JP2000003103A - High voltage generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a highly accurately optimum load current even though the load fluctuation is caused by environments or the like. SOLUTION: This high voltage generating device is allowed to generate high voltage by switch/controlling a boosting transformer 1 by means of a switching circuit 2, and to supply the DC output voltage generated by rectifying and smoothing the high voltage by a rectifying circuit 9 to the load. The device detects the voltage value by converting the DC output voltage into low voltage, and moreover detects the load current. In the above mentioned structure, voltage detecting circuits R1 and R2, are connected with a current detecting circuit 9, without being directly connected to grounding potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a high voltage generator used in an image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus employing an electrophotographic system is provided with a high-voltage power supply circuit, which is indispensable for an image forming process on paper or the like. As the high-voltage power supply circuit, there are various modularized power supplies such as a charging high-voltage power supply, a developing high-voltage power supply, a transfer high-voltage power supply, and a fixing high-voltage power supply. Each of these high-voltage modules has different specifications depending on the configuration of the image forming apparatus, for example, a module in which an AC power supply is superimposed on a DC power supply,
Various configurations such as superimposed DC plus power supply on DC minus power supply, and various specifications such as specified voltage and specified current, constant current control method and constant voltage control method, single value output, multi-step value control output, load condition, etc. Specifications. Among them, it is indispensable to use a constant voltage control circuit or a constant current control circuit so that a constant voltage or current can be output under various conditions.

Usually, a constant voltage control circuit is provided with a voltage detection circuit, and a constant current control circuit is provided with a current detection circuit. In some cases, constant voltage control is performed while monitoring the value. In addition, a constant voltage control circuit and a constant current control circuit, or both a voltage detection circuit and a current detection circuit are provided to perform a constant current control operation, a voltage value at that time is monitored, and arithmetic processing is performed using the voltage. To perform a constant voltage control operation. This is because if the bias is applied only by the constant voltage control, the resistance value of the transfer roller and the like greatly changes depending on the environment, particularly humidity, so that the transfer current fluctuates and the transfer failure easily occurs. When the voltage is applied, when the size (width) of the transfer material passing over the transfer roller is small, both the area where the transfer material exists and the area where the transfer material does not exist on the transfer roller are treated as the output load of the transfer bias. Will be Since the impedance of the region where the transfer material is not present is lower than that of the region where the transfer material is present, current flows to the region where the transfer material is not present, and the region where the transfer material is present tends to cause transfer failure due to insufficient current. This is because there was a problem.

FIG. 3 is a block circuit diagram showing a schematic configuration of a high voltage generation circuit employing a conventional constant voltage control method (conventional example 1).

In FIG. 1, a high voltage control circuit includes a step-up transformer 101, a switching unit 102, a high voltage rectifier diode 103, a high voltage capacitor 104, and a constant voltage control unit 10.
5, a voltage detecting unit 106 and a resistor 107.

In the above configuration, the switching unit 102
Drives the step-up transformer 101 at a predetermined frequency and a predetermined duty ratio. Switching unit 10
The step-up transformer 101, which is switched and driven by a predetermined input voltage by step 2, boosts the input voltage and generates a high voltage having a predetermined pulsating waveform. The high voltage of the pulsating waveform generated by the step-up transformer 101 is rectified and smoothed by the high-voltage rectifier diode 103 and the high-voltage capacitor 104, thereby generating a high DC voltage. This high DC voltage is supplied to the load 110. The output voltage to the load 110 is constantly monitored by the voltage detection unit 106.

[0007] The voltage detecting section 106 is composed of the step-up transformer 101 and the high-voltage rectifier diode 103,
The bleeder resistor 107 has a built-in high resistance value for discharging the electric charge charged in 4 and is configured to convert a high voltage output voltage to a low voltage detection signal level. The constant voltage control unit 105 constantly monitors the detection signal from the voltage detection unit 106, and controls the switching unit 102 so that the high voltage output voltage generated by the step-up transformer 101 becomes a desired value. With this configuration, according to Conventional Example 1 shown in FIG. 3, it is possible to obtain a high-voltage power supply of a constant voltage control system capable of outputting a desired output voltage under various conditions.

FIG. 4 is a block circuit diagram showing a schematic configuration of another high-voltage generator employing a conventional constant current control method (conventional example 2).

In FIG. 1, a high voltage control circuit includes a step-up transformer 111, a switching unit 112, a high voltage rectifier diode 113, a high voltage capacitor 114, and a bleeder resistor 11.
7, a constant current control section 118 and a current detection section 119.

