Power supply device and image forming device

Abstract

To provide a power supply device that can independently adjust a positive voltage waveform and a negative voltage waveform of an AC voltage waveform, and suppresses discrepancy between average values of voltage at an output terminal.SOLUTION: A power supply device comprises: a DC output unit 400 for generating DC voltage; an AC output unit 300 for generating AC voltage and generating output voltage obtained by superimposing the DC voltage and the AC voltage; and a control unit 200 for allowing the DC output unit 400 to generate the DC voltage of a prescribed voltage value, and allowing the AC output unit 300 to generate the AC voltage of a prescribed voltage value. The AC output unit 300 has resistors R301 and R302 to be damping resistance of the output voltage, and an AC diode D301 connected in parallel with the resistor R301. The control unit 200 adjusts a voltage value of the DC voltage on the basis of an average value of the output voltage.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a power supply device that generates an AC voltage and an image forming apparatus equipped with such a power supply device. [Background technology]

[0002] An electrophotographic or electrostatic recording image forming apparatus includes a developing unit. The developing unit is capable of efficiently developing an electrostatic latent image with toner by applying a voltage in which a DC voltage and an AC voltage are superimposed. In particular, by making the waveform of the AC voltage a square wave, the charging efficiency of the toner for the electrostatic latent image (the ratio of toner charge combined with latent image charge) is improved. The square wave shape of the AC voltage changes depending on a damping resistor connected to an AC transformer provided in a power supply device that generates the AC voltage. The damping resistor is set to an appropriate resistance value for each image forming apparatus.

[0003] In order to improve image quality, the positive voltage amplitude (Vp+) and the negative voltage amplitude (Vp-) of the AC voltage may be set to different values. In this case, the AC voltage waveform is called a "biased duty waveform." A biased duty ratio (Vp+:Vp-) of 4:6 to 2:8 is generally used. In a partial duty cycle waveform, when the frequency of the AC voltage is high and the partial duty ratio is 2:8, the positive voltage is prone to overshoot because its amplitude level is low. To suppress the overshoot, a large resistance value is set for the damping resistor.

[0004] However, when a damping resistor with a large resistance is used, the negative voltage, which has a large amplitude and a short output time, may not rise completely within the time. Conversely, if the resistance value of the damping resistor is reduced so that the negative voltage rises within the time, an overshoot occurs in the positive voltage. In other words, it is difficult to optimize both the positive voltage waveform and the negative voltage waveform of the AC voltage.

[0005] Patent Document 1 proposes a configuration in which a diode is connected in parallel to one (first damping resistor) of two damping resistors (first and second damping resistors) connected in series to the output section of an AC transformer that generates an AC voltage. In this configuration, when a positive voltage is output, the sum of the resistance values ​​of the first and second damping resistors becomes the resistance value of the damping resistor, and when a negative voltage is output, only the resistance value of the second damping resistor becomes the resistance value of the damping resistor. This makes it possible to adjust the rising waveforms of the positive and negative AC voltages independently. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2022-77437 Summary of the Invention [Problem to be solved by the invention]

[0007] In the configuration of Patent Document 1, the voltage Vx across the secondary side of the AC transformer has an average value of 0 [V]. The voltage Vy output from the power supply device is output from the AC transformer via a damping resistor. The voltage Vy has a waveform in which high-frequency components have been removed from the voltage Vx across both ends by the damping resistor and the load capacitance. The voltage Vy has a different positive voltage waveform area and a different negative voltage waveform area because the resistance value of the damping resistor when a positive voltage is output is different from the resistance value of the damping resistor when a negative voltage is output. The difference between the positive voltage waveform area and the negative voltage waveform area is the deviation amount of the average value of the voltage Vy from the average value of the voltage Vx across both ends. In other words, the voltage Vy of the output section includes an AC waveform, and thus the average value deviates from 0 [V].

