JP6942518B2 - High-voltage generator and image forming device - Google Patents

Description

The present invention relates to a high-voltage generator that generates high voltage and an image forming apparatus that uses the high-voltage generator.

Conventionally, in an electrophotographic image forming apparatus, a high voltage is applied to a process unit such as a charging roller or a primary transfer roller, and the current flowing at that time is detected to feed back to various controls. The high-voltage output and current detection are performed by the high-voltage board in the device, and the high-voltage board is required to apply a voltage to the load and detect the current flowing through the load with high accuracy.

For example, Patent Document 1 describes a configuration in which a voltage detection unit that detects an applied voltage is not directly grounded but is connected to an operational amplifier feedback unit in a current detection circuit that uses operational amplifier feedback. A predetermined offset potential is given to the reference voltage (positive terminal voltage of the operational amplifier) in this current detection circuit. By doing so, even if there is a current flowing in from another load, the operational amplifier output unit does not reach the GND level, so that the reference voltage of the voltage detection unit can be kept constant.

Japanese Unexamined Patent Publication No. 2001-169546

However, when a negative voltage is applied to the charging roller, for example, to charge the photosensitive drum using the current detection circuit of Patent Document 1, the detected value of the current flowing through the charging roller is proportional to the output current from the offset potential. It goes down. At this time, if a part of the photosensitive drum is scratched, when the scratched portion reaches the photosensitive drum and the charging roller nip, a larger current than in normal use may flow at that moment. Depending on the current value, the current detection value reaches the GND level, and the voltage of the feedback unit of the current detection circuit cannot be kept constant. Further, since the voltage of the feedback unit is the reference voltage for voltage detection, constant voltage control cannot be performed, and the output value deviates greatly from the target value. As a result, toner and carriers are spit out in a streak pattern on the printed image.

Further, if a larger current flows between the charging roller and the photosensitive drum, the photosensitive drum and the photosensitive drum may be significantly damaged. Therefore, when an attempt is made to implement protection that stops the circuit at a predetermined current value, when the current detection value reaches the GND level, no further current value can be detected, so it is necessary to widen the current detection range. However, the resolution of current detection deteriorates.

In order to solve the above-mentioned problems, the high-voltage generator of the present invention includes a transformer that boosts the input voltage, a rectifying means that rectifies the output of the transformer and supplies a DC voltage to the load, and the load. The DC current to flow is input to the first input terminal, and the reference value is input to the second input terminal. The output of the electric current is fed back to the first input terminal of the electric current via a current detection resistor. , A current detecting means that detects the DC current flowing through the load as a voltage generated in the current detecting resistor, and a DC voltage that is connected to the first input terminal of the operational capacitor and is supplied to the load from the rectifying means. The current detecting means has a voltage dividing means for dividing the output of the operational amplifier as a detection value of a DC current flowing through the load, and a DC current flowing through the load as a first threshold value. When it reaches, it is provided with a bypass means for passing a current from the connection portion between the voltage detecting means and the first input terminal of the operational amplifier to the output terminal of the operational amplifier, and further, even when a current flows through the bypass means. It is characterized by having a protective means for reducing the output power of the transformer when the DC current flowing through the load reaches a second threshold value larger than the first threshold value.

According to the present invention, a bypass means is provided so that a current flows from the feedback terminal portion of the operational amplifier to the output terminal portion of the operational amplifier even if a large current flows through the load, and the protection circuit is operated by the current value flowing through the bypass means. This makes it possible to prevent the operational amplifier output unit from reaching the GND level and causing an abnormality in the high voltage output without deteriorating the resolution of current detection.

It is a block diagram of the image forming apparatus 1 of this Example. It is a board block diagram of this Example. It is a circuit block diagram of the charged high voltage circuit 300a of this embodiment. It is explanatory drawing of the output current and the voltage of each part in the current detection circuit of this Example. It is explanatory drawing of the operation of each part at the time of the resistance value change of the charging roller 2 of this Example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus using an electrophotographic process according to an embodiment of the present invention.

In the figure, the image forming section 10 is provided with four image forming sections, which are photoconductor drums 1a to 1d, charging rollers 2a to 2d, laser scanners 3a to 3d, developing machines 4a to 4d, and an intermediate transfer belt. 5. Primary transfer rollers 6a to 6d and secondary transfer rollers 7 are arranged. The subscripts a to d of the numbers correspond to the image forming portions of yellow, magenta, cyan, and black, respectively. However, the image forming color of each image forming portion is not limited to this.

