JPH0228670A - Corona discharge device for electrophotographic device - Google Patents

Abstract

PURPOSE:To electrostatically charge a photosensitive body in a constantly stabilized way, to miniaturize the title device and to extend the life thereof by impressing a DC bias voltage between a corona discharge wire and the photosensitive body and also a pulse voltage in a polarity opposite to that of the DC bias voltage between a back plate and the corona discharge wire. CONSTITUTION:A corona discharge device equipped with a plate-like dielectric body 2 which has the back plate 3 arranged on one side thereof and the corona discharge wire 4 provided on or near to the other side is arranged near to the photosensitive body 5. The DC bias voltage VDC is impressed between the corona discharge wire 4 and the photosensitive body 5. The pulse voltage VAC in the polarity opposite to that of the DC bias voltage is impressed between the back plate 3 and the corona discharge wire 4 by a high voltage power supply provided on the title device. As a result, the photosensitive body can be electrostatically charged uniformly so as to have stabilized electrostatic charge potential. In addition, the miniaturization of the device and the extension of the life thereof can be thereby achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a corona discharge device in an electrophotographic apparatus such as a copying machine or a laser printer.

[Conventional technology]

Conventionally, a scorotron and a corotron are known as a corona discharge device of a corona discharge device provided for charging a photoreceptor in an electrophotographic apparatus. The high-voltage power supply that supplies high voltage to these to generate corona discharge controls the output current at a constant current.

As a result, the charging current of the photoreceptor remains constant even with changes in the environment such as temperature, humidity, and atmospheric pressure around the corona discharger, which has the effect of stabilizing the charging potential.

[Problem to be solved by the invention]

However, in such a conventional corona discharge device, the corona discharge wire 21 is connected to the photoreceptor 23 as shown in FIG.
Since a corona discharger 20 surrounded by a shield electrode 22 with only the surface facing the corona discharge wire 21 open is used, the output current Ip of the high voltage electric current g24 that supplies high voltage to the corona discharge wire 21 is
are the charging current Id of the photoreceptor 2'5 and the shield electrode current Ic
Therefore, if this diversion ratio (distribution ratio) changes due to dirt on the shield electrode 22, the charging current Id will fluctuate even if the output current Ip is constant1, and the charging potential of the photoreceptor will change accordingly. There were drawbacks.

Furthermore, a spatial distance must be provided between the corona discharge wire 21 and the shield electrode 22, making it difficult to downsize the corona discharger. This is because high voltage is applied to the corona discharge wire 21 even if the photoreceptor is forgotten to be attached.

There was also the risk of electric shock and the possibility of arc discharge occurring between the shield electrode 22 and the shield electrode 22.

This invention has been made in view of the above points, and it is possible to always stably charge a photoreceptor.

Moreover, it is an object of the present invention to provide a corona discharge device that is small in size and has a long life.

Another object of the present invention is to provide a safe corona discharge device that is free from the risk of electric shock or arc discharge even if a photoreceptor is forgotten to be attached.

[Means to solve the problem]

In order to achieve the object described in -F, this invention provides a corona discharger that is provided with a back electrode on one surface of a plate-shaped dielectric material and a corona discharge wire on the other surface or near the photoreceptor. An electrophotographic device equipped with a high-voltage power supply that applies a DC bias voltage between the corona discharge wire and the photoreceptor and a pulse voltage of opposite polarity to the DC bias voltage between the back electrode and the corona discharge wire. The present invention provides a corona discharge device according to the present invention.

In addition, the high voltage power supply of the corona discharge device in this electrophotographic apparatus includes a constant current control means for controlling the charging current of the photoreceptor at a constant current, and a constant current control means that applies constant current to the corona discharge wire and the back electrode when the charging current becomes below a predetermined value. It is preferable to include a high voltage output stop means for not outputting the high voltage.

Alternatively, the high-voltage power supply may include means for detecting the DC bias voltage, and when the DC bias voltage detected by the means exceeds a predetermined value or falls below a predetermined value, the corona discharge wire and the back electrode are connected to the high voltage power supply. It may also include high voltage output stopping means for stopping the output of the applied high voltage.