[0008] In view of the above-mentioned problems, the main object of the present invention is to provide a power supply device that is capable of independently adjusting the positive and negative voltage waveforms of an AC voltage waveform and that suppresses deviation from the average value of the voltage at the output terminal. [Means for solving the problem]

[0009] The power supply device of the present invention comprises: DC voltage generation means for generating a DC voltage; AC voltage generation means for generating an AC voltage and generating an output voltage by superimposing the DC voltage and the AC voltage; and control means for causing the DC voltage generation means to generate the DC voltage of a predetermined voltage value and for causing the AC voltage generation means to generate an AC voltage of the predetermined voltage value, wherein the AC voltage generation means has a plurality of resistors that serve as damping resistance for the output voltage and a diode connected in parallel to some of the plurality of resistors, and is configured such that a current flows through the plurality of resistors when the AC voltage is output as a positive voltage, and a current does not flow through some of the resistors when the AC voltage is output as a negative voltage, the DC voltage generation means has voltage detection means for detecting an average value of the output voltage, and the control means transmits a control signal to the DC voltage generation means for adjusting the voltage value of the DC voltage based on the average value detected by the voltage detection means. Effect of the Invention

[0010] According to the present invention, it is possible to adjust the positive voltage waveform and the negative voltage waveform of the AC voltage waveform independently, and to suppress the deviation of the average value of the voltage at the output terminal. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. 4 is an explanatory diagram of the voltage waveforms of each part of the AC output section. [Figure 6] 5A and 5B are explanatory diagrams of output operations of a DC voltage and a developing voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0013] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to the present embodiment. The image forming apparatus 1000 according to the present embodiment employs an electrophotographic system, but may employ an electrostatic recording system. The image forming apparatus 1000 includes a plurality of image forming units according to the number of colors of the image to be formed. In the present embodiment, four image forming units 10a, 10b, 10c, and 10d are provided to form images of four colors, namely, yellow (Y), magenta (M), cyan (C), and black (K). The image forming apparatus 1000 includes a paper cassette 9, an intermediate transfer belt 5, a secondary transfer roller 7, and a fixing unit 8. The image forming apparatus 1000 includes a controller 500 that controls the operation of each component.

[0014] The image forming units 10a to 10d include photosensitive drums 1a to 1d, charging rollers 2a to 2d, laser scanners 3a to 3d, developing units 4a to 4d, and primary transfer rollers 6a to 6d. The photosensitive drums 1a to 1d are drum-shaped photosensitive bodies having a photosensitive layer on their surfaces, and rotate around the drum axis in the direction of arrow A. The charging rollers 2a to 2d uniformly charge the surfaces of the rotating photosensitive drums 1a to 1d. The laser scanners 3a to 3d expose the charged surfaces of the photosensitive drums 1a to 1d based on image signals representing images of the corresponding colors to form electrostatic latent images. The developing units 4a to 4d attach developer (toner) of the corresponding colors to the electrostatic latent images, thereby forming toner images on the photosensitive drums 1a to 1d.

[0015] A yellow toner image is formed on the photosensitive drum 1a. A magenta toner image is formed on the photosensitive drum 1b. A cyan toner image is formed on the photosensitive drum 1c. A black toner image is formed on the photosensitive drum 1d. The toner images of each color formed on the photosensitive drums 1a to 1d are transferred onto the intermediate transfer belt 5 by the primary transfer rollers 6a to 6d. The intermediate transfer belt 5 rotates in the direction of arrow B, and the toner images are transferred from the photosensitive drums 1a to 1d in order so as to be superimposed on top of each other. The intermediate transfer belt 5 transports the transferred toner images of each color to the secondary transfer roller 7 by rotating.

[0016] A sheet of paper S, which is a recording medium, is conveyed from a paper cassette 9 to the secondary transfer roller 7 in synchronization with the timing at which the toner image is conveyed by the intermediate transfer belt 5. The secondary transfer roller 7 transfers the toner images of each color carried by the intermediate transfer belt 5 all at once onto the sheet of paper S. The sheet of paper S onto which the toner images have been transferred is conveyed to a fixing device 8. The fixing device 8 applies heat and pressure to the sheet of paper S to melt and fix the toner image onto the sheet of paper S. In this manner, a color image is printed on the sheet of paper S. The sheet of paper S on which the color image has been printed is discharged outside the image forming apparatus 1000.

