage location of the control program 122 is not limited to the storage device 120, and the control program 122 includes a storage area of the power supply device 50, a storage area of the main body control device 70 (for example, a cache), a ROM 102, a RAM 103, and an external device (for example, an external device). It may be stored in a server) or the like.

The control program 122 may be provided as a part of an arbitrary program, not as a single program. In this case, the control process according to the present embodiment is realized in cooperation with an arbitrary program. Even a program that does not include such a part of modules does not deviate from the purpose of the control program 122 according to the present embodiment. Further, some or all of the functions provided by the control program 122 may be realized by dedicated hardware. Further, the image forming apparatus 100 may be configured in the form of a so-called cloud service in which at least one server executes a part of the processing of the control program 122.

[Power supply device 50]
As described above, the power supply device 50 applies a voltage of a different magnitude to each device in the image forming device 100. As an example, the power supply device 50 has a charging voltage applied to the charging device 11, a developing voltage applied to the developing roller 14, a primary transfer voltage applied to the primary transfer roller 31, and a secondary transfer voltage applied to the secondary transfer roller 33. Supply.

As for the charging voltage and the developing voltage, an AC voltage is superimposed on the DC voltage in order to improve the image quality. The primary transfer voltage is a negative polarity DC voltage. The secondary transfer voltage is a positive polarity DC voltage. Therefore, a positive polarity DC voltage is required to clean the primary transfer roller 31, and a negative polarity DC voltage is required to clean the secondary transfer roller 33. As described above, since the power supply device 50 outputs many different voltages, a considerable number of transformers are required.

The charging device 11, the developing roller 14, and the primary transfer roller 31 are provided in each of the image forming units 1Y, 1M, 1C, and 1K. Therefore, the power supply device 50 outputs four voltages corresponding to each color of YMCK for the charging voltage, the developing voltage, and the primary transfer voltage. If separate transformers are provided to output the four voltages corresponding to each color, the cost of the power supply device becomes high. Therefore, the power supply device 50 includes one shared transformer for each of the charging voltage, the developing voltage, and the primary transfer voltage, and outputs four voltages corresponding to each color from the shared transformer.

The power supply device 50 that supplies the primary transfer voltage to the primary transfer rollers 31 of the image forming units 1Y, 1M, 1C, and 1K will be described below. Since the power supply device 50 that supplies the charging voltage and the developing voltage has the same configuration as the power supply device 50 that supplies the primary transfer voltage, the description thereof will be omitted.

(1. First reference example of power supply device)
First, before explaining the power supply device 50 according to the first embodiment, the power supply device 150 as a first reference example for the first embodiment will be described with reference to FIG. FIG. 3 is a diagram showing an example of the circuit configuration of the power supply device 150.

As shown in FIG. 3, the power supply device 150 includes a control unit 51, a transformer 54, a detection unit 56, an amplifier D, bandpass filters F1 to F4, F11 to F14, and conversion circuits T1 to T4. It is composed of.

The control unit 51 includes frequency control units DC1 to DC4 and an adder A0. The frequency control units DC1 to DC4 of the control unit 51 may be incorporated in the main body control device 70.

The power supply 150 can output four different AC voltages from one transformer 54. Each AC voltage is converted to a DC voltage and output to the corresponding primary transfer roller 31. Since the power supply device 150 is composed of one transformer 54, the configuration of the power supply device 150 is simplified, and the power supply device 150 can be miniaturized and reduced in cost.

Frequency controller DC1 generates an alternating voltage _{f 1} of a predetermined frequency for black (K). The frequency of the AC voltage f ₁ is, for example, 100 kHz. The AC voltage f ₁ is output to the adder A0.

Frequency controller DC2 generates an alternating voltage _{f 2} of a predetermined frequency for yellow (Y). The frequency of the AC voltage f ₂ is, for example, 200 kHz. The AC voltage f ₂ is output to the adder A0.

Frequency controller DC3 generates an alternating voltage _{f 3} of a predetermined frequency for magenta (M). Frequency of the AC voltage _{f 3} is, for example, 300kHz. AC voltage _{f 3} is output to the adder A0.

Frequency control unit DC4 generates an alternating voltage _{f 4} of a predetermined frequency for cyan (C). The frequency of the alternating voltage _{f 4} is, for example, 400kHz. AC voltage _{f 4} is output to the adder A0.

The adder A0 superimposes the AC voltages f _{1 to} f ₄ to generate the superposed voltage f. The superimposed voltage f is amplified by the amplifier D and then output to the transformer 54.

The transformer 54 is composed of a primary winding W1 and a secondary winding W2. The transformer 54 amplifies the superposed voltage f to the superposed voltage f'. The superimposed voltage f'is output to each of the bandpass filters F1 to F4.

Band-pass filter F1, of the AC component of the superimposed voltage f ', passing an alternating current component of the same frequency as the AC voltage f _1. As an example, the bandpass filter F1 passes an AC voltage of 100 kHz. The superimposed voltage f'passed through the bandpass filter F1 is output to the conversion circuit T1 as an output voltage f ₁ '.

The bandpass filter F2 passes an AC component having the same frequency as the AC voltage f ₂ among the AC components of the superimposed voltage f'. As an example, the bandpass filter F2 passes an AC voltage of 200 kHz. The superimposed voltage f'passed through the bandpass filter F2 is output to the conversion circuit T2 as an output voltage f ₂ '.

Band-pass filter F3, of the AC component of the superimposed voltage f ', passing an alternating current component of the same frequency as the alternating voltage f _3. As an example, the bandpass filter F3 passes an AC voltage of 300 kHz. Superimposed voltage f which has passed through the band-pass filter F3 ', the output voltage f _3' is output to the conversion circuit T3 as.

Band-pass filter F4, of the AC component of the superimposed voltage f ', passing an alternating current component of the same frequency as the alternating voltage f _4. As an example, the bandpass filter F4 passes an AC voltage of 400 kHz. Superimposed voltage f which has passed through the band-pass filter F4 ', the output voltage f _4' is output to the conversion circuit T4 as.

Conversion circuit T1 is rectified and then smoothed output voltage f _{1 ',} and outputs the DC voltages V ₁ obtained by converting the polarity negative. The DC voltage V ₁ is output to the black primary transfer roller 31. The DC voltage V ₁ is fed back to the frequency control unit DC1. Frequency controller DC1 is the magnitude of the DC voltage V ₁ is adjusted AC voltage f ₁ to be the target voltage value. As a result, the DC voltage V ₁ is stabilized.

Conversion circuit T2 is rectified and then smoothed output voltage f _{2 ',} and outputs the DC voltage V ₂ obtained by converting the polarity negative. The DC voltage V ₂ is output to the primary transfer roller 31 for yellow. Further, the DC voltage V ₂ is fed back to the frequency control unit DC 2. The frequency control unit DC ₂ adjusts the AC voltage f ₂ so that the magnitude of the DC voltage V ₂ becomes the target voltage value. As a result, the DC voltage V ₂ is stabilized.

