JP2015204675A - Power-supply unit, image forming apparatus, electrical equipment, and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of an output voltage of a power-supply unit.SOLUTION: A control signal generation circuit 505 generates a control signal on the basis of a pulse signal that repeats a high level and a low level. An output control circuit 506 and a high voltage generation circuit 507 generate an output voltage Vout in accordance with the control signal. A detection circuit 508 detects the output voltage generated by the high voltage generation circuit 507 and outputs a detection signal. A buffer 201 converts a high level voltage among voltage levels of input pulse signals into a level of a reference voltage 3.3 Vref supplied to the detection circuit 508 and outputs the voltage of the converted level to the control signal generation circuit 505. Consequently, even when a reference voltage from a power source 3.3 Vd and the reference voltage from the power source 3.3 Vref are varied reversely, influences upon the output voltage Vout are reduced.

Description

  The present invention relates to a power supply device, an image forming apparatus, an electrical apparatus, and a control method.

  The electrophotographic image forming apparatus includes a high-voltage power source that supplies a high voltage to the process unit. Patent Document 1 describes a high-voltage circuit that applies a high voltage to a secondary transfer roller.

JP-A-2005-70083

  A high-voltage power supply that outputs a high voltage generates a charging voltage to be applied to the charging roller, generates a developing voltage to be applied to the developing sleeve, and generates a primary transfer voltage to be applied to the primary transfer roller. If these voltages cannot be generated stably, the density of the toner image may be uneven. In particular, when the reference voltages supplied from a plurality of reference power sources provided inside the high-voltage power supply vary from one another, the output voltage output from the high-voltage power supply also varies. Therefore, a circuit configuration that makes it difficult for variations in the reference voltage to affect the output voltage is required. Accordingly, an object of the present invention is to improve the accuracy of the output voltage of the power supply device.

The present invention is, for example,
A signal generation circuit that generates a control signal based on a pulse signal that repeats a high level and a low level;
A voltage generation circuit for generating an output voltage according to the control signal;
A detection circuit that detects an output voltage generated by the voltage generation circuit and outputs a detection signal;
A power supply apparatus comprising: a voltage conversion circuit that converts a high level of a voltage level of an input pulse signal to a reference voltage level supplied to the detection circuit and outputs the reference voltage to the signal generation circuit. provide.

  According to the present invention, it is possible to improve the accuracy of the output voltage of the power supply device.

1 is a block diagram of a control board of a high voltage power supply and an image forming apparatus according to a first embodiment of the present invention. Block diagram of control board of conventional high voltage power supply and image forming apparatus Configuration diagram of detection circuit Diagram showing deviation from high voltage output target value Schematic configuration diagram of copier The figure which shows an example of a buffer circuit

  FIG. 1 shows a high-voltage power supply 200 and a control board 500 of the image forming apparatus according to the embodiment. FIG. 2 shows a high voltage power source 504 and a control board 500 of the image forming apparatus of a comparative example. Here, the same reference numerals are assigned to the common parts to simplify the description. As can be seen by comparing FIG. 1 and FIG. 2, in the comparative example, the PWM pulse input to the signal conversion circuit 505 is generated based on the logic power supply 3.3Vd. The reference power supply 3.3Vref and the logic power supply 3.3Vd of the detection circuit 508 that detects the output voltage Vout are different power supplies. On the other hand, the PWM pulse of this embodiment is input to the signal conversion circuit 505 via the voltage conversion circuit. The voltage conversion circuit is a circuit that converts the high level of the PWM pulse generated based on the reference voltage of the logic power supply 3.3Vd so as to match the reference voltage of the reference power supply 3.3Vref. An example of this voltage conversion circuit is a buffer 201. The buffer 201 is a buffer circuit that operates by being supplied with a reference voltage from a reference power supply 3.3 Vref. In addition, the detection circuit 508 and the buffer 201 are connected to a common reference power supply 3.3 Vref. This common power supply makes it easy to match the high level of the PWM pulse to the reference voltage of the reference power supply 3.3 Vref, and improves the accuracy of the output voltage Vout of the high-voltage power supply.

  As shown in FIG. 1, the control board 500 includes a pulse generation circuit 501 that generates PWM pulses and a CPU 502 that controls the image forming apparatus. The high-voltage power supply 200 includes a buffer 201, a signal conversion circuit 505 that converts a PWM pulse into a DC signal, an output control circuit 506 that performs feedback control so that the output voltage Vout becomes a target value, a high-voltage generation circuit 507 that generates the output voltage Vout, A detection circuit 508 that detects the output voltage Vout is included. In this example, the output voltage Vout is applied to the primary charging roller 102 that uniformly charges the photosensitive drum 101. However, the high-voltage power supply 200 may be employed as a power supply device that generates a development voltage, a primary transfer voltage, a secondary transfer voltage, and the like.

