JP5597587B2 - High voltage power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a high-voltage power supply device that generates a voltage obtained by superimposing a DC voltage on an AC voltage, and an image forming apparatus including the same.

  In an image forming apparatus adopting an electrophotographic system, a high voltage power supply device is provided for a developing bias or a charging bias. As this high-voltage power supply device, one that outputs a high voltage obtained by superimposing a DC voltage on an AC voltage is used. For example, a DC voltage is connected between the low-voltage side of the secondary winding of the AC transformer that generates the AC voltage and the ground. By connecting a DC power source for generating a voltage, a high voltage in which an AC voltage and a DC voltage are superimposed is generated on the high voltage output side of the secondary winding of the AC transformer.

  For example, Patent Document 1 below discloses a positive peak detection circuit that detects a positive peak voltage of a superimposed voltage obtained by superimposing output voltages of an AC high voltage power supply and a DC high voltage power supply, and a negative peak voltage that detects a negative peak voltage of the superimposed voltage. A peak detection circuit, and by adjusting the average voltage of the DC high-voltage power supply and the voltage amplitude of the AC high-voltage power supply based on the detection results from the two detection circuits, the output voltage as the developing bias applied to the developing device can be accurately A well controlled high voltage power supply is described.

JP 2006-126630 A

  In the high-voltage power supply device as shown in Patent Document 1, the superimposed voltage obtained by superimposing the AC voltage and the DC voltage has an amplitude corresponding to the output of the AC transformer across the voltage generated by the DC power supply. The voltage becomes unstable when superimposing with the AC voltage is started or when the AC voltage is changed. For this reason, the maximum value (or minimum value) of the superimposed output voltage is higher (lower) than the leakage voltage value, and spark discharge may occur.

  The present invention has been made in view of such circumstances. For example, when a high-voltage power supply device generates a superimposed voltage obtained by superimposing a DC voltage on an AC voltage, for example, for developing bias of an image forming apparatus, The object is to prevent a situation in which the superimposed voltage exceeds the leakage voltage.

The invention according to claim 1 is a pulse oscillation unit that outputs a pulse signal used for waveform formation of an alternating voltage;
A level shift circuit that generates a predetermined high level or a predetermined low level pulsed AC voltage in accordance with the pulse signal output from the pulse oscillation unit;
A transformer that transforms the alternating voltage input to the primary side and generates the transformed alternating voltage on the secondary side;
An inverting amplifier circuit that outputs an AC voltage obtained by inverting and amplifying a difference between the pulsed AC voltage input to the inverting input terminal from the level shift circuit and a reference voltage input to the non-inverting input terminal to the primary side of the transformer; ,
A DC voltage superimposing unit that superimposes a DC voltage on the AC voltage generated on the secondary side of the transformer ;
A reference voltage input circuit that outputs to the non-inverting input terminal a voltage having a predetermined voltage value used when applying a superimposed voltage on which a DC voltage is superimposed by the DC voltage superimposing unit to a load;
And switchable reference voltage changing unit before Kimoto quasi voltage 0 (V) or pre Ki予 Me voltage value determined,
At the start of output of the pulse signal by the pulse oscillation unit, the reference voltage changing unit is caused to change the reference voltage to 0 (V), and the waveform of the AC voltage amplified by the inverting amplification circuit is set to 0 (V). A control unit that changes the reference voltage from 0 (V) to the predetermined voltage value in the reference voltage changing unit when the superimposed voltage is applied to a load .
The reference voltage changing unit includes a transistor connected in parallel with the reference voltage input circuit between the non-inverting input terminal and the ground.
When the control unit causes the reference voltage changing unit to change the reference voltage to 0 (V), the transistor is switched on, the non-inverting input terminal is grounded, and the reference voltage changing unit is When changing the reference voltage to the predetermined voltage value, the transistor is switched off, and the high voltage is used to output the voltage of the predetermined voltage value from the reference voltage input circuit to the non-inverting input terminal. It is a power supply device.

