JP6623116B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a power supply device having a current detection function for detecting an output current of a step-up transformer, and an image forming apparatus using the power supply device.

  Conventionally, as a power supply apparatus having a current detection function and an image forming apparatus using the same, for example, there is one disclosed in Patent Document 1. In this type of power supply device, the voltage of the rectifier circuit provided on the secondary side of the boosting transformer is controlled at a constant voltage, and connected to the load via an output resistor. Also, accurate current detection is performed by making the current path flowing through the load equivalent to the output current of an operational amplifier (hereinafter referred to as “op-amp”).

JP 2013-005650 A

  However, the conventional power supply apparatus and the image forming apparatus using the same have the following problems.

  Since an output resistor is provided between the secondary side rectifier circuit of the step-up transformer and the load, the component cost increases, and if there is a large amount of current flowing through the output resistor, the loss increases and wasted power. Will be consumed. Furthermore, for example, when a piezoelectric transformer that cannot take a large load current is used as a step-up transformer, if the output resistance is not provided, the output voltage decreases when the load current is excessive, and the drive frequency becomes the resonance frequency during frequency control. There were problems such as being controlled to a lower frequency.

A power supply apparatus according to the present invention is a power supply apparatus that outputs a DC high-voltage output voltage to a load, and compares the input high-voltage output instruction voltage with a divided voltage of the DC high-voltage output voltage and outputs a comparison result; A transformer driving circuit that outputs a drive voltage using the output of the comparison result; a transformer that boosts the drive voltage to generate an AC voltage; and a rectifier that rectifies the AC voltage and outputs the DC high-voltage output voltage. A voltage dividing circuit that has a plurality of voltage dividing resistors, divides the DC high-voltage output voltage and generates the divided voltage to be input to the comparison circuit, and a part of the plurality of voltage dividing resistors. A current detection resistor that is connected in series with the voltage resistor, and that flows a load current flowing from the rectifier circuit to the load, and an operational amplifier are provided.

Then, the operational amplifier has an inverting input terminal, a non-inverting input terminal, an output terminal for outputting the及beauty output voltage, the non-inverting input terminal grounded, in a state where the inverting input terminal is virtual ground The current input side of the rectifier circuit and the part of the voltage dividing resistor are connected, and the output terminal and the inverting input terminal are connected via the part of the voltage dividing resistor and the current detecting resistor. The voltage dividing circuit is connected between the output side of the DC high-voltage output voltage of the rectifier circuit and the inverting input terminal, and the load current is the output terminal of the operational amplifier, the current detection resistor, The voltage dividing resistor, the current input side of the rectifier circuit, the output side of the DC high-voltage output voltage of the rectifier circuit, and the load path, the transformer so that the comparison result becomes zero. The drive circuit is controlled The suppressing DC high output voltage in response to the load current, and, and detects the load current flowing to the load from the output terminal of the operational amplifier.

  The image forming apparatus of the present invention includes the power supply device.

  According to the power supply device and the image forming apparatus of the present invention, since the feedback potential of the DC high voltage output voltage control is changed according to the current flowing through the current detection resistor, the same as when the output resistor is mounted. A voltage drop can be obtained. Thereby, it becomes possible to make an output resistance unnecessary.

FIG. 1 is a block diagram showing a configuration of the high-voltage power supply device 60A. FIG. 2 is a schematic configuration diagram illustrating the image forming apparatus 1 according to the first exemplary embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a control circuit for controlling the operation of the image forming apparatus 1 of FIG. FIG. 4 is a circuit diagram showing a configuration example of the high-voltage power supply device 60A of FIG. FIG. 5 is a block diagram illustrating a configuration of a high-voltage power supply device 60B according to the second embodiment of the present invention. FIG. 6 is a circuit diagram showing a configuration example of the high-voltage power supply device 60B of FIG. FIG. 7 is a circuit diagram illustrating another configuration example of the high-voltage power supply device 60A according to the third embodiment of the present invention. FIG. 8 is a block diagram illustrating a configuration of a high-voltage power supply device 60C according to the fourth embodiment of the present invention. FIG. 9 is a circuit diagram showing a configuration example of the high-voltage power supply device 60C of FIG. FIG. 10 is a load characteristic diagram of the piezoelectric transformer 120C in FIG. FIG. 11 is a block diagram illustrating a configuration of a high-voltage power supply device 60D according to the fifth embodiment of the present invention. FIG. 12 is a circuit diagram showing a configuration example of the high-voltage power supply device 60D of FIG. FIG. 13 is a circuit diagram illustrating a configuration example of a high-voltage power supply device 60E according to the sixth embodiment of the present invention.

  Modes for carrying out the present invention will become apparent from the following description of the preferred embodiments when read in light of the accompanying drawings. However, the drawings are only for explanation and do not limit the scope of the present invention.

  (Configuration of Example 1)

  FIG. 2 is a schematic configuration diagram illustrating the image forming apparatus 1 according to the first exemplary embodiment of the present invention.

  The image forming apparatus 1 is, for example, a color electrophotographic direct transfer printer, and includes a housing 1a. In the upper part of the housing 1a, cartridge type developing devices 10 for four colors (for example, a black (K) developing device 10K, a yellow (Y) developing device 10Y, a magenta (M) developing device 10M, And a cyan (C) developing device 10C) are detachably mounted. The developing devices 10 of the respective colors have the same configuration except that the color of the toner as the developer to be used is different.

  Each color developing device 10 includes a toner container 11, a photosensitive drum 12 as an image carrying means, a supply roller 13 as a developer supplying means, a developing roller 14 as a developing means, a developing blade 15 as a layer forming means, and a charging means. And a cleaning blade 17 as a cleaning means.

  The toner container 11 is arranged at the upper part of the developing device 10, and below this, a supply roller 13, a developing roller 14, and a developing blade 15 are arranged. The photosensitive drum 12 is in contact with the developing roller 14. Further, a charging roller 16 and a cleaning blade 17 are in contact with the outer peripheral surface of the photosensitive drum 12.

  Near each color developing device 10 (10K, 10Y, 10M, 10C), a light emitting diode (hereinafter referred to as “LED”) head 18 (for example, a K LED head 18K, a Y LED head) as an exposure unit for each color. 18Y, M LED head 18M, and C LED head 18C) are disposed.

  Below the developing units 10K, 10Y, 10M, and 10C for four colors, a transfer unit 20 for transferring a toner image onto a sheet 27 as a printing medium is provided. The transfer unit 20 includes a tension roller 21, a drive roller 22, an endless transfer belt 23, and transfer rollers 24 for four colors (for example, a transfer roller 24K for K, a transfer roller 24Y for Y, a transfer roller 24M for M, And C transfer roller 24C). The stretching roller 21 and the driving roller 22 are arranged at a predetermined distance, and the transfer belt 23 is stretched between the stretching roller 21 and the driving roller 22. On the inner side of the upper side of the transfer belt 23, a transfer roller 24 for each color is disposed so as to face the photosensitive drum 12 for each color.

