JP2009128529A - Power supply device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent increase in driving current flowing to a primary side of a transformer for increasing AC voltage and prevent degradation of component reliability caused by a temperature rise due to a loss at a drive element even when a load fluctuates, when maintaining a constant level of superimposed voltage to be supplied to the load as an image forming voltage. <P>SOLUTION: A power supply device includes: a step-up transformer 111 for generating an AC voltage, a DC voltage generation circuit 121 for superimposing a DC voltage on the secondary side of the step-up transformer 111, a DC voltage control circuit 122 for controlling the level of the DC voltage generated by the DC voltage generation circuit 121, an auxiliary power circuit 102 for complementing the DC voltage generated by the DC voltage generation circuit 121, and a control part 101 for changing the DC voltage level complementarily output by the auxiliary power circuit 102 according to the DC voltage level generated by the DC voltage generation circuit 121 under the DC voltage control circuit 122 to maintain the DC voltage superimposed on the AC voltage on the secondary side of the step-up transformer 111 at a required voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply device and an image forming apparatus, for example, to a technique for generating and outputting a voltage to be applied to a developing device or a charging device of the image forming apparatus.

Conventionally, in an electrophotographic image forming apparatus such as a copying machine or a printer, as a power supply device for applying a driving voltage to a developing device or a charging device, a DC voltage obtained by rectifying an AC voltage and an AC generated by boosting are used. A power supply device that supplies a voltage superimposed with a voltage is used. As such a power supply device, for example, as shown in Patent Document 1, in order to supply the superimposed voltage to a plurality of loads such as a developing device, a direct current voltage (AC voltage) supplied from a single power source is used. DC voltage obtained by rectification) is converted into a plurality of DC voltages, superimposed on the AC voltage in each control circuit provided for each of the plurality of loads, and the superimposed voltage is applied to each load. A power supply device has been proposed.
Japanese Patent No. 3309579

  However, in the power supply device disclosed in Patent Document 1, when performing control to maintain the superimposed voltage level supplied to the load as an image forming voltage at a required level, the load of the transformer increases the AC voltage when the load becomes heavy. Since the drive current flowing on the primary side increases, the loss of the drive element is dissipated as heat, and this heat may increase the ambient temperature and significantly reduce the reliability of the components. Further, as a problem when supplying DC voltages to a plurality of loads, it is necessary to increase the capacity of a transformer used for the DC power supply in order to enable supply of DC voltage for each load from a single DC power supply. There is a problem.

  The present invention has been made to solve the above-described problem, and when performing control for maintaining the voltage level after superimposition supplied to the load as an image forming voltage at a required level, even if the load fluctuates, It is an object of the present invention to not increase the drive current flowing on the primary side of the transformer that boosts the AC voltage, and to prevent the reliability of the component from being lowered due to the temperature rise caused by the loss of the drive element.

The invention according to claim 1 of the present invention is provided corresponding to a load, and a step-up transformer that boosts an AC input signal to generate an AC voltage;
A DC voltage generating circuit provided for the step-up transformer, rectifying the AC voltage to generate a DC voltage, and superimposing the DC voltage on an AC voltage generated on the secondary side of the step-up transformer;
A direct-current voltage control circuit that is provided for the direct-current voltage generation circuit and controls the level of the direct-current voltage generated by the direct-current voltage generation circuit;
An auxiliary power supply circuit comprising a power supply that outputs a DC voltage, and supplementing the DC voltage generated by the DC voltage generation circuit under the control of the DC voltage control circuit;
The DC voltage level output to the auxiliary power supply circuit for the compensation is changed according to the DC voltage level generated by the DC voltage control circuit in the DC voltage generation circuit, and the secondary side AC voltage of the step-up transformer is changed. It is a power supply device provided with the control part which performs control which maintains the direct current voltage superimposed on a required voltage.