In the present invention, the control unit is, at the time of output start of the pulse signal by the pulse oscillation section, the criteria voltage to a reference voltage changing unit is changed to 0 (V), the waveform of the AC voltage amplified by the inverting amplifier circuit is 0 The waveform of the AC voltage at the start of amplification by the inverting amplifier circuit performed based on the output of the pulse signal should be output at, for example, 0 (V) or less originally. The waveform is pulled up to 0 (V) and output from the inverting amplifier circuit . For this reason, even when the value of the AC voltage input to the inverting amplifier circuit changes abruptly, the waveform of the AC voltage output from the inverting amplifier circuit is close to 0 (V) at the initial output. The voltage average value does not change abruptly before and after the start of the output. Thus, even if the DC voltage superimposing unit superimposes the DC voltage on the AC voltage obtained by transforming the AC voltage output from the inverting amplifier circuit with the transformer, the superimposed superimposed voltage is prevented from exceeding the leakage voltage.

The invention described in claim 2 includes an image forming unit that forms an image on a recording medium,
A charging bias used in a developing unit provided in the image forming unit and used in a developing unit that performs a developing process in an image forming process, or used in a charging unit that is provided in the image forming unit and performs a charging process in an image forming process. An image forming apparatus provided with the high-voltage power supply device according to claim 1 as at least one of the outputs.

  In the present invention, since the superimposed voltage generated by the high-voltage power supply device according to claim 1 is used for the output of the developing bias or the charging bias in the image forming apparatus, the same effect as that of the invention according to claim 1 is obtained. Further, it is possible to prevent a situation where the output voltage of the developing bias or the charging bias exceeds the leakage voltage.

The invention according to claim 3 includes an image forming unit that forms an image on a recording medium,
The high-voltage power supply device according to claim 1 is provided for output of a developing bias used in a developing unit that is provided in the image forming unit and performs development processing in an image forming process,
The control unit is a case where image formation is performed by the image forming unit, and when the superimposed voltage by the DC voltage superimposing unit is applied as a developing bias to the developing unit, the reference voltage changing unit is supplied with the reference In the image forming apparatus, the voltage is changed from 0 (V) to the predetermined voltage value.

  In this invention, the control unit is a case where image formation is performed by the image forming unit, and when applying the superimposed voltage as a developing bias to the developing unit, the reference voltage is changed from 0 (V) to the reference voltage changing unit. Since the voltage is changed to the predetermined voltage value, a superimposed voltage having a waveform suitable for the development process generated by voltage amplification based on the reference voltage is applied to the development unit during the development process by the development unit. Is possible.

  According to the present invention, when the high-voltage power supply device outputs a superimposed voltage obtained by superimposing a DC voltage on an AC voltage, for example, for developing bias of the image forming apparatus, the situation where the superimposed voltage exceeds the leakage voltage is prevented. It becomes possible.

1 is an explanatory diagram illustrating a printer as an example of an image forming apparatus to which a high-voltage power supply device according to the present invention is applied. It is a sectional side view of a developing device. It is a schematic block diagram of the high voltage power supply device which concerns on this invention. (A) is a figure which shows the time-sequential change of the waveform which shows the voltage level in the points P1-P5 in the control circuit of the conventional high voltage power supply device, (b) is in the control circuit of the high voltage power supply device 100 which concerns on this embodiment. It is a figure which shows the time-sequential change of the waveform which shows the voltage level in points P1-P5.

  Hereinafter, a high-voltage power supply device and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a printer 10 as an example of an image forming apparatus according to the present invention includes a sheet storage unit 12 that stores sheets S to be subjected to a printing process, and a sheet bundle S1 stored in the sheet storage unit 12. An image forming unit 13 that performs an image transfer process on each sheet S that is fed out, and a fixing unit 14 that performs a fixing process on the sheet S subjected to the transfer process in the image forming unit 13. The apparatus main body 11 is further provided with a paper discharge section 15 on the top of the apparatus main body 11 for discharging the paper S that has been subjected to fixing processing by the fixing section 14.

  Also, the printer 10 is a diagram for data communication with an unillustrated operation unit for inputting various operation instructions such as an input operation for image data to be printed, and an external device such as an external computer. An abbreviated network interface section is provided.