[0017] FIG. 2 is a configuration diagram of a developing high voltage generating unit that generates a developing voltage applied to the developing unit 4a when developing an electrostatic latent image. A developing high voltage generating unit 100 is provided for each of the developing units 4a to 4d. The developing high voltage generating unit 100 is a power supply device controlled by a controller 500. The developing high voltage generating unit 100 includes a control unit 200, an AC output unit 300, and a DC output unit 400, and generates a developing voltage (Vac+Vdc) that is an output voltage obtained by superimposing an AC voltage on a DC voltage. The AC output unit 300 is an AC voltage generating unit that generates an AC voltage. The DC output unit 400 is a DC voltage generating unit that generates a DC voltage. The developing voltage (Vac+Vdc) is applied to the developing unit 4a from an output terminal of the developing high voltage generating unit 100.

[0018] The control unit 200 performs serial communication with the controller 500. The control unit 200 transmits various control signals (drive signals, setting signals, etc.) to the DC output unit 400 and the AC output unit 300 in response to commands from the controller 500. The control unit 200 acquires a DC voltage detection signal, which is a signal indicating the detection result of the direct current voltage, from the DC output unit 400. The control unit 200 of this embodiment is composed of semiconductor devices such as an MPU (Micro-Processing Unit) and a CPU (Central Processing Unit) and peripheral components. The control unit 200 may also be composed of an ASIC (Application Specific Integrated Circuit).

[0019] The control unit 200 has a storage unit 201. The storage unit 201 stores a computer program for operating in response to commands from the controller 500, data required for transmitting various control signals (drive signals, setting signals, etc.), and the like.

[0020] The DC output unit 400 includes a DC drive unit 410, a DC transformer T401, a DC rectifying and smoothing unit 420, and a DC voltage detection unit 430. The DC output unit 400 generates and outputs a DC voltage Vdc based on a DC drive signal obtained from the control unit 200. The DC drive signal is a control signal for adjusting the average value Vave of the development voltage (Vac+Vdc) finally output from the development high voltage generation unit 100 to a predetermined target value. The average value Vave of the development voltage (Vac+Vdc) is ideally the same as the target value of the DC voltage Vdc.

[0021] The DC driver 410 is composed of a transistor Q411, which is a FET (Field Effect Transistor), and capacitors C411 and C412. The transistor Q411 is an Nch-FET. The DC driver 410 generates a potential difference between both ends of the primary winding of the DC transformer T401 based on a DC drive signal acquired from the control unit 200. A voltage of +24 [V] is applied to one end of the primary winding of the DC transformer T401, and a ground potential or a voltage according to the amount of charge of the capacitor C411 is applied to the other end of the primary winding. The DC drive signal is a clock signal. The control unit 200 can change the ON width of the DC drive signal to change the potential difference (voltage applied to the primary winding) generated between the primary windings of the DC transformer T401. In other words, the voltage value of the DC voltage Vdc is adjusted by adjusting the ON width of the DC drive signal.

[0022] In the DC transformer T401, one end of the secondary winding is grounded, and an AC voltage that is the amplified AC voltage generated in the primary winding is generated in the other end of the secondary winding. The AC voltage generated in the other end of the secondary winding is input to the DC rectifying and smoothing unit 420.

[0023] The DC rectifying and smoothing unit 420 is composed of a high-voltage diode D421, a high-voltage capacitor C421, and a resistor R421. The DC rectifying and smoothing unit 420 rectifies and smoothes the negative voltage peak of the AC voltage generated on the high-voltage side (the other end) of the secondary winding of the DC transformer T401 using the diode D421 and the capacitor C421, and generates and outputs a DC voltage Vc. The diode D421 has a cathode connected to the secondary winding of the DC transformer T401 and an anode connected to the resistor R421 and the capacitor C304. The resistor R421 is provided for the purpose of separating the DC output unit 400 from the AC output unit 300 so that the AC current flowing through the AC output unit 300 does not flow into the DC output unit 400.

[0024] The DC voltage detection unit 430 is composed of resistors R431 to R434 and a capacitor C431. The DC voltage detection unit 430 converts the average voltage value Vave of the development voltage (Vac+Vdc), which is a high voltage, to a voltage level that can be input to the control unit 200. The resistors R431, R432, and R433 convert the DC voltage Vdc to a low voltage level. The resistor R434 and the capacitor C431 form a filter for removing high frequency components superimposed on the DC voltage detection signal.