  In the present invention, an auxiliary power supply circuit that compensates the DC voltage generated by the DC voltage generation circuit is provided, and when the control unit causes the auxiliary power supply circuit to perform the compensation, the DC voltage control circuit generates the DC voltage generation circuit. The DC voltage superimposed on the secondary side AC voltage of the step-up transformer is maintained at the required voltage by changing the DC voltage level output to the auxiliary power circuit according to the DC voltage level to be generated. As a result, the present invention allows the superimposed voltage supplied to the load to be at a required level without increasing the drive current flowing to the primary side of the step-up transformer even when the load becomes heavy (the load resistance becomes small). Therefore, the load on the transformer can be reduced, and the loss of the driving element does not occur. Therefore, the loss does not dissipate as heat, and the reliability of the component does not decrease due to an increase in the ambient temperature.

The invention according to claim 2 is provided for each of a plurality of loads, and a plurality of step-up transformers that generate an AC voltage by boosting an AC input signal;
A plurality of DC voltage generation circuits provided for each of the step-up transformers, generating a DC voltage by rectifying the AC voltage, and superimposing the DC voltage on an AC voltage generated on the secondary side of the step-up transformer;
A plurality of DC voltage control circuits which are provided for each of the DC voltage generation circuits and control the level of the DC voltage generated by the corresponding DC voltage generation circuit;
An auxiliary power supply circuit comprising a single power supply that outputs a DC voltage, and supplementing the DC voltage generated by the DC voltage generation circuit under the control of the DC voltage control circuit;
The DC voltage level output to the auxiliary power supply circuit for the compensation is changed according to the DC voltage level generated by the corresponding DC voltage generation circuit by the corresponding DC voltage generation circuit, and the secondary voltage of the step-up transformer is changed. It is a power supply device provided with the control part which performs control which maintains the direct current voltage superimposed on the alternating voltage of the side at a required voltage.

  In the present invention, an auxiliary power supply circuit that compensates the DC voltage generated by the DC voltage generation circuit is provided, and when the control unit causes the auxiliary power supply circuit to perform the compensation, the DC voltage control circuit generates the DC voltage generation circuit. The DC voltage superimposed on the secondary side AC voltage of the step-up transformer is maintained at the required voltage by changing the DC voltage level output to the auxiliary power circuit according to the DC voltage level to be generated. As a result, the present invention provides the necessary level of the superimposed voltage supplied to the load without increasing the drive current flowing to the primary side of the step-up transformer even if the load becomes heavy (the load resistance becomes small). Therefore, the load on the transformer can be reduced, and the loss of the drive element does not occur, so that the loss does not radiate as heat, and the reliability of the components does not decrease due to the increase in the ambient temperature.

  The invention according to claim 3 is the power supply device according to claim 1 or 2, wherein the control unit performs control to reduce a peak value of the AC voltage in accordance with a change in the load. When performing, the DC voltage level to be output to the auxiliary power supply circuit for the compensation is increased by the decrease in the DC voltage level generated by the DC voltage generation circuit according to the decrease in the peak value.

  According to the present invention, when the control unit performs control to reduce the peak value of the AC voltage in accordance with the change of the load, the control unit is equivalent to the DC voltage level generated by the DC voltage generation circuit that decreases due to the decrease in the peak value. Since the DC voltage level to be output to the auxiliary power supply circuit is increased to compensate for the DC voltage generated by the DC voltage generation circuit, the superposition supplied to the load without increasing the drive current flowing on the primary side of the step-up transformer The voltage can be kept at the required level.

  Further, the invention according to claim 4 is the power supply device according to any one of claims 1 to 3, wherein the control unit is configured such that the level of the DC voltage generated by the DC voltage generation circuit is the DC voltage. When the voltage is set low by the voltage control circuit, the DC voltage level output to the auxiliary power supply circuit for the compensation is lowered by an amount corresponding to the level drop of the DC voltage.

  According to the present invention, the control unit is configured such that the DC voltage level generated by the auxiliary power supply circuit is low when the level of the DC voltage generated by the DC voltage generating circuit is set low by the DC voltage control circuit. If this is sufficient, the level of the DC voltage output to the auxiliary power supply circuit is lowered by the level drop of the DC voltage, so that it is possible to prevent loss due to excessive compensation from the auxiliary power supply circuit.