[For production]

The corona discharge device in an electrophotographic apparatus according to the present invention applies a pulse voltage between the corona discharge wire and the back electrode provided via the dielectric, and connects the photoreceptor and the corona discharge wire arranged in the vicinity thereof. By applying a DC bias voltage between them, the charging potential of the photoreceptor can be stabilized and charged uniformly, and moreover, it is possible to realize miniaturization and a longer life.

Furthermore, if you perform constant current control of the charging current,
When the charging potential of the photoreceptor can be stabilized by mm and the charging current is below a predetermined value, or when the DC bias voltage is above a predetermined value or below a predetermined value, the output is open or short-circuited. Since the high-voltage power supply stops outputting high voltage, even if the photoreceptor is forgotten or there is a short circuit between the electrodes, there is no risk of electric shock or arc discharge.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.6 FIG. 1 is a circuit diagram showing the configuration of a corona discharge device in an electrophotographic apparatus according to a first embodiment of the present invention.

A corona discharger 1 of this corona discharge device consists of a back electrode 3 printed on one side of a plate-shaped dielectric 2, and a corona discharge wire 4 provided close to the other side, and placed near a photoreceptor 5. will be placed in

The photoreceptor 5 is, for example, a PC drum or belt, and has a PC photoreceptor layer 5b formed on a conductor base 5a.

10 is a high voltage power supply, and its input terminals +IN and -IN are connected to the driving power supply 6. Also.

The output terminal HV1 is connected to the corona discharge wire 4, and the output terminal HVz is connected to the back electrode 3. Also, other output terminal G
is grounded together with the conductor base 5a of the photoreceptor 5.

Trigger terminal P is connected to control circuit 11 .

One end of the primary winding N1 of the step-up transformer T is the input terminal +IN
The other end is connected to the collector of the transistor Q, the emitter of the transistor Q is connected to the input terminal -IH, and the base is connected to the output terminal of the control circuit 11.

One end of the secondary winding N2 of the step-up transformer T is connected to the output terminal Hv1.
and the other end is connected to the output terminal HV2, respectively.
Furthermore, capacitors C1 and C2 and diodes D1 and Dz
A voltage doubler rectifier circuit 12 consisting of a discharge resistor R and a discharge resistor R are connected in parallel.

The output terminal of the voltage doubler rectifier circuit 12 is connected to the charging current detection circuit 1.
3 to the output terminal G.

The detection output of this charging current detection circuit 13 is input to the control circuit 11.

Next, the operation of this corona discharge device will be explained.

When an "on signal" is input to the trigger terminal P from a control circuit (not shown) of the entire electrophotographic apparatus, the control circuit 11 outputs a switching pulse of a constant period to the transistor Q.
starts switching, and the high voltage power supply 10 starts up.

As a result, the current flowing through the primary winding N1 of the step-up transformer T is interrupted, a high voltage is induced in the secondary winding N2, and the output terminals HV1 and HV2 are connected to the back electrode 3 of the corona discharger 1 and the corona discharge wire 4. A pulsed alternating current voltage (hereinafter referred to as “
In addition, a negative DC bias voltage VDC generated by a voltage doubler rectifier circuit 12 is applied between the corona discharge wire 4 and the conductive base 5a of the photoreceptor 5.

FIG. 2 is a diagram showing the output waveform of the high voltage power supply 10 in FIG. 1, where (a) is the voltage waveform of the corona discharge wire 4 when the back electrode 3 is referenced, and (b) is the voltage waveform of the corona discharge wire 4 when the back electrode 3 is referenced. This is the voltage waveform of the corona discharge wire 4 when

In the waveform of FIG. 2(a), which is the induced voltage in the secondary winding N2 of the step-up transformer T, tl is one period of the pulse voltage, and -
This corresponds to the switching period of the transistor Q that drives the next winding N1, and is set to "400 μS" in this embodiment.

tl corresponds to the on-time of the transistor Q, which is "30 μS" in this embodiment. During this period tl, corona discharge occurs mainly around the corona discharge wire 4, and ions of both positive and negative polarities are generated.