Conversion circuit T3 is rectified and then smoothed output voltage f _{3 ',} and outputs the DC voltage V ₃ obtained by converting the polarity negative. The DC voltage V ₃ is output to the primary transfer roller 31 for magenta. Further, the DC voltage V ₃ is fed back to the frequency control unit DC 3. The frequency control unit DC ₃ adjusts the AC voltage f ₃ so that the magnitude of the DC voltage V ₃ becomes the target voltage value. As a result, the DC voltage V ₃ is stabilized.

Conversion circuit T4 is rectified and then smoothed output voltage f _{4 ',} to output a DC voltage V ₄ obtained by converting the polarity negative. The DC voltage V ₄ is output to the primary transfer roller 31 for cyan. Further, the DC voltage V ₄ is fed back to the frequency control unit DC ₄ . The frequency control unit DC ₄ adjusts the AC voltage f ₄ so that the magnitude of the DC voltage V ₄ becomes the target voltage value. As a result, the DC voltage V ₄ is stabilized.

The detection unit 56 sequentially detects the current flowing through the secondary winding W2 and outputs a detection signal indicating the magnitude of the current. The detection signal is output to each of the bandpass filters F11 to F14. The detection signal is used to interlock the magnitude of the voltage of the superimposed voltage f ', is on the detection signal contains the same frequency components and the AC voltage f ₁ ~f _4.

Band-pass filter F11, of the AC component of the detection signal output from the detection unit 56, passes the AC component of the same frequency as the AC voltage f _1. As an example, the bandpass filter F11 passes a detection signal of 100 kHz. The detection signal that has passed through the bandpass filter F11 is output to the frequency control unit DC1. Frequency controller DC1 calculates the current value from the detected signal passed through the band-pass filter F11, the current value to adjust the AC voltage f ₁ to a predetermined target current value. As an example, the current value is calculated as the average of the magnitudes of the detection signals detected within a certain period of time. As a result, the current flowing through the circuit on the secondary side of the transformer 54 is stabilized.

Thus, the frequency control unit DC1 is to the current flowing based on the detection result by the detection unit 56 to the circuit on the secondary side of the transformer 54 may be stabilized, AC based on the fed-back DC voltages V ₁ The DC voltage V ₁ can also be stabilized by adjusting the voltage f ₁ .

The frequency control unit DC1 is configured to receive the setting of the control mode of the power supply device 50 from the main body control device 70. The control mode includes a current control mode for suppressing current fluctuation and a voltage control mode for suppressing voltage fluctuation. When the voltage control mode is set, the control signal CV is output to the frequency control unit DC1. When the current control mode is set, the control signal CC is output to the frequency control unit DC1. Frequency controller DC1, in the voltage control mode, the magnitude of the DC voltage V ₁ is adjusted AC voltage f ₁ to be the target voltage value (predetermined voltage value). Frequency controller DC1, in the current control mode, adjusting the AC voltage f ₁ so that the current value calculated based on the detection signal passed through the band-pass filter F11 is a target current value (a predetermined current value).

The frequency control unit DC1 is configured to receive at least one setting of a target voltage value (predetermined voltage value) and a target current value (predetermined current value) from the main body control device 70. As a result, the power supply device 150 can stabilize the output current at an arbitrary current value in the current control mode, and can stabilize the output voltage at an arbitrary voltage value in the voltage control mode.

Band-pass filter F12, of the AC component of the detection signal output from the detection unit 56, passes the AC component of the same frequency as the AC voltage f _2. As an example, the bandpass filter F12 passes a detection signal of 200 kHz. The detection signal that has passed through the bandpass filter F12 is output to the frequency control unit DC2. Frequency control unit DC2, like the frequency controller DC1, calculates a current value from the detected signal passed through the band-pass filter F12, the current value to adjust the AC voltage f ₂ to be a predetermined target current value .. The frequency control unit DC2 accepts the setting of the control mode in the same manner as the frequency control unit DC1.

Band-pass filter F13, of the AC component of the detection signal output from the detection unit 56, passes the AC component of the same frequency as the alternating voltage f _3. As an example, the bandpass filter F13 passes a detection signal of 300 kHz. The detection signal that has passed through the bandpass filter F13 is output to the frequency control unit DC3. Frequency controller DC3, like the frequency controller DC1, calculates a current value from the detected signal passed through the band-pass filter F13, the current value to adjust the AC voltage f ₃ to a predetermined target current value ..

Band-pass filter F14, of the AC component of the detection signal output from the detection unit 56, passes the AC component of the same frequency as the alternating voltage f _4. As an example, the bandpass filter F14 passes a detection signal of 400 kHz. The detection signal that has passed through the bandpass filter F14 is output to the frequency control unit DC4. Frequency control unit DC4, like the frequency controller DC1, calculates a current value from the detected signal passed through the band-pass filter F14, to adjust the AC voltage f ₄ as the current value becomes a predetermined target current value ..

(2. Second reference example of power supply device)
Next, a power supply device as a second reference example for the first embodiment will be described. In the power supply device 150 of the first reference example shown in FIG. 3, the AC voltage generated in the secondary winding W2 is separated into AC voltages for each predetermined band by using a plurality of bandpass filters. On the other hand, the power supply device of the second reference example outputs the AC voltage for each predetermined band without using the bandpass filter.

(2-1. Basic principle of transformer applied to the second reference example)
The basic principle of the transformer 54A applied to the second reference example will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing an example of the transformer 54A. FIG. 5 is a diagram showing the transmission characteristics of the transformer 54A.

As shown in FIG. 4, the transformer 54A includes one primary winding W and secondary windings W2A, W2B. A superimposed voltage is applied to the primary winding W. At this time, a stray capacitance CA (stray capacitance) is generated in the secondary winding W2A, and a stray capacitance CB is generated in the secondary winding W2A.

The resonance frequency fa of the secondary winding W2A is represented by the following equation (1). “L1” in the formula (1) represents the leakage inductance of the secondary winding W2A. “C1” in the formula (1) represents the capacitance of the stray capacitance CA.
fa = 1 / 2π√ (L1, C1) ... (1).

The resonance frequency fb of the secondary winding W2B is represented by the following equation (2). “L2” in the formula (2) represents the leakage inductance of the secondary winding W2B. “C2” in the formula (2) represents the capacitance of the stray capacitance CB.
fb = 1 / 2π√ (L2 ・ C2) ... (2).

FIG. 5 shows the transmission characteristic 96 of the secondary winding W2A and the transmission characteristic 97 of the secondary winding W2B. The transmission characteristic shows the relationship between the frequency of the AC voltage applied to the primary winding W and the magnitude of the voltage generated in the secondary winding. The magnitude of the voltage is expressed, for example, as the ratio (that is, gain) of the voltage generated in the secondary winding to the voltage applied to the primary winding.

As shown in the transmission characteristic 96, in the secondary winding W2A, the gain of the voltage at the resonance frequency fa is higher than that of the other frequencies. That is, when a superimposed voltage including resonance frequencies fa and fb is applied to the primary winding W, an AC voltage having a resonance frequency fa is generated in the secondary winding W2A.

As shown in the transmission characteristic 97, in the secondary winding W2B, the gain of the voltage at the resonance frequency fb is higher than that of the other frequencies. That is, when a superimposed voltage including the resonance frequencies fa and fb is applied to the primary winding W, an AC voltage having the resonance frequency fb is generated in the secondary winding W2B.