In the above configuration, the step-up transformer 111,
The switching unit 112, the high-voltage rectifier diode 113, the high-voltage capacitor 114, and the bleeder resistor 117 function in the same manner as the high-voltage generator shown in the first conventional example. The direct current flowing through the load 120 formed in the output unit forms a current loop along a path A shown in the drawing, and the load current is detected by the current detection unit 119.

[0011] The constant current control section 118 controls the current detection section 1
The load current value detected by 19 is constantly monitored, and the switching unit 112 is controlled so that the current value flowing into the load 120 from the high voltage output unit becomes a desired value.

With this configuration, according to the conventional example 2 shown in FIG. 4, a high voltage power supply of a constant current control type capable of outputting a desired output current under various conditions can be obtained.

In the high voltage generating circuits of the first and second conventional examples, the constant voltage control unit 105 or the constant current control unit 11
There are many configurations in which the constant voltage control value and the constant current control value used for each of the components 8 are variably controlled to output multi-gradation control voltages and control currents.

However, in the high voltage generating circuit of the constant voltage control method or the high voltage generating circuit of the constant current control method described above, the high voltage generating circuit of the constant voltage control method configured to monitor the output current value. In recent years, a generation circuit and a high voltage generation circuit having both a constant current control method and a constant voltage control method configured to monitor an output voltage value have been required.

FIG. 5 is a block circuit diagram showing a schematic configuration of a conventional high voltage generating circuit having both a constant current control method and a constant voltage control method.

In FIG. 1, a high voltage control circuit includes a step-up transformer 121, a switching unit 122, a high voltage rectifier diode 123, a high voltage capacitor 124, and a constant voltage control unit 12.
5, a bleeder resistor 127, a current detector 129, a voltage detector 126, and a controller 128. The step-up transformer 121, the switching unit 122, the high-voltage rectifier diode 123, the high-voltage capacitor 124, the bleeder resistor 127, and the current detection unit 129 function similarly to the corresponding components in the high-voltage generation circuit shown in FIG. 3 or FIG. I do.

The voltage detector 126 is provided with the rectifier diode 12
6a, a capacitor 126b and a resistor 126c. In the step-up transformer 121, there are three windings 121a, 121b and 121c including a voltage detecting winding 121c, and the respective windings are magnetically coupled to each other. A voltage is generated at the end of the winding 121c with a voltage value that has been tracked to the corresponding voltage value. Conversely, the voltage generated at the end of the winding 121c is
This is a voltage value that tracks the voltage generated at the end b. Therefore, the DC voltage obtained by rectifying and smoothing the output voltage at the end of the winding 121c is converted to a constant voltage control unit 125.
In the above, the output voltage after the rectification and smoothing at the end of the winding 121b can be controlled to a desired voltage value by performing the constant voltage control. The DC current flowing through the load 130 connected to the output unit forms a current loop along the path B shown in the figure, and the current detection unit 129 detects the load current. The controller 128 includes a current detector 129
Is constantly monitoring the load current value detected by
The set voltage of constant voltage control section 125 is appropriately changed such that a desired DC current flows to load 130. With this configuration, according to Conventional Example 3 shown in FIG. 5, it is possible to provide a constant voltage power supply that can supply an appropriate load current to the load 130 that fluctuates due to an environment or the like.

FIG. 6 shows a high-voltage generating circuit employing both the constant current control method and the constant voltage control method having means for monitoring the output voltage value (conventional example 4).

FIG. 6 is a block circuit diagram showing a schematic configuration of a conventional high voltage generating circuit having both a constant current control method and a constant voltage control method.

In FIG. 1, the high voltage control circuit is a winding 1
Step-up transformer 1 having 31a, 131b and 131c
31, high voltage rectifier diode 133, high voltage capacitor 134, bleeder resistor 13
7, a constant voltage / constant current dual control unit 135, and a current detection unit 1
39, rectifier diode 136a, capacitor 136b
And a voltage detector 136 including a resistor 136c and a controller 138. Step-up transformer 13
1, switching unit 132, high voltage rectifier diode 13
3, the high-voltage capacitor 134, the bleeder resistor 137, and the current detector 139 function in the same manner as the corresponding components in the high-voltage generation circuit shown in FIG. Voltage detector 136
Is connected to a winding 131c in the step-up transformer 131, and is configured to detect a voltage generated in the winding 131c.

In the above configuration, since the three windings 131a, 131b, and 131c in the step-up transformer 131 are magnetically coupled to each other, the winding 131c has a voltage value tracking the voltage value generated at the end of the winding 131b. Voltage is generated at the end. Conversely, the voltage generated at the end of the winding 131c is
It is a voltage value that tracks the voltage generated at the end of the winding 131b. Therefore, by monitoring the DC voltage obtained by rectifying and smoothing the output voltage at the end of the winding 131c by the controller 138, the voltage of the output unit can be calculated.