  A paper cassette 121 is provided in the paper storage unit 12 so as to be detachable with respect to the apparatus main body 11. A pickup roller 122 is provided at the upstream end (right side in FIG. 1) of the sheet cassette 121 to feed out the sheets S one by one from the sheet bundle S1. The paper S fed out of the paper cassette 121 by driving the pickup roller 122 is supplied to the image forming unit 13 through the paper feed conveyance path 123 and the registration roller pair 124 provided at the downstream end of the paper feed conveyance path 123. Paper.

  The image forming unit 13 performs a transfer process on the paper S based on image information input from an external computer or the like, and is rotatable around a drum axis extending in the front-rear direction (a direction orthogonal to the paper surface of FIG. 1). A charging device 30, an exposure device 40, a developing device 50, a transfer roller 60, and a cleaning device 70 are provided in a clockwise direction from a position directly above the photosensitive drum 20 along the peripheral surface of the provided photosensitive drum 20. It will be.

  The photosensitive drum 20 is for forming an electrostatic latent image on the peripheral surface and then forming a toner image along the electrostatic latent image, and an amorphous silicon layer is laminated on the peripheral surface. The photosensitive drum 20 is coaxially and integrally supported by a drum shaft extending in the front-rear direction (a direction perpendicular to the paper surface of FIG. 1) at a substantially central portion of the apparatus main body 11, and is driven by driving means (not shown). The drum shaft is configured to rotate integrally with the drum shaft by the rotation in the clockwise direction.

  A charging device (an example of a charging unit in the claims) 30 forms a uniform charge on the peripheral surface of the photosensitive drum 20 rotating in the clockwise direction of the drum shaft. The charging device 30 performs charging by a corona discharge method in which a charge is applied to the peripheral surface of the photosensitive drum 20 by corona discharge from a wire.

  The exposure device 40 irradiates the peripheral surface of the rotating photosensitive drum 20 with laser light to which intensity is applied based on image data input from an external computer or the like, and the portion irradiated with the laser light An electrostatic latent image is formed on the peripheral surface by erasing the electric charges.

  A developing device (an example of a developing unit in the claims) 50 attaches toner to a portion where an electrostatic latent image is formed on the peripheral surface by supplying toner as a developer to the peripheral surface of the photosensitive drum 20. Thus, a toner image is formed on the peripheral surface of the photosensitive drum 20. In the present embodiment, a so-called one-component developer composed only of toner is employed as the developer. The developer is not limited to the one-component system composed only of the toner, but a so-called two-component system composed of toner and carrier may be adopted as the developer.

  The transfer roller 60 transfers the positively charged toner image formed on the peripheral surface of the photosensitive drum 20 to the paper S with respect to the paper S sent to a position immediately below the photosensitive drum 20. A negative charge having a polarity opposite to that of the toner image is applied to the paper S. Therefore, the sheet S that has passed the position immediately below the photosensitive drum 20 is pressed and sandwiched between the transfer roller 60 and the photosensitive drum 20, and the toner image on the circumferential surface of the positively charged photosensitive drum 20 is negatively charged. The sheet S is peeled off toward the surface of S, whereby a transfer process is performed on the sheet S.

  The cleaning device 70 removes and cleans the toner remaining on the peripheral surface of the photosensitive drum 20 after the transfer process. The peripheral surface of the photoconductive drum 20 cleaned by the cleaning device 70 goes to the charging device 30 again for the next image forming process.

  The fixing unit 14 performs a fixing process by heating the toner image of the paper S subjected to the transfer process by the image forming unit 13, and includes a heat roller 141 in which an energizing heating element such as a halogen lamp is mounted, A pressure roller 142 having a peripheral surface disposed opposite to the lower portion of the heat roller 141 is configured.

  Then, the sheet S after the transfer processing is between the heat roller 141 that is driven to rotate clockwise around the roller center and the pressure roller 142 that is driven to rotate counterclockwise around the roller center. By passing through the nip portion, the heat from the heat roller 141 is obtained and the fixing process is performed. The sheet S subjected to the fixing process is discharged to the paper discharge unit 15 through the paper discharge conveyance path 143.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper S is formed at the bottom of the recess.