The invention according to claim 5 includes the power supply device according to any one of claims 1 to 4,
The image forming apparatus uses the power supply device as a power supply for generating a developing bias for the developing device or a charging bias for the charging device.

  According to the present invention, it is possible to obtain the same operation as that of any one of the first to fourth aspects.

  According to the power supply device according to the present invention, when control is performed to maintain the DC voltage superimposed on the AC voltage on the secondary side of the step-up transformer at the required voltage, even if the load fluctuates, The drive current flowing on the primary side is not increased, and the reliability of the component can be prevented from being lowered due to the temperature rise due to the loss of the drive element.

  Hereinafter, a power supply device and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of a printer to which a power supply device according to an embodiment of the present invention is applied. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. The image forming apparatus according to the present invention may be an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having both of them. In this embodiment, a color printer is taken as an example. I will explain.

  In FIG. 1, a color printer 1 (hereinafter simply referred to as printer 1) includes a paper feed cassette 13, an image forming unit 20, a fixing unit 30, a paper discharge unit 40, a paper transport path 50, and a control unit 101. The paper cassette 13, the image forming unit 20, the fixing unit 30, the paper conveyance path 50, and the control unit 101 are housed in the substantially box-shaped apparatus main body 2, and the paper discharge unit 40 is provided at the top of the apparatus main body 2. Is provided.

  The paper feed cassette 13 stores recording paper P as an example of a transfer material used for printing processing, and feeds the recording paper P under the control of the control unit 101. A predetermined number (one in the present embodiment) of the sheet feeding cassettes 13 is provided so as to be detachable from the apparatus main body 2. A pickup roller 15 is provided at the upstream end of the paper feed cassette 13 (upper left of the paper feed cassette 13 in the example shown in FIG. 1) to feed the recording paper P from the paper bundle one by one. The recording paper P fed out of the paper feed cassette 13 by driving the pickup roller 15 is fed into the paper transport path 50.

  Under the control of the control unit 101, the image forming unit 20 transfers the image to the recording paper P fed out from the sheet bundle stored in the paper feed cassette 13 based on image data received from a computer or the like by an interface circuit (not shown). Processing is performed. The interface circuit is connected to an external device such as a computer via a LAN (Local Area Network) or the like, and transmits / receives various signals to / from the external device. For example, a network interface (10 / 100Base-TX) Etc. are used. The image forming unit 20 includes color units 21Y, 21M, 21C, and 21K that form toner images, and a transfer device 27 that transfers the toner images formed by the image forming unit 21 onto the recording paper P. Yes.

  The image forming unit 21 includes a magenta unit 21M, a cyan unit 21C, a yellow unit 21Y, and a black unit that are sequentially arranged in a substantially horizontal direction from the upstream side (the right side of the paper surface in FIG. 1) to the downstream side. 21K and an exposure unit 24 disposed at the lower position of each unit. Each of these units 21M, 21C, 21Y, and 21K has the same configuration, and is positioned and attached to each device in the apparatus main body 2 with a predetermined relative positional relationship.

  Each of these units 21M, 21C, 21Y, and 21K includes a photosensitive drum (image carrier) 22, a charging device 23, a developing device 25, and a cleaning device 26. The photosensitive drum 22 is arranged in the front-rear direction. 1 is provided so as to be rotatable around a drum shaft extending in a direction (perpendicular to the paper surface of FIG. 1), and from the position directly below the photoconductive drum 22 along the peripheral surface of the photoconductive drum 22, A charging device 23, a developing device 25, and a cleaning device 26 are arranged in a counterclockwise direction that is a rotation direction.

