JP2689902B2 - High voltage power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage power supply device used in electrophotographic printers and copying machines.

[0002]

2. Description of the Related Art As represented by a laser beam printer in recent years, electrophotographic printing apparatuses are required to have high resolution from 300 dpi or 400 dpi to 600 dpi or 1200 dpi. In this type of electrophotographic printing device, a printed image is formed by charging the photosensitive member and writing an image on the photosensitive member with a laser beam, so the charging on the photosensitive member is uniform, and even if the environment changes. Must be stable. Further, when writing an image with laser light, high-speed pulsed light, which has a fast rise and fall and has large energy in a short time, is required.

In order to realize the above high resolution performance, one method of uniformizing the charging of the photosensitive member is to provide a box-shaped metal member with a wire electrode held at a constant distance by an insulator, There is non-contact charging by a corona discharger obtained by applying a high voltage of 5 to 10 kV between the wire electrode and the photoconductor, but in the corona discharger, ozone is generated due to generation of ozone having a peculiar odor. Since a prevention filter is required and a high-voltage power supply device that generates a high voltage of 5 to 10 kV is required, there is a drawback in that the printer device cannot be manufactured inexpensively.

For this reason, in recent electrophotographic printers, contact charging which directly gives a high voltage to a photosensitive member by a conductive material having a medium resistance of 10 ⁴ to 10 ⁶ Ω has become the mainstream. 1 as a high voltage power supply due to charging
It has become a relatively low voltage of about 1.5 kV. For this reason, as the high-voltage power supply device, the current can be suppressed to about several μA to several tens of μA, so that the power becomes small, the cost can be reduced, and the price of the entire printer device can be reduced. Has become.

FIG. 5 is a sectional view showing the structures of a conventional contact charging roller and charging brush. The contact medium between the photosensitive member used in the contact charging, including a conductive medium by the metal shaft 501 and the conductive sponge 502 as shown in FIG. 5 (a) high as a conductive roller of about 10 ⁴ to 10 ⁶ Omega Some apply a voltage, and some apply a high voltage using a conductive brush 504 fixed to a metal support 503 as shown in FIG. 5B. However, if a high DC voltage is simply applied, the charging state greatly depends on the surface state of the material of the conductive sponge 502 forming the charging roller and the number of bristles per unit area of the conductive brush 504. However, the higher the printing resolution is, the more it appears as uneven charging of the photoconductor.

FIG. 6 is a high voltage output waveform diagram for uniform charging in the conventional contact charging. As shown in FIG. 6, the charging voltage is 200 to 500 Hz AC high voltage AC.
^{By using} a waveform in which ^PP has a DC bias Vdc of about -800 V, uneven charging can be eliminated and the charging state can be made uniform due to the correlation between the change in charging potential and the movement of the photosensitive member surface. It came to be done.

[0007]

However, the frequency of the AC voltage AC ^PP that modulates a DC high voltage is related to the moving speed (rotation speed) of the surface of the photoconductor, which is the printing speed, but it is as low as 200 to 500 Hz. It becomes frequency. Therefore, unlike the switching frequency of 20 to 50 kHz that constitutes the normal switching power supply of the device main body, the magnetic material of the step-up transformer that constitutes the high-voltage power supply device cannot be realized by the ferrite core due to the relationship of the saturation magnetic flux density, and the carbon steel sheet. It becomes the iron core which laminated. Also, in order to lower the frequency, the number of turns of the coil forming the transformer must be increased, and the increase in the number of turns of the coil requires a large core size.
It could only consist of a large and heavy transformer. Further, the circuit that drives the primary side of the transformer cannot be realized by a simple switching circuit. FIG. 7 is a block diagram of a circuit configuration for equalizing the charging in the conventional example. As shown in FIG. 7, in addition to the oscillation circuit 701, a power operational amplifier 702 drives a primary side of a step-up transformer 703 to form a high-voltage power supply device. Since it had to be configured, it had the drawback that the price as a power supply would not be cheap.

