JPH0221587B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power supply device for a corona charger with a control electrode, and particularly for monitoring the charging current of a corona charger suitable for charging a photosensitive member of a copying machine. The present invention relates to a power supply device for the corona charger, which is equipped with a monitor.

Prior Art In addition to a wire-shaped discharge electrode and an elongated shield that surrounds this electrode and is open on one side for discharge of charge, there are multiple control electrodes between the discharge electrode and the charged member to control the discharged charge. That is, a corona charger equipped with a grid is well known, and in order to operate this corona charger, a high voltage source that applies a high voltage to a corona discharge electrode and a shield, and a predetermined voltage that controls the amount of discharged charge to a control electrode are used. A power supply device is used with a controlled voltage source that provides a controlled voltage source.

Generally, in the power supply device of a corona charger,
In order to know the amount of charge on the charged member, a monitor circuit is provided to detect the charging current that returns from the charged member to the high voltage source, and the amount of charge can be determined from the output from this circuit. There is. Such monitor circuits work well in corona chargers without control electrodes or grids, but in corona chargers with grids, the charge trapped in the grid is routed through the monitor circuit as it returns to the high voltage source. This caused the problem that the true charging current could not be detected.

For this reason, an attempt was made to return the current from the control electrode, or grid, to the high voltage source without passing through the monitor circuit, but the voltage due to the feedback current from the charged member returning to the high voltage source was The control voltage changes, making it impossible to properly control the amount of emitted charge.

OBJECT OF THE INVENTION Therefore, an object of the present invention is to charge a charging current to a charged member by a corona charger with a control electrode (grid) without adversely affecting the control voltage source.
An object of the present invention is to provide a power supply device equipped with a monitor circuit capable of accurate detection.

Structure of the Invention In order to achieve the above object, according to the present invention,
The current from the control electrode, that is, the grid, is configured to be returned to the high voltage source via the control voltage source without passing through the monitor circuit, and the monitor circuit uses an operational amplifier with differential input and high gain.
A corona charger with a grid, characterized in that the operational amplifier is configured as a current-voltage conversion circuit, and the inverting input terminal of the operational amplifier is connected to a high voltage to detect the charging current of the charged member. A power supply is provided.

EXAMPLES Before describing the preferred embodiments of the present invention, the first
A conventional power supply device for a grid-equipped corona charger will be described with reference to the drawings and FIG.

In FIG. 1, a wire-shaped discharge electrode 2 of a corona charger 1 and an elongated shield 3 surrounding the wire-shaped electrode 2 and having an opening for discharging charges on the lower side are connected to a first voltage source. A high voltage source 4 is connected,
When a high voltage is applied from the high voltage source 4, a corona discharge is generated within the shield 3, and corona ions, that is, charges are emitted toward the charged member 5, which is, for example, a photoreceptor of a copying machine. The corona charger 1 is provided with a plurality of control electrodes or grids 6 between the discharge electrode 2 and the member to be charged 5 to control the amount of charge released from the opening of the shield 3. A predetermined voltage is applied to the grid 6 from a control voltage source 7 serving as a second voltage source, and the amount of charge released is controlled in accordance with the control voltage.

The amount of charge released should be adjusted according to the actual amount of charge on the member 5 to be charged, and for this reason, a circuit is provided to detect the charging current flowing through the member 5 to be charged during charging. This detection circuit is the monitor circuit 8. The monitor circuit 8 is provided with an amplifier 9, a resistor 10 is connected to the input of the amplifier 9, and the other end of this resistor is grounded. Furthermore, the input of the amplifier 9 is connected to a line 11 of the high voltage source, which is connected to the shield 3.

In this monitor circuit 8, the current _i1 flowing through the charged member 5 reaches the resistor 10 via the ground, and the resistor 10
Since the voltage is fed back to the line 11 from the resistor 10, the voltage appearing on the resistor 10 indicates the charging current, and a voltage corresponding to the charging current is outputted to the output terminal 12 of the amplifier 9. However, it should be noted here that the charge trapped in grid 6 is
More specifically, through the output transistor 13
The currents i ₂ and i ₃ flow through the voltage dividing resistors 14 and 15 to the ground. These currents i ₂ and i ₃ are
Since it is returned to the line 11, it passes through the resistor 10 of the monitor circuit 8. Therefore, the current i _S flowing through the resistor 10 is the sum of the currents i ₁ , i ₂ and i ₃ , and the output terminal 1
2 no longer accurately indicates the charging current.