  A cleaning blade 25 for removing residual toner is in contact with the outside of the lower side of the transfer belt 23. Residual toner on the transfer belt 23 is removed by a cleaning blade 25, and the removed waste toner is accommodated in a waste toner container 26.

  A sheet cassette 28 for accommodating a plurality of stacked sheets 27 is detachably attached to the lower part of the housing 1a. On the paper discharge side of the paper cassette 28, a hopping roller 29 for taking out the paper 27 one by one is provided. The paper 27 taken out from the hopping roller 27 is transported to the downstream side of the transport path by a transport roller (not shown), and the paper is tilted by the registration roller pair 30a and 30b, and then onto the transfer belt 23 at a predetermined timing. It is supposed to be sent. A sheet detection sensor 31 for detecting the leading edge of the sheet 27 is provided between the registration roller pair 30 a and 30 b and the driving roller 22. When the leading edge of the paper 27 is detected by the paper detection sensor 31, the above timing is taken based on this detection signal.

  A fixing device 32 is provided on the downstream side of the stretching roller 21. The fixing device 32 fixes the toner image transferred onto the paper 27 by heating and pressing, and includes a heating roller 32a and a pressing roller 32, for example. The paper 27 on which the toner image has been fixed by the fixing device 32 is discharged via a conveyance guide 33 to a paper discharge tray 1b formed on the top of the housing 1a.

  FIG. 3 is a block diagram showing a configuration of a control circuit for controlling the operation of the image forming apparatus 1 of FIG.

  This control circuit has a host interface unit 40 connected to a host device such as a personal computer. The host interface unit 40 receives a print command (command) and print data from the host device, and a command / image processing unit 41 is connected to the output side. The command / image processing unit 41 performs command analysis and image processing for printing on the print command and print data received by the host interface unit 40. On the output side, the LED head interface unit 42 and the printer engine A control unit 43 is connected.

  The LED head interface unit 42 receives an output signal from the command / image processing unit 41 and controls driving of the LED heads 18 (18K, 18Y, 18M, 18C) of the respective colors. The printer engine control unit 43 controls the drive mechanism unit of the image forming apparatus 1 based on the output signal of the command / image processing unit 41.

  The printer engine control unit 43 includes an LED head interface unit 42, a hopping motor 44 that rotates the hopping roller 29, a registration motor 45 that rotates the registration roller pair 30a and 30b, and a belt motor that rotates the driving roller 22 for driving the transfer belt. 46, a fixing roller motor 47 for rotating the roller of the fixing device 32, and a drum motor 48 for rotating the photosensitive drum 24 of each color are connected. The printer engine control unit 43 further stores a fixing device heater 49 for heating the heating roller 32a, a temperature sensor (for example, thermistor) 50 for detecting the ambient temperature of the fixing device 32, a paper detection sensor 31, and data and programs. The storage means 51 and the high voltage power supply device 60 as the power supply device in the first embodiment are connected.

  The high voltage power supply device 60 has a high voltage setting signal output unit 61. The high voltage setting signal output unit 61 outputs a high voltage output instruction voltage, which is a high voltage setting signal, based on a control signal from the printer engine control unit 43, and is a microcomputer having a calculation and control function (hereinafter referred to as "microcomputer"). ) Etc. A charging bias generator 62, a developing bias generator 63, and a transfer bias generator 64 are connected to the output side of the high voltage setting signal output unit 61.

  The charging bias generation unit 62 generates a DC high voltage charging bias based on the high voltage setting signal output from the high voltage setting signal output unit 61, and develops each color developing device 10 (= 10K, 10Y, 10M,. 10C). The developing bias generator 63 generates a developing bias of DC high voltage based on the high voltage setting signal output from the high voltage setting signal output unit 61, and develops each color developing device 10 (= 10K, 10Y, 10M,. 10C). Further, the transfer bias generating unit 64 generates a DC high voltage transfer bias based on the high voltage setting signal output from the high voltage setting signal output unit 61, and the transfer rollers 24 (= 24K, 24Y, 24K) for each color as a load. 24M, 24C).

  FIG. 1 is a block diagram showing a configuration of the high-voltage power supply device 60A.

  The high-voltage power supply device 60A includes a high-voltage setting signal output unit 61 and a transfer bias generation unit 64 in the high-voltage power supply device 60 in FIG.

  The high voltage setting signal output unit 61 is constituted by a microcomputer having an arithmetic control function, and an analog voltage output port 91 that outputs a high voltage output instruction voltage V91 and an analog voltage that inputs an analog detection voltage V160 as an output voltage detection value. Input port 92 and the like. The analog voltage output port 91 has a digital / analog conversion (hereinafter referred to as “DAC”) function for converting a digital signal into an analog high voltage output instruction voltage V91. The analog voltage input port 92 has an analog / digital conversion (hereinafter referred to as “ADC”) function for converting the analog detection voltage V160 into a digital signal.

  The transfer bias generator 64 includes a detection value comparison circuit 100 for inputting the high-voltage output instruction voltage V91. The comparison circuit 100 is a circuit that compares the high-voltage output instruction voltage V91 and the divided voltage Va obtained by dividing the direct-current high-voltage output voltage Vout to obtain a comparison result, and a transformer driving circuit 110 is connected to the output side. ing. The transformer drive circuit 110 is a circuit that drives the comparison result of the comparison circuit 100 and outputs a drive voltage. A boosting transformer 120 is connected to the output side. The transformer 120 is constituted by, for example, a winding type electromagnetic transformer, and boosts the drive voltage of the transformer drive circuit 110 to output an AC voltage. On the output side, a positive rectifier circuit as a rectifier circuit is provided. 130 is connected. The rectifier circuit 130 is a circuit that rectifies the AC voltage boosted by the transformer 120 and outputs the rectified DC high-voltage output voltage Vout to the transfer roller 24 that is a load.

  A voltage dividing circuit 140 for detecting an output voltage is connected to the output side of the rectifier circuit 130. The voltage dividing circuit 140 is a circuit that divides the DC high-voltage output voltage Vout and outputs a divided voltage Va, a high-voltage dividing resistor 141, a connection point 140a that outputs the divided voltage Va, and a voltage dividing resistor. 142 and an output end connection point 140b. The connection point 140 a is connected to the input side of the comparison circuit 100. The connection point 140b is connected to the current input side of the rectifier circuit 130 and the inverting input terminal 150b of the operational amplifier 150.

  The operational amplifier 150 has a non-inverting input terminal 150a that is virtually grounded, an inverting input terminal 150b that is connected to the connection point 140b, and an output terminal 150c for outputting the output voltage Vo. The output terminal 150c and the inverting input terminal 150b are feedback-connected by a series circuit of a current detection resistor 170 and a voltage dividing resistor 142. The output terminal 150c of the operational amplifier 150 and the current detection resistor 170 are connected at a connection point 150d.

  The analog voltage input port 92 of the high voltage setting signal output unit 61 is connected to the connection point 150d through the smoothing circuit 160. The smoothing circuit 160 is a circuit that smoothes the output voltage Vo on the connection point 150d and outputs a detection voltage V160 as an output voltage detection value to the analog voltage input port 92 of the high-voltage setting signal output unit 61.