[0025] The control unit 200 acquires a DC voltage detection signal from the DC voltage detection unit 430 at a predetermined cycle. The control unit 200 determines the ON width of the DC drive signal by PID calculation based on the difference between the acquired DC voltage detection signal and the target value of the DC voltage Vdc set by the controller 500. The control unit 200 supplies the DC drive signal with the ON width determined to the DC drive unit 410. As a result, the control unit 200 performs feedback control so that the DC voltage Vdc becomes the target value.

[0026] The AC output unit 300 has an AC transformer T301, transistors Q301-Q306, resistors R301, R302, capacitors C301-C304, and a diode D301. The AC output unit 300 outputs a developing voltage (Vac+Vdc) generated by superimposing an AC voltage Vac generated by the AC transformer T301 on a DC voltage Vdc output from the DC output unit 400. The output developing voltage (Vac+Vdc) is supplied to the developing unit 4a.

[0027] A voltage of +24 [V] is applied to each of the collector terminals of transistors Q305 and Q306. The base terminal of transistor Q305 receives an analog Vp(+) setting signal from control unit 200. The base terminal of transistor Q306 receives an analog Vp(-) setting signal from control unit 200. Transistors Q305 and Q306 are configured as emitter followers. The Vp(+) setting signal is a signal for setting the positive voltage amplitude of AC voltage Vac. The Vp(-) setting signal is a signal for setting the negative voltage amplitude of AC voltage Vac.

[0028] The voltage Va at the emitter terminal of transistor Q305 is a voltage value that is lower than the Vp(+) setting signal by the base-emitter voltage of transistor Q305. The voltage Vb at the emitter terminal of transistor Q306 is a voltage value that is lower than the Vp(-) setting signal by the base-emitter voltage of transistor Q306. In this embodiment, the Vp(+) setting signal and the Vp(-) setting signal are set so that the voltage Va is 5 [V] and the voltage Vb is 20 [V]. To stabilize the voltages Va and Vb, capacitors C301 and C302 are connected to the emitter terminals of each.

[0029] The transistors Q301-Q304 are FETs. The transistors Q301-Q304 are switching elements that function as electronic switches constituting a so-called H-bridge circuit, with the primary winding of the AC transformer T301 and the capacitor C303 as loads. A drive signal is input from the control unit 200 to the gate terminals of the transistors Q301-Q304. The on state (conducting state) and off state (cutoff state) of the transistors Q301-Q304 are each controlled based on the drive signal. The capacitor C303 is connected to point B, which is one end of the primary winding of the AC transformer T301, and has the function of absorbing imbalance between the positive and negative voltages of the AC voltage.

[0030] The transistor Q301 functions as a first switching element for setting the voltage applied to point A, which is the connection point with the transistor Q302, to voltage Va. The transistor Q302 functions as a second switching element for setting point A to ground potential. In this embodiment, the transistors Q301 and Q302 are not turned on at the same time. Therefore, the potential at point A becomes voltage Va or ground potential, and the potential at one end of the primary winding of the AC transformer T301 becomes voltage Va or ground potential.

[0031] The transistor Q303 functions as a third switching element for setting the voltage at point C, which is the other end of the capacitor C303 connected to point B, to voltage Vb. The transistor Q304 functions as a fourth switching element for setting the voltage at point C to ground potential. In this embodiment, the transistors Q303 and Q304 are never on at the same time. Therefore, the potential at point C is voltage Vb or ground potential.

[0032] A voltage corresponding to the potential difference between points A and B is applied to the primary winding of the AC transformer T301. The voltage applied to the primary winding of the AC transformer T301 is determined by the drive signals input to the transistors Q301 to Q304. The secondary winding of the AC transformer T301 generates an AC voltage Vac corresponding to the voltage applied to the primary winding. In addition, a voltage Vdc is applied to one end of the secondary winding of the AC transformer T301 from the DC output unit 400. Therefore, the voltage output from the other end of the secondary winding of the AC transformer T301 is a voltage in which the DC voltage Vdc is superimposed on the AC voltage Vac.