The constant voltage / constant current dual control unit 135 is configured to switch between constant voltage control and constant current control in accordance with a control signal from the controller 138. First, the controller 138 sends a signal to the constant voltage / constant current dual control unit 135 so as to perform constant current control using the current detection unit 139, and drives the high voltage generation circuit at a constant current. The output voltage value is monitored using the voltage detection unit 136 during the constant current driving. Next, the controller 138 switches to the constant voltage control so that the detected output voltage value is constantly output at a constant level, and switches the switching section so that the high-voltage output voltage generated by the step-up transformer 131 becomes a desired value. 132.

With this configuration, according to the conventional example 4 shown in FIG. 6, a high-voltage power supply capable of appropriately controlling a load current that fluctuates due to an environment or the like is supplied while being a constant-voltage power supply. Can be.

As described above, the step-up transformers 121 and 131 of the conventional examples 3 and 4 have three windings including the voltage detecting winding 121c or 131c, and the winding 121b or 131b and the winding 121c or 131c. And tracking operation.

However, the windings are only magnetically coupled to each other, and the windings 121b or 131b
b is for generating a high voltage, and the winding 121c or 131c is a voltage detecting winding that is wound for only several tens of turns, whereas it is wound for several thousand turns with a very fine wire. Individual errors occur in the relative ratio of the output values. This error directly causes an increase in the error of the detection level. Therefore, the conventional configuration has a problem that it is difficult to detect both the current and the voltage and to detect the output voltage with high accuracy.

As described above, in the above conventional example, it was difficult to accurately detect the output voltage. Therefore, for example, the bleeder resistor 117 shown in FIG. A technique for improving the detection accuracy has been considered.

FIG. 7 is a block diagram showing a schematic configuration of such a conventional high voltage generating circuit. In the figure, the high voltage control circuit includes a step-up transformer 141, a switching unit 142, a high voltage rectifier diode 143, a high voltage capacitor 144, a voltage detection unit 146, and a constant voltage control unit 14.
5, a current detector 149, and a controller 148. As shown in FIG.
Are configured to detect the voltage of the output unit itself. The output voltage value detected by the voltage detector 146 is sent to the constant voltage controller 145. With this configuration, it is possible to accurately detect the output voltage.

[0028]

However, even in the high voltage generating circuit as shown in FIG.
49 detects a current obtained by adding the currents flowing through the paths C and D shown in FIG. Here, the path C is a current loop flowing into the voltage detection unit 146, and the path D is a load current loop. That is, even with the configuration shown in FIG. 7, there is a problem that the accuracy of detecting the load current is reduced instead of improving the accuracy of voltage detection.

It is an object of the present invention to provide a high-voltage generator capable of supplying an optimum and highly accurate load current even if a load fluctuation due to an environment or the like occurs.

It is another object of the present invention to provide a high voltage generator that employs both the constant voltage control method and the constant current control method and can detect current and voltage with high accuracy.

[0031]

According to the present invention, there is provided a high-voltage generating circuit used in an image forming apparatus employing an electrophotographic system, comprising: a boosting transformer;
A switching circuit for driving the step-up transformer, a rectifier circuit for rectifying and smoothing a pulsating voltage output from the step-up transformer to generate a DC output voltage, and a voltage for detecting a DC output voltage generated by the rectifier circuit A detection circuit, and a current detection circuit for detecting a current flowing to a load to which the DC output voltage is applied, wherein the voltage detection circuit is not directly connected to the ground potential, but is connected to the current detection circuit. Things.

Further, the present invention provides a first transformer for outputting a positively-biased pulsating voltage, a first switching circuit for driving the first transformer, and a pulsating current output by the first transformer. A first rectifier circuit for rectifying and smoothing the voltage to generate a DC output voltage, a second transformer for outputting a negatively biased pulsating voltage, and a second transformer connected to the first rectifier circuit; A second rectifier circuit that rectifies and smoothes the pulsating voltage output by the first rectifier circuit and generates a DC output voltage; and the first rectifier circuit is connected in parallel with the first rectifier circuit and the second rectifier circuit. A voltage detecting means for detecting a DC output voltage generated by the circuit and the second rectifier circuit; and a load to which a DC output voltage generated by the first rectifier circuit and the second rectifier circuit is applied. Detect current Has a current posting circuit, and the voltage detection circuit is not directly connected to the pair ground potential is intended to be connected to the current detection circuit.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) First, a first embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a diagram showing a schematic configuration of a high voltage generating circuit according to the present embodiment. In FIG. 1, a high voltage control circuit includes a step-up transformer 1 for generating a high voltage, a switching unit 2 as a switching unit for driving the step-up transformer, and a first control unit as a first control unit for controlling a switching state of the switching unit 2. A rectifier 30 as a rectifier including a constant voltage control unit 31, a resistor R1 and a resistor R2 for detecting a voltage signal serving as an element for calculating and calculating a ground voltage of the load output unit, and a current flowing through the load 10 (load A current detection unit 9 as current detection means for detecting current);
And a controller 20 as second control means for controlling the constant voltage controller 31 in accordance with the detection signal of the current detector 9.