These ions are applied to the photoreceptor 5 by a DC electric field between the corona discharge wire 4 and the grounded photoreceptor 5 due to the DC bias voltage VDC as shown in FIG.

As a result, a charging current Ip flows, and the photoreceptor layer 5 of the photoreceptor 5
b is negatively charged.

The period T2 during which this output pulse voltage is the highest voltage is:
As shown in FIG. 2(b), the polarity of each winding of the step-up transformer T is set so that the polarity is opposite to that of the DC bias voltage VDC.

This is to prevent vibration of the corona discharge wire 4 due to the electrostatic attraction between them and the tension of the corona discharge wire 4 by lowering the potential difference between the corona discharge wire 4 and the ground. As a result, it is possible to extend the life of the corona discharge wire 4 and prevent arc discharge.

On the other hand, the charging current rp due to ions applied to the photoreceptor 5
is detected as a voltage by the charging current detection circuit 13 and fed back to the control circuit 6.

In the control circuit 6, the on-time t2 of the transistor Q is controlled by the pulse width (duty) of the switching pulse so that this detection signal is maintained at a predetermined value. As a result, the 1F electric current 1p is controlled to be a constant current, and stable charging can be performed without being affected by temperature/humidity, changes over time, dirt, etc.

FIG. 3 shows only the main parts of a high voltage power supply according to a second embodiment of the invention, and FIG. 4 shows its output waveform.

Note that in FIG. 3, the same parts as in FIG. 1 are indicated by the same reference numerals, and the same applies to each subsequent time), and the parts omitted from illustration are also the same as in FIG. 1.

The difference between this embodiment and the previous embodiment is that the photoreceptor 5 is positively charged.

Therefore, the DC bias voltage VDC generated by the voltage doubler rectifier circuit 12' is made to have a positive polarity with respect to the earth output terminal G, and the maximum voltage of the pulse voltage VAC between this DC bias VDC and the output terminals VHt and VH2 is The primary winding N of the step-up transformer T is
The winding directions of the winding 1 and the secondary winding N2 are reversed from those of the previous embodiment.

Therefore, the voltage applied to the corona discharge wire 4 when viewed from the ground is as shown in FIG.

FIG. 5 is a circuit diagram similar to FIG. 1 showing a third embodiment of the invention.

The difference from the embodiment shown in FIG. 1 is that the DC bias voltage VDC is generated from a dedicated winding of a step-up transformer. That is, a half-wave rectifier circuit 25 consisting of a diode DI, a capacitor C1, and a discharge resistor R is connected to the tertiary winding N3 provided in the step-up transformer T', and a negative polarity DC bias voltage VDC is output.

Since the polarities of the secondary winding N2 and the primary winding N1 are the same as in FIG. 1, the pulse voltage VAC and the DC bias voltage VDC have opposite polarities as well.

The advantage of this embodiment is that the number of turns of the tertiary winding N3 can be set arbitrarily without being influenced by the secondary winding N2, and therefore the ratio between the pulse voltage VAC and the DC bias voltage VDC can be set freely. .

FIG. 6 is a circuit diagram showing a fourth embodiment of the invention.

This embodiment differs from the embodiment shown in FIG. 1 in that the configurations of the corona discharger 1 and the high voltage power supply 10 are partially different.

The corona discharger 1 is provided with a corona discharge wire 4 in contact with the lower surface of a dielectric 2. In addition, the high voltage power supply 10 is connected to an AC power supply @10A'C that outputs a pulse voltage VAC, and a DC power supply 113X1 that outputs a DC bias voltage VDC.
Consists of two 0DC power supplies.

The AC power supply 10AC is composed of a step-up transformer T1, a switching transistor Q1, and a switching circuit 26, and the switching circuit 26 applies a switching pulse of a constant pulse @ (on time) at a constant cycle to the base of the transistor Q1. There is.

Therefore, the pulse voltage VAC output between the output terminals HV and HV2 has the same waveform as shown in FIG.
The on period t2 is constant.