  FIG. 2 is a side sectional view of the developing device 50. The developing device 50 includes a first spiral feeder 51 that feeds toner supplied from the toner cartridge 59 toward the rear while stirring the toner supplied from the toner cartridge 59, and the toner delivered from the first spiral feeder 51 to the front. A second spiral feeder 52 that transports the toner toward the surface, and a developing sleeve 53 that receives the toner being transported by the second spiral feeder 52 and supplies the toner to the latent image area on the circumferential surface of the photosensitive drum 20. It is constituted by.

  The casing 58 has a bottom plate 581 inclined leftward from a substantially central position in the left-right direction in FIG. 2 and a left end portion facing the photosensitive drum 20, and a top plate disposed to face the bottom plate 581 at the top. 582, a pair of side plates 583 extending in the front-rear direction between the front and rear ends of the bottom plate 581 and the top plate 582, and a toner receiving tray 584 installed between the pair of side plates 583.

  The top plate 582 is formed in a stepped shape with one step higher on the left side. The lower top plate 582a on the right side, the higher top plate 582b on the left side, the left edge of the lower top plate 582a, and the higher top plate It is comprised from the vertical top plate 582c constructed between the right end edge part of 582b. A toner receiving port (not shown) for receiving toner from the toner cartridge 59 is provided at the front end of the lower top plate 582a. Further, between the left end edge of the high top plate 582 b and the left end edge of the bottom plate 581, the toner in the housing 58 faces the peripheral surface of the photosensitive drum 20 so as to face the peripheral surface of the photosensitive drum 20. A toner supply port 586 for supply is opened.

  The toner receiving tray 584 includes a first tray 584a that accommodates the first spiral feeder 51, a second tray 584b that accommodates the second spiral feeder 52, and a third tray 584c that is opposed to the developing sleeve 53 at the bottom. I have. The first to third trays 584a, 584b, 584c are formed in an arc shape in front view corresponding to the first and second spiral feeders 51, 52 and the developing sleeve 53, respectively. Further, a right side wall 587 is provided at the right end of the first tray 584a, and the right side in the casing 58 is closed by the right side wall 587 being installed between the right ends of the bottom plate 581 and the lower top plate 582a. ing.

  The first spiral feeder 51 includes a first feeder shaft 511 penetrating between a pair of side plates 583 at a position directly above the first tray 584a, and a first spiral fin that is concentrically fitted and fixed to the first feeder shaft 511. 512. The first spiral fin 512 is formed in a left-handed spiral shape, and the first feeder shaft 511 rotates in the clockwise direction when viewed from the front, thereby conveying the toner on the first tray 584a backward.

  The second spiral feeder 52 includes a second feeder shaft 521 penetrating between the pair of side plates 583 at a position immediately above the second tray 584b, and a second spiral fin that is concentrically fitted and fixed to the second feeder shaft 521. 522. The second spiral fin 522 is formed in a right-handed spiral shape, and the second feeder shaft 521 rotates clockwise in a front view to convey the toner on the second tray 584b forward. .

  A partition wall 585 is provided between the first and second trays 584a and 584b. A front circulation port (not shown) is opened at the front position of the partition wall 585, and a rear circulation port (not shown) is opened at the rear position. The toner introduced from the toner cartridge 59 into the housing 58 via the toner receiving port is first conveyed backward in the first tray 584a by the driving rotation of the first spiral feeder 51, and is then moved to the rear flow port 585b. Through the second tray 584b, conveyed forward in the second tray 584b by the driving rotation of the second spiral feeder 52, and thereafter circulated between the first and second trays 584a and 584b. Are supplied to the developing sleeve 53.

  The developing sleeve 53 includes a sleeve shaft 534 penetrating between a pair of side plates 583 and a sleeve body 532 that is concentrically fitted to the sleeve shaft 534 so as to be relatively rotatable. The developing sleeve 53 is set at a position above the third tray 584c so that the circumferential surface of the sleeve body 532 faces the circumferential surface of the photosensitive drum 20 through the toner supply port 586, and driving means (not shown) is provided. 2, the toner rotated around the sleeve shaft 534 in the counterclockwise direction in FIG. 2, and thereby the toner fed onto the third tray 584 c is directed toward the peripheral surface of the photosensitive drum 20.