Although only two secondary windings W2A and W2B are shown in FIG. 4, the transformer 54A also includes two secondary windings W2C and W2D in addition to the secondary windings W2A and W2B. When a superimposed voltage including a resonance frequency corresponding to each of the secondary windings W2C and W2D is applied to the primary winding W, the transformer 54A applies an AC voltage having a resonance frequency from each of the secondary windings W2C and W2D. Output.

In this way, the transformer 54A utilizes the different transmission characteristics of the secondary winding to separate the superimposed voltage into a plurality of different frequency voltages.

(2-2. Internal structure of transformer applied to the second reference example)
Next, the internal structure of the transformer 54A will be described. As shown in the above equation (1), the transmission characteristic of the secondary winding W2A can be adjusted according to the inductance “L1” or the capacitance “C1”. At this time, the capacitance "C1" depends on the ratio of the number of turns of the secondary winding W2A to the primary winding W. Since it is easier to adjust the inductance "L1" than to adjust the turns ratio, the transmission characteristic of the secondary winding W2A is adjusted by the inductance "L1". Similarly, the transmission characteristic of the secondary winding W2B is adjusted by the inductance "L2".

The inductance "L1" is a leakage inductance, and as the magnetic flux not shared by the primary winding W1 and the secondary winding W2A increases, the inductance "L1" increases. The magnetic flux varies depending on, for example, the distance between the primary winding W1 and the secondary winding W2A. Focusing on this point, the distance between the primary winding W1 and the secondary winding W2A is adjusted so that the secondary winding W2A has a desired transmission characteristic. That is, a predetermined distance is provided between the primary winding W1 and the secondary winding W2A so that an output voltage of a predetermined frequency is generated from the secondary winding W2A. Preferably, the distance is the distance between the outer circumference of the primary winding W1 and the outer circumference of the secondary winding W2A.

Similarly, the distance between the primary winding W1 and the secondary winding W2B is adjusted so that the secondary winding W2B has the desired transmission characteristics. That is, a predetermined distance is provided between the primary winding W1 and the secondary winding W2B so that an output voltage of a predetermined frequency is generated from the secondary winding W2B.

A specific example of the structure of the transformer 54A applied to the second reference example will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing the appearance of the transformer 54A. FIG. 7 is an exploded view of the transformer 54A.

As shown in FIGS. 6 and 7, the transformer 54A is composed of cores 61A and 61B and bobbins B1 and B2.

The cores 61A and 61B are, for example, E-shaped, and are composed of a middle leg and two outer legs sandwiching the middle leg. A tubular bobbin B1 is attached to the middle leg of the core 61A. A tubular bobbin B2 is attached to the middle leg of the core 61B.

The diameter of the bobbin B2 is larger than the diameter of the bobbin B1, and the bobbin B1 is included in the bobbin B2. The bobbins B1 and B2 may be integrally configured or may be configured separately. The bobbins B1 and B2 are made of, for example, a resin.

A primary winding W is wound around the bobbin B1 (primary bobbin). One end of the primary winding W is connected to the electrode E1A. The other end of the primary winding W is connected to the electrode E1B. A superimposed voltage is applied between the electrodes E1A and E1B.

The bobbin B2 (secondary bobbin) has two or more winding portions of the secondary winding. In the examples of FIGS. 6 and 7, the bobbin B2 has four winding portions B2A to B2D. Each of the winding portions B2A to B2D is separated by, for example, a separator.

A secondary winding W2A is wound around the winding portion B2A. One end of the secondary winding W2A is connected to the electrode E2A1. The other end of the secondary winding W2A is connected to the electrode E2A2. An AC voltage corresponding to the transmission characteristics of the secondary winding W2A is generated between the electrodes E2A1 and E2A2.

A secondary winding W2B is wound around the winding portion B2B. One end of the secondary winding W2B is connected to the electrode E2B1. The other end of the secondary winding W2B is connected to the electrode E2B2. An AC voltage corresponding to the transmission characteristics of the secondary winding W2B is generated between the electrodes E2B1 and E2B2.

A secondary winding W2C is wound around the winding portion B2C. One end of the secondary winding W2C is connected to the electrode E2C1. The other end of the secondary winding W2C is connected to the electrode E2C2. An AC voltage corresponding to the transmission characteristics of the secondary winding W2C is generated between the electrodes E2C1 and E2C2.

A secondary winding W2D is wound around the winding portion B2D. One end of the secondary winding W2D is connected to the electrode E2D1. The other end of the secondary winding W2D is connected to the electrode E2D2. An AC voltage corresponding to the transmission characteristics of the secondary winding W2D is generated between the electrodes E2D1 and E2D2.

A distance d1 is provided between the bobbin B1 and the winding portion B2A. A distance d2 is provided between the bobbin B1 and the winding portion B2B. A distance d3 is provided between the bobbin B1 and the winding portion B2C. A distance d4 is provided between the bobbin B1 and the winding portion B2D. The distances d1 to d4 are different from each other. As a result, the transmission characteristics between the secondary windings W2A to W2D are different, and AC voltages having different frequencies are output from each of the secondary windings W2A to W2D.

When the primary winding W1 and the secondary windings W2A to W2D are arranged side by side, the inductance of the secondary winding far from the primary winding W1 becomes too large, and the desired transmission characteristics may not be obtained. Since the distances d1 to d4 can be adjusted accurately by including the primary winding W1 in the secondary windings W2A to W2D, the frequency and magnitude of the output voltage of the secondary windings W2A to W2D are as intended. Is adjusted to.

(2-3. Circuit configuration of power supply device in the second reference example)
The circuit configuration of the power supply device 150A of the second reference example will be described with reference to FIG. FIG. 8 is a diagram showing an example of the circuit configuration of the power supply device 150A.

The power supply device 150 shown in FIG. 3 is provided with bandpass filters F1 to F4, F11 to F14, but the power supply device 150A shown in FIG. 8 is provided with bandpass filters F1 to F4, F11 to F14. Not. Further, the power supply device 150A includes transformers 54A including a plurality of secondary windings W2A to W2D instead of the transformer 54, and includes detection units 56A to 56D instead of the detection unit 56, as shown in FIG. It is different from the power supply device 150. Since the other points are the same as those of the power supply device 150 shown in FIG. 3, the description thereof will not be repeated below.

The secondary windings W2A to W2D have different transmission characteristics and resonate at different frequencies. Secondary winding W2A is configured to resonate at the AC voltage f ₁ and the same frequency. As a result, the superimposed voltage f of the AC voltage f ₁ ~f ₄ is applied to the primary winding W1, the secondary winding W2A is an output voltage f _{1 'including} the AC voltage f ₁ same AC component and To do. Similarly, when the superimposed voltage f is applied to the primary winding W1, the secondary winding W2B outputs an output voltage f _{2 'containing} the same AC component and the AC voltage f _2. When superimposed voltage f is applied to the primary winding W1, the secondary winding W2C outputs an output voltage f _{3 'containing} the same of the AC component and the alternating voltage f _3. When superimposed voltage f is applied to the primary winding W1, the secondary winding W2D outputs an output voltage f _{4 'containing} the same of the AC component and the alternating voltage f _4. In this way, the secondary windings W2A to W2D simultaneously generate AC voltages of different frequencies.