The switching unit 2 includes a transistor TR
1, a capacitor C2 and a diode D2, which are connected to the step-up transformer 1 and the constant voltage controller 31. A clock having a predetermined frequency and a predetermined duty is input from a generator (not shown) to the base of the transistor TR1, and the TR1 switches and drives the step-up transformer 1. The input windings N1 and N2 of the step-up transformer 1 are bifilar wound and tightly coupled. The input windings N1 and N2 and the diode D2 constitute a snubber circuit. The diode D2 conducts at a voltage at which the collector voltage of the transistor TR1 becomes twice the input voltage (TR2 emitter voltage), and the collector voltage of the transistor TR1 is increased. Is clamped. The capacitor C2 smoothes the emitter voltage of the transistor TR2, and the voltage smoothed by the capacitor C2 is supplied to the step-up transformer 1.

The step-up transformer 1 which is switched and driven by the switching unit 2 at a predetermined input voltage boosts the input voltage and generates a high voltage having a predetermined pulsating waveform. A rectifier 30 is connected to an output side of the step-up transformer 1, and a high voltage having a pulsating waveform generated by the step-up transformer 1 is supplied to a high-voltage rectifier diode D1, a high-voltage capacitor C1, and a resistor R1.
And R2 are rectified and smoothed by a rectifier 30 having a built-in R2 to generate a high DC voltage. The output side of the rectifier 30 is connected to a load output unit that outputs a high voltage to the load 10 that operates by receiving power from a drive circuit in the image forming apparatus, and the DC high voltage generated by the rectifier 30 is: Output to the load 10 via the load output unit.

The output voltage generated by the rectifier 30 is
Resistors R1 and R2 provided in the rectifier 30
, And the resistors R1 and R2 convert the high voltage output voltage to a low voltage detection signal level. The resistors R1 and R2 also have a function of a bleeder resistor for discharging the electric charge charged in the high-voltage capacitor C1 by the step-up transformer 1 and the high-voltage rectifier diode D1. The detection voltage (hereinafter referred to as R1R2 divided voltage) obtained by the voltage division of the resistor R1 and the resistor R2 is
2 is not grounded, and therefore does not directly indicate the ground potential of the load output unit, but depends on both the potential of the portion where the current detection unit 9 and the rectifier 30 are connected and the potential of the load output unit. Indicates a value that is uniquely determined.

In order to correct the detection deviation of the load output voltage caused by one end of the resistor R2 not being at the ground potential,
In the high voltage generation circuit of the present embodiment, the reference value generated based on the data transmitted by the controller 20 is corrected using the load current detection value.

The resistors R1 and R2 in the rectifier 30 are connected to an arithmetic unit 33 in the constant voltage control unit 31.
The R2 divided voltage is monitored by the calculator 33. Further, the current detector 9 is provided with the correction calculator 3 in the constant voltage controller 31.
2 and the controller 20, and the detection signal of the load current detected by the current detection unit 9 is
2 and the controller 20. The constant voltage control unit 31 performs constant voltage control by comparing and controlling the output signals of the arithmetic unit 33 and the correction arithmetic unit 32.

The constant voltage control unit 31 is connected to the switching unit 2 and the controller 20, and performs a series regulator operation of the transistor TR2, an arithmetic unit 33 monitoring the R1R2 divided voltage, and outputs a load current detection signal. And an operational amplifier OP for performing comparison operation control of output signals of the operation unit 33 and the correction operation unit 32
1 and a threshold setting unit 12 for generating a predetermined reference voltage based on transmission data from the controller 20.