  In the developing device 50, the toner is stirred by the stirring action of the first spiral feeder 51 and the second spiral feeder 52, and the toner is positively (+) charged. A bias voltage (developing bias) in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve 53 by a high-voltage power supply device described later. The positive (+) polarity electrostatic latent image formed on the photosensitive drum 20 is reversely developed by the developer held and conveyed by the magnetic force of the developing sleeve 53, and is formed on the surface of the photosensitive drum 20. A toner image is formed.

  FIG. 3 is a diagram showing a schematic configuration of the high-voltage power supply device according to the present invention. The high-voltage power supply device 100 includes an AC (alternating current) bias generation circuit 80 and a DC (direct current) bias generation circuit 90.

  The AC bias generation circuit 80 is a circuit that generates an AC voltage. The AC bias generation circuit 80 includes a control circuit 81, a level shift circuit 82, an AC amplification circuit 83, and a transformer circuit 84.

  The control circuit 81 includes a pulse oscillating unit 811 and a switch control unit 812. The pulse oscillating unit 811 oscillates a pulse signal used for forming an AC voltage waveform.

  When the pulse oscillation unit 811 starts outputting the pulse signal, the switch control unit 812 causes the reference voltage changing unit 833 (described later) to change the reference voltage of the AC amplifier circuit 83 to 0 (V) and is amplified by the AC amplifier circuit 83. Make sure that the AC voltage waveform does not fall below 0 (V). The switch control unit 812 is a case where image formation is performed by the image forming unit 13, and a superimposed voltage generated by a transformer circuit 84 and a DC bias generation circuit 90 described later is used as a developing bias for the developing device 50. When the time to apply is reached, at this time, the reference voltage changing unit 833 changes the reference voltage from 0 (V) to a predetermined voltage value. As the reference voltage as the predetermined value, a voltage value that uses the value of the AC voltage output from the AC amplifier circuit 83 as a value to which the superimposed voltage can be applied as the developing bias is used. As shown in FIG. 3, in this embodiment, the AC amplifier circuit 83 is driven by +24 (V). In this case, the predetermined voltage value as the reference voltage value is, for example, an intermediate voltage +12 Set to (V). The predetermined voltage value can be changed as appropriate by changing the resistance constant.

  The level shift circuit 82 includes an inverting circuit 821 and a switching element 822. The inversion circuit 821 inverts the pulse signal output from the pulse oscillation unit 811 and outputs the inverted pulse signal toward the switching element 822.

  The switching element 822 switches on / off of switching according to on / off indicated by the input pulse signal. When the switching element 822 is turned on by the input pulse signal, the switching element 822 outputs a predetermined low level voltage (for example, 0 (V)) to the power operational amplifier 832 via the capacitor 831. On the other hand, when the switching element 822 is switched off, the switching element 822 outputs a predetermined high level voltage (for example, 6 (V)) to the power operational amplifier 832 via the capacitor 831. Note that the voltage levels indicated by the low level and the high level are resistance elements provided in the level shift circuit 82, and are adjusted in advance according to the resistance value of the resistance element connected to the power supply voltage Vcc.

  The AC amplifier circuit 83 includes a capacitor 831 and a power operational amplifier 832. The capacitor 831 is provided between the level shift circuit 82 and the power operational amplifier 832 and functions as a noise removal filter. The power operational amplifier 832 is, for example, an inverting amplifier circuit. In the power operational amplifier 832, the AC voltage composed of the Low level voltage and the High level voltage input from the level shift circuit 82 via the capacitor 831 is input to the − input terminal, while the reference voltage is input to the + input terminal. The The power operational amplifier 832 supplies the AC voltage obtained by amplifying and inverting the difference between the AC voltage input from the level shift circuit 82 and the reference voltage to the transformer circuit 84 via the capacitor 842.