The outline of the image forming operation will be described. After the photoconductor drums 1a to 1d having a conductive layer on the surface are uniformly charged by the charging rollers 2a to 2d, the laser scanners 3a to 3d perform exposure based on the image signal corresponding to the image to be formed. , An electrostatic latent image is formed on the photoconductor drums 1a to 1d. After that, the formed electrostatic latent image is developed as a toner image by the developers 4a to 4d, and each toner image is multiplex-transferred to the intermediate transfer belt 5 by the primary transfer rollers 6a to 6d. The toner image transferred to the intermediate transfer belt 5 is transferred to the recording material P conveyed from the paper cassette 9 by the secondary transfer roller 7, and fixed by the fixing device 8 to obtain a color image.

FIG. 2 is a block diagram of the charging rollers 2a to 2d, the charging developing substrates 200a to 200d as a high voltage generator for generating a high voltage applied to the developing units 4a to 4d, and the control substrate 100.

The charged development substrate 200a has a high voltage charging circuit 300a that generates a high voltage output (charged high voltage) applied to the charging roller 2a and a developing high voltage circuit 400a that generates a high voltage output (development high voltage) applied to the developer 4a. It is a board.

The charged development substrate 200b has a high voltage charging circuit 300b that generates a high voltage output (charged high voltage) applied to the charging roller 2b and a developing high voltage circuit 400b that generates a high voltage output (development high voltage) applied to the developer 4b. It is a board.

The charge development substrate 200c has a high voltage charge circuit 300c that generates a high voltage output (charged high voltage) applied to the charging roller 2c, and a developing high voltage circuit 400c that generates a high voltage output (development high voltage) applied to the developer 4c. It is a board.

The charge development substrate 200d has a high voltage charge circuit 300d that generates a high voltage output (charged high voltage) applied to the charging roller 2d, and a developing high voltage circuit 400d that generates a high voltage output (development high voltage) applied to the developer 4d. It is a board.

The control substrate 100 controls the overall image forming operation by starting the operation, setting the output voltage, and acquiring the detected value for each of the charged developing substrates 200a to d.

Here, since the charge-developing substrates 200a to 200d in the present embodiment are all substrates of the same circuit, only the charge-development substrate 200a will be described as a representative in the following description.

FIG. 3 is an explanatory diagram of a charged high-voltage circuit 300a as a high-voltage generator. The charged high-voltage circuit 300a is composed of a PWM smoothing unit 301, a constant voltage control unit 302, a transformer drive unit 303, a high-voltage rectifying unit 304, a voltage detection unit 305, and a current detection unit 306, and has a high voltage of negative direct current to the charging roller 2. Output HVout. A PWM signal and a transformer drive clock CLK are input from the control board 100 to the charged high-voltage circuit 300a, and 3.4V voltage and 24V voltage output from the control board 100 are further supplied. Further, the detected value (charged current detection value Isns) of the direct current (charged current Iout) flowing through the charging roller 2 is fed back to the control board 100.

<PWM smoothing part 301>
The PWM smoothing unit 301 is a low-pass filter composed of a resistor R1 and a capacitor C1 and converts an input PWM signal into a DC voltage at a predetermined cutoff frequency. The charge output (HVout) can be changed by changing the duty ratio of the input PWM signal. For example, when the duty ratio is 50%, about -800V is output, and when the duty ratio is 0%, about -1500V is output.

<Constant voltage control unit 302>
The constant voltage control unit 302 includes an operational amplifier IC1 and a capacitor C2, a transistor Q1 and an electrolytic capacitor C3. In the operational amplifier IC1, the DC voltage output from the PWM smoothing unit 301 is input to the-terminal, the voltage detection value Vsns described later is fed back to the + terminal, and the output voltage is adjusted so that the voltages of the + terminal and the-terminal match. It is an inverting amplifier circuit. Further, the capacitor C2 is an integrating element for the purpose of stabilizing the output voltage of the amplifier circuit. Further, the output of the operational amplifier IC1 is connected to the base of the transistor Q1 grounded by the collector, and the emitter of the transistor Q1 is lower than the voltage of the output terminal of the operational amplifier IC1 by the voltage between the base and emitter of the transistor Q1 (about 0.6V). Become. An electrolytic capacitor C3 for voltage stabilization is connected to the emitter of the transistor Q1.