  The photosensitive drum 22 is for forming an electrostatic latent image and a toner image (visible image) according to the electrostatic latent image on the peripheral surface. The charging device 23 forms a uniform charge on the peripheral surface of the photosensitive drum 22 rotating counterclockwise around the drum axis. For example, the peripheral surface is in contact with the peripheral surface of the photosensitive drum 22. A charging roller is provided that applies a charge to the photosensitive drum 22 while being driven to rotate while being in contact therewith.

  The developing device 25 supplies toner to the peripheral surface of the photosensitive drum 22 to attach the toner to the portion where the electrostatic latent image is formed on the peripheral surface, and thereby the toner image is formed on the peripheral surface of the photosensitive drum 22. To form. In the present embodiment, in order to cope with color, yellow (Y) toner is stored in the developing device 25Y of the yellow unit 21Y, and magenta (M) toner is stored in the developing device 25M of the magenta unit 21M. The cyan (C) toner is stored in the developing device 25C of the cyan unit 21C, and the black (K) toner is stored in the black developing device 25K of the black unit 21K. . A power supply device 10 according to an embodiment of the present invention is provided in the printer 1 to supply a developing bias voltage to the developing devices 25M, 25C, 25Y, and 25K.

  The cleaning device 26 is for removing the toner remaining on the peripheral surface of the photosensitive drum 22 after the transfer process and cleaning it. The peripheral surface of the photosensitive drum 22 cleaned by the cleaning device 26 is again directed to the charging device 23 for the next image forming process.

  The exposure unit 24 irradiates the rotating surface of the photosensitive drum 22 between the charging device 23 and the developing device 25 with a laser beam to which intensity is applied according to the image data. An electrostatic latent image is formed on the peripheral surface. The exposure unit 24 applies the laser beams corresponding to the colors yellow, magenta, cyan, and black to the photosensitive drums 22M, 22C, 22Y, and 22K in the units 21M, 21C, 21Y, and 21K in order to correspond to the colors. It is configured to irradiate. When the peripheral surface of the charged photoconductive drum 22 is irradiated with laser light, the charged portion of the irradiated portion is erased according to the intensity of the laser light, whereby an electrostatic latent image is formed on the peripheral surface of the photoconductive drum 22. It is formed. The image data includes yellow, magenta, cyan, and development colors generated by the control unit 101 by performing a process such as a known color correction process on an image signal from an external device such as a computer received by an unillustrated interface circuit. Each image data is black.

  The transfer device 27 is a device for transferring the toner image formed on the peripheral surface of the photosensitive drum 22 of each unit 21M, 21C, 21Y, 21K to the recording paper P. A transfer roller 272, a drive roller 273, a driven roller 274, and a secondary transfer roller 275 are provided. The intermediate transfer belt 271 is endlessly rotatable and is stretched to a position immediately above the units 21M, 21C, 21Y, and 21K by a primary transfer roller 272, a driving roller 273, and a driven roller 274, and the driving roller 273 is driven to rotate. It can be rotated clockwise by force. The primary transfer rollers 272 are provided so as to correspond to the photosensitive drums 22M, 22C, 22Y, and 22K of the units 21M, 21C, 21Y, and 21K, respectively, and hold the intermediate transfer belt 271 from the photosensitive drum 22 to the intermediate transfer belt 271. Is arranged to prevent the floating. The secondary transfer roller 275 is disposed at a position facing the drive roller 273 on the outer peripheral surface of the intermediate transfer belt 271.

  While the toner image in the image area is primarily transferred from the photosensitive drum 22 to the intermediate transfer belt 271, the primary transfer roller 272 is applied with a voltage having a polarity opposite to the toner charging polarity as a primary transfer bias. Further, while the toner image on the intermediate transfer belt 271 is secondarily transferred to the recording paper P, the secondary transfer roller 275 is applied with a voltage having a polarity opposite to that of the toner as a secondary transfer bias. As described above, the printer 1 uses the secondary transfer roller 275 to transfer the color toner image composed of the toner images of the respective colors superimposed on the intermediate transfer belt 271 from the intermediate transfer belt 271 to the recording paper P. This is a transfer method.