  The reference voltage changing unit 833 sets the reference voltage of the AC amplifier circuit 83 to (1) at least 0 (V) and (2) the transformer circuit 84 and the DC bias generation circuit 90 in accordance with the instruction signal from the switch control unit 812. Is changed to the above-mentioned predetermined voltage value used when the superimposed voltage generated by the above is applied to the developing device 50 as a developing bias. For example, the reference voltage changing unit 833 includes a transistor and is connected in parallel to the reference voltage input unit 834 that inputs the reference voltage to the + input terminal. The emitter side of the transistor is grounded, and the collector side is connected to a reference voltage input line to the power operational amplifier 832. Further, the base of the transistor is connected to the switch control unit 812. In accordance with a switching signal from the switch controller 812, the transistor turns on / off. When the transistor as the reference voltage changing unit 833 is switched on by the switching signal from the switch control unit 812, the voltage from the reference voltage changing unit 833 side is input to the power operational amplifier 832 as the reference voltage, and the reference voltage changing unit Since 833 is grounded, the reference voltage input to the power operational amplifier 832 is 0 (V). When the reference voltage changing unit 833 is switched off, a reference voltage (set to 12 (V) in this embodiment) is input to the power operational amplifier 832 from the reference voltage input unit 834.

  The transformer circuit 84 includes a transformer 841 and a capacitor 842. The circuits 81 to 84 are connected to other circuit elements such as pull-up resistors and diodes shown in the drawing.

  The capacitor 842 is provided between the AC amplifier circuit 83 and the transformer 841. The transformer 841 transforms the AC voltage supplied from the AC amplifier circuit 83 to the primary side winding side via the capacitor 842 and generates the transformed AC voltage on the secondary side winding side of the transformer 841.

  The DC bias generation circuit 90 is a circuit that generates a DC voltage, and is connected between the low voltage side of the secondary winding of the transformer 841 and the ground. As a result, the DC bias generation circuit 90 generates a voltage in which an AC voltage and a DC voltage are superimposed on the high voltage output side of the secondary winding of the transformer 841. The superimposed voltage is applied to the developing device 50 (developing sleeve 53), for example.

  The level shift circuit 82, the AC amplifier circuit 83, and the transformer circuit 84 are a part of the AC voltage generation unit in the claims, and the DC bias generation circuit 90 is an example of the DC voltage superimposing unit in the claims.

  The voltage application control by the high-voltage power supply device 100 in this configuration will be described with reference to FIG. FIG. 4A is a diagram showing a time-series change of a waveform indicating voltage levels at points P1 to P5 in the control circuit of the conventional high-voltage power supply device, and FIG. 4B is a control of the high-voltage power supply device 100 according to the present embodiment. It is a figure which shows the time-sequential change of the waveform which shows the voltage level in the points P1-P5 in a circuit.

  Also, the time-series changes in the waveforms shown in the dotted line parts in FIGS. 4A and 4B indicate the average values of the voltage levels at the points P3 to P5 from the oscillation start time t0. However, for the sake of explanation, the detailed undulations are shown in a simplified manner in the figure.

  In the following, as a specific example, a pulse signal that causes the pulse oscillation unit 811 to start oscillation will be described by using a signal with 90% duty cycle indicating ON for 90% of the period and OFF for 10% of the period. To do. Note that the duty ratio of the pulse signal that causes the pulse oscillating unit 811 to start oscillation is not limited to this. In addition, the duty ratio of a pulse signal that causes the pulse oscillation unit 811 to start oscillation is input from the operation unit, the network interface unit, or the like.

  At the start of voltage application control by the high-voltage power supply device 100, the switch control unit 812 outputs a switch signal that instructs the reference voltage changing unit 833 to switch on. When the above-described transistor as the reference voltage changing unit 833 is switched on by the switching signal from the switch control unit 812, the voltage from the reference voltage changing unit 833 that is grounded is supplied to the power operational amplifier 832 as a reference. The reference voltage input to the power operational amplifier 832 is 0 (V).

  When outputting a pulse signal with a duty ratio of 90%, the pulse oscillation unit 811 outputs a signal indicating a level indicating OFF when the pulse signal is not oscillated as shown in the P1 column of FIG. From time t0, which is the time, a pulse signal for starting to turn on AC voltage application is output. The pulse signal output from the pulse oscillating unit 811 is output with the on / off state inverted by the inversion circuit 821 as shown in the P2 column of FIG. 4B.

  The pulse signal output from the inverting circuit 821 is input to the switching element 822. When the switching element 822 is switched off, a voltage of 6 (V), which is a predetermined high level voltage, passes through the capacitor 831 as shown by the solid line portion in the P3 column of FIG. When the input is made to the negative input terminal side of the power operational amplifier 832 and the switching element 822 is turned on, a voltage of 0 (V) which is a predetermined low level is inputted through the capacitor 831 to the negative input of the power operational amplifier 832. Input to the terminal side.