  In the transfer bias generation unit 64 of FIG. 1, only one output is illustrated among the four outputs for the four colors K, Y, M, and C. In the first embodiment, four identical circuits are juxtaposed. Is done. In this case, one high-voltage setting signal output unit 61 is provided with four sets of input / output ports (91, 92).

  FIG. 4 is a circuit diagram showing a configuration example of the high-voltage power supply device 60A of FIG.

  In the high voltage setting signal output unit 61, the analog voltage output port 91 outputs a high voltage output instruction voltage V 91 of 0 to 3.3 V in 256 steps according to the 8-bit value set inside the high voltage setting signal output unit 61. . The analog voltage input port 92 converts the input detection voltage V160 of 0 to 3.3 V into a 10-bit digital value. The high voltage setting signal output unit 61 is supplied with a DC voltage from a 3.3 V power supply 93.

  In the comparison circuit 100, an RC filter including a resistor 101 and a capacitor 102 and a capacitor 103 are provided on the input side, and an operational amplifier 104 is connected to the output side of the RC filter and capacitor 103. The operational amplifier 104 is connected to a 24V power supply 105 that supplies a power supply voltage to the operational amplifier 104. An integrating circuit including a capacitor 106 and a resistor 107 connected in series is provided between the inverting input terminal and the output terminal of the operational amplifier 104.

  The transformer drive circuit 110 includes an RC filter including an input-side resistor 111 and a capacitor 112, a resistor 113 connected to the output side of the RC filter, and a base connected to the resistor 113 via the primary side of the transformer 120. It is constituted by a self-excited oscillation circuit having a connected NPN transistor 114 and a 24 V power supply 115 for supplying a power supply voltage to the transformer driving circuit 110.

  A rectifier circuit 130 is connected to the secondary side of the transformer 120. The rectifier circuit 130 includes two diodes 131 and 132 for rectification and two capacitors 133 and 134 for smoothing. A 100 MΩ first voltage dividing resistor 141 is branchedly connected to the output side of the rectifier circuit 130. These transformer 120, rectifier circuit 130, and voltage dividing resistor 141 are integrated to form a mold transformer MT. A 33 kΩ second voltage dividing resistor 142 is connected in series to the voltage dividing resistor 141.

  The operational amplifier 150 is connected to a 24V power supply 151 that supplies a power supply voltage thereto. A filter comprising two capacitors 153 and 155 and a resistor 154 is connected to the input side of the operational amplifier 150, and a capacitor 152 constituting the filter is also connected between the filter and the output terminal 150c of the operational amplifier 150. ing. The smoothing circuit 160 connected to the output terminal 150 c of the operational amplifier 150 is configured by an RC filter including a resistor 161 and a capacitor 162.

  (Overall operation of image forming apparatus)

  The overall operation of the image forming apparatus 1 will be described with reference to the image forming apparatus 1 in FIG. 2 and the control circuit in FIG.

  In the control circuit of FIG. 3, print data in a predetermined format described in a page description language (PDL) or the like is input from an external host device (not shown) via the host interface unit 40. The input data is converted into bitmap data by the command / image processing unit 41. Under the control of the printer engine control unit 43, the fixing device heater 49 is turned on, and the heating roller 32a in the fixing device 32 is heated. When the ambient temperature of the fixing device 32 is detected by the thermistor 50 and the heating roller 32a reaches a predetermined temperature, the printing operation is started under the control of the printer engine control unit 43.

  In the image forming apparatus 1 of FIG. 2, the paper 27 accommodated in the paper cassette 28 is taken out one by one by the hopping roller 29 and conveyed in the direction of the downstream registration roller pair 30a, 30b. The sheet 27 is conveyed onto the transfer belt 23 by the registration roller pair 30a, 30b at a timing synchronized with the image forming operation by the developing devices 10 (10K, 10Y, 10M, 10C) for four colors and the transfer unit 20.

  A toner image is formed on the photosensitive drum 12 in each color developing device 10 by the electrophotographic process of the developing devices 10 (10K, 10Y, 10M, 10C) for four colors. At this time, the LED heads 18 (18K, 18Y, 18M, and 18C) of the respective colors are turned on according to the bitmap data, and are irradiated onto the photosensitive drums 12 of the respective colors.

  Under the control of the high voltage setting signal output unit 61, a DC high voltage output voltage Vout, which is a transfer bias output from the transfer bias generating unit 6, is supplied to the transfer rollers 24 (24K, 24Y, 24M, 24C) of the respective colors. The toner images developed by the developing devices 10 of the respective colors are sequentially transferred onto the paper 27 conveyed on the transfer belt 23 by the transfer rollers 24 of the respective colors. The paper 27 to which the toner image has been transferred is fixed by heating and pressurization of the fixing device 32 and then discharged to the paper discharge tray 1b via the conveyance guide 33.

  At this time, prior to the printing operation on the paper 27, the transfer belt 23 is driven in a state in which the paper 27 is not conveyed, and a DC high-voltage output voltage Vout as a transfer bias is applied to the transfer rollers 24 of each color. The flowing current value is detected. Thus, the resistance value of the transfer roller 24 for each color is calculated, and the DC high voltage output voltage Vout, which is the transfer bias depending on the resistance value and the paper type, is supplied to the printer engine control unit 43 in advance from data obtained in advance by experiments or the like. The selection is determined based on the stored table or the like.

  (Operation of high-voltage power supply)

  First, the operation of the high-voltage power supply device 60A shown in FIG. 1 will be described.

  The output current of the output terminal 150c of the operational amplifier 150 is equal to the load current flowing through the transfer roller 24 that is a load. In addition to the output current of the operational amplifier 150 flowing in the voltage dividing resistor 142, the current flowing in the voltage dividing resistor 141 is applied by the DC high voltage output voltage Vout of the positive rectifier circuit 130. The analog output voltage Vo of the operational amplifier 150 is a voltage obtained by adding a load current and a high voltage divided current to the voltage dividing resistor 142. The analog voltage input port 92 of the high voltage setting signal output unit 61 AD converts the voltage value of the output voltage Vo. The high voltage setting signal output unit 61 calculates a load current by the positive output voltage determined by the voltage set by the analog voltage output port 91 and the AD conversion.

For example, the voltage dividing resistor 141 is 100 MΩ, and the voltage dividing resistor 142 and the current detecting resistor 170 are 33 kΩ. Set the setting value of the analog voltage output port 91 to 4Dh (77 dec),
3.3 × 77/255 ≒ 1V
Is output. The comparison circuit 100 supplies the current of the comparison result to the transformer drive circuit 110 so that the divided voltage Va divided by the 100 MΩ voltage dividing resistor 141 and the 33 kΩ voltage dividing resistor 142 becomes equal to 1V. .