[0033] Fig. 3 is an explanatory diagram of the developing voltage (Vac+Vdc) output from the developing high voltage generating unit 100. In Fig. 3, only the configuration of the AC transformer T301, resistors R301 and R302, and diode D301 is shown. The developing voltage (Vac+Vdc) is applied to a capacitive load. In Fig. 2, the capacitive load is the developer 4a. Resistors R301 and R302 are damping resistors for shaping the waveform of the AC voltage Vac. A diode D301 is connected in parallel to the resistor R301. The cathode of the diode D301 is connected to the secondary winding of the AC transformer T301, and the anode is connected to the junction between the resistors R301 and R302. Therefore, when the voltage on the secondary winding side of the AC transformer T301 is higher than the junction between the resistors R301 and R302, a current flows through the resistors R301 and R302, but no current flows through the diode D301. When the voltage on the secondary winding side of the AC transformer T301 is lower than the junction between the resistors R301 and R302, a current flows through the diode D301 and the resistor R302, but no current flows through the resistor R301.

[0034] In this configuration, the resistance value of the damping resistor when the developing voltage (Vac+Vdc) is a positive voltage output is the sum of the resistance values ​​of resistors R301 and R302. The resistance value of the damping resistor when the developing voltage (Vac+Vdc) is a negative voltage output is the resistance value of resistor R302 excluding resistor R301 connected in parallel with diode D301. Therefore, it is possible to independently adjust the rising waveforms of the positive and negative voltages of the AC voltage Vac.

[0035] Fig. 4 is an explanatory diagram of a voltage waveform in the configuration of Fig. 3. The voltage Vx generated across the secondary side of the AC transformer T301 is represented by a dotted line, and its average value is the voltage Vdc (Vx average value). The voltage Vy at the output end of the AC output unit 300 is the voltage Vx across both ends with high frequency components removed by the damping resistor and the load capacitance (solid line).

[0036] At this time, the damping resistance value when a positive voltage is output is different from the damping resistance value when a negative voltage is output, so the positive voltage waveform area and the negative voltage waveform area of ​​the voltage Vy are different. Therefore, the difference between the positive voltage waveform area and the negative voltage waveform area of ​​the voltage Vy is the deviation amount from the average value of the voltage Vx. In this embodiment, since the DC voltage Vdc is applied to one end of the secondary winding of the AC transformer T301, the average value of the voltage Vx across both ends is the voltage value of the DC voltage Vdc. In other words, the difference between the positive voltage waveform area and the negative voltage waveform area of ​​the voltage Vy is the deviation amount from the DC voltage Vdc.

[0037] 5 is an explanatory diagram of the voltage waveforms of the various parts of the AC output section 300 of the development high voltage generation section 100. Note that the DC output section 400 outputs the DC voltage Vdc before the AC output section 300 outputs the AC voltage Vac.

[0038] Before outputting the development voltage, the control unit 200 sets the transistors Q301 and Q303 to the ON state, and sets the transistors Q302 and Q304 to the OFF state. After that, during the period to, the control unit 200 outputs the Vp(+) setting signal and the Vp(-) setting signal. This generates the voltages Va and Vb of predetermined voltage values. In this embodiment, the control unit 200 outputs the Vp(+) setting signal and the Vp(-) setting signal such that the voltage value of the voltage Vb is 20 [V] and the voltage value of the voltage Va is 5 [V].

[0039] At this time, since both transistors Q301 and Q303 are on, a current flows between the emitter terminals of transistors Q305 and Q306. This charges capacitor C303, and the potential difference across capacitor C303 eventually stabilizes at 15V (=Vb-Va). In this embodiment, the period t0 is 100 milliseconds.

[0040] Thereafter, the on and off states of transistors Q301-Q304 are switched, and AC voltage Vac is output from AC transformer T301. First, during period ta, transistor Q301 transitions from on to off, and transistor Q302 transitions from off to on. During this period, the potential at point A is the ground potential, and the potential at point C is voltage Vb (=20 V).

[0041] The capacitor C303 is charged so that the potential difference between both ends is 15 [V], so the voltage at point B is 5 [V]. After the voltage stabilizes and no current flows through the capacitor C303, the potential difference between BC is 5 [V]. At this time, a voltage of +5 [V] (when point B is the positive direction) is generated between AB, which are both ends of the primary winding of the AC transformer T301. As a result, a positive voltage of +200 [V] is generated on the secondary side of the AC transformer T301. An AC current Vac flows through the developer 4a, which is a capacitive load, and a potential difference is generated between the resistors R301 and R302. The generation of voltage across the resistors R301 and R302 at the rise of the positive voltage makes it possible to output the developing voltage without overshooting the positive voltage on the secondary side of the AC transformer T301.