  The PWM pulse output from the pulse generation circuit 501 is a rectangular wave signal having a constant frequency (period) and variable duty. The duty of the PWM pulse is changed according to the target value of the output voltage Vout specified by the CPU 502. The CPU 502 stores PWM duty setting data determined in advance for each target value of the output voltage Vout in a memory. The CPU 502 reads out setting data corresponding to the environmental temperature and environmental humidity and sets them in the pulse generation circuit 501. The pulse generation circuit 501 adjusts the duty of the PWM pulse according to the received setting data. The pulse generation circuit 501 also generates a pulse signal CLK for driving the transformer T51 and outputs the pulse signal CLK to the high voltage generation circuit 507. The pulse signal CLK is a rectangular wave signal with a constant frequency and duty.

  The pulse generation circuit 501 generates a PWM pulse based on a reference voltage supplied from a logic power supply 3.3 Vd that is a voltage source. For example, the high level of the PWM pulse is 3.3V and the low level is 0V. That is, the high level of the PWM pulse matches the reference voltage supplied from the logic power supply 3.3Vd. If the reference voltage supplied from the logic power supply 3.3Vd varies, the high level of the PWM pulse also varies accordingly.

  In this embodiment, the PWM pulse output from the pulse generation circuit 501 is input to the buffer 201. The buffer 201 is a circuit for converting the voltage level, and converts the high level of the input PWM pulse into a voltage level proportional to the reference voltage supplied from the reference power supply 3.3 Vref and outputs the voltage level. As a result, the high level of the PWM pulse output from the buffer 201 becomes a voltage level dependent on the reference power supply 3.3Vref without depending on the logic power supply 3.3Vd. The output from the buffer 201 is input to the signal conversion circuit 505. The signal conversion circuit 505 includes a resistor R51 and a capacitor C51, and converts the PWM pulse into a DC control signal Vcont. The control signal Vcont is input to the negative input terminal of the operational amplifier OP51 of the output control circuit 506.

The buffer 201 operates with the reference voltage supplied from the reference power supply 3.3Vref. The signal level of the control signal Vcont is expressed by the following equation.
Vcont = 3.3V (voltage value of the reference power supply 3.3Vref) × PWM duty For example, if the duty of the PWM pulse is 50%, Vcont is 1.65V.

  The detection signal Vsns generated by the detection circuit 508 is input to the + input terminal of the operational amplifier OP51. The detection circuit 508 divides the output voltage Vout to generate a detection signal Vsns. The detection circuit 508 includes voltage dividing resistors R52, R53, and R54 and a reference power supply 3.3Vref. The voltage conversion circuit 512 generates the reference power supply 3.3Vref by converting the voltage of 24V generated by the power supply 24V.

  From the output terminal of the operational amplifier OP51, an output signal at a level such that the detection signal Vsns and the control signal Vcont are at the same level is transmitted to the base of the transistor Q51. The transistor Q51 outputs a voltage corresponding to the output signal of the operational amplifier OP51. A capacitor C52 is inserted between the output terminal and the + input terminal of the operational amplifier OP51. The collector of the transistor Q51 is connected to the power supply 24V. The emitter of the transistor Q51 is grounded via the capacitor C53. Further, the emitter of the transistor Q51 is connected to one end of the primary side winding of the transformer T51 of the high voltage generation circuit 507. The other end of the primary side winding of the transformer T51 is connected to the drain of the FET Q52. The drain of the FET Q52 is grounded via the capacitor C55.

  The pulse signal CLK supplied from the pulse generation circuit 501 is input to the gate of the FET Q52. The source of the FET Q52 is grounded. The FET Q52 performs a switching operation by the pulse signal CLK to drive the transistor Q1, thereby converting a DC voltage into an AC voltage on the primary side of the transformer T51. The transformer T51 boosts the AC voltage applied to the primary winding and outputs it to the secondary winding. The high voltage output to the secondary winding is rectified by the rectifier diode D51 and smoothed by the smoothing capacitor C54. As a result, a DC output voltage Vout is generated. Note that one end of the secondary winding is connected to the output terminal of the high-voltage power supply 200 via a rectifier diode D51. The smoothing capacitor C54 is inserted between one end and the other end of the secondary winding. The other end of the secondary winding is grounded. Thus, the high voltage power supply 200 maintains the output voltage Vout constant by controlling the output signal level of the operational amplifier OP51 so that the detection signal Vsns and the control signal Vcont are at the same level.