The controller 20 sends data to the threshold setting unit 12 so as to obtain a desired load output voltage. The threshold setting unit 12 generates a predetermined threshold voltage according to the data transmitted by the controller 20 and outputs the predetermined threshold voltage to the correction calculator 32. The load current detection value detected by the current detector 9 is also output to the correction calculator 32,
Numeral 2 corrects the threshold voltage and the detected current value according to a predetermined arithmetic expression, and generates a reference voltage for performing a constant voltage operation of the load output unit. The arithmetic unit 33 shifts the R1R2 divided voltage according to a predetermined arithmetic expression and converts the divided voltage into a voltage value that can be compared with a reference voltage. The operational amplifier OP1 is a correction arithmetic unit 32
Is constantly monitored, and the transistor TR2 is driven and controlled such that the voltage value of the load output section becomes a value uniquely determined by the reference voltage.

The direct current (load current) flowing through the load 10 connected to the load output unit forms a current loop through a path H shown in the figure. The detection of the load current is performed by the rectifier 30.
And a current detection unit 9 which is connected to the path H and constitutes a part of the path H. The load current is detected by flowing through resistors R3 and R4 and then through resistor R5. For example, if the resistor constants are R3 = 10 KΩ, R4 = 2.
When 7KΩ and R5 = 180KΩ are set, the voltage divided by the resistors R3 and R4 hardly fluctuates due to the load current, and the voltage dropped by the voltage drop caused by the load current flowing through the resistor R5 is It is sent to the controller 20 as load current information. That is, the resistor R5 mainly serves as a current detection resistor. However, since the load current is a very small current (〜20 μA), unless the controller 20 to which the connection is made has a high impedance input, the current flows in and an error occurs. Therefore, the current detection unit 9
Is connected to the controller 20 via the impedance converter 11 having high impedance input and low impedance output characteristics.
Connected to. Further, the current detection unit is AC grounded by a capacitor C3.

The controller 20 shifts the constant voltage value of the load output unit by sequentially changing data transmitted to the threshold setting unit 12 in the constant voltage control unit 31 so that a desired DC current flows to the load 10. The load current value at that time is monitored by the current detection unit 9. This process is repeated until the load current value matches the desired value. As a result, it is possible to provide a high-voltage power supply of a constant voltage control type capable of flowing a desired current value to the load 10 whose state fluctuates variously.

As described above, according to the present embodiment, since the resistors R1 and R2 in the rectifier 30 are configured not to be grounded but to float on the current detecting section 9, a conventional high voltage generating circuit is used. Unlike FIG. 7, the current detector 9 can detect only the load current with high accuracy. In addition, since the load output unit and the voltage detection unit are configured depending on the voltage generated from the same winding of the step-up transformer, the resistors R1 and R2 are elements that calculate the output voltage of the load with high accuracy. The signal can be detected, and by performing arithmetic processing with the detection signal of the current detection unit 9, the potential of the load output unit can be detected with high accuracy. Also, since it has detection control means for both the load current and the load voltage,
It can be easily operated as a current limiter and a voltage limiter. Therefore, it is possible to provide a constant-voltage control type high-voltage generation circuit that can supply an optimum load current value with much higher precision than in the past.

Further, by employing the high voltage generating circuit configured as described above in an image forming apparatus, it is possible to prevent an operation failure such as a transfer failure due to a change in a transfer current and to make each unit in the image forming apparatus available. The effect that it becomes possible to operate appropriately is obtained.

In this embodiment, the rectifier is of a single rectifier type for the sake of convenience. However, double rectification or higher rectification may be used. Although the operational amplifier is used for the constant voltage control unit, other comparison operation means may be used.
Although a bifilar-wound transformer is used for the step-up transformer 1, a step-up transformer including a single-turn input winding may be used.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. FIG.
FIG. 2 is a diagram illustrating a schematic configuration of a high-voltage generation circuit according to the present embodiment. In the configuration of the present embodiment, the positive bias power source is superimposed on the negative bias power source to enable both positive and negative outputs.
1 and R2 and the correction arithmetic unit 32 are applied, and a bias power supply capable of positive / negative output is reconfigured to obtain the same effect.

In the figure, the high voltage control circuit forms a positive bias generator and a negative bias generator. The positive bias generation unit includes a step-up transformer 51 that generates a high voltage, a switching unit 52 that drives the step-up transformer, a constant voltage control unit 31 as first control means that controls a switching state of the switching unit 52, A rectifier 50 for rectifying the output of the transformer 51, a voltage detection unit 70 for detecting a voltage signal serving as an element for calculating and calculating a ground voltage of the load output unit, and a current (load current) flowing through the load 10 are detected. It comprises a current detector 9 and a controller 20 as second control means for controlling the constant voltage controller 31 according to a detection signal of the current detector 9.

The negative bias generator of this embodiment does not control the output voltage. The boost transformer 61 generates a high voltage, the switching unit 62 drives the boost transformer, and rectifies the output of the boost transformer 61. Rectifier 6
0.