[0042] During period tb, transistor Q302 transitions from on to off, and transistor Q301 transitions from off to on. After that, transistor Q303 transitions from on to off, and transistor Q304 transitions from on to on. During period tb, point C is at ground potential, and the voltage across capacitor C303 is 15V, so the potential at point B is -15V. Since voltage Va is 5V at point A, a voltage of -20V is generated between A and B, which are the two ends of the primary winding of AC transformer T301. This generates a negative voltage of -800V on the secondary side of AC transformer T301.

[0043] Also, at the moment when the states of transistors Q301-Q304 transition, an AC current flows through developer 4a, which is a capacitive load, causing a potential difference to occur across resistors R301 and R302. However, unlike period ta, during period tb, the voltage generated across resistor R302 exceeds the forward voltage of diode D301, so the current flows through diode D301 instead of resistor R301. Because diode D301 reduces the voltage generated across resistor R301, it becomes possible to output a developing voltage without causing excessive sluggishness in the voltage rise during negative voltage output.

[0044] During period tc, transistor Q301 transitions from on to off, and transistor Q302 transitions from off to on. After that, transistor Q304 transitions from on to off, and transistor Q303 transitions on. The potential at point A becomes ground potential, and the potential at point C becomes voltage Vb (=20V). Both ends of capacitor C303 are charged at 15V, so the voltage at point B becomes 5V. In other words, the state during period tc is the same as that during period ta.

[0045] Therefore, a voltage of +5 [V] is generated between A and B, which are both ends of the primary winding of the AC transformer T301, and a positive voltage of +200 [V] is generated on the secondary side. Thereafter, while the AC output unit 300 outputs an AC voltage, the operations of the above-mentioned periods tb and tc are alternately repeated in the AC output unit 300.

[0046] As described above, a diode (diode D301) is connected in parallel to a part of the damping resistors (resistors R301 and R302) connected in series to the secondary side of the AC transformer T301. With this configuration, it is possible to adjust the developing voltage (Vac+Vdc) so that it has a gradual rise shape with suppressed overshoot when a positive voltage is output, and a rapid rise shape when a negative voltage is output.

[0047] 6 is an explanatory diagram of the output operation of the DC voltage Vdc and the developing voltage (Vac+Vdc). In the period to, a negative DC voltage Vdc is superimposed on the developing voltage. In the period to, the DC voltage Vdc output from the DC output unit 400 and the developing voltage have the same voltage value. The period to indicates the period from when the superimposition of the DC voltage on the developing voltage starts to when the superimposition of the AC voltage starts.

[0048] In period t1, an AC voltage Vac is superimposed on the developing voltage in addition to the DC voltage Vdc. Period t1 indicates the period from when the superimposition of the AC high voltage Vac on the developing voltage begins to occur until the leading edge of the electrostatic latent image is developed. As described above, application of the AC voltage Vac causes the average value Vave of the developing voltage to deviate from the DC voltage Vdc (Vave=Vdc+Voffset). Voffset is the amount of deviation of the average value Vave from the DC voltage Vdc.

[0049] However, the control unit 200 adjusts the average value Vave of the developing voltage so that the DC voltage Vdc is equal to the average value Vave of the developing voltage, based on the average value Vave of the developing voltage detected by the DC output unit 400. In other words, the voltage output from the DC output unit 400 is adjusted to a voltage (Vdc-Voffset) obtained by subtracting Voffset from the DC voltage Vdc. As a result, the average value Vave of the developing voltage becomes equal to the DC voltage Vdc by offsetting the DC voltage output from the DC output unit 400 in the opposite direction to compensate for the offset caused by the superposition of the AC voltage Vac.

[0050] As described above, in the development high voltage generating unit 100 of this embodiment, a plurality of resistors that become a damping resistor are connected in series to one end of the secondary winding of the AC transformer T301, and a diode D301 is connected in parallel to a part of the damping resistor (resistor R301). The cathode of the diode D301 is connected to one end of the secondary winding, and the anode is connected between the resistors. Therefore, when the development voltage (Vac+Vad) (AC voltage (Vac)) is output as a positive voltage, the sum of the resistance values ​​of the plurality of resistors becomes the resistance value of the damping resistor. When the development voltage (Vac+Vad) (AC voltage (Vac)) is output as a negative voltage, the sum of the resistance values ​​of the resistors excluding some of the resistors becomes the resistance value of the damping resistor. In this configuration, it is possible to set the rising waveforms of the AC voltage Vac independently when the positive voltage is output and when the negative voltage is output.