<Improvement of output accuracy by buffer 201>
Next, it will be described that the output accuracy of the high-voltage power supply 200 of this embodiment is improved as compared with the high-voltage power supply 504 of the comparative example. As shown in FIG. 2, in the control signal generation circuit 503 of the comparative example, the buffer 201 is omitted from the control signal generation circuit 202 of the embodiment.

Details of the detection circuit 508 will be described with reference to FIG. Here, the resistance value of the resistor R52 is 10 MΩ. The resistance value of the resistor R53 is set to 220 kΩ. The resistance value of the resistor R54 is 30 kΩ. In this detection circuit 508, the output voltage Vout can represent the resistors R52, R53, R54 and the detection signal Vsns by the following expression.
Vout = (Vsns * (30 kΩ * 220 kΩ + 10 MΩ * 220 kΩ + 10 MΩ * 30 kΩ) −3.3 Vref * 10 MΩ * 220 kΩ) / (30 kΩ * 220 kΩ) Equation 1
Since the detection signal Vsns is at the same level as the control signal Vcont, Equation 1 can be expressed as follows.
Vout = (Vcont * (30 kΩ * 220 kΩ + 10 MΩ * 220 kΩ + 10 MΩ * 30 kΩ) −3.3 Vref * 10 MΩ * 220 kΩ) / (30 kΩ * 220 kΩ) Equation 2
In the high voltage power source 200, a buffer 201 is provided between the pulse generation circuit 501 and the signal conversion circuit 505. further. The buffer 201 and the detection circuit 508 are connected to a reference power supply 3.3 Vref which is a common power supply. That is, the power source used to generate the control signal Vcont and the detection voltage Vsns is the same.

  In FIG. 4, the horizontal axis represents the control voltage Vcont, and the vertical axis represents the deviation ΔV of the output voltage Vout from the target value. In FIG. 4, the broken line i indicates the output accuracy of the high-voltage power supply 504 of the comparative example. Here, the target value is set to −700 V and the output accuracy is compared. The logic power supply 3.3Vd is shifted + 1% from 3.3V, and the reference power supply 3.3Vref is shifted −1% from 3.3V. As a result, the output voltage Vout of the high voltage power supply 504 of the comparative example is about −685V, which is deviated by about + 15V from the target value. The broken line ii shows the output accuracy when the logic power supply 3.3Vd is shifted by −1% from 3.3V and the reference power supply 3.3Vref is shifted by + 1% from 3.3V in the high voltage power supply 504 of the comparative example. The output voltage Vout is about −715V, which is shifted from the target value by about −15V.

  A solid line iii indicates the output accuracy of the high-voltage power supply 200 of this embodiment. Here, it is assumed that the reference power supply 3.3Vref is shifted by + 1% from 3.3V. The output voltage Vout is about −707V, which is a deviation of about −7V from the target value. The solid line iv indicates the output accuracy when the reference power supply 3.3Vref is shifted by −1% from 3.3V in the high-voltage power supply 200 of the present embodiment. The output voltage Vout is about −693V, which is a deviation of about + 7V from the target value.

  As described above, in this embodiment, since the reference power supply of the control signal Vcont and the reference power supply of the detection circuit are the same, even if the output voltage of the reference power supply varies, the control signal Vcont and the detection voltage Vsns vary in the same direction. For this reason, it is the worst case (when the reference power supply varies by 3.3 V ± 1%), and the output accuracy of this embodiment is improved compared to the comparative example.

<Example of image forming apparatus>
FIG. 5 shows an example of the image forming apparatus 100 that can employ the control board 500 and the high-voltage power supply 200. The image forming apparatus 100 can be commercialized as, for example, a facsimile machine, a copying machine, or a laser beam printer. The image forming apparatus 100 includes four image forming units and forms a multicolor image. The configuration of the four image forming units is common except that the toner colors are different. The photosensitive drum 101 rotates counterclockwise, and the surface is uniformly charged by the primary charging roller 102. The primary charging roller 102 is an example of a charging unit that charges the photosensitive member. The laser unit 103 irradiates the uniformly charged surface of the photosensitive drum 101 with laser light to form an electrostatic latent image. The laser unit 103 is an example of an exposure unit that exposes a charged photoreceptor to form an electrostatic latent image. The developing sleeve 104 develops the electrostatic latent image with toner and forms a toner image. The developing sleeve 104 is an example of a developing unit that develops an electrostatic latent image with toner to form a toner image. The primary transfer roller 105 is in contact with the intermediate transfer belt 106 and primarily transfers the toner image from the photosensitive drum 101 to the surface of the intermediate transfer belt 106. The primary transfer roller 105 is an example of a transfer unit that transfers a toner image to an intermediate transfer member. The yellow, magenta, cyan, and black toner images are sequentially transferred onto the surface of the intermediate transfer belt 106 in order to form a multicolor image. When the multicolor image carried on the intermediate transfer belt 106 passes through the secondary transfer inner roller 107 and the secondary transfer outer roller 108, it is secondarily transferred to the paper 113 fed from the paper cassette 110. The secondary transfer inner roller 107 and the secondary transfer outer roller 108 are examples of a transfer unit that transfers a toner image to a sheet. The sheet 113 is conveyed to the fixing device 111 and is pressurized and heated to fix the toner image on the surface of the sheet 113. The fixing device 111 is an example of a fixing unit that fixes a toner image on a sheet.

  The AC voltage supplied from the commercial power supply 114 is supplied to the AC / DC power supply 116 via the main switch 115. That is, when the main switch 115 is turned on, an alternating voltage is supplied to the AC / DC power supply 116. The AC / DC power supply 116 is a power supply for operating the image forming apparatus 100, and converts the AC voltage supplied from the commercial power supply 114 into several types of DC voltages. The AC / DC power supply 116 has a plurality of high-voltage power supplies 200. The plurality of high-voltage power supplies 200 supply voltages to the primary charging roller 102, the developing sleeve 104, the primary transfer roller 105, and the secondary transfer outer roller 108, respectively. FIG. 1 merely shows a high-voltage power supply that supplies a charging voltage to the primary charging roller 102 as an example. By adopting the above-described high-voltage power supply 200, the output accuracy of the output voltage Vout is improved, so that the density of the toner image is also stabilized. For example, since the charging voltage is accurately controlled to the target value, the density of the toner image will be maintained at the target density.

  In the embodiment, the power supply apparatus that mainly supplies the charging voltage to the charging roller has been described. However, the technical idea of the present invention can also be applied to a power supply device that supplies a developing voltage to a developing device and a power supply device that supplies a transfer voltage to a transfer roller. Furthermore, the present invention may be applied not only to an image forming apparatus but also to a power supply apparatus that supplies a high voltage to electrical equipment and machines. In the present embodiment, the constant voltage control type power supply apparatus that controls the output voltage to be constant has been described. However, the present invention can also be applied to a constant current control type power supply apparatus that controls the output current to be constant.

<Example of buffer circuit>
FIG. 6 is a circuit diagram showing an example of the buffer 201. The buffer 201 is composed of a CMOS logic circuit. However, the circuit configuration of the buffer 201 is only an example, and any circuit that can convert the high level of the input PWM pulse into the power supply voltage level of the detection circuit 508 is sufficient.

<Summary>
In the above embodiment, the control signal generation circuit 202 has been described as an example of a signal generation circuit that generates a control signal based on a pulse signal that repeats a high level and a low level. Further, the output control circuit 506 and the high voltage generation circuit 507 have been described as examples of the voltage generation circuit that generates the output voltage according to the control signal. Further, the detection circuit 508 has been described as an example of a detection circuit that detects the output voltage generated by the high voltage generation circuit 507 and outputs a detection signal. In particular, the present embodiment uses a voltage conversion circuit that converts the high level of the voltage level of the input pulse signal to the level of the reference voltage supplied to the detection circuit and outputs it to the signal generation circuit. Therefore, even if the reference voltage from the power supply 3.3Vd and the reference voltage from the power supply 3.3Vref vary in opposite directions, the influence on the output voltage is reduced.

  The buffer 201 has been described as an example of the voltage conversion circuit having such a function. As described with reference to FIG. 6, since the buffer 201 can be configured with a relatively simple circuit, it is possible to improve the accuracy of the output voltage while suppressing an increase in manufacturing cost.