The positive bias output state will be described. The switching unit 52 includes a transistor TR10, a capacitor C11, and a diode D11, and is connected to the step-up transformer 51 and the constant voltage control unit 31. A clock having a predetermined frequency and a predetermined duty is input from a generator (not shown) to the base of the transistor TR10, and the TR10 switches and drives the boosting transformer 51. The input windings N1 and N2 of the step-up transformer 51 are bifilar wound and tightly coupled. The input windings N1 and N2 and the diode D11 form a snubber circuit. The diode D11 conducts at a voltage at which the collector voltage of the transistor TR10 becomes twice the input voltage (TR11 emitter voltage), and the collector voltage of the transistor TR10 is increased. Is clamped. The capacitor C11 smoothes the emitter voltage of the transistor TR11, and the voltage smoothed by the capacitor C11 is supplied to the step-up transformer 51.

The step-up transformer 51, which is switched by the switching unit 52 at a predetermined input voltage, boosts the input voltage and generates a high voltage having a predetermined pulsating waveform in the secondary winding. A rectifier 50 is connected to the output side of the step-up transformer 51, and a high voltage of a pulsating waveform generated by the step-up transformer 51 is output by a rectifier 30 including a high-voltage rectifier diode D10, a high-voltage capacitor C10, and a resistor R10. By rectifying and smoothing, a high DC voltage (positive bias) is generated.

The output side of the rectifier 50 is connected to a load output unit that outputs a high voltage to the load 10 in the image forming apparatus, and the DC high voltage generated by the rectifier 50 passes through the load output unit. It is output to the load 10 and the voltage detection unit 70. However, since the output voltage is applied so that current flows through a path through the resistor R20 in the rectifier 60, a high voltage drop occurs in R20 having a high resistance value. In other words, a positive high voltage is generated on the load output side of the resistor R10 and a negative high voltage is generated on the resistor R20 side with respect to the ground point as a reference of 0V.

The output voltage generated at the load output terminal is constantly monitored by resistors R30 and R31 provided in the voltage detector 70, and the high voltage output voltage is converted to a low voltage detection signal level. You. A detection voltage (hereinafter referred to as R30R) obtained by dividing the voltage of the resistor R30 and the resistor R31.
Since the resistor R31 is not grounded, it does not directly indicate the ground potential of the load output unit, but the potential of the portion where the current detector 9 and the rectifier 60 are connected and the load output. It shows a value that is uniquely determined according to both the potential of the unit.

In order to correct the amount of detection error of the load output voltage caused by one end of the resistor R31 being not at the ground potential, in the high voltage generation circuit of this embodiment, the controller 20 is used.
The reference value generated based on the data transmitted by the above is corrected according to the detected load current value.

The resistors R30 and R31 are connected to an arithmetic unit 33 in the constant voltage control unit 31, and the R30R31 divided voltage is monitored by the arithmetic unit 33. Further, the current detector 9 is connected to the correction calculator 32 in the constant voltage controller 31 and the controller 20, and the detection signal of the load current detected by the current detector 9 is supplied to the correction calculator 32 and the controller 20. Is monitored by The constant voltage control unit 31 performs constant voltage control by comparing and controlling the output signals of the arithmetic unit 33 and the correction arithmetic unit 32.

The constant voltage control section 31 is connected to the switching section 52 and the controller 20, and includes a transistor TR11 for performing a series regulator operation, and a transistor R30R3.
A computing unit 33 that monitors the 1-divided voltage, a correction computing unit 32 that monitors the load current detection signal, and a computing unit 3
And a threshold setting unit 1 for generating a predetermined reference voltage based on transmission data from the controller 20.
And 2.

The controller 20 transmits data to the threshold setting unit 12 so that the load output voltage becomes a predetermined value. The threshold setting unit 12 generates a predetermined threshold voltage according to the data transmitted by the controller 20 and outputs the predetermined threshold voltage to the correction calculator 32. The load current detection value detected by the current detection unit 9 is also output to the correction calculator 32. The correction calculator 32 corrects the threshold voltage and the current detection value according to a predetermined calculation formula, To generate a reference voltage for performing the constant voltage operation. The calculator 33 shifts the voltage value of the R30R31 divided voltage according to a predetermined calculation formula, and converts the voltage value into a voltage value that can be compared with the reference voltage. The operational amplifier OP10 constantly monitors the load output voltage detection signal output from the correction arithmetic unit 32, and sets the transistor TR11 so that the voltage value of the load output unit becomes a value uniquely determined by the generated reference voltage. Drive control.