  An intermediate transfer belt cleaning device 276 is provided on the right side of the driven roller 274 in FIG. 1, and the toner remaining on the surface of the intermediate transfer belt 271 after the toner image is transferred to the recording paper P. The intermediate transfer belt 271 that has been removed by the intermediate transfer belt cleaning device 276 and cleaned thereby is directed toward the photosensitive drum 22.

  The fixing unit 30 performs a fixing process by heating the toner image of the recording paper P that has been subjected to the transfer process by the image forming unit 20 under the control of the control unit 101, and an energization heating element is mounted inside. A heat roller 31 and a pressure roller 32 facing the heat roller 31 and having circumferential surfaces facing each other are provided. Then, the recording paper P after the transfer process includes a heat roller 31 that is driven to rotate clockwise around the roller axis, and a pressure roller that is driven to rotate counterclockwise around the roller axis. By passing through the nip portion between the heat roller 32 and the heat roller 31, heat from the heat roller 31 is obtained and the fixing process is performed. The recording paper P after the fixing process is discharged to the paper discharge unit 40 through the paper conveyance path 50.

  The paper discharge unit 40 discharges the recording paper P on which the fixing process has been performed by the fixing unit 30 and stores the discharged recording paper P. The paper discharge unit 40 is formed by recessing the top of the apparatus main body 2, and a paper discharge tray 41 for receiving the discharged recording paper P is formed at the bottom of the concave recess.

  The paper conveyance path 50 conveys the recording paper P fed from the paper feed cassette 13 to the paper discharge unit 40 via the apparatus main body 2 and the fixing unit 30 under the control of the control unit 101.

  The control unit 101 is connected to the paper feed cassette 13, the apparatus main body 2, the fixing unit 30, the paper conveyance path 50, the power supply device according to the embodiment of the present invention, and controls these operations, thereby controlling the printer 1. For example, a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores various programs executed by the CPU, data necessary for the execution in advance, a so-called working of the CPU It is constituted by a microcomputer having a RAM (Random Access Memory) serving as a memory and its peripheral circuits.

  Next, a power supply device according to an embodiment of the present invention will be described. FIG. 2 is a block diagram showing a schematic configuration of a power supply device according to an embodiment of the present invention. A power supply device 10 according to an embodiment of the present invention is provided in the printer 1 to supply a developing bias voltage to the developing devices 25M, 25C, 25Y, and 25K described above. The power supply device 10 superimposes a DC voltage and an AC voltage, performs control to maintain the level of the superimposed voltage at a required level, and supplies the superimposed voltage as a drive voltage to a load. Moreover, the power supply device 10 performs control for keeping the DC voltage superimposed on the AC voltage on the secondary side of the step-up transformer at a required voltage.

  The power supply device 10 includes power supply devices 10M, 10C, 10Y, and 10K provided in the developing devices 25M, 25C, 25Y, and 25K for each color for color image formation. Furthermore, the power supply device 10 includes a control unit 101 and an auxiliary power supply circuit 102. Since the power supply devices 10M, 10C, 10Y, and 10K have the same configuration, detailed illustration of the power supply devices 10C, 10Y, and 10K is omitted, and the power supply device 10M will be described below as an example.

  The power supply apparatus 10 </ b> M includes an AC voltage generation unit 11 and a DC voltage generation unit 12. The AC voltage generator 11 generates an AC voltage based on the AC input signal input from the controller 101. The AC voltage generator 11 includes a step-up transformer 111, an AC input control circuit 112, and a step-up transformer drive circuit 113.

  The control unit 101 uses the built-in D / A conversion converter to change and control the amplitude of the AC input signal (HVCLK), and outputs the AC input signal (HVCLK) after the control to the AC input control circuit 112. The AC input control circuit 112 causes the step-up transformer drive circuit 113 to amplify the AC input signal (HVCLK) to a level suitable for driving the primary side coil of the step-up transformer 111. The step-up transformer drive circuit 113 drives the primary winding of the step-up transformer 111 using the amplified AC input signal (HVCLK). In the step-up transformer 111, the winding ratio between the primary side and the secondary side is set to a predetermined value, and when the primary side winding is driven by the amplified AC input signal (HVCLK), An AC voltage boosted by a predetermined amount is generated on the secondary side.