  At this time, the low voltage (0 (V)) and high voltage (6 (V)) AC voltage is inverted and amplified and output from the power operational amplifier 832. As described above, since the reference voltage 0 (V) is input by grounding by the reference voltage changing unit 833, the output of the power operational amplifier 832 in this case is shown in the P4 column of FIG. As indicated by a two-dot chain line and a solid line, the entire waveform of the power operational amplifier 823 is 12 (V) which is the voltage difference between the two reference voltages, rather than the output of the power operational amplifier 832 when the reference voltage is +12 (V). Pulled down.

  Here, the output of the power operational amplifier 832 when the reference voltage is 0 (V) has a waveform below 0 (V) at the point P4, as indicated by a broken line and a solid line in the P4 column of FIG. 4B. There is nothing.

  As a result, at the point P4, the voltage average value from the oscillation start time t0 gradually increases from 0 (V) as shown by the dotted line in the P4 column of FIG. 4B.

  The AC voltage output from the power operational amplifier 832 is transformed by the transformer 841, and then the DC voltage is superimposed by the DC bias generation circuit 90. As shown in the P5 column of FIG. 4B, about -1.2 (kV ) To about 0.8 (kV), and is input to the point P5. Further, the average voltage value from the oscillation start time t0 at the point P5 gradually increases as in the dotted line portion of the P4 column as shown by the dotted line portion of the P5 column in FIG. 4B.

  Then, the switch control unit 812 executes image formation by the image forming unit 13 based on a determination based on an operator operating the operation unit of the printer 10 and inputting an instruction to execute image formation to the printer 10. If it is determined that it is time to apply the superimposed voltage as a developing bias to the developing device 50, a switch signal that instructs the reference voltage changing unit 833 to switch off is output. When the reference voltage changing unit 833 is switched off, the above-mentioned reference voltage (+12 (V) in this embodiment) is input to the power operational amplifier 832 from the reference voltage input unit 834. For this reason, after the output of the switch signal instructing the switch-off by the switch control unit 812, the AC voltage having the waveform shown in the P4 column of FIG. 4A is output from the power operational amplifier 832 and shown in FIG. A superimposed voltage having a waveform shown in the P5 column is applied as a developing bias.

  Conventionally, in the case of the AC amplifier circuit 83 that does not have the reference voltage changing unit 833, as shown in the dotted line portion of the P3 column in FIG. 4A at the start of voltage application control by the high-voltage power supply device 100. The average voltage value from the oscillation start time t0 at the point P3 is determined in advance from 0 (V) to a level of about 5.4 (V) obtained by multiplying the ratio indicated by the duty ratio 90% by 6 (V). 4A, which is larger than the average value (3 (V)) of the high level voltage value and the predetermined low level voltage value, by about 5.4 (V) level. As shown in the column P4, the rapidly increasing voltage is inverted and amplified by the power operational amplifier 832, and in this case, the average voltage level from the oscillation start time t0 is further decreased and rapidly decreased. . For this reason, when the DC voltage is superimposed on the AC voltage at the voltage level at the point P4 by the DC bias generation circuit 90 via the transformer 841, the superimposed voltage and its voltage as shown in the P5 column of FIG. The average voltage value (broken line in the P5 column of FIG. 4A) may be greatly reduced at the beginning of the voltage application control to be lower than the leak voltage.

  However, in the present embodiment described above, at the start of voltage application control by the high-voltage power supply device 100, the switch control unit 812 outputs a switch signal that instructs the reference voltage changing unit 833 to switch on, and Since the voltage changing unit 833 is switched on, and the voltage from the reference voltage changing unit 833 is input to the power operational amplifier 832 as the reference voltage 0 (V), at the start of the voltage application control, FIG. ), The AC voltage waveform amplified and output by the power operational amplifier 832 does not fall below 0 (V), so that the voltage output from the point P4 passes through the transformer 841. When a DC voltage is superimposed by the DC bias generation circuit 90, as shown in the P5 column of FIG. 4B, the superimposed voltage and its average voltage value (FIG. 4 ( ) P5 column dashed) does not occur a situation below the leak voltage rapidly decreases.