For example, when the load current is 0A,
(1/33000) × (100000000 × 33000) ≈3031V
Thus, the DC high voltage output voltage Vout output from the positive rectifier circuit 130 is controlled. At this time, since the current flowing through the current detection resistor 170 is 0 A, the output voltage Vo of the operational amplifier 150 is 1 V. From the detection voltage V160 input to the analog voltage input port 92, the output voltage of the analog voltage output port 91 is When a certain high voltage output instruction voltage V91 is subtracted, it becomes 0V, and it can be calculated that the current value of the load current is 0A.

Here, it is assumed that a load current of 10 μA flows through the transfer roller 24 which is a load under the same conditions. A current of 10 μA flows through the current detection resistor 170, and the potential difference between both ends of the 33 kΩ current detection resistor 170 is
33000 × 10 × 10 ⁻⁶ = 0.33V
It becomes. The potential difference between both ends of the voltage dividing resistor 142 remains 1 V, and 0.33 V of that is a potential difference caused by the load current. Therefore, the remaining 0.67 V is the DC high-voltage output output from the positive rectifier circuit 130. This is a voltage obtained by dividing the voltage Vout. Therefore,
(0.67 / 33000) × (100000000 + 33000)
≒ 2031V
Thus, the positive direct current high voltage output voltage Vout is controlled. A voltage drop of 1000 V occurs with respect to 3031 V of the DC high-voltage output voltage Vout at the time of no load.

This is because a load current of 10 μA flows when an output resistance of 100 MΩ is provided between the positive rectifier circuit 130 and the transfer roller 24 as a load, as in the prior art.
(10 × 10 ⁻⁶ ) × (100 × 10 ⁶ ) = 1000 V
This is the same drop that causes a voltage drop of. In this case, the detection voltage V160 of the analog voltage input port 92 is 1.33 V. Therefore, if the voltage 0.33 V obtained by subtracting the high-voltage output instruction voltage V91 is divided by the resistance value 33 kΩ of the current detection resistor 170, the load A current value of 10 μA can be calculated.

  It can be detected that the DC high-voltage output voltage Vout output from the positive rectifier circuit 130 is 2031 V from the current value of 10 μA with respect to 3031 V at no load. Only the current equivalent to the load current flows through the current detection resistor 170, and the combined current of the load current and the current flowing through the voltage dividing resistor 141 flows through the voltage dividing resistor 142. As a result, the positive DC high-voltage output voltage Vout drops according to the load current, and even if there is no output resistance, the DC high-voltage output voltage Vout is suppressed as in the case where the conventional output resistance exists. . In addition, the current detection resistor 160 enables both current detection and conventional detection.

  Furthermore, the detailed operation of the high-voltage power supply device 60A will be described with reference to the circuit diagram of FIG.

  The high voltage setting signal output unit 61 outputs a high voltage instruction voltage V91 from the analog voltage output port 91. Since the voltage dividing resistor 141 is 100 MΩ and the voltage dividing resistor 142 is 33 kΩ, a range of about 0 to 10,000 V can be specified in about 40 V steps.

  In the first embodiment, the voltage dividing resistors 141 and 142 are set to 100 MΩ and 33 kΩ, but it is obvious that any value can be taken.

  The high voltage instruction voltage V91 output from the analog voltage output port 91 is smoothed by an RC filter including the resistor 101 and the capacitor 102, and the rising edge is blunted and input to the non-inverting input terminal of the operational amplifier 104. The divided voltage Va divided by the 100 MΩ voltage dividing resistor 141 and the 33 kΩ voltage dividing resistor 142 is smoothed by the capacitor 103 and input to the non-inverting input terminal of the operational amplifier 104.

  The output voltage of the operational amplifier 104 is controlled by an integration circuit including the capacitor 106 and the resistor 107 so that the non-inverting input terminal voltage and the inverting input terminal voltage of the operational amplifier 104 are equal to each other with a predetermined time constant. As a result, current flows between the base and emitter of the NPN transistor 114 via the resistors 111 and 113 and the auxiliary winding on the primary side of the step-up transformer 120, and the transformer drive circuit 110 self-oscillates. AC high voltage is generated on the secondary side. The AC high voltage is rectified by the diodes 131 and 132 and the capacitors 133 and 134, and the rectified DC high-voltage output voltage Vout is supplied to the transfer roller 24 as a load.

  The operational amplifier 150 supplies the current from the output terminal 150c of the operational amplifier 150 to the anode side of the diode 132 by grounding the non-inverting input terminal and virtually grounding the inverting input terminal to set the non-inverting input terminal to the ground level. When the load current does not flow, the current flowing from the diode 132 circulates through the resistor 141 and the resistor 142, and no current flows from the output terminal 150c of the operational amplifier 150. However, when the current flows to the transfer roller 24 as a load, An equal current is output from the output terminal 150 c of the operational amplifier 150 and supplied to the anode of the diode 132 through the resistor 170 and the resistor 142. Since the output current of the operational amplifier 150 becomes an alternating current for switching of the transformer 120, the output voltage Vo of the operational amplifier 150 is smoothed by the RC filter including the resistor 161 and the capacitor 162 and is input to the analog voltage input port 92.

  Here, the voltage applied to the transfer roller 24 that is a load corresponds to a value obtained by multiplying the value of the resistor 141 by the value of the current flowing through the transfer roller 24 from the value of the high voltage output instruction voltage V91 of the analog voltage output port 91. Causes a voltage drop. Further, the current value flowing through the transfer roller 24 can be calculated by dividing the potential difference between the high voltage output instruction voltage V91 and the detection voltage V160 of the analog voltage input port 92 by the resistance value of the current detection resistor 170.

  (Effect of Example 1)

  According to the high voltage power supply device 60A and the image forming apparatus 1 of the first embodiment, there are the following effects (a) to (c).

  (A) Even if an output resistor is not mounted, the DC high-voltage output voltage Vout can be immediately lowered when the load current increases. As a result, for example, in the image forming apparatus 1, it is possible to suppress excessive bias application without an output resistance in a region where a load resistance such as a gap between sheets during continuous printing decreases.

  (B) That is, according to the first embodiment, a part of the voltage dividing resistor 142 of the voltage dividing circuit 140 is connected in series to the current detecting resistor 170. As a result, the same voltage drop as when a conventional output resistor is mounted can be obtained without an output resistor, and it is possible to achieve both accurate current detection without increasing the number of components. . Note that a resistance of less than 100 kΩ other than the high withstand voltage resistance such as the resistance 141 can use a chip resistance or the like, so that the increase in the number of points hardly affects the cost change.

  (C) Even when a failure such as a load short-circuit occurs, the DC high-voltage output voltage Vout drops to improve safety.

  (Configuration of Example 2)

  FIG. 5 is a block diagram illustrating a configuration of a high-voltage power supply device 60B according to the second embodiment of the present invention.

  The high-voltage power supply device 60B of the second embodiment includes a high-voltage setting signal output unit 61 similar to that of the first embodiment shown in FIG. 1 and a transfer bias generator 64B having a different configuration from the transfer bias generator 64 of the first embodiment. It is comprised by.