<Transformer drive unit 303>
The transformer drive unit 303 is a circuit for driving a transformer T1 that boosts the input voltage. It is composed of a pull-down resistor R2, a damping resistor R3, and a FET Q2, and repeats ON / OFF of the FET Q2 according to the transformer drive clock CLK. In the present embodiment, the transformer drive clock CLK has a period of 50 kHz and a duty ratio of 25%. This makes it possible to control the start and stop of the operation of the transformer T1.

<High voltage rectifier 304>
The high-voltage rectifying unit 304 is composed of a high-voltage diode D1 and a high-voltage ceramic capacitor C4, rectifies and smoothes the negative voltage of the AC voltage output from the transformer T1, and charges the negative DC voltage HVout (0V to -1500V output). Output as.

<Voltage detector 305>
The voltage detection unit 305 is composed of two resistors R4 and R5, and outputs a voltage obtained by dividing the voltage between the charged output HVout and Vref2 described later by R4 and R5 as a voltage detection value Vsns (0 to 3.0V). ..

<Current detector 306>
The current detection unit 306 is composed of an operational amplifier IC2, a plurality of resistors R7 to R12, and a diode D2, and sets the charging current Iout when the charging output HVout is applied to the charging roller as a charging current detection value Iss of 0 to 3.0V. It is a circuit to output. The Ins is detected by the value obtained by dividing the output of the operational amplifier IC2 by the resistors R8 and R11. Here, the directions of the currents (Iout and Ir7, Id2, I1, I2 described later) flowing through the circuit will be described with the direction of FIG. 3 as positive. The voltage of each part and the current flowing through each part in the output current Iout will be described later.

<Overcurrent protection unit 307>
The overcurrent protection unit 307 includes a comparator IC3, a FET Q3, and resistors R13 to R17. When the voltage Vref2 is applied, a voltage drop occurs in the resistor R12 due to the current Id2 flowing through the resistor R12 in the current detection unit 306 and the diode D2. The voltage value (Vic3) after the drop is input to the comparator IC3 and compared with the voltage Vref3. When the voltage Vic3 drops to the voltage Vref3, the FET Q3 turns on, the FET Q2 turns off, and the charged high-voltage output HVout drops.

Next, the resistance constants of the current detection unit 306 are R7: 20kΩ, R8: 3.3kΩ, R9: 2kΩ, R10: 15kΩ, R11: 1kΩ, R12: 10kΩ, and the resistances of the overcurrent protection unit 307 are R13: 24kΩ. , R14: 10 kΩ. The voltage of each part in the charging current Iout in this case is shown in FIG. Since the behavior of the voltage of each part of the circuit of FIG. 3 changes in the region (current detectable region (i), current bypass region (ii), protection region (iii)) within the range taken by the value of the charging current Iout, each of them The area will be described below.

<Current detectable region (i)>
The current-detectable region (i) is a region in which the charging current detection value Isns is represented by a linear expression with respect to the charging current Iout.

Since the voltage Vref1 at the + terminal of the operational amplifier IC2 is a value obtained by dividing the voltage of 3.4V by the resistors R9 and R10, Vref1 [V] = 3.4 × R10 / (R9 + R10) = 3V (R9 + R10) = 3V as shown in the following equation. 1)
Will be.

The charging current Iout is input to the-terminal (first input terminal) of the operational amplifier IC2, and the voltage Vref1 as a reference value is input to the + terminal (second input terminal). Further, since the output terminal portion (point c) of the operational amplifier IC2 is fed back to the-terminal portion (point a) of the operational amplifier IC2 by the resistor R7 as a current detection resistor, the voltage Vref2 at the point a is a + terminal by virtual grounding. It is equal to the voltage Vref1 of the unit and becomes a constant value.
Vref2 [V] = 3V (2)

A voltage detection unit 305 is also connected to point a, and the point a voltage Vref2 is also used as a reference voltage for voltage detection.

Since the charged output HVout is a negative high voltage output, the charged current Iout flows along the path indicated by the dotted arrow in the figure. That is, the charging current Iout passes through the transformer T1 from the charged high-voltage output terminal, and flows from the point a to the point b, R11, and GND via R7. As described above, since the point a voltage Vref2 is a constant value at 3V, the voltage at point b is a voltage that is lower than the voltage at R7 due to the charging current Iout flowing from Vref2 to R7. It can be detected as a detected value Isns. Isns is as shown in the following equation: Isns [V] = Vref2-Iout × R7 (3)
As shown by the broken line in FIG. 4, it is represented by a linear expression of 3V when Iout is 0 μA and 1V when Iout is 100 μA.