  The DC voltage generation unit 12 includes a DC voltage generation circuit 121 and a DC voltage control circuit 122. The DC voltage control circuit 122 controls the value (level) of the DC voltage generated by the DC voltage generation circuit 121 based on a DC voltage control signal VBM (analog output signal) that is an instruction signal from the control unit 101. The DC voltage generation circuit 121 rectifies the AC voltage boosted by the step-up transformer 111 and generates a DC voltage having a value controlled by the DC voltage control circuit 122. The DC voltage generation circuit 121 is connected to the secondary side of the step-up transformer 111 and superimposes the generated DC voltage on the AC voltage after boosting generated on the secondary side of the step-up transformer 111.

  That is, when a DC current flows through the diode D2 connected between the secondary side of the step-up transformer 111 and the ground in the direction indicated by the solid line in FIG. 2, the DC voltage controlled to the above value in the DC voltage control circuit 122 is Applied across capacitor C5. When the DC voltage is applied, the boosted AC voltage generated on the secondary side of the step-up transformer 111 is in a state where the voltage level is shifted by the DC voltage applied across the capacitor C5. At this time, the current goes back and forth between the developing device 25M, which is a load, and the capacitor C5, as indicated by a broken line in FIG. As a result, the boosted AC voltage generated on the secondary side of the step-up transformer 111 and the DC voltage across the capacitor C5 are superimposed, and the superimposed voltage is applied to the developing device 25M. The DC voltage superimposed on the boosted AC voltage generated on the secondary side of the step-up transformer 111 is set to about 100V to 1KV.

  When the control unit 101 performs control to maintain the level of the superposed voltage supplied to the load as an image forming voltage at a required level, the toner charging due to the influence of load fluctuation (for example, environmental fluctuation (temperature, humidity)) Control is performed to change the peak value of the AC voltage according to the amount, that is, the variation in concentration. For example, when the control unit 101 changes the amplitude of the AC input signal (HVCLK) and decreases the peak value of the AC voltage after being boosted by the step-up transformer 111 in response to the increase in concentration, When the direct current flowing through the diode D2 decreases, a sufficient direct voltage cannot be obtained by rectification. For this reason, the control unit 101 ensures a necessary DC voltage by causing a current to flow from the auxiliary power supply circuit 102 to the DC voltage control circuit 122.

  In addition, when the control unit 101 causes the DC voltage control circuit 122 to set the value of the DC voltage generated by the DC voltage generation circuit 121 to be low, the control unit 101 removes from the auxiliary power supply circuit 102 by an amount corresponding to the level drop of the DC voltage. Reduce the output voltage level. That is, when the level of the DC voltage generated by the DC voltage generation circuit 121 is low, the loss due to excessive compensation from the auxiliary power supply circuit 102 by the control of lowering the DC voltage level output to the auxiliary power supply circuit 102 by the control unit 101 is sufficient. Is prevented from occurring.

  The auxiliary power supply circuit 102 is composed of a single power supply that outputs a DC voltage, and a DC voltage at a level instructed by the control unit 101 is used to compensate for the DC voltage generated by the DC voltage generation circuit 121. Output to the control circuit 122. That is, the auxiliary power supply circuit 102 compensates for the DC voltage generated by the DC voltage generation circuit 121 under the control of the DC voltage control circuit 122.

  FIG. 3 is a circuit diagram of the power supply device 10. The power supply device 10 will be further described with reference to FIG.

  In the DC voltage generation circuit 121, the resistor R8 connected in series with the diode D2 is a current limiting resistor for allowing a DC current to flow to such an extent that the AC voltage after being boosted by the step-up transformer 111 is not distorted due to bias. The direct current flows from the resistor R8 and the diode D2 to the step-up transformer 111 and then flows to the resistors R31 and R32. The DC voltage control circuit 122 controls the collector current of the transistor Q5 so that the voltage generated across the resistor R32 becomes equal to the DC voltage control signal VBM from the control unit 101.

  When the amplitude of the AC input signal (HVCLK) is set low by the AC voltage control signal ACCONT from the control unit 101, the DC current flowing from the diode D2 decreases and the voltage generated in the series resistors R31 and R32 is low. Therefore, the comparison voltage generated at both ends of the resistor R32 is also reduced. When the control unit 101 outputs the DC voltage control signal VBM to the DC voltage control circuit 122, the DC voltage control circuit 122 starts from the auxiliary power supply circuit 102 until the comparison voltage reaches the voltage indicated by the DC voltage control signal VBM. A constant DC voltage is maintained by supplying current to resistor R30.

  Conversely, when the DC voltage in the DC voltage control circuit 122 is set low by the DC voltage control signal VBM from the control unit 101, the collector of the transistor Q5 is connected to the current from the auxiliary power circuit 102 via the resistor R30. Flows in. If the DC voltage control signals VBC, VBY, VBK are all set low, the loss of the auxiliary power supply increases due to the current flowing from the auxiliary power supply circuit 102 to the resistors R30, R24, R18, R12. In order to prevent this, the auxiliary DC voltage (maximum auxiliary DC voltage) set by the auxiliary DC power supply voltage control signal DCCONT is set to 100 V higher than the maximum control DC voltage for the maximum control DC voltage of the DC voltage control circuit 122. Set up to a higher voltage. The auxiliary DC voltage set with respect to the value of the control DC voltage controlled by the DC voltage control circuit 122 is set to a value reduced according to the decrease of the value of the control DC voltage, and the minimum control DC voltage of the DC voltage control circuit 122 is set. For the voltage, the minimum auxiliary DC voltage is set to 0 V (see FIG. 4 described later).

  The graph shown in FIG. 4 shows a control DC voltage (a DC voltage that the DC voltage control circuit 122 generates in the DC voltage generation circuit 121) and an auxiliary DC voltage in the auxiliary power supply circuit 102 (a DC voltage generated by the DC voltage generation circuit 121). FIG. 6 is a diagram showing a relationship between the auxiliary power supply circuit 102 and a direct-current voltage output to the direct-current voltage control circuit 122).

  The auxiliary DC voltage output from the auxiliary power supply circuit 102 is set higher than the control DC voltage controlled by the DC voltage control circuit 122 and is set to be lower as the load current increases. Note that the maximum auxiliary DC voltage from the auxiliary power supply circuit 102 is set to be about 100 V higher than the maximum control DC voltage of the DC voltage control circuit 122 as described above. In the example shown in FIG. 3, if the maximum control DC voltage of the DC voltage control circuit 122 is set to 500 V and the DC voltage is saturated at 500 V, the auxiliary DC voltage 600 V is supplied from the auxiliary power supply circuit 102 to the DC voltage control circuit 122. The control DC voltage flows in and is kept at 600V.

  As described above, according to the power supply device 10, by adding the auxiliary DC voltage generated and output by the single auxiliary power supply circuit 102 and the control DC voltage of the DC voltage control circuit 122, the AC voltage Even when the peak value and frequency can be varied, stable DC voltage can be generated. Therefore, a plurality of DC power sources are not required to generate a plurality of DC voltages superimposed on a plurality of AC voltages. Further, according to the conventional technique for extracting a plurality of DC voltages from a single DC power source, it is necessary to cope with an increase in loss accompanying an increase in load current (increasing the capacity of the transformer, etc.), resulting in an increase in cost. However, according to the power supply device 10, a stable high-voltage power supply for image formation can be provided efficiently and inexpensively.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the power supply device 10 is provided in the printer 1 for supplying a developing bias voltage to the developing devices 25M, 25C, 25Y, and 25K. It may be provided to supply power to other devices. For example, the power supply device 10 may be applied to supply a charging bias voltage to the charging device 23.

  In the above embodiment, the configurations and settings of the power supply apparatus 10 and the printer 1 shown in FIGS. 1 to 4 are merely examples, and the present invention is not limited to the embodiment.

1 is a diagram illustrating a schematic configuration of a printer to which a power supply device according to an embodiment of the present invention is applied. It is a block diagram which shows schematic structure of the power supply device which concerns on one Embodiment of this invention. It is a circuit diagram of the power supply device concerning one embodiment of the present invention. It is a figure which shows the relationship between a control DC voltage and an auxiliary DC voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 10 Power supply device 10M, 10C, 10Y, 10K Power supply device 101 Control part 102 Auxiliary power supply circuit 11 AC voltage generation part 111 Step-up transformer 112 AC input control circuit 113 Step-up transformer drive circuit 12 DC voltage generation part 121 DC voltage generation circuit 122 DC voltage control circuit 23 Charging device 25 Developing device 25M, 25C, 25Y, 25K Developing device
C5 capacitor
D2 diode
DCCONT Auxiliary DC power supply voltage control signal
Q5 transistor
R8, R30, R31, R32 resistors
VBM DC voltage control signal

Claims (5)

A step-up transformer that is provided corresponding to a load and boosts an AC input signal to generate an AC voltage;
A DC voltage generating circuit provided for the step-up transformer, rectifying the AC voltage to generate a DC voltage, and superimposing the DC voltage on an AC voltage generated on the secondary side of the step-up transformer;
A direct-current voltage control circuit that is provided for the direct-current voltage generation circuit and controls the level of the direct-current voltage generated by the direct-current voltage generation circuit;
An auxiliary power supply circuit comprising a power supply that outputs a DC voltage, and supplementing the DC voltage generated by the DC voltage generation circuit under the control of the DC voltage control circuit;
The DC voltage level output to the auxiliary power supply circuit for the compensation is changed according to the DC voltage level generated by the DC voltage control circuit in the DC voltage generation circuit, and the secondary side AC voltage of the step-up transformer is changed. And a control unit that performs control to maintain a DC voltage superimposed on the required voltage. A plurality of step-up transformers that are provided for each of a plurality of loads and that generate an AC voltage by boosting an AC input signal;
A plurality of DC voltage generation circuits provided for each of the step-up transformers, generating a DC voltage by rectifying the AC voltage, and superimposing the DC voltage on an AC voltage generated on the secondary side of the step-up transformer;
A plurality of DC voltage control circuits which are provided for each of the DC voltage generation circuits and control the level of the DC voltage generated by the corresponding DC voltage generation circuit;
An auxiliary power supply circuit comprising a single power supply that outputs a DC voltage, and supplementing the DC voltage generated by the DC voltage generation circuit under the control of the DC voltage control circuit;
The DC voltage level output to the auxiliary power supply circuit for the compensation is changed according to the DC voltage level generated by the corresponding DC voltage generation circuit by the corresponding DC voltage generation circuit, and the secondary voltage of the step-up transformer is changed. And a control unit that performs control to maintain the DC voltage superimposed on the AC voltage on the side at the required voltage.   The control unit, when performing control to reduce the peak value of the AC voltage according to the fluctuation of the load, the amount of decrease in the DC voltage level generated by the DC voltage generation circuit according to the decrease in the peak value, The power supply apparatus according to claim 1, wherein a DC voltage level output to the auxiliary power supply circuit for the compensation is increased.   When the level of the DC voltage generated by the DC voltage generation circuit is set low by the DC voltage control circuit, the control unit is configured to compensate for the amount corresponding to a decrease in the level of the DC voltage. The power supply apparatus according to any one of claims 1 to 3, wherein a DC voltage level output to the auxiliary power supply circuit is lowered. A power supply device according to any one of claims 1 to 4, comprising:
An image forming apparatus using the power supply device as a power supply for generating a developing bias for a developing device or a charging bias for a charging device.

Images