  In the above-described embodiment, the example in which the high-voltage power supply device 100 according to the present invention is applied for output of the developing bias of the developing device 50 has been described. The high-voltage power supply apparatus 100 may be applied for outputting the applied voltage (charging bias).

  In the above embodiment, the printer is described as an example of the image forming apparatus according to the present invention. However, the present invention is not limited to this, and the image forming apparatus according to the present invention includes the image reading apparatus according to the present invention. It may be an image forming apparatus such as a printer, a copier, a scanner, or a fax machine.

  The present invention is not limited to the configuration of the above-described embodiment, and various modifications can be made. The configurations and processes shown in FIGS. 1 to 4 are merely examples of the embodiment according to the present invention, and are not intended to limit the present invention to the embodiment.

10 Printer 100 High Voltage Power Supply Device 13 Image Forming Unit 30 Charging Device 50 Developing Device 80 AC Bias Generation Circuit 81 Control Circuit 811 Pulse Oscillation Unit 812 Switch Control Unit 82 Level Shift Circuit 821 Inversion Circuit 822 Switching Element 83 AC Amplification Circuit 831 Capacitor 832 Power Operational amplifier 833 Reference voltage changing unit 834 Reference voltage input unit 84 Transformer circuit 841 Transformer 90 DC bias generation circuit

Claims (3)

A pulse oscillating unit for outputting a pulse signal used for waveform formation of an alternating voltage;
A level shift circuit that generates a predetermined high level or a predetermined low level pulsed AC voltage in accordance with the pulse signal output from the pulse oscillation unit;
A transformer that transforms the alternating voltage input to the primary side and generates the transformed alternating voltage on the secondary side;
An inverting amplifier circuit that outputs an AC voltage obtained by inverting and amplifying a difference between the pulsed AC voltage input to the inverting input terminal from the level shift circuit and a reference voltage input to the non-inverting input terminal to the primary side of the transformer; ,
A DC voltage superimposing unit that superimposes a DC voltage on the AC voltage generated on the secondary side of the transformer ;
A reference voltage input circuit that outputs to the non-inverting input terminal a voltage having a predetermined voltage value used when applying a superimposed voltage on which a DC voltage is superimposed by the DC voltage superimposing unit to a load;
And switchable reference voltage changing unit before Kimoto quasi voltage 0 (V) or pre Ki予 Me voltage value determined,
At the start of output of the pulse signal by the pulse oscillation unit, the reference voltage changing unit is caused to change the reference voltage to 0 (V), and the waveform of the AC voltage amplified by the inverting amplification circuit is set to 0 (V). A control unit that changes the reference voltage from 0 (V) to the predetermined voltage value in the reference voltage changing unit when the superimposed voltage is applied to a load .
The reference voltage changing unit includes a transistor connected in parallel with the reference voltage input circuit between the non-inverting input terminal and the ground.
When the control unit causes the reference voltage changing unit to change the reference voltage to 0 (V), the transistor is switched on, the non-inverting input terminal is grounded, and the reference voltage changing unit is When changing the reference voltage to the predetermined voltage value, the transistor is switched off, and the high voltage is used to output the voltage of the predetermined voltage value from the reference voltage input circuit to the non-inverting input terminal. Power supply. An image forming unit for forming an image on a recording medium;
A charging bias used in a developing unit provided in the image forming unit and used in a developing unit that performs a developing process in an image forming process, or used in a charging unit that is provided in the image forming unit and performs a charging process in an image forming process. An image forming apparatus comprising the high-voltage power supply device according to claim 1 as at least one of the outputs. An image forming unit for forming an image on a recording medium;
The high-voltage power supply device according to claim 1 is provided for output of a developing bias used in a developing unit that is provided in the image forming unit and performs development processing in an image forming process,
The control unit is a case where image formation is performed by the image forming unit, and when the superimposed voltage by the DC voltage superimposing unit is applied as a developing bias to the developing unit, the reference voltage changing unit is supplied with the reference An image forming apparatus that changes a voltage from 0 (V) to the predetermined voltage value.

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