Further, the resistor R11 is a pull-down resistor, and the current I1 flowing through the resistor R11 is
I1 [μA] = Isns / R11 (4)
Therefore, the output current Iic2 of the operational amplifier IC2 is Iic2 [μA] = I1-Iout (5).
Will be. Therefore, the voltage Vic2 of the operational amplifier IC2 output terminal (c) is Vic2 [V] = Isns + Iic2 × R8 (6).
Will be. As shown by the alternate long and short dash line in FIG. 4, the voltage Vic2 is 12.9 V when the charging current Iout is 0 μA and 3.97 V when the charged current Iout is 100 μA, so that the change is large as compared with Isns. Here, the resistor R8 is a protective resistor for preventing the output terminal of the operational amplifier IC2 from being destroyed by static electricity. In the present embodiment, the resistor R11 is arranged on the charged developing substrate 200a, but may be arranged on the control substrate 100, and the calculation formula is the same in that case as well.

The condition for the current to flow through the diode D2 is as follows with respect to Vic2 obtained by using the equation (6), where Vf is the forward voltage of the diode D2.
Vref2-Vic2 ≧ Vf (7)

In the current-detectable region (i), since Vref2-Vic2 is not equal to or lower than the forward voltage Vf of the diode D2, the current Id2 does not flow and the diode D2 is also in the off state, so that Vic3 has the same potential of 3V as Vref2. (Solid line in FIG. 4).

<Current bypass region (ii)>
When the charging current Iout is large, such as 200 μA, Isns is calculated to be -1V from Eq. (3). However, in reality, Since Isns cannot be less than 0V, Vref2 cannot maintain 3V and rises to 4V (200 μA × 20 kΩ). When Vref2 exceeds 3V, for example, 4V, the reference voltage for voltage detection deviates, so that the voltage detection value Vsns deviates from the actual value, and as a result, the charged output HVout deviates from the appropriate value.

In order to prevent this, in the present embodiment, a bypass means composed of a series connection circuit of the diode D2 and the resistor R12 is connected between the points c and a. The function of this bypass means is that even if a large current flows through the charging roller 2 due to scratches on the conductive layer on the surface of the photosensitive drum 1 or foreign matter adhering to the surface, the voltage detection circuit 305 and the operational amplifier IC2 have the function of the first. The charging current Iout flows from the connection portion with the 1 input terminal to the diode D2 side instead of the resistor R7 side. The resistor R12 as a bypass means and the diode D2 are connected in parallel to the resistor R7 as a current detection resistor, and the cathode of the diode D2 is arranged on the output terminal side of the operational amplifier IC2. At this time, the conditions under which the current flows through the diode D2 are as described in the above equation (7).

For example, when the charging current Iout is 50 μA, Vref2-Vic2 is −5.44 V, so no current flows through the diode D2. When the charging current Iout is 200 μA, Vref2-Vic2 becomes 7.96 V, and a current flows through the diode D2.

Further, assuming that the current at which the current starts to flow in the diode D2 is Iout', Iout' is the case where the equation (7) holds, and Iout'[μA] = (R11 / (R11 /) using the equations (2) to (7). R7 x R8 + R8 x R11 + R11 x R7))
× (Vf + (R8 / R11) × Vref2) (8)
Will be. When Vf is 0.6V, Iout'is 117.6 μA. Further, the charge current detection value Isns' when the current starts to flow in the diode D2 is 0.648V from the equation (3). This voltage of 0.648V is the upper limit of the charging current detection value Isns. Therefore, when the Ins exceeds 0.648V as a predetermined value, the current Id2 flows through the diode D2, so that the Iss becomes a constant value at 0.648V regardless of the output current Iout. Therefore, the voltage Vref2 can maintain 3V regardless of the output current Iout.

Further, as can be seen from FIG. 4, Vic2 is a signal having a large change with respect to the output current Iout. Therefore, even if the resistance value and the Vf value in the current detection unit 305 vary, the variation in Iout'is small, and it is possible to suppress it to about ± 5 μA (± 0.1 V in Isns').

Further, in the current bypass region (ii), Vref2 is constant at 3V, and Vic3 is a value dropped from Vref2 by the voltage generated in R12 by the bypass current Id2. Therefore, Vic3 is obtained by the following equation (9).
Vic3 = Vref2-Id2 * R12 (9)

Since Id2 is Iout-Iout', it is a linear expression by Iout.

<Protected area (c)>
When a larger current flows through the charging roller 2, the charging roller 2 may be significantly damaged. Therefore, when a large current flows through the charging roller 2, the overcurrent protection unit 307 limits the output power of the transformer T1.

Since the voltage Vref3 input to the positive input terminal of the comparator IC3 is a voltage obtained by dividing 3.4V by R13 and R14, it can be obtained by the following equation (10).
Vref3 = 3.4 × R13 / (R13 + R14) = 1V (10)

Therefore, when the voltage Vic3 input to the negative input terminal of the comparator IC3 becomes 1 V or less, the overcurrent protection circuit 307 performs a protection operation. The bypass current Id2 at this time is obtained from Eq. (9): Id2 = (Vref2-Vic3) / R12 (11)
Then, the current Id2 becomes 200 μA. Further, at this time, since the current flowing through the resistor R7 is 117.6 μA, the protection threshold value (second threshold value) of Iout is 317.6 μA. When Iout reaches 317.6 μA, the output end of the comparator IC3 is opened and the FET Q3 is turned on. Therefore, the drive of the FET Q2 that drives the transformer T1 is stopped, the charged high-voltage output HVout decreases, and the output current Iout decreases. As the output current Iout decreases, the current Id2 flowing through the resistor R12 decreases, and as a result, Vic3 becomes higher than 1V. Therefore, the output end of the comparator IC3 reaches the GND level, and when the FET Q3 is turned off, the FET Q2 operates again. As a result, the transformer T1 is driven and the charged output HVout rises. That is, the charged high-voltage circuit 300 operates to adjust the charged output HVout so that the output current Iout becomes a constant value at 317.6 μA when a large current flows (constant current operation).

FIG. 5 shows that the load resistance of the charging high-voltage circuit 300 (corresponding to the combined resistance value of the charging roller 2 and the photosensitive drum 1) is 20 MΩ, and the charging output HVout is −1000 V output (Iout 50 μA), and the load is loaded by scratches on the photosensitive drum 1. It is explanatory drawing of the operation of each part when a resistance changes. Note that FIG. 6A shows a case where the load resistance changes to 5 MΩ when the diode D2 and the resistor R12 are not provided. FIG. 3B shows the case where the load resistance changes to 5 MΩ when the diode D2 and the resistor R12 are present, and FIG. 3C shows the case where the load resistance changes to 1 MΩ when the diode D2 and the resistor R12 are present. There is.

When there is no diode D2 and resistor R12 (Fig. 5 (a)), Iout (negative value) gradually rises from 50 μA at the timing Tc when the load resistance changes to 5 MΩ, and when it reaches 150 μA, Isons reaches the GND level. Reach. When the Ins reaches the GND level, Vref2 is no longer maintained at 3V and Vref2 rises. When Vref2 rises, the voltage detection value VSNS also rises, so the constant voltage control unit 302 considers that the charged output HVout is lower than the target value and tries to raise the output voltage. However, since the VSNS does not match the target value, the HVout becomes the maximum output of -1500V, and the output current reaches up to 300μA. Since R7 is 20 kΩ, Vref2 at this time is 6 V or more.

On the other hand, when the diode D2 and the resistor R12 are present (FIG. 5 (b)), Iout (negative value) gradually increases from 50 μA to 117.6 μA (first threshold value) at the timing Tc when the load resistance changes. At the reached timing Td, the current Id2 flows on the diode D2 side. At this time, Isns becomes 3V-117.6 μA × 20 kΩ = 0.648 V from the equation (3), and continues to be a constant value thereafter. 117.6 μA as the first threshold value is larger than the value of Iout in the normal state where the surface condition of the conductive layer of the photosensitive drum is not scratched (as a negative value). The current Id2 flowing through the diode D2 causes Vref2 to be maintained at 3V, so that the charged output HVout is maintained at −1000V. That is, the current Iout (-117.6 μA) that flows in the load when the Ins reaches the predetermined value of 0.648 V is the DC current Iout (−17.6 μA) that flows in the load when the Iss reaches the GND level in the absence of the bypass means. It is lower than 150 μA). After the timing Td, a current of 82.4 μA flows through the resistor R12 of the bypass means, so that the voltage of Vic3 becomes 2.176 V at 3 V-82.4 μA × 10 kΩ.