  In the transfer bias generator 64B of the second embodiment, a voltage dividing circuit 140B having a configuration different from that of the voltage dividing circuit 140 of the first embodiment is provided. Further, between the positive rectifier circuit 130 and the connection point 140b, A new resistor 156 has been added. In the voltage dividing circuit 140B according to the second embodiment, a third voltage dividing resistor 143 is newly added between the first voltage dividing resistor 141 and the second voltage dividing resistor 142.

  FIG. 6 is a circuit diagram showing a configuration example of the high-voltage power supply device 60B of FIG.

  In the circuit of FIG. 6, a voltage dividing resistor 143 is added to the circuit of FIG. 4 of the first embodiment. A resistor 156 and a capacitor 157 are added to the current supply side of the rectifier circuit 130. Further, a clamping diode 163 and a 3.3V power source 164 are added to the input side of the analog voltage input port 92 in the high voltage setting signal output unit 61. The diode 163 protects the high voltage setting signal output unit 61 when the output voltage Vo of the operational amplifier 150 exceeds 3.3V.

  For example, the current detection resistor 170 is 51 kΩ, the voltage dividing resistor 141 is 100 MΩ, the voltage dividing resistors 142 and 143 are 33 kΩ, the resistor 156 is 10 MΩ, and the capacitor 157 is 1000 pF.

  Other configurations of the second embodiment are the same as those of the first embodiment.

  (Operation of the circuits of FIGS. 5 and 6)

  In the second embodiment, since the voltage dividing resistor 143 is added, the ratio of the voltage suppressed by the load current flowing through the transfer roller 24 that is a load can be adjusted without depending on the value of the voltage dividing resistor 141. .

  A 10 MΩ resistor 156 is added. The resistor 156 has a function of not only causing a voltage drop by the suppression circuit when an abnormality such as a load short-circuit occurs but also limiting the current by the resistor 156 provided on the input side. The resistance values are, for example, 100 MΩ for the voltage dividing resistor 141, 33 kΩ for the voltage dividing resistors 142 and 143, and 51 kΩ for the current detecting resistor 170.

  Of the voltage dividing resistor 143 and the voltage dividing resistor 142, 142 is a resistor through which a current flows in the surplus current flowing through the transfer roller 24, which is a load. Therefore, when the voltage is divided by the voltage dividing resistors 141, 143, and 142, The rate at which the feedback voltage rises due to the load current is halved. Therefore, the voltage drop corresponding to the load current has the same effect as when a 50 MΩ resistor is connected. Thereby, even if the value of the voltage dividing resistor 141 is constant, the output suppression voltage can be adjusted.

In this case, if the high voltage output instruction voltage V91 is x (V), the set value of the high voltage output instruction voltage V91 output from the analog voltage output port 91 is
(X) × (33 × 10 ³ + 33 × 10 ³ )
/ (100 × 10 ⁶ + 33 × 10 ³ + 33 × 10 ³ ) × 255 / 3.3
It becomes. When the load current is y (μA) and the output voltage Vo of the operational amplifier 150 is z (mV),
z = y × (51 + 33) +
{(Xy × 100 × (33/66)) / 100.066} × 33
It becomes.

That is, the element of the operational amplifier output voltage z is that the load current flows through the resistors 170 and 142, and this voltage is
y × (51 + 33)
It corresponds to. The remainder is a voltage obtained by dividing the DC high-voltage output voltage Vout output from the positive rectifier circuit 130 by the voltage dividing resistors 141, 143, and 142.
{(Xy × 100 × (33/66)) / 100.066} × 33
It corresponds to. Of these,
y × 100 × (33/66)
Is the amount that the DC high-voltage output voltage Vout drops with respect to the high-voltage output instruction voltage V91. Solving this,
y = (z−0.329782x) /67.51088
become. Approximate
y≈ (z−0.33x) /67.5
May be used for detecting the transfer current of the image forming apparatus 1.

  (Detailed operation of the circuit of FIG. 6)

The boosting transformer 120 in the mold transformer MT is driven on the primary side by the transformer driving circuit 110, and generates a high voltage boosted by alternating current from the secondary side. For example, when the high voltage output instruction voltage V91 is 3000V,
3000 × (33 × 10 ³ + 33 × 10 ³ )
/ (100 × 10 ⁶ + 33 × 10 ³ + 33 × 10 ³ )
× 255 / 3.3 ≒ 153
99 hex is set, and a voltage of 1.98 V is output from the analog voltage output port 91. At this time, for example, if the transfer roller 24 as a load is equivalent to 50 MΩ, the voltage dividing resistor 141 is 100 MΩ, and each of the voltage dividing resistors 143 and 142 is 33 kΩ, so that the output voltage drop is equivalent to the case where there is an output resistance of 50 MΩ. Become. Therefore, an output equivalent to a total 100 MΩ load connection is obtained for a 3000 V output.

The load current flowing through the transfer roller 24 is 30 μA. As a circuit operation, the DC high voltage output voltage Vout is suppressed to 1500 V by the transformer drive circuit 110 with respect to 3000 V of the high voltage output instruction voltage V91, and a current of 30 μA flows through the transfer roller 24 as a load. The total of the load current 30 μA and the voltage dividing circuit current flows through the voltage dividing resistor 142. The potential increase for a load current of 30 μA is
(33 × 10 ³ ) × (30 × 10 ⁻⁶ ) ≈1V
It becomes. When this is subtracted from the DC high voltage output voltage Vout,
1500-1 = 1499V
It becomes. 1499V divided by the voltage dividing resistance 1499 / (100 × 10 ⁶ + 33 × 10 ³ + 33 × 10 ³ ) ≈15 μA
Flows. Therefore, a current of 45 μA flows through the voltage dividing resistor 142. 15 μA calculated above flows through the voltage dividing resistor 143, and a current of 30 μA flows through the current detecting resistor 170. Thereby, the potential difference between both ends of the voltage dividing resistor 142 is
(33 × 10 ³ ) × (45 × 10 ⁻⁶ ) = 1.485V
It becomes.

Furthermore, the potential difference across the voltage dividing resistor 143 is:
(33 × 10 ³ ) × (15 × 10 ⁻⁶ ) = 0.495V
It becomes. The inverting input terminal voltage of the operational amplifier 104 is
1.485 + 0.495 = 1.98V
Thus, it becomes equal to the high-voltage output instruction voltage V91, and constant voltage control is performed. At this time, the potential difference between both ends of the current detection resistor 170 is
(51 × 10 ³ ) × (30 × 10 ⁻⁶ ) = 1.53V
The output voltage Vo of the operational amplifier 150 is
1.485 + 1.53 = 3.015V
It becomes.

Formula y≈ (z−0.33x) /67.5
Than,
y = (3.015 × 1000−0.33 × 3000) /67.5
= 30 μA
And the load current can be calculated.

  As described above, since the DC high-voltage output voltage Vout is suppressed according to the load current, the DC high-voltage output voltage Vout can be stably controlled even if the conventionally required output resistance is eliminated. Depending on the paper size, the transfer current, which is a load current, is usually 40 μA or less. In order to flow this transfer current, the DC high-voltage output voltage Vout is supplied as a transfer bias at a constant voltage, but it is ideal to apply the transfer bias only while the paper 27 is in the nip portion with the transfer roller 24. . Even during continuous printing, the transfer bias between the sheet 27 and the next sheet 27 is turned off or switched to a low voltage.

  However, when printing is to be performed with as little margin as possible from the leading edge of the paper to the trailing edge, the transfer bias application timing must be performed at the same time as the leading edge of the paper reaches the nip portion. Similarly, the transfer bias is continuously applied until the trailing edge of the sheet is reached. In such a case, a transfer bias may be applied even when the paper 27 is not in the nip portion due to a paper conveyance deviation or the like. The resistance values of the transfer belt 23 and the transfer roller 24 are lower than the resistance value of the paper 27. When the same voltage is applied and the transfer bias is applied at a constant voltage to this end portion, if a current limiting resistor is not provided, an excessive current flows, the history remains on the photosensitive drum 12, and a horizontal band-like shape is generated. An image defect may occur. Conventionally, in such a case, an output resistance of about 50 MΩ to 100 MΩ is provided so that an excessive current does not flow. On the other hand, in the first embodiment, since the circuit suppresses the voltage even in such a case, the output resistance can be eliminated.

In addition, when a load current of 60 μA flows when the 3000 V output instruction is set, the DC high voltage output voltage Vout is suppressed to 0 V, but the current flows through the resistor 156 of 10 MΩ, so that the potential difference between both ends of the resistor 156 Becomes 600V. The anode potential of the diode 132 becomes −600V. The DC high-voltage output voltage Vout is 0 V, but the step-up transformer 120 is driven with a load of 600 V and a load of 60 μA, and the operation is stabilized. When the load current decreases, the DC high-voltage output voltage Vout immediately increases. The operation is less than 60 μA except in the case of an abnormality such as a load short circuit. At the current of 60 μA, the operational amplifier output voltage is
((51 + 33) × 10 ³ ) × (60 × 10 ⁻⁶ ) = 5.04V
However, the input voltage of the analog voltage input port 92 is clamped to 3.3 V by the diode 163 and protected.

  Similar to the first embodiment, in the second embodiment, the 24V power supply 105 is always supplied to the circuit. However, the operation of the transformer drive is stopped by configuring the 24V power supply 105 to be on / off. You may make it the structure which performs. Thereby, malfunction can be prevented.

  (Effect of Example 2)

  According to the second embodiment, there are substantially the same effects as the first embodiment.

  (Configuration of Example 3)

  FIG. 7 is a circuit diagram illustrating another configuration example of the high-voltage power supply device 60A according to the third embodiment of the present invention.

  In the high-voltage power supply device 60A of FIG. 4 showing the first embodiment, the transformer drive circuit 110 is configured by a self-excited oscillation circuit. In the third embodiment, the transformer drive circuit 110 is configured by a separately excited oscillation circuit. Yes.

  That is, in the third embodiment, a high voltage setting signal output unit 61B having a configuration different from that of the high voltage setting signal output unit 61 of the first embodiment is provided, and further, a transformer driving having a configuration different from that of the transformer driving circuit 110 of the first embodiment. A circuit 110B is provided.

  The high voltage setting signal output unit 61B of the third embodiment is replaced with the analog voltage input port 92 similar to that of the first embodiment, the newly added analog voltage input port 94, and the analog voltage output port 91 of the first embodiment. And a pulse width modulation (hereinafter referred to as “PWM”) output port 95. The added analog voltage input port 94 has a function of inputting the analog divided voltage Va output from the voltage dividing circuit 140 and converting it into a digital signal. The added PWM output port 95 has a function of comparing the digital signal converted by the analog voltage input port 94 with the internally set high-voltage output instruction voltage V91 and outputting a comparison result composed of PWM pulses. are doing. The comparison result output from the PWM output port 95 is sent to the transformer drive circuit 110B via the resistor 101.

The transformer driving circuit 110B includes a separately-excited oscillation circuit. The 24V power source 115 is the same as that of the first embodiment, and an N-channel field effect transistor (hereinafter “ FET ") 116 and a backflow prevention diode 117.
Other configurations of the third embodiment are the same as those of the first embodiment.

  (Operation of Example 3)

  The analog divided voltage Va output from the voltage dividing circuit 140 is input to the analog voltage input port 94 of the high voltage setting signal output unit 61B and converted into a digital signal. The converted digital signal is compared with the high voltage output instruction voltage V91 set in the high voltage setting signal output unit 61B, and the comparison result is PWM-modulated and output from the PWM output port 95. The PWM-modulated comparison result is input to the transformer drive circuit 110B via the resistor 101, and the FET 117 is turned on / off to generate a drive signal. The generated drive signal is boosted by the transformer 120 and then rectified by the positive rectifier circuit 130 to generate a DC high-voltage output voltage Vout and supplied to the transfer roller 24 as a load, as in the first embodiment. Is done.

  (Effect of Example 3)

  According to the third embodiment, instead of the transformer drive circuit 110 configured by the self-excited oscillation circuit of the first embodiment, the transformer drive circuit 110B configured by the separately excited oscillation circuit is provided. There is a similar effect. Furthermore, since the function of the comparison circuit 100 of the first embodiment is provided in the high voltage setting signal output unit 61B, the circuit configuration in the transfer bias generation unit 64 is simplified.

  (Configuration of Example 4)

  FIG. 8 is a block diagram illustrating a configuration of a high-voltage power supply device 60C according to the fourth embodiment of the present invention.

  The high-voltage power supply device 60C according to the fourth embodiment is different from the high-voltage setting signal output unit 61 and the transfer bias generation unit 64 in the high-voltage power supply device 60A shown in FIG. A section 61C and a transfer bias generating section 64C are provided.

  The high voltage setting signal output unit 61C of the fourth embodiment includes a logic output port 96 in addition to the analog voltage output port 91 and the analog voltage input port 92 similar to those of the first embodiment. The logic output port 96 has a function of controlling power supply in the transfer bias generator 64C.

  In the transfer bias generator 64C of the fourth embodiment, a piezoelectric transformer 120C made of piezoelectric ceramics is provided instead of the winding electromagnetic transformer 130 of the first embodiment. A transformer driving circuit 110C having a configuration different from that of the transformer driving circuit 110 according to the first embodiment is connected to the input side of the piezoelectric transformer 120C. A positive rectifier circuit 130C having a configuration different from that of the positive rectifier circuit 130 according to the first embodiment is connected to the output side of the piezoelectric transformer 120C. A newly added power supply circuit 180 is connected to the transformer driving circuit 110C. The power supply circuit 180 is a circuit that turns on / off the power supply to the transformer drive circuit 110 </ b> C based on a control signal output from the logic output port 96.

  Other configurations of the fourth embodiment are the same as those of the first embodiment.

  FIG. 9 is a circuit diagram showing a configuration example of the high-voltage power supply device 60C of FIG.

  Similar to the first embodiment, the comparison circuit 100 in FIG. 8 includes an integration circuit including an operational amplifier 104, a 24V power source 105, a capacitor 106, and a resistor. The transformer driving circuit 110C includes a voltage controlled oscillator (hereinafter referred to as “VCO”) 116 whose oscillation frequency changes according to the output voltage of the operational amplifier 104, an FET 117 that is turned on / off by the output voltage of the VCO 116, and a drain of the FET 117. The inductor 118 is connected to the FET 117 and the capacitor 119 is connected in parallel to the drain and source of the FET 117. The inductor 118 and the capacitor 119 constitute an LC resonance circuit. A power supply circuit 180 is connected to the inductor 118.

  The power supply circuit 180 includes a 24V power supply 181, a bias resistor 182 connected to the 24V power supply 181, an N-channel FET 183 that turns on / off the power supply current supplied from the 24V power supply 181, and the gate of the FET 183. The resistor 184 and the NPN transistor 185 are connected in series between the NPN transistor 185 and the ground, and the resistor 186 is connected between the base of the NPN transistor 185 and the logic output port 96.

  The piezoelectric transformer 120 </ b> C is a transformer that vibrates due to a resonance current of a resonance circuit including an inductor 118 and a capacitor 119 and outputs an alternating high voltage. The positive rectifier circuit 130 </ b> C is a circuit that rectifies the output voltage of the piezoelectric transformer 120 </ b> C and outputs a DC high-voltage output voltage Vout, and includes two diodes 131 and 132 and one capacitor 133.

  As in the first embodiment, the voltage dividing resistor 141 is 100 MΩ, the voltage dividing resistor 142 is 33 kΩ, and the current detecting resistor 170 is 33 kΩ.

  Other configurations of the fourth embodiment are the same as those of the first embodiment.

  (Operation of Example 4)

  FIG. 10 is a load characteristic diagram of the piezoelectric transformer 120C in FIG.

  The horizontal axis in FIG. 10 is the frequency, and the vertical axis is the output voltage of the piezoelectric transformer 120C. The output voltage of the resonance frequency fx when the load resistance is small is larger than the output voltage of the resonance frequency fy when the load resistance is large.

  The overall operation of the image forming apparatus 1 including the high-voltage power supply device 60C of FIGS. 8 and 9 is the same as that of the first embodiment. However, since the high-voltage power supply device 60C of the fourth embodiment has a circuit configuration different from that of the high-voltage power supply device 160 of the first embodiment, the operation thereof is also different as follows.

  In the high voltage power supply device 60C of the fourth embodiment, a piezoelectric transformer 120C is used instead of the winding electromagnetic transformer 120 of the first embodiment. In the transformer driving circuit 110C for driving the piezoelectric transformer 120C, the N-channel FET 117 is switched by a pulse output from the VCO 116, and the inductor 118, the capacitor 119, and the piezoelectric transformer 120C are connected to the primary side of the piezoelectric transformer 120C. A sinusoidal wave is applied. Then, a boosted AC voltage is generated on the secondary side of the piezoelectric transformer 120C according to the frequency of the VCO 116.

  The VCO 116 receives a voltage from the operational amplifier 104. The higher the input voltage, the higher the frequency, and the lower the input voltage, the lower the frequency. The operational amplifier 104 forms an integrating circuit by the capacitor 106 and the resistor 107, and the divided voltage Va divided by the voltage dividing resistors 141 and 142 and the high voltage output instruction voltage V91 output from the analog voltage output port 91 are obtained. The operational amplifier output voltage is controlled to be equal. As a result, the voltage applied to the VCO 116 changes so that the divided voltage Va of the DC high-voltage output voltage Vout becomes equal to the high-voltage output instruction voltage V91 output from the analog voltage output port 91, and is stable at a predetermined frequency. To do.

  When the high voltage is off, the logic output port 96 of the high voltage setting signal output unit 61C sets the output signal to L level, turns off the P-channel FET 183 via the NPN transistor 185, and turns off the voltage applied to the inductor 118. Thereby, even if the output voltage of the VCO 116 is applied to the gate of the N-channel FET 117, the high voltage output can be turned off.

  At the timing when the high voltage output is turned on, the high voltage setting signal output unit 61C sets the output signal of the logic output port 96 to the H level. As a result, the NPN transistor 185 is turned on and the P-channel FET 183 is turned on. Then, the voltage of the 24V power supply 181 is applied to the drain of the N-channel FET 117 via the P-channel FET 183 and the inductor 118 that are in the on state. The VCO 116 starts switching of the N-channel FET 117 at the upper limit frequency depending on the input voltage, and the high voltage output instruction voltage V91 output from the analog voltage output port 91 is equal to the divided voltage Va of the voltage dividing resistors 141 and 142. The VCO applied voltage is reduced until As a result, the output frequency of the VCO 116 decreases and the boost ratio of the piezoelectric transformer 120C increases.

  Hereinafter, the current detection operation and the output voltage suppression operation are the same as those in the first embodiment, and thus will be omitted.

  As shown in FIG. 10, the output voltage of the piezoelectric transformer 120C varies greatly depending on the load resistance. For example, when a conventional high-voltage power supply device is configured without an output resistor, when a high load output instruction voltage is increased and a large amount of load current flows, it is controlled to a low frequency exceeding the resonance frequencies fx and fy, There is a risk of loss of control. On the other hand, as in the fourth embodiment, even when the piezoelectric transformer 120C is used, the DC high voltage output voltage Vout can be suppressed according to the load current, and the characteristic change of the piezoelectric transformer 120C due to the size of the load is absorbed and stabilized. Control becomes possible.

  In the fourth embodiment, the voltage drop corresponding to 100 MΩ and 50 MΩ of load resistance is generated. However, the present invention is not limited to this. It is also possible to adjust the step-down ratio by matching the characteristics through experiments or the like so that the voltage drop matches the load characteristics shown in FIG. In that case, it is also possible to adjust the frequency characteristics so as not to change depending on the load by adding an output resistance or the like.

  (Effect of Example 4)

  According to the fourth embodiment, even when the piezoelectric transformer 120C is used, constant voltage control is possible without an output resistance and without departing from the control range even when the load current increases.

  That is, since the DC high voltage output voltage Vout can be lowered according to the load current, the DC high voltage output voltage Vout can be suppressed without providing an output resistance between the load and the DC high voltage output voltage terminal. Become. Accordingly, it is possible to realize the high voltage power supply device 60C that can detect the current flowing through the load without being controlled to the low frequency side exceeding the resonance frequency fy when the load is increased.

  FIG. 11 is a block diagram illustrating a configuration of a high-voltage power supply device 60D according to the fifth embodiment of the present invention.

  In the transfer bias generator 64D in the high-voltage power supply device 60D of the fifth embodiment, as in FIG. 5 of the second embodiment, the third voltage dividing resistor is included in the transfer bias generator 64C in the high-voltage power supply device 60C of the fourth embodiment. 143 has been added.

  Therefore, the current-to-output voltage ratio for suppressing the output voltage can be adjusted by the resistance ratio between the voltage dividing resistor 143 and the voltage dividing resistor 142.

  FIG. 12 is a circuit diagram showing a configuration example of the high-voltage power supply device 60D of FIG.

  A voltage dividing resistor 143 of 33 kΩ is added. For example, the voltage dividing resistor 141 is 100 MΩ, the voltage dividing resistor 143 is 33 kΩ, the voltage dividing resistor 142 is 33 kΩ, and the current detecting resistor 170 is 51 kΩ.

  In FIG. 12, when the voltage dividing resistor 141 is 100 MΩ and the voltage dividing resistor 142 is 33 kΩ, the same voltage drop as when the conventional output resistance is 50 MΩ is obtained with respect to the load current flowing through the transfer roller 24 as a load. Is possible. This drop ratio can be adjusted by changing the resistance ratio between the voltage dividing resistor 143 and the voltage dividing resistor 142. For example, if the voltage dividing resistor 143 is set to 66 kΩ, it can be changed to a voltage drop equivalent to the output resistance of 33 MΩ.

  FIG. 13 is a circuit diagram illustrating a configuration example of a high-voltage power supply device 60E according to the sixth embodiment of the present invention.

  In the high-voltage power supply device 60E of the sixth embodiment, the function of the comparison circuit 100 in the high-voltage power supply device 60C of FIG. 9 showing the fourth embodiment is provided in the high-voltage setting signal output unit 61E. The high voltage setting signal output unit 61E has substantially the same configuration as the high voltage setting signal output unit 61B in FIG.

  According to the high-voltage power supply device 60E of the sixth embodiment, the function of the comparison circuit 100 of the fourth embodiment is provided in the high-voltage setting signal output unit 61E. Therefore, the divided voltage Va of the circuit is detected by the analog voltage input port 94, the output signal of the PWM output port 95 is adjusted, and the input voltage of the VCO 116 is adjusted so that the detected voltage value becomes a predetermined voltage. Control the frequency. Thereby, there exists an effect substantially the same as Example 3, 4. FIG.

  (Modification of Examples 1-6)

  This invention is not limited to the said Examples 1-6, A various utilization form and deformation | transformation are possible.

  For example, in the first to sixth embodiments, the present invention is applied to the high-voltage power supply device of the tandem direct transfer image forming apparatus, but it can also be applied to other high-voltage power supply devices to which a positive bias is applied. Further, it can be applied not only to a color but also to a monochrome image forming apparatus.

1 Image forming apparatus 10 (10K, 10Y, 10M, 10C) Developer 20 Transfer unit 24 (24K, 24Y, 24M, 24C) Transfer roller 32 Fixing device 60A, 60B, 60C, 60D, 60E High voltage power supply 61, 61B, 61C, 61E High voltage setting signal output unit 64, 64B, 64C, 64D Transfer bias generation unit 100 Comparison circuit 110 Transformer drive circuit 120 Transformer 120C Piezoelectric transformer 130 Rectifier circuit 140, 140B Voltage division circuit 141, 142, 143 Voltage division resistance 150 Operational amplifier (Operational amplifier)
170 Resistance for current detection

Claims (8)

In a power supply device that outputs a DC high-voltage output voltage to a load,
A comparison circuit that compares the input high-voltage output instruction voltage with the divided voltage of the DC high-voltage output voltage and outputs a comparison result;
A transformer drive circuit that outputs a drive voltage using the output of the comparison result;
A transformer that boosts the drive voltage to generate an AC voltage;
A rectifier circuit that rectifies the AC voltage and outputs the DC high-voltage output voltage;
A voltage dividing circuit that has a plurality of voltage dividing resistors, and divides the DC high-voltage output voltage and generates the divided voltage to be input to the comparison circuit;
A current detection resistor that is connected in series to a partial voltage dividing resistor of the plurality of voltage dividing resistors, and that causes a load current to flow from the rectifier circuit to the load ;
With operational amplifier
With
The operational amplifier is
Inverting input terminal, a non-inverting input terminal, an output terminal for outputting the及beauty output voltage, the non-inverting input terminal grounded, a current input side of the rectifier circuit in a state where the inverting input terminal is virtual ground And the partial voltage dividing resistor, and the output terminal and the inverting input terminal are connected via the partial voltage dividing resistor and the current detecting resistor,
The voltage dividing circuit is connected between an output side of the DC high-voltage output voltage of the rectifier circuit and the inverting input terminal,
The load current includes the output terminal of the operational amplifier, the current detection resistor, the partial voltage dividing resistor, the current input side of the rectifier circuit, the output side of the DC high-voltage output voltage of the rectifier circuit, And flow to the load path,
The transformer driving circuit is controlled so that the comparison result becomes zero, the DC high-voltage output voltage is suppressed according to the load current, and the load current flowing from the output terminal of the operational amplifier to the load is reduced. Detecting a power supply device. The power supply device according to claim 1, further comprising:
An arithmetic means for detecting the output voltage of the operational amplifier to obtain an output voltage detection value, and calculating the load current based on the value of the high voltage output instruction voltage and the output voltage detection value;
The power supply device according to claim 1, further comprising: The computing means is
The power supply apparatus according to claim 2, wherein the DC high-voltage output voltage is calculated based on the high-voltage output instruction voltage and the load current. The voltage dividing circuit includes:
It is constituted by two first and second voltage dividing resistors connected in series,
A connection point between the first voltage dividing resistor and the second voltage dividing resistor is connected to the output terminal of the operational amplifier via the current detection resistor,
The divided voltage is extracted from a connection point of the first voltage dividing resistor, the second voltage dividing resistor, and the current detection resistor, and is input to the comparison circuit.
The divided voltage is compared with the high voltage output instruction voltage by the comparison circuit, and the DC high voltage output voltage is a voltage of (the resistance value of the first voltage dividing resistor × the current value of the load current) according to the load current. The power supply apparatus according to claim 1, wherein the power supply apparatus drops by a value. The voltage dividing circuit includes:
It is constituted by three first, second and third voltage dividing resistors connected in series,
A connection point between the second voltage dividing resistor and the third voltage dividing resistor is connected to the output terminal of the operational amplifier via the current detection resistor,
The divided voltage is taken out from a connection point between the first voltage dividing resistor and the third voltage dividing resistor, and is input to the comparison circuit.
The divided voltage is compared with the high-voltage output instruction voltage by the comparison circuit, and a resistance value ratio between the resistance value of the second voltage dividing resistor and the resistance value of the third voltage dividing resistor is appropriately set. Thus, the DC high-voltage output voltage is [resistance value of the first voltage dividing resistor × (resistance value of the third voltage dividing resistor / resistance value of the second voltage dividing resistor) × load current according to the load current. The power supply device according to claim 1, wherein the power supply device drops by a voltage value of a current value]. The transformer is
6. The power supply device according to claim 1, wherein the power supply device is a piezoelectric transformer made of piezoelectric ceramics. The transformer is
6. The power supply device according to claim 1, wherein the power supply device is a wound electromagnetic transformer. The power supply device according to any one of claims 1 to 7,
An image forming apparatus comprising:

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