The direct current (load current) flowing through the load 10 formed in the load output section forms a current loop through a path J shown in the figure. The detection of the load current is performed by the current detection unit 9 connected to the rectifier 60 and constituting a part of the path J. The load current is detected by flowing through the resistors R40 and R41, and then flowing through the resistor R42. For example, if the resistor constants are R3 = 10 KΩ, R4 = 2.
When 7KΩ and R5 = 180KΩ are set, the resistor R40
And the voltage divided by the resistor R41 hardly fluctuates due to the load current, and the voltage dropped by the load current and the voltage drop of the resistor R42 is sent to the controller 20 as the load current information. That is, mainly the resistor R4
2 plays the role of a current detection resistor. However, since the load current is a very small current (〜20 μA), unless the controller 20 to which the connection is made has a high impedance input, the current flows in and an error occurs. Therefore, the current detection unit 9 is connected to the controller 20 via the impedance converter 11 having high impedance input and low impedance output characteristics. The current detecting section is grounded by C40 in terms of AC.

The controller 20 shifts the constant voltage value of the load output unit by sequentially changing data transmitted to the threshold setting unit 12 in the constant voltage control unit 31 so that a desired DC current flows to the load 10. The load current value at that time is monitored by the current detection unit 9. This process is repeated until the load current value matches the desired value. As a result, it is possible to provide a high-voltage power supply of a constant voltage control type capable of flowing a desired current value to the load 10 whose state fluctuates variously.

The negative bias generator will be described. The switching unit 62, the step-up transformer 61, and the rectifier 60
Each functions in the same manner as the switching unit 52 of the positive bias generation unit, the step-up transformer 51, and the rectifier 50, and the resistor R
A high voltage negative bias is generated across the 20.

Here, a specific example will be given. Controller 2
Data transmitted from 0 to the threshold setting unit 12 (00h to FF
The threshold voltage for h) is set as follows. (00h → 5.66V, 12h → 6.51V, 90h → 12.45V, F
Fh → 17.69V) R30 = 40MΩ, R31 = 560KΩ, R40 = 10KΩ,
R41 = 2.7 KΩ, R42 = 180 KΩ, Vcc = 21.5 V, and the arithmetic expression of the arithmetic unit 33 is set as follows.

Corrected load detection voltage = 5306 × load output section voltage + 0.379 × load current detection value + 2.498 Correction calculator 32 for calculating the load current detection value and the threshold value
Is set as follows.

Corrected reference voltage (data) = 8264 + 6.0106 × da
ta (decimal) / 255 + 0.38427 x load current detection value By using the calculator set as above,
The following results are obtained.

[0064]

[Table 1]

Under the condition that the load output voltage is constant,
The load current fluctuates according to the fluctuation of the load resistance, and R30R3
The one-divided voltage also fluctuates. However, since the reference voltage and the R30R31 divided voltage are corrected using the arithmetic unit, the load output voltage does not change even if the load resistance changes.

However, in this setting, since the detection current is set to about 20 μA, the threshold value setting (FFh) and the load resistance 3
At 0 MΩ, the load current detection value is a negative value.

As described above, according to the present embodiment, the detection resistor R31 is configured not to be grounded but to be floated on the current detection section 9, so that it differs from the conventional high voltage generation circuit (FIG. 7). The current detecting section 9 can detect only the load current with high accuracy. Further, the resistors R30 and R31 are directly connected to the load output section and the current detection section 9 to keep the potential of the load output section constant regardless of the voltage drop value generated in the resistor R20 in the negative bias generation circuit. Can be operated. Further, the resistors R30 and R31 can detect a voltage signal serving as an element for calculating and calculating the output voltage of the load with high accuracy. Can be detected with high accuracy. In addition, since it has detection control means for both the load current and the load voltage, it can be easily operated as a current limiter and a voltage limiter. Therefore, it is possible to provide a constant-voltage control type high-voltage generation circuit that can supply an optimum load current value with much higher precision than in the past.

Further, by employing the high voltage generating circuit configured as described above in an image forming apparatus, it is possible to prevent an operation failure such as a transfer failure due to a variation in a transfer current and to reduce each load in the image forming apparatus. The effect that it becomes possible to operate appropriately is obtained.

In this embodiment, the rectifier is of a single rectifier type for convenience, but may be a voltage doubler rectifier or a voltage doubler rectifier more than that. Although the operational amplifier is used for the constant voltage control unit, other comparison operation means may be used.
Although a bifilar winding step-up transformer is used, a step-up transformer including a single-turn input winding may be used.

[0070]

As described above, according to the present invention, the current loop flowing through the voltage detection circuit and the load current loop flowing through the current detection circuit have different path configurations, and the current detection circuit can accurately detect the overload current. Can be detected.