On the other hand, the DC power supply 100C includes a step-up transformer T2, a switching transistor Q2, a control circuit 11, and a diode D1 connected to the secondary side of the step-up transformer T2. The detection signal of the charging current detection circuit 13 is fed back to the control circuit 11, and the control circuit 11 adjusts the on-time of the transistor Q2 so that the detection signal becomes a predetermined value. is controlled.

Therefore, in this embodiment, only the DC bias voltage VDC is controlled so that the charging current Ip becomes a constant current.

Further, in this embodiment as well, the winding direction of each winding of the step-up transformer T1 is set so that the polarities of the pulse voltage VAC and the DC bias voltage VDC are opposite to each other as in the previous embodiments.

In this embodiment, since the pulse voltage VAC and the DC bias voltage VDC are output from separate power supplies, in addition to the advantages of the above-mentioned embodiment, the switching frequency of the transistor Q2 of the DC'R power supply 0DC can be increased to a high frequency. , the input and output conversion efficiency can be improved. Also, capacitor C
There is also the advantage that 1 can be made smaller and smaller in capacity.

As described above, according to each of the above embodiments, corona discharge is performed by applying a pulse voltage between the back electrode provided through the dielectric and the corona discharge wire, and the pulse voltage is applied between the corona discharge wire and the photoreceptor. Since the charging current is controlled at a constant current by applying a DC bias voltage of opposite polarity to the voltage, the charging potential of the photoreceptor can be stabilized, and a corona discharge device that is small and has a long life can be provided.

FIG. 7 is a circuit diagram showing a fifth embodiment of the invention.

This fifth embodiment differs from the first embodiment (FIG. 1) described above in that a load open detection circuit 14 is inserted between the output terminal of the voltage doubler rectifier circuit 12 and the charging current detection circuit 13, The only difference is that the detection signal FBI of the charging current detection circuit 13 and the detection signal FB2 of the load open detection circuit 14 are input to the control circuit 11, and the other configurations and operations are the same as in the first embodiment. The explanation will be omitted.

The control circuit 11 controls the on-time of the transistor Q by the pulse width (duty) of the switching pulse so that the detection signal FBI from the charging current detection circuit 13 becomes a predetermined value.

As a result, the charging current rp is controlled to be a constant current, and the charging potential of the photoreceptor 5 can always be kept constant even against environmental changes such as temperature and humidity, dirt, and the like.

On the other hand, in the load open detection circuit 14, the charging current detection circuit 1
The charging current Ip is detected at a level different from 3 and fed back to the control circuit 11.

As a result, in the control circuit 11, when the detection signal FB2 corresponding to the charging current Ip is below a predetermined value while the ON signal is input to the trigger terminal P, the load circuit (corona discharger 1 and photoreceptor 5) is activated. It is determined that it is open, and the output of the switching pulse is stopped, leaving the transistor Q in the off state.

Therefore, a high voltage is no longer induced in the secondary winding N2 of the step-up transformer T, and the high voltage power supply 10 is connected to the corona discharge wire 4.
And the high voltage output applied to the back electrode 3 is stopped. Also,
Even when the corona discharge wire 4 and the back electrode 3 are short-circuited, the charging current Ip stops flowing, so the output of the high-voltage power supply 10 is stopped as in the case described above.

FIG. 8 shows the waveform of the voltage applied between the photoreceptor 5 and the corona discharge wire 4.

During the period t2 when the transistor Q is conducting, the secondary winding M
, N2 The polarity of each winding of the step-up transformer T is set so that the pulse voltage VAC induced in N2 and the DC bias voltage VDC have polarities that cancel each other out.

Periods other than t2 of one cycle t1 of the pulse voltage VAC have an oscillating waveform due to the time constants of the high voltage transformer T and the corona discharger 1. Since both the pulse voltage VAC and the DC bias voltage VDC are taken out from the secondary winding N2 of the step-up transformer T, feedback for constant current control of the charging current Ip applies to both.