Further, in order to reduce the cost of the entire high-voltage power supply device, normally, the charging output is branched to generate the voltage of the developing bias and the auxiliary potential for transfer or the like. However, since the output of the step-up transformer 703 has a low frequency, in the DC bias generating circuit 704 and the rectifying / smoothing circuit 705 of the auxiliary output for other outputs such as development, a large-capacity capacitor is used as a smoothing capacitor after the rectifying diode. C is needed,
Since high withstand voltage is required, there is a problem that the number of parts increases, such as connecting a plurality of capacitors having small capacitances in parallel.

Further, in a device in which a high voltage output terminal appears in the opening when the capacitance of the capacitor C becomes large, the capacitance of the smoothing circuit influences the discharge time, which makes it difficult to design for safety. There was a point.

In view of the above points, an object of the present invention is to provide a low-cost high-voltage power supply device having a simplified circuit while maintaining the same charging characteristics as the conventional device.

[0011]

A high-voltage power supply device of the present invention comprises a first switching means, a first step-up transformer and a first step-up transformer .
First direct current high voltage generating means including one rectifying means ;
The second switching means, the second step-up transformer and the second
Second direct current high voltage generating means including rectifying means
The output of the first rectifying means and the output of the second rectifying means.
A high voltage power source device in which the radical 19 are connected in series, the
First DC high voltage generating means and second DC high voltage generating means
Has a third switching means for controlling the operation of the live means.
The third switching means is configured to operate the first DC high voltage
Generating means or the second DC high voltage generating means
At least one control means for controlling one operation,
First DC high voltage output from the DC high voltage generator of
And a second direct current output from the second DC high voltage generating means.
Equipped with a voltage that is the difference from the high voltage as an offset voltage
Generate a pulsating voltage .

[0012]

[0013]

[0014]

[Action]

(1) Since the first DC high voltage generating means is controlled by the first switching means and the third switching means,
The DC high voltage output is a rectangular wave modulated by the switching frequency of the third switching means, and a charging characteristic equivalent to that of a conventional sine wave is obtained.

(2) Since the second DC high voltage generating means is controlled by the second switching means, the second DC high voltage generating means always operates, and the second DC high voltage output is the DC voltage. The auxiliary output circuit can be simplified.

(3) Since at least one of the first to third switching means is realized by means for receiving a control signal from the microcomputer, the circuits of the first to third switching means can be simplified. .

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration and an operation of a high voltage power supply device according to a first embodiment of the present invention. FIG. 1A is a circuit configuration block diagram, and FIG. 1B is an operating voltage waveform diagram showing a change in a control signal and a high voltage output voltage.

The structure of FIG. 1A will be described. The positive high voltage block 101 produces a positive high voltage output + V. The negative high voltage block 102 produces a negative high voltage output -V. The control signal CONT_IN for controlling the entire charging output is a positive high voltage control gate 103 and a negative high voltage control gate 104.
The positive high voltage output + V and the negative high voltage output −
Turn V on and off at once. The control signal generator 105 is C
ONT + is output, and CONT + is positive high voltage control gate 1
Input to only 03 to turn on / off the positive high voltage output + V. The positive high voltage control gate 103 outputs the gate output 111 controlled by CONT_IN and CONT + to control the operation of the positive high voltage block 101. The negative high voltage control gate 104 outputs the gate output 112 controlled by CONT_IN to control the operation of the negative high voltage block 102.

In the first embodiment, CONT + is input to the positive high voltage control gate 103 to control the operation of the positive high voltage block 101. However, CONT + is input to the negative high voltage control gate 104 and the negative voltage is supplied to the negative high voltage control gate 104. The operation of the high pressure block 102 may be controlled.

The inside of the positive high voltage block 101 is a normal DC / DC converter, and the primary side power supply voltage E
A drive transistor TR1 and an oscillation circuit 10 for causing a current from V to flow through the primary side of the positive step-up transformer T1.
6. A rectifying / smoothing circuit 108 that obtains a positive high-voltage output + V is provided on the secondary side of the positive step-up transformer T1.
have. The inside of the negative high-voltage block 102 is also a normal DC / DC converter like the positive high-voltage block 101, and is a drive for flowing the current from the primary side power supply voltage EV through the primary side of the negative step-up transformer T2. It has a transistor TR2 and an oscillation circuit 107.
A rectifying / smoothing circuit 109 that obtains a negative high voltage output -V is provided on the secondary side of the step-up transformer T2. These high voltage outputs + V and −V are connected in series and output to the output terminal 110.

The operation of FIG. 1A will be described. In the positive high voltage block 101, the oscillation circuit 106 is adapted to perform an oscillation operation when the gate output 111 for the control signal becomes a low level (hereinafter, referred to as an L level). A switching current flows through the primary side of the step-up transformer T1 and a positive high voltage output + V is output. However, on the positive oscillation circuit 106 side, CONT_IN and CONT are passed through the positive high-voltage control gate 103.
Since + and are applied, as shown in FIG. 1B, the positive high voltage output + V is output in the intermittent state.

FIG. 1 (b) shows the time variation of the voltage of the output terminal 110, and shows the case where the positive high voltage output + V is smaller than the negative high voltage output -V. First, in the period TA where CONT_IN is at L level,
Since the gate outputs 111 and 112 of the positive high-voltage control gate 103 and the negative high-voltage control gate 104 for the control signal both become high level (hereinafter, referred to as H level), the oscillation circuits 106 and 107 do not operate, The voltage of the output terminal 110 is 0V.

Next, a period T when CONT_IN is at H level
In B, since the oscillation circuit 107 operates, a negative high voltage output −V is output.

At this time, the period T when CONT + is at L level
In C, since the oscillation circuit 106 does not operate, a positive high voltage is not generated, and the output voltage is only the negative high voltage output −V. Further, during the period TD in which CONT + is at H level, the oscillation circuit 106 operates, so that the positive high voltage output + V
Occurs, the positive output voltage output + V is added to the negative high voltage output −V, and the combined voltage −V ₂ (−V ₂ = (−
V) + (+ V)).

As described above, in the high voltage power supply device of the first embodiment, the positive high voltage block 101 for generating the positive high voltage output + V and the negative high voltage block 102 for generating the negative high voltage output −V are provided. Having and these high pressure blocks 10
Since 1 and 102 can be configured as a switching power supply with a frequency of 20 to 50 kHz, a small ferrite core can be used for the step-up transformers T1 and T2, and even if the transformer portion is 2 blocks, the weight is the iron core core. It is significantly lighter than the conventional structure and requires a small number of coil windings, so a large mounting area is not required. Further, the circuit that drives the primary side of the transformer may simply be a switching circuit, which is realized by a general switching power supply circuit such as the RCC method configured by one switching transistor and one oscillation circuit. Therefore, it is not necessary to use a power operational amplifier as in the conventional case.

With the above configuration, the voltage output from the output terminal 110 has a high voltage output waveform that is modulated by the frequency generated by the control signal generator 105,
The output is equivalent to the output voltage of the conventional AC transformer. The output waveform is not a sine wave but a rectangular wave, but since uniform charging is performed by a change in charging potential, the charging characteristic is equivalent to that of a conventional sine wave.

In the first embodiment, the switching circuit on the primary side of the transformer is composed of the drive transistor and the oscillation circuit. However, by adding an auxiliary winding for feedback to the winding of the transformer, the drive transistor A general RCC circuit that itself serves as an oscillation circuit can be easily realized.

FIG. 2 is a circuit configuration block diagram of a high-voltage power supply device according to a second embodiment of the present invention, which is a positive high voltage output + V.
The case where a control signal for turning on and off is generated by a microcomputer is shown. The positive high-voltage block 101 that generates the positive high-voltage output + V and the negative high-voltage block 102 that generates the negative high-voltage output −V have the same configuration as in FIG. 1A, and the positive high-voltage block is turned on. The control signal CONT + to turn off is given by the microcomputer 201. This is because the cycle of turning on / off the positive high voltage is 2 to 5 msec (500 to 200 Hz).
This is because the cycle can be sufficiently generated even by the microcomputer.

In the second embodiment, the control signal generator 105 for turning on / off the positive high voltage output + V is unnecessary, and the microcomputer 201 is added. However, the microcomputer is the engine of the printer. Since it can be incorporated in a part of a microcomputer that controls the unit, the circuit becomes simple because the control signal generator 105 is not provided.

FIG. 3 is a circuit configuration block diagram of a high-voltage power supply device according to a third embodiment of the present invention, showing a case where a switching signal is generated by a microcomputer. Drive transistor 3 for generating a positive high voltage as shown in FIG.
01 and a drive transistor 30 generating a negative high voltage
A PWM generator 306 in a microcomputer 305 for switching signals 303 and 304 connected to
And the signal from 307, the operation of PWM1 on the side that generates a positive high voltage is programmed for 2 to 5 ms.
Even if it is controlled by the cycle of ec, the circuit as a high voltage power supply device becomes simpler.

FIG. 4 is a circuit configuration block diagram of a high-voltage power supply device according to a fourth embodiment of the present invention, showing an output voltage extraction state when a charging output is branched to generate an auxiliary potential such as a developing bias. . As shown in FIG. 4, since the smoothing capacitor has a high switching frequency, the capacity can be reduced. In addition to charging output, auxiliary output terminal 4
Even when the auxiliary potential output such as the developing bias is obtained from 01, the negative high-voltage block 102 is always operating and the negative high-voltage output −V is direct current, so the auxiliary output terminal 401
The capacitor C is not required in the area of (2), the number of parts does not increase, and the voltage of the output terminal is rapidly discharged by the opening, so that there is no safety problem.

[0032]

As is apparent from the above description, the high voltage power supply device of the present invention has the following effects.

(1) By controlling the first DC high voltage generating means by the first switching means and the third switching means, the first DC high voltage output is generated by the third switching means. The high-voltage output waveform is modulated by the switching frequency, and the output is equivalent to the output voltage of the conventional AC transformer. The output waveform at this time is not a sine wave but a rectangular wave, but since uniform charging is performed by the change of the charging potential, the charging characteristics are equivalent to those of the conventional sine wave, and the charging characteristics similar to those of the conventional high voltage power supply device are used. It has the effect of obtaining characteristics.

As shown in the first embodiment, it has a positive high voltage block for generating a positive high voltage output and a negative high voltage block for generating a negative high voltage output, and these high voltage blocks are: By configuring it as a switching power supply with a frequency of 20 to 50 kHz, a small ferrite core can be used for the two step-up transformers, and even if the transformer part consists of two blocks, the weight is significantly higher than the conventional structure using an iron core. It is light and requires a small number of coil turns,
It does not require a large mounting area. Also, the circuit that drives the primary side of the transformer may simply be a switching circuit, which is realized by a general switching power supply circuit such as the RCC method configured by one switching transistor and one oscillation circuit. Therefore, it is not necessary to use a power operational amplifier as in the conventional case. For this reason, the circuit is simplified, and an inexpensive high-voltage power supply device can be realized.

(2) By implementing at least one of the first to third switching means by means for receiving a control signal from the microcomputer, the circuits of the first to third switching means can be simplified. It has the effect of being able to.

As shown in the second embodiment, the control signal generator for turning on / off the positive high voltage output is not required, and the microcomputer is added. However, the microcomputer is the engine part of the printer. By incorporating it in the part of the microcomputer that controls
In fact, the circuit is simplified by the absence of the control signal generator, and it is possible to realize a low-cost high-voltage power supply device.

Further, as shown in the third embodiment, a part corresponding to the control signal generator from the first embodiment to the oscillation circuit is realized by the PWM generator in the microcomputer to generate the switching signal. , CONT + of the first embodiment
By realizing the signal corresponding to (1) by the program of the microcomputer, the circuit is simplified, and similarly to the second embodiment, the low-cost high-voltage power supply device can be realized.

(3) By controlling the second DC high voltage generating means by the second switching means, the second DC high voltage generating means always operates, and the second DC high voltage output is DC voltage. Therefore, there is an effect that the auxiliary output circuit can be simplified.

As shown in the fourth embodiment, since the smoothing capacitors of the positive high voltage output circuit and the negative high voltage output circuit have a high switching frequency, a large capacity is unnecessary. Even when the charging output is branched and the auxiliary output such as the developing bias is obtained from the auxiliary output terminal, the negative high-voltage block is always operating and the negative high-voltage output is direct current. No capacitors are needed. Therefore, the mounting space for the auxiliary output circuit is also small, and even when the high voltage output terminal appears in the opening,
Since the capacity of the capacitor of the smoothing circuit is small, the voltage is discharged rapidly, which has the effect of facilitating safety design.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration and operation of a high-voltage power supply device according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration block diagram of a high-voltage power supply device according to a second embodiment of the present invention.

FIG. 3 is a circuit configuration block diagram of a high-voltage power supply device according to a third embodiment of the present invention.

FIG. 4 is a circuit configuration block diagram of a high-voltage power supply device according to a fourth embodiment of the present invention.

FIG. 5 is a cross-sectional view showing structures of a contact charging roller and a charging brush of a conventional example.

FIG. 6 is a high-voltage output waveform diagram for uniform charging in conventional contact charging.

FIG. 7 is a block diagram of a circuit configuration for uniform charging according to a conventional example.

[Explanation of symbols]

101 Positive High-Voltage Block 102 Negative High-Voltage Block 103 Positive High-Voltage Control Gate 104 Negative High-Voltage Control Gate 105 Control Signal Generation Units 106, 107 Oscillation Circuits 108, 109 Rectifier Smoothing Circuit 110 Output Terminals 111, 112 Gate Output 201 Microcomputer 301 , 302 Drive transistor 303, 304 Switching signal 305 Micro computer 306, 307 PWM generator 401 Auxiliary output terminal 501 Metal shaft 502 Conductive sponge 503 Metal support 504 Conductive brush 701 Oscillation circuit 702 Power operational amplifier 703 Step-up transformer 704 DC bias Generating circuit 705 Auxiliary output rectifying / smoothing circuit CONT + Output signal of control signal generator 105 CONT_IN Control signal for controlling overall charging output EV 1 Side power supply voltage T1 Positive step-up transformer T2 Negative step-up transformer TA CONT_IN is at L level TB CONT_IN is at H level TC CONT + is at L level TD CONT + is at H level TR1, TR2 Drive transistor + V High positive Voltage output −V Output voltage when + V is added to negative high voltage output −V ₂ −V

Claims (1)

(57) [Claims] Claim: What is claimed is: 1. A first direct current high voltage generating means having a first switching means, a first step-up transformer and a first rectifying means , a second switching means and a second step- up transformer .
Second DC high-voltage generating means including a battery and a second rectifying means.
An output of the first rectifying means and the second rectifier,
A high-voltage power supply device in which the output of the means is connected in series , wherein the first direct-current high-voltage generating means and the second direct-current high-voltage
It has a third switching means for controlling the operation of the generating means.
And the third switching means generates the first DC high voltage.
Means or at least one of the second DC high voltage generating means
And a first direct current output from the first direct current high voltage generating means.
A high voltage and a first high voltage output from the second direct current high voltage generating means
As the offset voltage, the voltage difference from the DC high voltage of 2
A high-voltage power supply device characterized by generating a pulsating voltage .