When the load resistance changes to 1 MΩ in the presence of the diode D2 and the resistor R12 (FIG. 5 (c)), the Isns decreases to 0.648 V at the timing Td as in the case of FIG. 5 (b), and then becomes constant. Become. Vic3 is lowered by the current flowing through the resistor 12 of the bypass means after the timing Td. Since the load resistance at this time is 1 MΩ, the output current Iout reaches 317.6 μA (second threshold value) and Vic3 reaches 1 V at the timing Te. Therefore, the overcurrent protection circuit 307 operates, and the charged output HVout drops to 317.6V so that Vic3 becomes 1V (Iout is -317.6μA).

Therefore, the presence of the diode D2 and the resistor R12, which are bypass means, makes it possible to execute constant voltage control until Iout reaches about -117.6 μA, and overcurrent protection when Iout reaches 317.6 μA. The unit 307 operates.

According to this embodiment, a bypass means for flowing a current from the feedback terminal portion of the operational amplifier IC2 to the operational amplifier output terminal portion is provided, and the protection operation is performed by the current value flowing through the bypass means. Therefore, it is possible to protect the operational amplifier output unit at an arbitrary current value while preventing the operational amplifier output unit from reaching the GND level and causing an abnormality in the high voltage output without deteriorating the resolution of current detection.

In the present embodiment, the overcurrent protection is performed by using the voltage at the connection point between the resistor R12 and the diode D2 as the bypass means, but the voltage on the cathode side of the diode D2 may be used for the overcurrent protection.

Further, in the present embodiment, the protection operation is performed so that the output current becomes constant when the overcurrent is detected, but the protection operation is performed intermittently so as to stop the circuit operation for a predetermined time when the overcurrent is detected. You may.

2 Charging roller 100 Control board 200 Charging development board 300 Charging high-voltage circuit 306 Current detector 307 Overcurrent protection circuit D2 Diode IC2, IC3 Operational amplifier Q2, Q3 FET
T1 transformer

Claims (7)

A transformer that boosts the input voltage and
A rectifying means that rectifies the output of the transformer and supplies a DC voltage to the load.
It has an operational amplifier in which the direct current flowing through the load is input to the first input terminal and the reference value is input to the second input terminal, and the output of the operational amplifier is the first input terminal of the operational amplifier via a current detection resistor. A current detecting means that detects the direct current flowing through the load as a voltage generated in the current detecting resistor.
It has a voltage detecting means connected to a first input terminal of the operational amplifier and detecting a DC voltage supplied from the rectifying means to the load.
The current detecting means includes a voltage dividing means that divides the output of the operational amplifier as a detection value of a DC current flowing through the load, and the voltage detecting means and the voltage detecting means when the DC current flowing through the load reaches a first threshold value. It is provided with a bypass means for passing a current from the connection portion with the first input terminal of the operational amplifier to the output terminal of the operational amplifier.
Further, even when a current flows through the bypass means, it has a protective means for reducing the output power of the transformer when the direct current flowing through the load reaches a second threshold value larger than the first threshold value. A high-voltage generator characterized by. The load has a conductive layer, and the resistance value decreases according to the state of the surface of the conductive layer, and the first threshold value is the direct current in a state where the surface state of the conductive layer is normal. The high-voltage generator according to claim 1, wherein the current is lower than the detected value. When the detected value of the DC current flowing through the load becomes the first threshold value, the DC current flowing through the load reaches the GND level when the detected value of the DC current flowing through the load reaches the GND level in the absence of the bypass means. The high-pressure generator according to claim 2, wherein the absolute value is smaller than the direct current flowing through the load. The bypass means is any one of claims 1 to 3, wherein the bypass means is connected between a connection portion between the first input terminal of the operational amplifier and the current detection resistor and the output terminal of the operational amplifier. The high pressure generator described. The high-voltage generator according to claim 4, wherein the bypass means includes a resistor and a diode connected in series with the resistor and having a cathode on the output terminal side of the operational amplifier. The high-voltage generator according to claim 5, wherein the bypass means is connected in parallel with the current detection resistor. The photoconductor on which the electrostatic latent image is formed and
The charging means for charging the photoconductor and
The high-voltage generator according to any one of claims 1 to 6 is provided.
The high-voltage generator is an image forming apparatus, characterized in that a negative high voltage is applied to the charging means, and the current detecting means detects a current flowing through the charging means.

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