JPH09247937A - Power supply circuit applied to image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit which can be used as both a constant voltage source and a constant current source and can apply voltages to 2 voltage application parts in common. SOLUTION: The secondary coil 505 of a power supply transformer 501 is divided into a 1st coil part 507 and a 2nd coil part 508 by a tap 506. The 1st coil part 507 is utilized to apply a discharge voltage to a discharge wire 45 and the 2nd coil part 508 is utilized to apply a voltage to a paper powder recovering brush 43. In this constitution, a current I1 which is supplied from a photosensitive element 41 following the discharge of the discharge wire 45 is fed back to a control unit 503 to control a primary voltage V1 which is applied to the primary coil 502 of the power supply transformer 501 and the constant current control by which the current I1 can be kept constant is performed. Both a constant current source and a constant voltage source can be realized by one power supply transformer and a complex construction can be eliminated. Further, the cost of the power supply circuit can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for an image forming apparatus that forms an image by, for example, electrophotography.

[0002]

2. Description of the Related Art As an apparatus for forming an image by an electrophotographic method, there are a printer and a copying machine. In such an image forming apparatus, the surface of the photoconductor is uniformly charged by the charger and then selectively exposed to form an electrostatic latent image. This electrostatic latent image is developed into a toner image by the developing device. Then, the toner image is transferred to a sheet by a transfer device, and finally, the toner particles are fixed on the sheet to form an image.

Paper dust and residual toner adhere to the surface of the photoconductor after transfer. A paper dust collecting brush may be provided to clean them. The paper dust collecting brush serves to remove paper dust and weaken the electrostatic coupling between the residual toner and the surface of the photoconductor. The residual toner whose electrostatic coupling is weakened is collected by the developing device. A high voltage for discharging is applied to the charger. Further, a predetermined bias voltage is applied to the developing device. Further, the bias voltage is also applied to the paper dust collecting brush. Conventionally, each of these voltages has been created by a dedicated power supply circuit.

[0004]

By the way, in the case of miniaturizing the image forming apparatus, it is desired that the power supply circuit is also shared from the viewpoint of simplification of the configuration. On the other hand, there are a constant voltage power source and a constant current power source, and it is difficult to share both.
For example, a constant current power source is used for the charger and a constant voltage power source is used for the paper dust brush, but it is difficult to share these power sources.

Therefore, an object of the present invention is to solve the above-mentioned technical problems, to be used as a constant voltage source and a constant current source, which can be shared when a voltage is applied to two voltage applying portions. Is to provide a power supply circuit applied to.

[0006]

The invention according to claim 1 for attaining the above object comprises a first voltage applying section and a second voltage applying section.
And a primary side coil to which a primary voltage is applied, and a first coil part and a second coil part that are separated by a tap, and the primary side coil has a primary voltage. Is applied to the first coil section and the second coil section, a power transformer including a secondary coil in which the first secondary voltage and the second secondary voltage are respectively induced, and the first coil section is induced. Generate a first direct current voltage from the generated first secondary voltage, apply the generated first direct current voltage to the first voltage applying section, and generate a direct current corresponding to the first direct current voltage. To keep constant
A constant current control unit for controlling a direct current component included in the primary voltage applied to the primary coil and a constant voltage element, and a second secondary voltage from a second secondary voltage induced in the second coil unit.
Constant voltage control means for generating the DC voltage of the second DC voltage, suppressing the second DC voltage to a constant voltage by a constant voltage element, and applying the constant voltage to the second voltage applying section. Power supply circuit.

In the present invention, the secondary coil of the power transformer is divided into a first coil portion and a second coil portion by taps. The power source using the first secondary voltage induced in the first coil portion is used as a constant current source, and the power source using the second secondary voltage induced in the second coil portion is used as a constant voltage source. ing. More specifically, in the constant current source, the first DC voltage is generated from the first secondary voltage, and the first DC voltage is applied to the first voltage application unit. Also, in order to keep the DC current corresponding to the first DC voltage applied constant,
The DC component contained in the primary voltage applied to the primary coil is controlled. Thereby, a constant DC voltage can be applied to the first voltage application unit regardless of changes in the surrounding environment.