[0051] In addition, it is possible to adjust the average value Vave of the developing voltage (Vac+Vdc) obtained by superimposing the DC voltage Vdc and the AC voltage Vac to a target value and output it. Note that although the waveform of the AC voltage Vac in this embodiment is a continuous square wave, the same effect can be obtained even if the waveform is a combination of a square wave and an intermittent operation. Note that the number of resistive elements serving as damping resistances may be two or more. The number of damping resistances to which diodes are connected in parallel may be one or more.

[0052] The developing high voltage generating section 100 configured as above may be a power supply device that supplies voltage to other components in the image forming apparatus 1000. Such components operate using a voltage obtained by superimposing an AC voltage on a DC voltage. For example, the power supply device of this embodiment can be used to generate a charging voltage when the charging rollers 2a to 2d charge the photosensitive drums 1a to 1d. Furthermore, the power supply device of this embodiment can be used not only for the image forming apparatus 1000 but also for devices that operate using a voltage obtained by superimposing an AC voltage on a DC voltage.

Claims

1. A DC voltage generating means for generating a DC voltage; an AC voltage generating means for generating an AC voltage and generating an output voltage obtained by superimposing the DC voltage and the AC voltage; a control means for causing the DC voltage generating means to generate the DC voltage of a predetermined voltage value and for causing the AC voltage generating means to generate an AC voltage of a predetermined voltage value, the AC voltage generating means includes a plurality of resistors serving as damping resistors for the output voltage, and a diode connected in parallel to some of the plurality of resistors, and is configured such that a current flows through the plurality of resistors when the AC voltage is a positive voltage output, and a current does not flow through the some of the resistors when the AC voltage is a negative voltage output, the DC voltage generating means has a voltage detecting means for detecting an average value of the output voltage, The control means transmits a control signal to the DC voltage generating means to adjust a voltage value of the DC voltage based on the average value detected by the voltage detecting means. power supply.

2. The control means transmits the control signal to the DC voltage generating means so that the average value becomes a target value of the DC voltage.

2. The power supply device according to claim 1.

3. the AC voltage generating means has a transformer which generates an AC voltage in a secondary winding corresponding to a voltage applied to a primary winding, the DC voltage is applied to one end of the secondary winding, and the damping resistor is connected to the other end of the secondary winding.

2. The power supply device according to claim 1.

4. the damping resistor includes a first resistor and a second resistor; the diode has a cathode connected to the other end of the secondary winding and an anode connected to a node between the first resistor and the second resistor, and is connected in parallel to the first resistor; When the AC voltage is a positive voltage output, a sum of the resistance values ​​of the first resistor and the second resistor is set as a resistance value of the damping resistor, and when the AC voltage is a negative voltage output, a resistance value of the second resistor is set as a resistance value of the damping resistor.

4. The power supply device according to claim 3.

5. the DC voltage generating means includes a transformer that generates, in a secondary winding, an AC voltage corresponding to a voltage applied to a primary winding, and a rectifying and smoothing means that rectifies and smoothes the AC voltage generated in the secondary winding to generate the DC voltage, 2. The power supply device according to claim 1.

6. The control means adjusts the ON width of the control signal to change the voltage applied to the primary winding of the transformer, thereby adjusting the DC voltage.

6. The power supply device according to claim 5.

7. A power supply device according to any one of claims 1 to 6, and a component that operates by the output voltage output from the power supply device to form an image. Image forming device.

8. A photoconductor; A charging means for uniformly charging the photoconductor; an exposure means for exposing the uniformly charged photoconductor to light to form an electrostatic latent image; a developing unit that develops the electrostatic latent image by applying the output voltage to the developing unit, 8. The image forming apparatus according to claim 7.

9. A photoconductor; a charging means for uniformly charging the photoconductor by applying the output voltage; an exposure means for exposing the uniformly charged photoconductor to light to form an electrostatic latent image; and a developing means for developing the electrostatic latent image.

8. The image forming apparatus according to claim 7.

Images