  In the example, a power supply of 3.3 Vd was adopted as the first power supply. In addition, a power supply 3.3 Vref is adopted as a second power supply that supplies a reference voltage independently of the first power supply. The pulse generation circuit 501 has been described as the generation circuit that generates the pulse signal supplied to the voltage conversion circuit based on the reference voltage supplied from the first power supply. In particular, since the detection circuit 508 and the buffer 201 are supplied with a common reference voltage from the power supply 3.3 Vref, the high level of the input pulse signal is set to the reference voltage supplied to the detection circuit 508 from the power supply 3.3 Vref. Easier to match the level.

  The output control circuit 506 has been described as an example of a control circuit that compares the detection signal from the detection circuit 508 with the target value and controls the high voltage generation circuit 507 according to the comparison result to adjust the output voltage to the target voltage. Incidentally, this target value is specified by a control signal generated according to the duty of the pulse signal. A 24 V power supply has been described as the third power supply for supplying a voltage to the high voltage generation circuit 507. When the high voltage generation circuit 507 generates a high voltage of several hundred volts, a higher voltage before conversion is used. An example of a signal conversion circuit that converts a pulse signal input from the buffer 201 into a DC level control signal is a signal conversion circuit 505.

  As described above, the power supply device of the present invention may be mounted on an electrical device such as an image forming apparatus. In the image forming apparatus, since the supplied voltage is stabilized, it is possible to reduce density unevenness of the image. In addition, it will be possible to operate the electrical apparatus stably.

505 ... Control signal generation circuit, 506 ... Output control circuit, 507 ... High voltage generation circuit, 508 ... Detection circuit, 201 ... Buffer

Claims (9)

A signal generation circuit that generates a control signal based on a pulse signal that repeats a high level and a low level;
A voltage generation circuit for generating an output voltage according to the control signal;
A detection circuit that detects an output voltage generated by the voltage generation circuit and outputs a detection signal;
A power supply device comprising: a voltage conversion circuit that converts a high level of a voltage level of an input pulse signal into a reference voltage level supplied to the detection circuit and outputs the reference voltage to the signal generation circuit.   The power supply apparatus according to claim 1, wherein the voltage conversion circuit includes a buffer circuit. The first power supply,
A generation circuit for generating a pulse signal supplied to the voltage conversion circuit based on a reference voltage supplied from the first power source;
A second power source that is independent of the first power source and supplies a reference voltage;
The power supply apparatus according to claim 1, wherein the detection circuit and the voltage conversion circuit are supplied with a common reference voltage from the second power supply. A control circuit that adjusts the output voltage to the target voltage by comparing the detection signal from the detection circuit with the target value and controlling the voltage generation circuit according to the comparison result;
4. The power supply device according to claim 1, wherein the target value is specified by the control signal generated according to a duty of the pulse signal. 5.   5. The power supply device according to claim 1, further comprising a third power supply that supplies a voltage to the voltage generation circuit. 6.   6. The power supply according to claim 1, wherein the signal generation circuit includes a signal conversion circuit that converts the pulse signal input from the voltage conversion circuit into the control signal having a DC level. apparatus. A photoreceptor,
Charging means for charging the photoreceptor;
Exposure means for exposing the charged photoreceptor to form an electrostatic latent image;
Developing means for developing the electrostatic latent image with toner to form a toner image;
Transfer means for transferring the toner image to a sheet or an intermediate transfer member;
Fixing means for fixing the toner image to a sheet;
A power supply device for supplying a voltage to any one of the charging unit, the developing unit, and the transfer unit,
The power supply device
A signal generation circuit that generates a control signal based on a pulse signal that repeats a high level and a low level;
A voltage generation circuit for generating an output voltage according to the control signal;
A detection circuit that detects an output voltage generated by the voltage generation circuit and outputs a detection signal;
An image forming apparatus comprising: a voltage conversion circuit that converts a high level of a voltage level of an input pulse signal to a level of a reference voltage supplied to the detection circuit and outputs the reference voltage to the signal generation circuit . A signal generation circuit that generates a control signal based on a pulse signal that repeats a high level and a low level;
A voltage generation circuit for generating an output voltage according to the control signal;
A detection circuit that detects an output voltage generated by the voltage generation circuit and outputs a detection signal;
A method of controlling a power supply device comprising:
Converting the high level of the voltage level of the input pulse signal to the level of the reference voltage supplied to the detection circuit, and outputting the level to the signal generation circuit;
In the signal generation circuit, generating the control signal based on the pulse signal whose voltage level has been converted;
And a step of controlling the voltage generation circuit according to the control signal and a detection signal from the detection circuit.   An electrical apparatus that operates by being supplied with a voltage from the power supply device according to any one of claims 1 to 6.