In this embodiment, the charging current detection circuit 13 and the control circuit 11 constitute a constant current control means, and the load release detection circuit 14 and the control circuit 11 constitute an output stopping means.

FIG. 9 is a circuit diagram similar to FIG. 7 showing a sixth embodiment of the present invention, and parts corresponding to those in FIG. 7 are given the same reference numerals.

In this embodiment, the trigger terminal P is connected to the base of a transistor Q3 that turns on and off the power of the control circuit 11.

The control circuit 11 includes a reference voltage generator 15 that generates a reference voltage VREF to be applied to a voltage dividing circuit including resistors R11 and R12 and a voltage dividing circuit including resistors R13 and R14, and diodes D11. It is composed of operational amplifiers 18 and 17 connected to the wired OR via D12, and a pulse width modulation circuit (PWM) 18 to which the output signal is input.

Further, the reference voltage VREF outputted by the reference voltage generator 15
A reference voltage Va, which is divided by a voltage dividing circuit made up of resistors R11 and R12, is connected to the non-inverting input terminal of the operational amplifier 17 through a resistor R.
A reference voltage vb divided by a voltage dividing circuit formed by R13 and R14 is applied to the inverting input terminal of the operational amplifier 16, respectively.

The load open detection circuit 14 includes a resistor R21 and a capacitor C2.
Furthermore, a charging current detection circuit 13 consisting of a parallel circuit of a resistor R22 and a capacitor D22 is connected between the ground terminal G and the ground terminal G.

The detection signal FB2 of the load open detection circuit 14 is the operational amplifier 1.
7, and the detection signal FBI of the charging current detection circuit 13 is fed back to the non-inverting input terminal of the operational amplifier 1.

Next, the operation of this embodiment will be explained.

When an on signal is input to the trigger terminal P, the transistor Q
3 becomes conductive, power is supplied to the control circuit 11, the pulse width modulation circuit 18 outputs a switching pulse of a constant period to start switching the transistor Q1, and the high voltage power supply 10 is activated.

As a result, a high voltage is induced in the secondary winding N2 of the step-up transformer T, and similarly to the embodiment shown in FIG. A corona discharge occurs, a charging current Ip flows, and the OPC photoreceptor layer 5b of the photoreceptor 5 is charged.

The charging current p is detected by both the charging current detection circuit 13 and the unloading detection circuit 14, and the respective detection signals FBI and FB2 are fed back to the control circuit 11, respectively.
In the control circuit 11, the reference voltage Va of the operational amplifier 17.18
, Vb, charging current detection circuit 13 and load open detection circuit 1
The detection signals FBI and FB2 are weighted by a constant of 4.

Normally, the output of the operational amplifier 16 is output from the pulse width modulation circuit 18.
, and controls the charging current Ip at a constant current.

On the other hand, the operational amplifier 17 outputs the detection signal FB2, which is normally at a sufficiently higher level than the reference voltage Va, to the output terminal HV.
If the level becomes lower than the reference voltage Va due to a short circuit between HV 1 and HV 2 or forgetting to attach the photoreceptor 5, the output is set to a high level and acts on the pulse width modulation circuit 18 with priority to the operational amplifier 1, and the transistor The output of the switching pulse that controls on/off of Q1 is stopped.

Incidentally, in order to prevent the operational amplifier 17 from acting when the high voltage power supply 10 is started up, the capacitors C1l and C12 are connected.

FIG. 10 shows the voltage waveforms of the reference voltage Va input to the operational amplifier 17 and the detection signal FB2 at startup.

In the figure, when an on signal is input to the trigger terminal P at time ta and the transistor Q3 becomes conductive, the reference voltage Va input to the non-inverting input terminal of the operational amplifier 17 is changed to the resistor R111R1.
2 and the time constant of the capacitor C1l, it gradually rises to show the time points tb and tc.

On the other hand, the detection signal FB2 input to the inverting input terminal rises faster than the reference voltage Va due to the charging current of the capacitor C12, so the output of the operational amplifier 17 remains at a low level and does not act on the pulse width modulation circuit 18. High voltage power supply 10
starts.

In addition, a decrease in the detection signal FB2 of the load open detection circuit 14 occurs when one or more of the output terminals HVt, HV2, and G are shorted or opened, but if this is short-circuited, it is caused by the discharge of the capacitors CZI and C22. High voltage output does not stop.

As described above, according to this embodiment, a pulse voltage is applied between the corona discharge wire 4 and the back electrode 3 provided via the dielectric 2, and the photoreceptor 5 and the corona discharge wire 4 arranged in the vicinity are connected to each other. A direct current bias voltage is applied between the two to control the charging current of the photoreceptor 5 at a constant current, and when the charging current is less than a predetermined value, the high voltage power supply 10 does not output high voltage and corona discharge is stopped. The photoreceptor 5 can be charged uniformly at all times,
Moreover, even if the photoreceptor 5 is forgotten to be attached, there is no risk of electric shock or arc discharge.

In each of the above embodiments, the corona discharge wire 4 is connected to the dielectric material 2.
Although the corona discharge wire 4 is provided near the surface opposite to the surface on which the back electrode 3 is provided, the corona discharge wire 4 may be provided so as to be in contact with the surface of the dielectric 3.

Next, other embodiments are shown in FIGS. 11 to 14, which ensure safety when the output is opened (for example, when the photoreceptor is forgotten to be attached) in the same way as these embodiments.

The aforementioned fifth embodiment (Fig. 7) and sixth embodiment (Fig. 9)
Well then! High voltage power supply 10 when the electric current is below a predetermined value.
However, in each of the embodiments to be described from now on, the DC bias voltage VDC is detected and the high voltage is output when the value exceeds a predetermined value or falls below a predetermined value. Avoid outputting voltage.

When the output is open (for example, if you forget to attach the photoconductor), the charging current Ip may decrease but the DC bias voltage VDC may rise, and when the output is short-circuited, the charging current remains unchanged but the DC bias voltage VDC decreases. This is because there is.

The seventh embodiment shown in FIG. 11 is the same as the fifth embodiment shown in FIG. 7 by adding a bias voltage detection circuit 20 and some functions of the control circuit 11.

The bias voltage detection circuit 20 detects the DC bias voltage VDC output from the voltage doubler rectifier circuit 12 and feeds back the detection signal FB9 to the control circuit 11.

When the control circuit 11 detects that the detection signal FB3 exceeds a preset first value (relatively high value).

That is, when the DC bias voltage VDC exceeds a predetermined value (relatively high value), it is determined that the load circuit is open, and the output of the switching pulse to the transistor Q is stopped.
Leave transistor Q in the off state. therefore,
The high voltage pulse voltage VAC applied to the corona discharge wire 4 and the back electrode 3 is no longer output.

Further, this control circuit 11 includes a bias voltage detection circuit 20
When the detection signal Fllll from the controller becomes less than a preset second value (relatively low value), that is, when the DC bias voltage VDC becomes less than a predetermined value (relatively low value),
It is determined that the load circuit is short-circuited, and the output of the switching pulse to the transistor Q is similarly stopped, leaving the transistor Q in an off state. Therefore, at this time as well, the high voltage pulse voltage VAC applied to the corona discharge wire 4 and the back electrode 3 is no longer output.

The eighth embodiment shown in FIG. 12 is obtained by omitting the load release detection circuit 14 of the seventh embodiment described above, and other configurations and functions are the same as those of the seventh embodiment shown in FIG. 11. The explanation will be omitted.

The ninth embodiment shown in FIG. 13 is the same as the sixth embodiment shown in FIG. and a diode I)t3.

And the resistance R23°R2 of the bias voltage detection circuit 20
When the detection signal FB3 obtained by dividing the DC bias voltage vDC by 4 becomes lower than the reference voltage Va, the operational amplifier 19
The output becomes high level, makes the diode D13 conductive, acts on the pulse width modulation circuit 18, and stops outputting the switching pulse.

As a result, pulse voltage VAC is no longer output.