On the other hand, the second secondary voltage induced in the constant voltage source changes in accordance with the control of the DC component contained in the primary voltage of the constant current source, but this voltage change is absorbed by the constant voltage element. . As a result, a constant voltage can be applied to the second voltage applying section. In this way, the constant current source and the constant voltage source can be realized by using one power transformer.

The second secondary voltage also changes in accordance with the control of the DC component contained in the primary voltage, but when the changed secondary voltage is lower than the voltage that should appear across the constant voltage element, However, there is a possibility that the constant voltage element does not function and the voltage cannot be applied to the second voltage applying section. Therefore, for example, if the configuration described in claim 2 is adopted, the voltage application to the second voltage application section can be compensated.

That is, the invention according to claim 2 is characterized in that the tap is connected to the secondary coil so that the second DC voltage does not become lower than the voltage that should appear across the constant voltage element. The power supply circuit according to claim 1.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing an external configuration of a printer according to an embodiment to which the present invention is applied. This printer is of a personal use type that is installed and used on the desk of each individual in an office or the like. Specifically, this printer is connected to a personal computer (personal computer) or the like used by each individual, and is used for the purpose of easily printing out documents, tables, etc. created by the individual on the personal computer or the like.

The apparatus main body 1 has an upper housing 4 and a lower housing 5 which are fitted to each other. A cover 3 that can be opened and closed is attached to the upper housing 4. Behind the cover 3, a paper feed tray 2 for loading paper is mounted in a state of extending obliquely upward and rearward. FIG. 2 is a diagram for explaining the internal configuration of the printer. The cover 3 can cover the upper surface of the front half of the printer. The cover 3 is attached to the apparatus main body 1 via fulcrums 6 provided at both ends of the rear portion. Therefore, the cover 3 is entirely covered by the arrow A.
It can be opened by pulling it up in the direction.

A tray insertion port 7 is formed behind the upper surface of the cover 3. The paper feed tray 2 is detachably attached to the tray insertion port 7. The paper feed tray 2 is preferably removed when the cover 3 is opened. A connector 8 for connecting a printer cable 9 is attached to the rear surface portion 4a of the upper housing.

A paper feed roller 21 is provided inside the apparatus main body 1 near the lower end of the paper feed tray 2.
The paper feed roller 21 feeds the paper placed on the paper feed tray 2
It is for supplying one by one. Further, the device body 1
Inside, the imaging unit 40 and the developing unit 5
0, a transfer unit 60 and a fixing unit 70 are provided. Imaging unit 40, developing unit 5
0 and the transfer unit 60 are for forming a toner image on the paper supplied from the paper supply roller 21.
The fixing unit 70 is for fixing the toner particles onto the sheet.

The transport path 90 through which the paper is transported is formed in a substantially straight line having a downward slope from the paper feed tray 2 toward the discharge port 80. The imaging unit 40 and the transfer unit 60 are arranged so as to sandwich the transport path 90. The fixing unit 70 is arranged near the discharge port 80. A laser light irradiation unit 30 is arranged below the developing unit 50. Laser light irradiation unit 3
0 is for generating a laser beam modulated based on the data given from the printer cable 9. The laser light irradiation unit 30 includes a semiconductor laser light source,
Includes lens system and polygon mirror. The lens system is for collimating the laser light into parallel light to generate the laser beam LB, and the polygon mirror is for scanning the laser beam. The generated laser beam LB is guided to the imaging unit 40.

The imaging unit 40 is the apparatus main body 1
A drum-shaped photosensitive member 41, a charger 42, and a paper dust collecting brush 43, which are arranged substantially at the center of the inside and are driven to rotate in the direction of arrow B in the figure, are held by a holding member 44. The charger 42 corresponds to the first voltage application unit, is arranged below the photoconductor 41, and uniformly charges the surface of the photoconductor 41 to a predetermined high potential. More specifically, the charger 42 is provided with a discharge wire 45 and a grid 46. The discharge wire 45 is
This is for generating corona discharge necessary for charging the surface of the photoconductor 41. The grid 46 is interposed between the discharge wire 45 and the photoconductor 41, and
5 for controlling the discharge.