The detection unit 56A detects the current flowing through the secondary winding W2A and outputs a detection signal indicating the magnitude of the current to the frequency control unit DC1. The detection signal is composed of the same frequency component and the alternating voltage f _1.

The detection unit 56B detects the current flowing through the secondary winding W2B and outputs a detection signal indicating the magnitude of the current to the frequency control unit DC2. The detection signal is composed of the same frequency component and the AC voltage f _2.

The detection unit 56C detects the current flowing through the secondary winding W2C and outputs a detection signal indicating the magnitude of the current to the frequency control unit DC3. The detection signal is composed of the same frequency component and the alternating voltage f _3.

The detection unit 56D detects the current flowing through the secondary winding W2D and outputs a detection signal indicating the magnitude of the current to the frequency control unit DC4. The detection signal is composed of the same frequency component and the alternating voltage f _4.

As described above, the power supply device 150A outputs AC voltages having different frequencies by using a plurality of secondary windings having different transmission characteristics. Since a bandpass filter is not required to output AC voltages of different frequencies, the circuit configuration of the power supply device 150A is simplified as compared with the first reference example.

(2-4. Problems with the power supply device in the second reference example)
The resonance frequencies of the secondary windings W2A to W2D of the transformer 54A are determined by the inductance or capacitance of the secondary windings W2A to W2D as described above. Therefore, the transmission characteristics of the secondary windings W2A to W2D may vary due to the following factors (a) to (c).

(A) The resonance frequency fluctuates due to changes in inductance and capacitance due to temperature and the like (environmental variation).

(B) Since the distances d1 to d4 shown in FIG. 7 vary from transformer 54A to transformer 54A, the resonance frequency varies from power supply device 150A (individual variation).

(C) The resonance frequency fluctuates with a change on the load side included in the image forming apparatus on which the power supply device 150A is mounted (load variation). For example, the resonance frequency varies due to the variation in the peripheral length of the photoconductor 10 for each image forming apparatus.

FIG. 9 is a diagram showing the transmission characteristics of the secondary winding W2B when the resonance frequency fluctuates. 9, the transmission characteristic 97 shows an ideal characteristic indicating an AC voltage f ₂ of the frequency and the same resonant frequency fb for yellow. Transfer characteristic 97a indicates that the resonance frequency fb1 fluctuates with the frequency fa side of the AC voltage f ₁ for black from the resonance frequency fb.

In an ideal transfer characteristics 97, since the gain of the frequency fa of the AC voltage f ₁ for black is substantially 0, the output voltage from the secondary winding W2B receives little influence of the alternating voltage f ₁ for black Absent. However, when the transmission characteristic of the secondary winding W2B fluctuates from the transmission characteristic 97 to the transmission characteristic 97a, the gain of the frequency fa in the transmission characteristic 97a becomes so large that it cannot be ignored, and the output voltage f ₂ from the secondary winding W2B ', the components caused by interference between the AC voltage f ₁ for black (hereinafter, referred to as fluctuation component) will contain.

In monochrome print mode, only black toner is printed, not yellow toner. At this time, the DC voltage V ₂ from the conversion circuit T2 for yellow should be 0V. However, _'when included fluctuation component, in the monochrome printing mode, the DC voltage V ₂ from the conversion circuit T2 for yellow, the output voltage f _2' output voltage f ₂ from the secondary winding W2B for yellow The voltage has a negative polarity (hereinafter referred to as the fluctuating voltage) according to the fluctuation component contained. This causes a problem that the yellow toner is printed even though the yellow toner should not be printed.

In FIG. 9, the secondary winding W2B for yellow has been described, but the same applies to the secondary winding W2C for magenta and the secondary winding W2D for cyan. Resonant frequency (i.e., transfer characteristic) by variation of the output voltage f ₃ from the secondary winding W2C and secondary windings W2D ', f _4', the variation component due to interference between the AC voltage f ₁ for black Can be included. As a result, in the monochrome printing mode, there arises a problem that magenta and cyan toners are printed even though they should not be printed.

(3. Circuit configuration of the power supply device 50 according to the first embodiment)
The power supply device 50 according to the first embodiment can solve the above problem. The circuit configuration of the power supply device 50 will be described with reference to FIG. FIG. 10 is a diagram showing an example of the circuit configuration of the power supply device 50.

As shown in FIG. 10, the power supply device 50 differs from the power supply device 150A shown in FIG. 8 in that it includes a reverse bias generation circuit 58 and adders A2 to A4. Since the other points are the same as those of the power supply device 150A shown in FIG. 8, the description thereof will not be repeated below.

Although not shown in FIG. 10, the frequency control units DC1 to DC4 have on / off, target voltage value, and control mode (either voltage control mode or current control mode) controlled by the main body as in FIG. It is set by the device 70. Hereinafter, it is assumed that the voltage control mode is set in the frequency control units DC1 to DC4.

Reverse bias generating circuit 58 on the basis of the output voltage f _{1 'of} the secondary winding W2A, the reverse bias voltage V _REV for canceling the DC voltage output from the converter circuit T2 to T4 (variable voltage) in the monochrome printing mode Is generated, and the generated reverse bias voltage V _REV is output to the adders A2 to A4. The specific circuit configuration of the reverse bias generation circuit 58 will be described later.

The adder A2 generates a superimposed voltage (DC voltage) Va ₂ in which the DC voltage V ₂ output from the conversion circuit T2 and the reverse bias voltage V _REV are superimposed, and the generated superimposed voltage Va ₂ is first-transferred for yellow. Output to the roller 31. Further, the superimposed voltage Va ₂ is fed back to the frequency control unit DC2. Frequency control unit DC2, the magnitude of the superimposed voltage Va ₂ to adjust the AC voltage f ₂ to be a target voltage value. As a result, the superimposed voltage Va ₂ is stabilized.

The adder A3 generates a superposed voltage Va ₃ in which the DC voltage V ₃ output from the conversion circuit T ₃ and the reverse bias voltage V _REV are superimposed, and outputs the generated superimposition voltage Va ₃ to the primary transfer roller 31 for magenta. To do. Further, the superimposed voltage Va ₃ is fed back to the frequency control unit DC3. Frequency controller DC3, the magnitude of the superimposed voltage Va ₃ adjusts the AC voltage f ₃ to be the target voltage value. As a result, the superimposed voltage Va ₃ is stabilized.

The adder A4 generates a superposed voltage Va ₄ in which the DC voltage V4 output from the conversion circuit T4 and the reverse bias voltage V _REV are superimposed, and outputs the generated superimposition voltage Va ₄ to the primary transfer roller 31 for cyan. .. Further, the superimposed voltage Va ₄ is fed back to the frequency control unit DC4. The frequency control unit DC ₄ adjusts the AC voltage f ₄ so that the magnitude of the superimposed voltage Va ₄ becomes the target voltage value. As a result, the superimposed voltage Va ₄ is stabilized.

The circuit configuration of the reverse bias generation circuit 58 will be described with reference to FIG. FIG. 11 is a diagram showing a circuit configuration of the reverse bias generation circuit 58.

As shown in FIG. 11, the reverse bias generation circuit 58 includes a diode D1, a capacitor C1, a resistor R1, and a Zener diode D2.

Diode D1 receives an output voltage f _{1 'including} the AC voltage f ₁ same AC component and the anode and a cathode connected to one end of the capacitor C1. The other end of the capacitor C1 is grounded. Diode D1 and the capacitor C1 functions as a half-wave rectifier circuit of the output voltage f _{1 ',} the connection node between the cathode and the capacitor C1 of the diode D1, and outputs a DC voltage of positive polarity.

A series circuit of the resistor R1 and the Zener diode D2 is connected in parallel to the capacitor C1. One end of the resistor R1 is connected to the connection node between the cathode of the diode D1 and the capacitor C1, and the anode of the Zener diode D2 is grounded. As a result, the reverse bias generation circuit 58 outputs the positive polarity constant voltage of the connection node between the resistor R1 and the Zener diode D2 as the reverse bias voltage V _REV .

Thus, the reverse bias generating circuit 58 on the basis of the output voltage f _{1 'of} the secondary winding W2A, generates a reverse bias voltage V _REV of positive polarity.

As described above, the secondary winding W2B, W2C, the output voltage _{f 2} from W2C ', _{f 3',} the _{f 4} ', can contain fluctuation component due to interference between the AC voltage _{f 1} for black There is. In consideration of manufacturing variations of the secondary windings W2B, W2C, W2C, the environment in which they are installed, and the influence of consumables in the image forming apparatus 100, the assumed maximum value of the variable component is set in advance by simulation or the like.

Here, when only the fluctuation component of the assumed maximum value is input to the conversion circuits T2, T3, and T4, the negative polarity DC voltage output from the conversion circuits T2, T3, and T4 is defined as Vmax2, Vmax3, and Vmax4. .. At this time, the resistance value of the resistor R1 and the breakdown voltage of the Zener diode D2 are set so that the magnitude of the reverse bias voltage V _REV is equal to or greater than the absolute value of Vmax2, Vmax3, and Vmax4.

(4. Operation of the power supply device 50 according to the first embodiment)
A specific operation of the power supply device 50 will be described with reference to FIG. FIG. 12 is a diagram showing an example of the primary transfer voltage output to the primary transfer rollers 31 for yellow, magenta, and cyan when the monochrome printing mode is set.

Here, change the transfer characteristic of the secondary winding W2B from ideal conditions, the output voltage f _{2 'from} the secondary winding W2B, include fluctuation component due to interference between the AC voltage f ₁ for black Shall be. In this case, also the DC voltage V ₂ output from the conversion circuit T2 which receives the output voltage f _{2 ',} include varying voltage of negative polarity corresponding to the fluctuation component. FIG. 12 shows a case where the fluctuating voltage generated by the interference with the AC voltage f ₁ is −20 V.

When the monochrome print mode is set, the yellow, magenta, and cyan toners are not printed, so 0 V is set as the target voltage value in the frequency control units DC2 to DC4. Therefore, the frequency control unit DC2~DC4 in the initial stage that has not yet received a feedback from the converter circuit T2 to T4, respectively alternating voltage _f 2 ~f ₄ is adjusted to be at 0V.

FIG. 12 (a) shows the case where the reverse bias voltage V _REV is 0 V (that is, the case where it is substantially the same as the power supply device 150A shown in FIG. 8), and FIG. 12 (b) shows the reverse bias voltage. The case where V _REV is + 100V is shown.

When the reverse bias voltage V _REV is 0V, the DC voltage V ₂ (= variable voltage -20V) is directly fed back from the conversion circuit T2 to the frequency control unit DC2. However, since the frequency control unit DC 2 sets the AC voltage f ₂ to the minimum value of 0, the magnitude of the DC voltage V ₂ cannot be further adjusted to return to the target voltage value (0 V). Therefore, as shown in FIG. 12A, the fluctuating voltage −20V is output to the primary transfer roller 31 as it is. As a result, yellow toner that should not be printed is printed.

On the other hand, when the reverse bias voltage V _REV is + 100V, the adder A2 superimposes the reverse bias voltage V _REV (= + 100V) on the DC voltage V ₂ (= -20V) output from the conversion circuit T2. (= + 80V) is fed back to the frequency control unit DC2.

Frequency controller DC2 which receives the superimposed voltage (= + 80V), the size of the superimposed voltage so that the target voltage value (0V), to adjust the AC voltage _{f 2.} Specifically, frequency control unit DC2 further outputs the AC voltage f ₂ as a DC voltage of -80V is outputted from the conversion circuit T2.

Thus, the output voltage f _{2 'from} the secondary winding W2B includes the same AC component and the AC voltage f _2, and the fluctuation component due to interference between the AC voltage f ₁ for black.

As shown in FIG. 12 (b), the conversion circuit T2 generates a DC voltage of −80 V (referred to as an adjusted voltage in the figure) based on the same AC component as the AC voltage f _2, and the AC voltage f ₁ A fluctuation voltage of -20V is generated based on the fluctuation component due to the interference with, and a total DC voltage V ₂ of -100V is output. The adder A2 outputs a superposed voltage Va ₂ (= 0 V) obtained by superimposing the reverse bias voltage V _REV (= + 100 V) on the DC voltage V ₂ (= −100 V) to the primary transfer roller 31. That is, it is possible to prevent the same voltage as the target voltage value (0V) from being output to the primary transfer roller 31 and unintentionally printing the yellow toner.

Similarly, in the monochrome printing mode, it is possible to prevent unintentional printing of magenta and cyan toners.

<Embodiment 2>
The power supply device according to the second embodiment is a power supply device 150 shown in FIG. 3 to which the reverse bias generation circuit 58 and adders A2 to A4 shown in FIGS. 10 and 11 are applied.

In the power supply device 150 shown in FIG. 3, one secondary from the AC component of the superimposed voltage f 'output from winding W2 transformer 54 comprising a bandpass filter F1~F4 each alternating voltage f ₁ ~f Pass the AC component of the same frequency as ₄ .

The pass band in the bandpass filters F1 to F4 may fluctuate due to individual differences of the bandpass filters F1 to F4, the environment, aging deterioration, and the like. Variation in the pass band of the band-pass filter F2 to F4 is generated, in the pass band of the band-pass filter F2 to F4, when included the frequency of the alternating voltage f ₁ for black, the output from the band-pass filter F2 to F4 the output voltage includes a portion of the output voltage f _{2 'for} black. As a result, similar to the power supply device 150A shown in FIG. 8, in the case of the monochrome printing mode, there arises a problem that magenta and cyan toners are printed even though they should not be printed originally.

The power supply device 50A according to the second embodiment can solve the above problem. The circuit configuration of the power supply device 50A will be described with reference to FIG. FIG. 13 is a diagram showing an example of the circuit configuration of the power supply device 50A.

Although not shown in FIG. 13, the frequency control units DC1 to DC4 have on / off, target voltage value, and control mode (either voltage control mode or current control mode) controlled by the main body as in FIG. It is set by the device 70. Hereinafter, it is assumed that the voltage control mode is set in the frequency control units DC1 to DC4.

As shown in FIG. 13, the power supply device 50A is different from the power supply device 150 shown in FIG. 3 in that the reverse bias generation circuit 58 and the adders A2 to A4 are provided. Other points are the same as those of the power supply device 150 shown in FIG. 8, and the description thereof will not be repeated below.

Reverse bias generating circuit 58 generates an output voltage _{f 2} 'receiving a reverse bias voltage _{V REV} output from band-pass filter F1, and outputs the generated reverse bias voltage _{V REV} to the adder A2 to A4. Since the specific circuit configuration of the reverse bias generation circuit 58 has been described in the first embodiment with reference to FIG. 11, detailed description will not be repeated here.

The adder A2, like the first embodiment, generates the superposed voltage Va ₂ obtained by superimposing a DC voltage V ₂ and the reverse bias voltage V _REV outputted from the conversion circuit T2, yellow and the resulting superimposed voltage Va ₂ It is output to the primary transfer roller 31 and the frequency control unit DC2.

The adder A3, like the first embodiment, the yellow and the DC voltage V ₃ reverse bias voltage to generate a superimposed voltage Va ₃ obtained by superimposing and V _REV, the generated superimposed voltage Va ₃ output from the conversion circuit T3 The voltage is output to the primary transfer roller 31 and the frequency control unit DC3.

Adder A4 is, as in the first embodiment, the yellow and the DC voltage V ₄ reverse bias voltage to generate a superimposed voltage Va ₄ obtained by superimposing and V _REV, the generated superimposed voltage Va ₄ output from the conversion circuit T4 The voltage is output to the primary transfer roller 31 and the frequency control unit DC4.

According to the second embodiment, even including the frequency of the alternating voltage f ₁ for black in the passband of the band-pass filter F2 to F4, the superposed voltage that is output from the adder A2 to A4, The target voltage value set in the frequency control units DC2 to DC4 can be set. As a result, it is possible to prevent unintentional printing of yellow, magenta, and cyan toners in the monochrome printing mode.

<Embodiment 3>
In the first embodiment described above, the power supply device 50 includes a reverse bias generation circuit 58 that generates a reverse bias voltage V _REV having a constant value. On the other hand, in the power supply device according to the third embodiment, a variable reverse bias voltage is generated according to the DC voltage output from the conversion circuits T2 to T4.

The circuit configuration of the power supply device 50B according to the third embodiment will be described with reference to FIG. FIG. 14 is a diagram showing an example of the circuit configuration of the power supply device 50B.

As shown in FIG. 14, the power supply device 50B differs from the power supply device 50 shown in FIG. 10 in that it includes a reverse bias generation unit 59 instead of the reverse bias generation circuit 58. Since the other points are the same as those of the power supply device 50 shown in FIG. 10, the description thereof will not be repeated below.

Reverse bias generating unit 59 includes an output voltage _{f 2} 'of the secondary winding W2A, based on the DC voltage _V 2 ~V ₄ output from the conversion circuit T2 to T4, the reverse bias voltage _{V REV2} for yellow, the reverse bias voltage _{V REV3} magenta, and generates a reverse bias voltage _{V REV4} for cyan. The reverse bias generation unit 59 outputs the reverse bias voltage V _REV2 to the adder A2, outputs the reverse bias voltage V _REV3 to the adder A3, and outputs the reverse bias voltage V _REV4 to the adder A4. The reverse bias voltages V _REV2 , V _REV3 , and V _REV4 are voltages for canceling the DC voltage (fluctuation voltage) output from the conversion circuits T2 to _T4 in the monochrome printing mode.

FIG. 15 is a block diagram showing an internal configuration of the reverse bias generation unit 59. As shown in FIG. 15, the reverse bias generation unit 59 includes generation circuits 59B to 59D.

Generating circuit 59B includes an output voltage _{f 2} 'of the secondary winding W2A, receives a DC voltage _{V 2} output from the conversion circuit T2, and generates a reverse bias voltage _{V REV2} for yellow, the reverse bias voltage V _REV2 is output to the adder A2.

Generating circuit 59C includes an output voltage _{f 3} 'of the secondary winding W2A, receives a DC voltage _{V 3} outputted from the conversion circuit T3, generates a reverse bias voltage _{V REV3} for magenta, the reverse bias voltage V _{The REV3} is output to the adder A3.

Generating circuit 59D receives the output voltage _{f 2} 'of the secondary winding W2A, a DC voltage _{V 4} outputted from the conversion circuit T4, and generates a reverse bias voltage _{V REV4} for cyan, the reverse bias voltage V _{The REV4} is output to the adder A4.

FIG. 16 is a diagram showing a circuit configuration of the generation circuit 59B. As shown in FIG. 16, the generation circuit 59B includes a diode D3, a capacitor C2, a switch S1, a switching element Q1, a switching unit 591, a variable voltage detecting unit 592, and a voltage changing unit 593.

Diode D3 receives the output voltage f _{1 'including} the AC voltage f ₁ same AC component and the anode and a cathode connected to one end of the capacitor C2. The other end of the capacitor C2 is grounded. Diode D3 and capacitor C2, the output voltage f _{1 'of} the AC half-wave rectification, the connection node between the cathode and the capacitor C1 of the diode D1, and outputs a DC voltage of positive polarity.

The switching element Q1 is an NPN transistor, the collector is connected to the connection node between the cathode of the diode D1 and the capacitor C1, and the emitter is grounded.

One end of the switch S1 is connected to the connection node between the cathode of the diode D1 and the capacitor C1, and the other end is connected to the adder A2. Therefore, when the switch S1 is in the open state, the reverse bias voltage V _{REV2 of} 0 V is output to the adder A2. On the other hand, when the switch S1 is in the closed state, a positive polarity reverse bias voltage V _REV2 corresponding to the switching frequency and the on / off duty ratio in the switching element Q1 is output to the adder A2.

When the fluctuating voltage detection unit 592 receives a detection instruction from the switching unit 591, the fluctuating voltage detection unit 592 detects the magnitude of the DC voltage V ₂ output from the conversion circuit T2 and outputs the detection result to the voltage change unit 593.

The voltage changing unit 593 controls at least one of the switching frequency and the on / off duty ratio in the switching element Q1 according to the detection result received from the variable voltage detecting unit 592. Specifically, the voltage changing unit 593 controls the switching element Q1 so as to satisfy the following conditions (a) and (b).

(A) The voltage of the collector of the switching element Q1 is equal to or higher than the absolute value of the voltage value indicated by the detection result from the fluctuating voltage detection unit 592.

(B) The larger the absolute value of the voltage value indicated by the detection result from the fluctuating voltage detection unit 592, the larger the voltage of the collector of the switching element Q1.

The switching unit 591 receives a selection mode identification signal indicating a selected mode from the monochrome print mode and the color print mode from the main body control device 70. Upon receiving the selection mode identification signal indicating that the color printing mode has been selected, the switching unit 591 opens the switch S1 and stops the operation of the voltage changing unit 593.

As a result, the generation circuit 59B outputs the reverse bias voltage V _REV2 of 0V to the adder A2 when the color printing mode is selected. At this time, the power supply device 50B is substantially in the same state as the power supply device 150A shown in FIG.

On the other hand, when the mode indicated by the selection mode identification information changes from the color print mode to the monochrome print mode, the switching unit 591 outputs a detection instruction to the variable voltage detection unit 592. Further, after outputting the detection instruction, the switching unit 591 closes the switch S1 and operates the voltage changing unit 593.

The monochrome printing mode, the frequency control unit DC2, since the target voltage value is set to 0V, and the initial value of the AC voltage f ₂ to 0V. Therefore, the fluctuating voltage detection unit 592, which receives the detection instruction at the timing of switching to the monochrome printing mode, detects the magnitude of the fluctuating voltage generated by the interference with the black output voltage f ₁ '. Here, the voltage change is the fluctuation component due to interference between the _'output voltage f ₁ for black in _the' output voltage f ₂ from the secondary winding W2B, a negative polarity of the voltage generated in the converter circuit T3.

The voltage changing unit 593, which receives the detection result indicating the magnitude of the fluctuating voltage from the fluctuating voltage detecting unit 592, is equal to or more than the absolute value of the fluctuating voltage, and the reverse bias voltage V _REV2 corresponding to the absolute value is output to the adder A2. The switching element Q1 is controlled so as to be performed. That is, the voltage changing unit 593 functions as an adjusting unit for adjusting the reverse bias voltage V _REV2 .

As a result, when the monochrome print mode is selected, the generation circuit 59B can output the reverse bias voltage V _REV2 larger than the absolute value of the fluctuating voltage and corresponding to the absolute value to the adder A2.

The generation circuits 59C and 59D also have the same circuit configuration as the generation circuit 59B shown in FIG. Therefore, the generation circuit 59C outputs a reverse bias voltage V _REV3 of 0 V to the adder A3 when the color print mode is selected, and reverse bias according to the magnitude of the fluctuation voltage when the monochrome print mode is selected. The voltage V _REV3 is output to the adder A3. Here varying voltage of, by fluctuation component in the output voltage f _{3 'from} the secondary winding W2C, a negative polarity of the voltage generated in the converter circuit T3.

Similarly, the generation circuit 59D outputs a reverse bias voltage V _REV4 of 0 V to the adder A4 when the color print mode is selected, and reverses the fluctuation voltage according to the magnitude when the monochrome print mode is selected. The bias voltage V _REV4 is output to the adder A4. Here varying voltage of, by fluctuation component in the output voltage f _{4 'from} the secondary winding W2D, a negative polarity of the voltage generated in the converter circuit T4.

According to the third embodiment, in the monochrome printing mode, a positive polarity reverse bias voltage V _REV2 equal to or _larger than the absolute value of the negative polarity fluctuation voltage is output to the adder A2. As a result, as in the first embodiment, even if the component due to interference between the AC voltage f ₁ for black is included in the output voltage f _{2 'from} the secondary winding W2B, output from the adder A2 The superimposed voltage can be set to a target voltage value (0V in the monochrome printing mode) set in the frequency control unit DC2. As a result, it is possible to prevent the yellow toner from being unintentionally printed in the monochrome printing mode.

Similarly, a positive polarity reverse bias voltage V _REV3 equal to or greater than the absolute value of the negative polarity fluctuation voltage is output to the adder A3, and a positive polarity reverse bias voltage V _REV4 equal to or greater than the absolute value of the negative polarity fluctuation voltage is added to the adder. It is output to A4. Therefore, it is possible to prevent unintentional printing of magenta and cyan toner in the monochrome printing mode.

Further, when the voltage changing unit 593 controls the switching element Q1 so that the difference between the absolute value of the reverse bias voltage and the absolute value of the fluctuating voltage detected by the fluctuating voltage detecting unit 592 is within a predetermined range. The difference between the magnitudes of the superimposed voltages Va ₂ , Va ₃ , and Va ₄ output from the adders A2, A3, and A4 and the target voltage value (0V) is also within the above predetermined range. As a result, the time required for feedback control in each frequency control unit DC2, DC3, DC4 can be shortened.

<Embodiment 4>
The power supply device according to the fourth embodiment is a power supply device 150 shown in FIG. 3 to which the reverse bias generation unit 59 and adders A2 to A4 shown in FIGS. 14 to 16 are applied.

The circuit configuration of the power supply device 50C according to the fourth embodiment will be described with reference to FIG. FIG. 17 is a diagram showing an example of the circuit configuration of the power supply device 50C.

As shown in FIG. 17, the power supply device 50C differs from the power supply device 50A shown in FIG. 13 in that it includes a reverse bias generation unit 59 instead of the reverse bias generation circuit 58. Since the other points are the same as those of the power supply device 50A shown in FIG. 13, the description thereof will not be repeated below.

Reverse bias generating unit 59 includes an output voltage _{f 2} 'output from the band-pass filter F1, based on a DC voltage _V 2 ~V ₄ output from the conversion circuit T2 to T4, the reverse bias voltage V for yellow _REV2, the reverse bias voltage _{V REV3} magenta, and generates a reverse bias voltage _{V REV4} for cyan. The reverse bias generation unit 59 outputs the reverse bias voltage V _REV2 to the adder A2, outputs the reverse bias voltage V _REV3 to the adder A3, and outputs the reverse bias voltage V _REV4 to the adder A4. In response to this, the reverse bias voltage V _REV2 is generated, and the generated reverse bias voltage V _REV2 is output to the adder A2.

Since the specific circuit configuration of the reverse bias generation unit 59 has been described in the third embodiment with reference to FIGS. 15 and 16, the detailed description will not be repeated here.

Similar to the third embodiment, the adder A2 generates a superimposed voltage Va _{2 in} which the DC voltage V ₂ output from the conversion circuit T2 and the reverse bias voltage V _{REV 2} are superimposed, and the generated superimposed voltage Va ₂ is yellow. It is output to the primary transfer roller 31 and the frequency control unit DC2.

Similar to the third embodiment, the adder A3 generates a superimposed voltage Va _{3 in} which the DC voltage V ₃ output from the conversion circuit T ₃ and the reverse bias voltage V _{REV 3} are superimposed, and the generated superimposed voltage Va ₃ is yellow. The voltage is output to the primary transfer roller 31 and the frequency control unit DC3.

Similar to the third embodiment, the adder A4 generates a superposed voltage Va _{4 in} which the DC voltage V ₄ output from the conversion circuit T ₄ and the reverse bias voltage V _{REV 4} are superposed, and the generated superposed voltage Va ₄ is yellow. The voltage is output to the primary transfer roller 31 and the frequency control unit DC4.

According to the fourth embodiment, in the monochrome printing mode, even including the frequency of the alternating voltage f ₁ for black in the passband of the band-pass filter F2 to F4, is output from the adder A2~A4 The superimposed voltages Va ₂ , Va ₃ , and Va ₄ can be set to the target voltage values set in the frequency control units DC2 to DC4. As a result, it is possible to prevent unintentional printing of yellow, magenta, and cyan toners in the monochrome printing mode.

Further, when the voltage changing unit 593 controls the switching element Q1 so that the difference between the absolute value of the reverse bias voltage and the absolute value of the fluctuating voltage detected by the fluctuating voltage detecting unit 592 is within a predetermined range. The difference between the magnitudes of the superimposed voltages Va ₂ , Va ₃ , and Va ₄ output from the adders A2, A3, and A4 and the target voltage value (0V) is also within the above predetermined range. As a result, the time required for feedback control in each frequency control unit DC2, DC3, DC4 can be shortened.

<Modification example>
In the respective embodiments described above, yellow, magenta, DC voltage V _2, V _3, a reverse bias voltage to V ₄ output from all converter T2~T4 cyan is superimposed. However, the reverse bias voltage may be superimposed only on the DC voltage output from a part of the conversion circuits T2 to T4.

Color is likely to vary component included in the output voltage caused by interference between the AC voltage f ₁ for black is the color of the AC voltage of the frequency closest to the frequency of the alternating voltage f ₁ for black is outputted. For example, when the AC voltage f ₁ for black is 100 kHz, the AC voltage f ₂ for yellow is 200 kHz, the AC voltage f ₃ for magenta is 300 kHz, and the AC voltage f ₄ for cyan is 400 kHz. , The frequency of the AC voltage f ₂ for yellow is the closest to the frequency of the AC voltage f ₁ for black. Therefore, the reverse bias voltage is superimposed only on the DC voltage V ₂ output from the conversion circuit T2 for yellow, and the reverse bias voltage is superimposed on the DC voltages V ₃ and V ₄ output from the conversion circuits T3 and T4 for magenta and cyan. Do not superimpose the bias voltage. As a result, the configuration of the power supply device can be simplified.

In the above description, it is assumed that the conversion circuits T2 to T4 output a negative polarity DC voltage, and the reverse bias generation circuit 58 and the reverse bias generation unit 59 generate a positive polarity reverse bias voltage. However, the polarity is not limited to this, and the conversion circuits T2 to T4 may output a positive polarity DC voltage, and the reverse bias generation circuit 58 and the reverse bias generation unit 59 may generate a negative polarity reverse bias voltage.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

10 Photoreceptor, 11 Charging device, 12 Exposure device, 13 Developing device, 14 Developing roller, 15C, 15K, 15M, 15Y Toner bottle, 17 Cleaning device, 30 Intermediate transfer belt, 31 Primary transfer roller, 33 Secondary transfer roller, 37 cassette, 38 driven roller, 39 drive roller, 40 timing roller, 41 transport path, 43 fixing device, 48 tray, 50, 50A to 50C power supply device, 51 control unit, 54, 54A transformer, 56, 56A to 56D detection Unit, 58 reverse bias generation circuit, 59 reverse bias generation unit, 59B to 59D generation circuit, 61A, 61B core, 70 main unit control device, 100 image forming device, 102 ROM, 103 RAM, 104 network interface, 107 operation panel, 120 Storage device, 122 control program, 591 switching unit, 592 fluctuating voltage detection unit, 593 voltage change unit (adjustment unit), A0, A2 to A4 adder, B1, B2 bobbin, DC1 to DC4 frequency control unit, F1 to F4 F11 to F14 band pass filter, Q1 switching element, T1 to T4 conversion circuit, W, W1 primary winding, W2, W2A to W2D secondary winding.

Claims (10)

A power supply device mounted on an image forming apparatus having a first mode in which an image is formed using a first color and a second mode in which an image is formed using at least the first color and the second color.
A control unit for generating a first superimposed voltage in which an AC voltage of a first frequency corresponding to the first color and an AC voltage of a second frequency corresponding to the second color are superimposed.
The primary winding to which the first superimposed voltage is applied and
A voltage for outputting the first output voltage of the first frequency and the second output voltage of the second frequency generated in the secondary winding, including the secondary winding interconnected with the primary winding. Output section and
A first conversion unit for converting the second output voltage into a first DC voltage,
A reverse bias voltage generator that generates a first reverse bias voltage for canceling the first DC voltage when the first mode is executed, and a reverse bias voltage generator.
A power supply device including a first adder for outputting a second superimposed voltage obtained by superimposing the first reverse bias voltage and the first DC voltage. The first reverse bias voltage has the opposite polarity to the first DC voltage.
The absolute value of the first reverse bias voltage is an absolute value or more of the first DC voltage when performing the first mode, the power supply device according to claim 1. The absolute value of the first reverse bias voltage is larger than the absolute value of the first DC voltage when the first mode is executed.
The power supply device according to claim 2, wherein the control unit adjusts the AC voltage of the second frequency so that the second superimposed voltage becomes a target voltage. The reverse bias voltage generator
A voltage detection unit for detecting the magnitude of the first DC voltage and
The power supply device according to any one of claims 1 to 3, further comprising an adjusting unit that adjusts the magnitude of the first reverse bias voltage according to a detection result by the voltage detecting unit. The power supply device according to any one of claims 1 to 4, wherein the reverse bias voltage generation unit generates the first reverse bias voltage from the first output voltage. In the second mode, the image forming apparatus forms an image using a third color in addition to the first color and the second color.
The control unit further superimposes the AC voltage of the third frequency corresponding to the third color on the first superposed voltage.
The voltage output unit outputs the third output voltage of the third frequency generated in the secondary winding, and outputs the third output voltage.
The power supply device further includes a second conversion unit for converting the third output voltage into a second DC voltage and outputting the voltage.
The reverse bias voltage generation unit generates a second reverse bias voltage for canceling the second DC voltage when the first mode is executed.
The power supply device according to claim 1, further comprising a second adder that outputs a third superposed voltage obtained by superimposing the second reverse bias voltage and the second DC voltage. In the second mode, the image forming apparatus forms an image using a third color in addition to the first color and the second color.
The control unit further superimposes the AC voltage of the third frequency corresponding to the third color on the first superposed voltage.
The voltage output unit outputs the third output voltage of the third frequency generated in the secondary winding, and outputs the third output voltage.
The power supply device further includes a second conversion unit for converting the third output voltage into a second DC voltage and outputting the voltage.
The difference between the third frequency and the first frequency is larger than the difference between the second frequency and the first frequency.
The power supply device according to claim 1, wherein the reverse bias voltage for canceling the second DC voltage when the first mode is executed is not superimposed on the second DC voltage. The voltage output unit
Among the AC components of the voltage generated in the secondary winding, the first filter for passing the AC component of the first frequency and outputting the AC component as the first output voltage,
Claim 1 includes, among the AC components of the voltage generated in the secondary winding, a second filter for passing the AC component of the second frequency and outputting the AC component as the second output voltage. The power supply device according to any one of 5 to 5. The voltage output unit serves as the secondary winding.
With the first secondary winding for mutual induction coupling with the primary winding to generate the first output voltage,
The power supply device according to any one of claims 1 to 5, further comprising a secondary winding for mutual induction coupling with the primary winding to generate the second output voltage. An image forming apparatus including the power supply device according to any one of claims 1 to 9.

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