In the tenth embodiment shown in FIG. 14, the capacitor C13 of the control circuit 11 in the ninth embodiment is omitted, and the operational amplifier 1
By swapping the non-inverting and inverting inputs of the day,
The high voltage output is stopped when the DC bias voltage VDC exceeds a predetermined value.

In this embodiment, the operational amplifier 17 and diode 012 in the load open detection circuit 14 and control circuit 11 in the ninth embodiment shown in FIG. 13 are also removed.

These embodiments can also prevent the danger of electric shock and the occurrence of arc discharge even if the photoreceptor 5 is forgotten to be attached or a short circuit between electrodes occurs.

〔Effect of the invention〕

As explained above, according to the corona discharge device for an electrophotographic apparatus according to the present invention, it is possible to provide a corona discharge device that is capable of stably charging a photoreceptor to a constant potential at all times, and that is small and has a long life. can.

Furthermore, even if the photoreceptor is forgotten to be attached or there is a short circuit between the electrodes, the risk of electric shock or arc discharge can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a corona discharge device according to a first embodiment of the present invention, FIG. 2 is a waveform diagram of the output voltage of the high voltage power supply 10, and FIG. 3 is a high voltage power supply according to a second embodiment of the present invention. FIG. 4 is a circuit diagram showing only the essential parts of the same. FIG. 5 is a circuit diagram of the third embodiment of the present invention. FIG. 6 is a circuit diagram of the fourth embodiment of the present invention. Figure 8 is a circuit diagram of the fifth embodiment of the present invention. Figure 8 is a waveform diagram of the output voltage of the high voltage power supply 10. Figure 9 is a circuit diagram of the sixth embodiment of the invention. Figure 10 is the start-up diagram. 11 is a circuit diagram of the seventh embodiment of the present invention, FIG. 12 is a circuit diagram of the eighth embodiment of the present invention, and FIG. 13 is a diagram of the waveforms of the two voltages input to the operational amplifier 17. FIG. 14 is a circuit diagram of a tenth embodiment of the present invention, and FIG. 15 is a circuit diagram showing the basic configuration of a conventional corona discharge device. DESCRIPTION OF SYMBOLS 1... Corona discharger 2... Dielectric 3... Back electrode 4... Corona discharge wire 5... Photoreceptor 6... Drive power supply 10... High voltage power supply 11... Control Circuit 12, 12'...Voltage doubler rectifier circuit 13...Charging current detection circuit 14...Load release detection circuit 15...Reference voltage generation circuit 18...Pulse width modulation circuit 20...Bias voltage Detection circuit 25...Half-wave rectifier circuit 26...Active circuit T, T
' , T1 r T2...Step-up transformer QI Ql~
Q3...Switching transistor VAC...
Pulse voltage VDC...DC bias voltage g2 (Q) (b) Figure 3 Figure 4 Figure 10

Claims (1)

[Scope of Claims] 1. A corona discharger having a back electrode on one surface of a plate-like dielectric and a corona discharge wire on or near the other surface is disposed near the photoreceptor, and the corona discharge wire An electrophotographic apparatus characterized in that a high voltage power source is provided for applying a DC bias voltage between the back electrode and the photoreceptor, and applying a pulse voltage of opposite polarity to the DC bias voltage between the back electrode and the corona discharge wire. Corona discharge device. 2. The corona discharge device for an electrophotographic apparatus according to claim 1, wherein the high-voltage power supply includes constant current control means for controlling the charging current of the photoreceptor at a constant current, and when the charging current becomes equal to or less than a predetermined value. A corona discharge device for an electrophotographic apparatus, characterized in that the corona discharge device includes a high voltage output stop means for stopping output of the high voltage applied to the corona discharge wire and the back electrode. 3. The corona discharge device for an electrophotographic apparatus according to claim 1 or 2, comprising: means for detecting the DC bias voltage; and when the DC bias voltage detected by the means exceeds a predetermined value or when a predetermined 1. A corona discharge device for an electrophotographic apparatus, characterized in that the corona discharge device for an electrophotographic apparatus is provided with a high voltage output stop means that stops outputting the high voltage applied to the corona discharge wire and the back electrode when the voltage exceeds a certain value.