The paper dust collecting brush 43 corresponds to the second voltage applying section, and is arranged upstream of the charger 42 in the rotational direction of the photoconductor 41. The paper dust collecting brush 43 collects the paper dust adhering to the surface of the photoconductor 41. Further, the electrostatic coupling between the residual toner adhering to the surface of the photoconductor 41 and the surface of the photoconductor 41 is weakened. The developing unit 50 includes a toner hopper 51 that contains toner, a sub roller 52, and a developing roller 53. In the developing unit 50, the sub roller 52 and the developing roller are rotated. As a result, the toner contained in the toner hopper 51 is positively charged and electrostatically attracted to the peripheral surfaces of the rollers 52 and 53. The sub roller 52 includes the developing roller 5
A voltage higher than 3 is applied. Therefore, the toner adhering to the peripheral surface of the sub-roller 52 does not adhere to the developing roller 5
Go to 3.

The transfer unit 60 is attached to the cover 3 and has a transfer roller 61. The transfer roller 61 is provided so as to face the photoconductor 41 with the transport path 90 interposed therebetween, and is rotatably held by a holding member 63 made of a plastic molded product. The paper detection switch 22 is attached to the holding member 63. The paper detection switch 22 is for detecting the paper supplied by the paper feed roller 21.

The fixing unit 70 is divided into an upper fixing unit portion 71 and a lower fixing unit portion 72 along the conveyance path 90. The lower fixing unit portion 72 is fixed to the lower housing 5, and the upper fixing unit portion 71 is rotatably attached to the lower fixing unit portion 72 at a fulcrum portion 73. The upper fixing unit portion 71 is pushed downward by the pressing portion 3 a protruding from the inside of the cover 3.

An upper fixing roller 74 and a lower fixing roller 75 are rotatably held in the upper fixing unit 71 and the lower fixing unit 72, respectively. Lower fixing roller 7
A heater (not shown) is built in the unit 4. When the cover 3 is closed, the upper fixing unit portion 71 has the pressing portion 3a.
Being pushed by. As a result, it is possible to apply pressure to the sheet passing between the upper fixing roller 74 and the lower fixing roller 75.

When forming an image, the surface of the photoconductor 41 is uniformly charged by the charger 42 to a predetermined high potential. The uniformly charged surface of the photoconductor 41 is exposed by the laser beam LB from the laser light irradiation unit 30. At this time, the charge in the exposed area escapes and becomes a low potential. As a result, an electrostatic latent image composed of the high potential region and the low potential region is formed. This electrostatic latent image moves to a position facing the developing unit 50 and is developed into a toner image. More specifically, the electrostatic latent image is developed into a toner image by adhering the positive toner adhering to the developing roller 53 to the exposure area which is a low potential area.

The toner image is transferred onto the lower surface of the paper supplied by the paper feed roller 21 by the operation of the transfer unit 60. The paper carrying the toner image on the lower surface is guided to the fixing unit 70. The heating and pressing action of the fixing unit 70 causes the toner particles to be fixed on the paper. The paper after the fixing process is the exit 8
The sheet is discharged to the outside of the apparatus main body 1 by an upper discharge roller 76 and a lower discharge roller 77 which are arranged near the transport path 90 near 0.

This printer is also equipped with an imaging high voltage unit (IHVU).
The IHVU is for applying a voltage to the discharge wire 45 and the paper dust brush 43 provided in the imaging unit 40. That is, the power supply circuit for applying the voltage to the discharge wire 45 and the paper dust brush 43 is shared.

FIG. 3 is a circuit diagram for explaining the configuration of the IHVU. The IHVU 500 is equipped with a power transformer 501. The DC voltage V _cc is supplied to the primary coil 502 of the power transformer 501. The DC voltage _Vcc is, for example, 24 (V). DC voltage V
_cc is converted into an AC voltage (hereinafter referred to as “primary voltage”) V ₁ under the control of the control unit 503. Specifically, the control unit 503 turns on / off the transistor 504 connected in series to the primary coil 502 at a constant chopping cycle. As a result, the DC voltage V _cc is chopped and the primary voltage V ₁ is generated.

Secondary coil 505 of power transformer 501
Is divided into a first coil portion 507 and a second coil portion 508 by a tap 506. The connection position of the tap 506 is determined in consideration of the brush voltage described later. When the primary coil 502 primary voltage V ₁ is applied, the first coil portion 507 is induced first secondary voltage V ₂₁ is, in the second coil portion 508 and the second secondary voltage V ₂₂ Be triggered.

A first rectifying circuit 509 is connected to the first coil section 507. The first rectifier circuit 509 includes a diode 510, a capacitor 511 and a resistor 5
12, 513 are included. The first secondary voltage V ₂₁ induced in the first coil unit 507 is the first rectifier circuit 50.
It is rectified by 9. As a result, the first DC voltage V
_t (for example, V _t = 3 to 4 (kV)) is generated.

The first DC voltage V _t is applied to the discharge wire 45 of the charger 42. As a result, the discharge wire 4
5 discharges. As a result, the surface of the photoconductor 41 is charged to a predetermined high potential. One end of a line 514 is connected to the photoconductor 41. The other end of the line 514 is connected to the control unit 503 on the primary side of the power transformer 501. At the time of discharging, a current I _t (for example, I _t = 10 (μA)) flows from the photoconductor 41 to the line 514 and is input to the control unit 503.

Further, one end of a line 515 is connected to the grid 46. The other end of the line 515 is connected to the line 514. A varistor 516 is provided on the line 515. At the time of discharging, a grid current I _g is induced in the grid 46. The grid current I _g is
Flow on line 515. As a result, a constant grid voltage V _g appears across the varistor 516.

In this way, a constant grid voltage V _g is applied to the grid 46. Therefore, the discharge current applied to the photoconductor 41 can be kept constant. Therefore, the charging potential of the surface of the photoconductor 41 can be kept constant. The second coil unit 508 includes the second rectifier circuit 51.
7 is connected. The second rectifier circuit 517 includes a diode 518, a capacitor 519 and a resistor 520. A varistor 521 whose one end is grounded is connected to the second coil unit 508. The paper dust collecting brush 43 is connected to the other end of the varistor 521.

The second coil portion 508 induces the second coil portion 508.
Secondary voltage V_{twenty two}Is rectified by the second rectifier circuit 517.
As a result, the second DC voltage V_b1(For example, V_b1= -60
0 (V)) is generated. Second DC voltage V_b1Is Bali
Varistor voltage V_vOnly the buck is concerned
DC voltage after step-down (hereinafter referred to as "brush voltage") V _b2
Appears at a point e corresponding to the other end of the varistor 521. That
As a result, the brush voltage V is applied to the paper dust collecting brush 43._b2Is applied
Is done. For example, varistor voltage V_vIs 100 (V)
Then, a brush of -500 (= -600 + 100) (V)
Voltage V_b2Is applied.

The first DC voltage V _t applied to the discharge wire 45 may fluctuate due to changes in the ambient environment such as humidity and temperature. In this case, the charging potential of the surface of the photoconductor 41 changes. As a result, the image quality may be affected. Therefore, in the present embodiment, this is dealt with as follows. Photoelectric body 41 following discharge
The current I _t flowing from, as described above, the line 514
And is input to the control unit 503. The current I _t, the first DC voltage V applied to the discharge wire 45
It changes according to the change of _t . That is, the control unit 503 receives the information about the change in the first DC voltage V _t applied to the discharge wire 45. The control unit 503, based on the current I _t to be input, so as to maintain the current I _t constant, the ON time of the transistor 504 in the chopping cycle is controlled.

Specifically, the on-time is shortened or lengthened according to the level of the current I _t . As a result, the DC component contained in the primary voltage V ₁ becomes lower or higher depending on the ON time. Along with this, the first DC voltage V _t generated from the first secondary voltage V ₂₁ also becomes lower or higher. Thus, current I _t is kept constant.

[0033] For example, the current I _t is higher than a certain value, the ON time of the transistor 504 is shortened. As a result, the DC component contained in the primary voltage V ₁ becomes low. Along with this, the first DC voltage V _t also decreases. That is, the current I _t is decreased. On the other hand, if low current I _t is below a certain value, the on time is long, the DC component increases contained in the primary voltage V _1. As a result, the first DC voltage V
_{As t} increases, the current I _t increases.

As described above, the first DC voltage V _t applied to the discharge wire 45 is controlled so that the current I _t becomes constant. As a result, the influence of the surrounding environment on the charging potential of the photoconductor 41 is compensated. On the other hand, the brush voltage V _b2 applied to the paper dust collecting brush 43 is basically, even if the second secondary voltage V ₂₂ fluctuates according to the level of the DC component included in the primary voltage V ₁ . The varistor 521, which is a constant voltage element, keeps the voltage constant.

However, if the second DC voltage V _b1 generated from the second secondary voltage V ₂₂ is not a voltage higher than the voltage required to make the varistor 521 conductive, the constant voltage of the brush voltage V _b2 is Not compensated. The voltage required to make the varistor 521 conductive is the varistor voltage V _v that should appear across the varistor 521. Therefore, in this embodiment, the tap 506 is connected to a position where the second DC voltage V _b1 is always equal to or higher than the varistor voltage V _v . As a result, the constant voltage of the brush voltage V _b2 is compensated.

[0036] Thus, according to this embodiment, the connecting the tap 506 on the secondary side of the power transformer 501, for controlling the further secondary voltage by feeding back the current I _t flowing from the photoreceptor 41 during discharge Then, the constant current source and the constant voltage source are realized by using one power supply transformer 501. Therefore, one power transformer is not required as compared with the case where the constant current source and the constant voltage source are separate power sources. As a result, the configuration can be simplified and the cost can be reduced.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above-described embodiment, the case where the present invention is applied to the IHVU 500 that supplies power to the imaging unit 40 has been described. However, the present invention can be widely applied to a power supply that applies a voltage to two voltage application units whose voltage application timings are the same.

In the above embodiment, the case where the present invention is applied to a small printer has been described. But,
It goes without saying that the present invention can also be applied to a copying machine or other apparatus having one power supply unit including a constant current source and a constant voltage source. Besides, it is possible to make various design changes within the scope of the technical matters described in the claims.

[0039]

As described above, according to the present invention, it is possible to realize a constant current source and a constant voltage source with a single power supply transformer, so that even when two power supply units share a power supply, You can use only one power transformer. Therefore, it is possible to prevent the power source from increasing in size and prevent the internal configuration of the image forming apparatus from becoming complicated. Further, cost can be reduced.

In particular, according to the second aspect of the present invention, the constant voltage element included in the constant voltage source is always applied with a voltage equal to or higher than the voltage that should appear across the constant voltage element.
It is possible to always apply a constant voltage to the voltage applying section.

[Brief description of drawings]

FIG. 1 is a perspective view showing an external configuration of a printer according to an embodiment to which the invention is applied.

FIG. 2 is a diagram illustrating an internal configuration of a printer.

FIG. 3 is a circuit diagram for explaining an IHVU (imaging high voltage unit).

[Explanation of symbols]

42 charger 43 paper dust collection brush 500 IHVU 501 power transformer 502 primary coil 503 controller 504 transistor 505 secondary coil 506 tap 507 first coil portion 508 second coil portion 521 varistor I _t current V ₁ primary voltage V ₂₁ second 1 of the secondary voltage V ₂₂ second secondary voltage V _t first DC voltage V _b1 second DC voltage V _b2 brush voltage

Claims (2)

[Claims] 1. A power supply circuit used in an image forming apparatus including a first voltage applying section and a second voltage applying section, wherein a primary side coil to which a primary voltage is applied, and a first coil section with a tap and When the primary voltage is applied to the primary coil, the secondary coil is divided into a second coil section and a first secondary voltage and a second secondary voltage are induced in the first coil section and the second coil section, respectively. A first DC voltage is generated from a power transformer including a side coil, and a first secondary voltage induced in the first coil unit, and the generated first DC voltage is converted into a first DC voltage.
Constant current control means for controlling the DC component contained in the primary voltage applied to the primary side coil so that the DC current corresponding to the first DC voltage is kept constant while being applied to the voltage applying unit And a second DC voltage is generated from the second secondary voltage induced in the second coil unit by including the constant voltage element, and the second DC voltage is suppressed to a constant voltage by the constant voltage element. A power supply circuit comprising: a constant voltage control means for applying a constant voltage to the second voltage application section. 2. The tap is connected to the secondary coil so that the second DC voltage does not become lower than the voltage that should appear across the constant voltage element. Power supply circuit.