In order to prevent such problems, a circuit shown in FIG. 2 was proposed. In this circuit, the control voltage source 7'
The circuit differs from the circuit shown in FIG. 1 in that the currents i ₂ and i ₃ returning from the grid 6 to the line 11 are returned directly to the line 11 without passing through the monitor circuit 8. In the circuit shown in FIG. 2, since currents i ₂ and i ₃ do not flow through the resistor 10 of the monitor circuit 8, the current i _S flowing through the resistor 10 becomes equal to the charging current i ₁ of the charged member 5, and the output An accurate charging current value appears at the end 12. However, in the circuit _{of this} FIG. It has been found that this causes the problem of varying the bias voltage at the midpoint or point of the control voltage source 7', thereby causing the grid voltage from the control voltage source 7' to vary.

FIG. 3 shows a preferred embodiment according to the invention. In FIG. 3, a high voltage source 4 serving as a first voltage source is connected to the discharge electrode 2 and the shield 3, and a control voltage source 7' serving as a second voltage source is connected to the grid 6. The power supply circuit shown in FIG. 1 _and FIG. ₂ is the same as that of FIG.

The power supply device of the present invention differs from those of FIGS. 1 and 2 in the monitor circuit 20. This monitor circuit 20 is composed of an operational amplifier 23 having differential inputs 21 and 22 and a high differential gain. A resistor 25 (and a capacitor 26) as impedance means is provided between the inverting input 21 and the inverting input 21.
A voltage corresponding to the current flowing through the output 24 appears at the output 24. The inverting input 21 is connected to the line 11 to the shield 3 of the high voltage source 4 and the non-inverting input 22
is grounded.

Before explaining the operation of the monitor circuit 20 having such a configuration, a general explanation of the operational amplifier 23 will be given. As described above, since the operational amplifier 23 has a high differential gain, the voltage between the inputs 21 and 22 is substantially zero under normal operating conditions in which an unsaturated voltage appears at the output. That is, under normal usage conditions, the voltage between the differential inputs is zero, and the voltage relationship appears to be in a shorted state (hereinafter, this state will be referred to as ``imaginary short''. , this relationship is only in terms of voltage, and it goes without saying that in reality both inputs are electrically isolated.) As mentioned above, the operational amplifier 23 constitutes a current-voltage conversion circuit. The charging current i ₁ from the charged member 5 flows as a current i _S to the inverting input 21, and a voltage corresponding to this current i _S appears at the output 24. As shown in FIG. is the current i _S
(=charging current i ₁ ) flows, it is always maintained at the ground potential. Therefore, the control voltage source 7'
The bias potential at the point at will no longer vary depending on the current i _S , and the voltage applied to the grid 6 can be accurately controlled. Incidentally, the grid voltage V _G is expressed as V _G × R ₁₄ /R ₁₅ + R ₁₄ (R ₁₄ and R ₁₅ are the resistance values of resistors 14 and 15), and the feedback current i _S (= charging current i ₁ ) It turns out that it has nothing to do with it.

Effects of the Invention According to the present invention, since the current from the control electrode, that is, the grid, does not pass through the monitor circuit, the charging current of the charged member can be detected accurately, and the reference voltage of the control voltage source for the grid is also Since it is fixed to the ground potential, the internal bias voltage can be detected accurately, and the control voltage will not fluctuate due to the charging current. Furthermore, the monitor circuit according to the present invention does not require an increase in the number of components compared to conventional ones, and is composed of an extremely simple circuit.
There is no increase in price, manufacturing time, etc.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a conventional power supply device for a corona charger with a control electrode, and FIG. 3 is a circuit diagram of a power supply device for a corona charger with a control electrode according to an embodiment of the present invention. . DESCRIPTION OF SYMBOLS 1...Corona charger with control electrode, 2...Discharge electrode, 3...Shield, 4...High voltage source (first voltage source), 5...Charged member, 6...Control electrode (grid), 7, 7'... Control voltage source (second voltage source),
8... Conventional monitor circuit, 20... Monitor circuit according to the present invention.

Claims (1)

[Claims] 1. A first voltage source that generates corona discharge by applying a high voltage between the corona discharge electrode and a shield that is open on one side so as to discharge electric charges, and a first voltage source that generates corona discharge between the corona discharge electrode and the charged member. A control circuit comprising a second voltage source that applies a voltage to a control electrode provided to control the amount of charge emitted to the charged member, and a monitor circuit that detects a charging current that returns from the charged member to the first voltage source. In the power supply device for a corona charger with an electrode, a second voltage source is connected to the first voltage source so as to feed back current from the control electrode to the first voltage source, and the monitor circuit uses an operational amplifier. The power supply device comprises a current-voltage conversion circuit, and an inverting input terminal of the amplifier is connected to the first voltage source.