Further, the summer detection circuit can detect a voltage signal for calculating and calculating the output voltage of the load with high accuracy, and by calculating with the undetectable current value, the load voltage can also be detected with high accuracy. .

Further, since a detection control circuit is provided for both the load current and the load voltage, it can be operated as a current limiter and a voltage limiter.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a schematic configuration of a high voltage generation circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a schematic configuration of a high voltage generation circuit according to a second embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a schematic configuration of a conventional high voltage generation circuit (conventional example 1).

FIG. 4 is a block circuit diagram showing a schematic configuration of a conventional high voltage generation circuit (conventional example 2).

FIG. 5 is a block circuit diagram showing a schematic configuration of a conventional high voltage generation circuit (conventional example 3).

FIG. 6 is a block circuit diagram showing a schematic configuration of a conventional high voltage generation circuit (conventional example 4).

FIG. 7 is a block circuit diagram showing a schematic configuration of a conventional high voltage generation circuit (conventional example 5).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Step-up transformer 2 Switching circuit 9 Current detection circuit 30 Rectifier circuit 31 Constant voltage control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 ZA01 2H032 AA05 5G065 AA00 DA07 EA01 HA04 HA08 JA01 LA01 LA02 MA01 MA03 MA09 MA10 NA02 NA09 5H730 AA04 AS01 AS02 AS04 BB43 BB57 BB85 CC22 CC28 DD02 EE02 EE31 FG25 FD25

Claims (10)

[Claims] 1. A high-voltage generating circuit used in an image forming apparatus adopting an electrophotographic system, comprising: a step-up transformer; a switching circuit for driving the step-up transformer; A rectifier circuit that generates a DC output voltage by performing smoothing; a voltage detection circuit that detects a DC output voltage generated by the rectifier circuit; and a current detection circuit that detects a current flowing to a load to which the DC output voltage is applied. Wherein the voltage detection circuit is not directly connected to the ground potential but is connected to the current detection circuit. A first control circuit connected between the voltage detection circuit and the switching circuit, the first control circuit being configured to drive and control the switching circuit so that an output value of the voltage detection circuit becomes a predetermined voltage value. The high voltage generator according to claim 1, further comprising: 3. A second control circuit connected between the current detection circuit and the first control circuit for controlling the first control circuit so that an output value of the current detection circuit becomes a predetermined current value.
3. The high voltage generator according to claim 2, further comprising a control circuit. 4. The method according to claim 1, wherein the first control circuit generates a single signal value by performing a predetermined calculation process using an output value of the current detection circuit and an output value of the second control circuit as parameters. 4. The high voltage generator according to claim 3, wherein: 5. The high voltage generator according to claim 1, wherein said voltage detecting means has a resistor for dividing a DC output voltage generated by said rectifier circuit. 6. A first transformer for outputting a positively biased pulsating voltage, a first switching circuit for driving the first transformer, rectification and rectification of the pulsating voltage output by the first transformer. A first rectifier circuit that generates a DC output voltage by performing a smoothing operation, a second transformer that outputs a negatively biased pulsating voltage, and that is connected to the first rectifier circuit and output by the second transformer. A second rectifier circuit for rectifying and smoothing the pulsating voltage to generate a DC output voltage; connected to the first rectifier circuit and the second rectifier circuit in parallel, the first rectifier circuit and the second rectifier circuit; Voltage detecting means for detecting a DC output voltage generated by the second rectifier circuit, and a current flowing to a load to which the DC output voltage generated by the first rectifier circuit and the second rectifier circuit is applied. Current posting times A high-voltage generation device, comprising: a path; and the voltage detection circuit is not directly connected to the ground potential, but is connected to the current detection circuit. 7. The high voltage generator according to claim 6, wherein said voltage detecting means has a resistor for dividing a DC output voltage generated by said first rectifier circuit and said second rectifier circuit. apparatus. 8. A driving circuit, which is connected between the voltage detection circuit and the first switching circuit and controls the driving of the first switching circuit so that an output value of the voltage detection circuit becomes a predetermined voltage value. 7. The high voltage generator according to claim 6, further comprising one control circuit. 9. A second control circuit connected between the current detection circuit and the first control circuit for controlling the first control circuit so that an output value of the current detection circuit becomes a predetermined current value.
9. The high-voltage generator according to claim 8, further comprising a control circuit. 10. The first control circuit generates one signal value by performing predetermined arithmetic processing using an output value of the current detection circuit and an output value of the second control circuit as parameters. The high voltage generator according to claim 9, wherein: