JPS63183464A - Electric charger - Google Patents

Abstract

PURPOSE:To stabilize the potential of a shield or grid of an electric charger for a copying machine or the like by detecting the voltage between the shield or grid and gland by resistance division, subjecting the detected voltage to current amplification, further amplifying the same with a high-voltage transistor and connecting a varister and the high-voltage TR in parallel. CONSTITUTION:The voltage divided by resistors R1-R3 is inserted between the shield 2a or grid 2b and the gland G is connected via a current amplifying transistor TR1 to the high-voltage transistor TR2. The emitter of the TR2 is maintained at a constant voltage by a constant voltage diode ZD. The voltage V1 of the shield 2a or grid 2b is V1=(VZ+2VBE).(R1+R2+R3)/R3 if the voltage of the diode ZD is designated as VZ and the sum of the base-emitter voltages of the TR1, TR2 is designated as 2VBE. Said voltage, therefore, has the constant potential. The varister 7 is for breakdown protection of the TR2.

Description

Detailed Description of the Invention A. Object of the Invention [Industry-1 Field of Application] The present invention relates to a charger in an electrophotographic apparatus such as a copying machine or printer, and particularly to a charger for keeping the potential of its shield or grid at a constant potential. Regarding the control method.

[Conventional technology]

First, an outline of an electrophotographic charging system to which the present invention is applied will be explained with reference to FIG.

The charging system of the electrophotographic apparatus applies high voltage generated by a high-voltage power source 1 to a primary charger 2 to charge the surface potential of the photosensitive drum 3' to a predetermined potential. Next, an electrostatic image is formed on the photosensitive drum 3 by exposure with reflected light of the image or laser light 4, toner is deposited on the photosensitive drum by the developer 5, and toner is placed on the copy paper P by the transfer charger 6. ing.

Further, the copy paper is then fixed with toner on the paper by a fixing device.

Here, the potentials of the shield 2a and grid 2b of the primary charger 2 are maintained at a predetermined voltage to obtain a stable image.

As a means of maintaining the potential of the shield 2a and the grid 2b at a predetermined value, as shown in FIG. is adjusted to obtain a predetermined potential.

[Problem that the invention seeks to solve]

The above method has the problem that the variable resistor 9 must be adjusted because the varistor voltage varies by about ±10%, and the varistor changes over time.

The present invention provides a charger equipped with a shield potential control method that eliminates the adjustment of such a variable resistor and constantly detects the grid potential or shield potential, thereby making it possible to eliminate changes in the varistor over time. It is something.

Summary: Structure of the Invention [Means for Solving Problems] The present invention provides a means for maintaining a shield potential or grid potential of a charger in an electrophotographic apparatus such as a copying machine or a printer at a predetermined value. It is characterized by including a high voltage transistor and a varistor in parallel between the ground, detecting the potential by resistor division between the shield or the grid and the ground, and providing current amplification means between the voltage detection means and the high voltage transistor. It is a charger that

[For production]

A high withstand voltage transistor and a varistor are included in parallel between the shield or grid and the ground, and the potential of the shield or grid is detected by resistive division between the shield or grid and the ground, and current amplification is performed between this voltage detection means and the high withstand voltage transistor. With the arrangement provided with the means, the shield or grid voltage (1) can be determined by the already-valued number of the above-mentioned components.

〔Example〕

2 to 4 show embodiments of the present invention. First, in FIG. 2, resistors R1 to R3 are connected to the shield 2.
a or between grid 2b and graph 10. That R1
A voltage determined by the voltage division ratio of +R2 and R3 is connected to the base of the high voltage transistor TR2 via the current amplification transistor TRI. Further, the emitter side of TR2 is set at a predetermined potential by a constant voltage diode ZD. Here T
The reason why TRI is provided before R2 is because the DC current amplification factor of a high voltage transistor is usually very low, and it is difficult to control it with just TR2. R6 is a resistor for constant voltage of the Zener diode ZD, and R4 and R5 are adjustment resistors.

In the above configuration, the shield or grid voltage vI is calculated as follows: (1)...The voltage set to the constant voltage diode ZD, 2VBE...The sum of the voltages between each pace emitter of transistors TR1 and TR2. , the numerical values of each element all take fixed values, from which the shield or grid voltage V1 can be determined. Also, there is a varistor 7 between the shield or grid and the graph 10.
are connected in parallel, but this is necessary for the purpose of shielding or stabilizing the grid voltage due to voltage protection of TR2 and capacitance component of the varistor.

Although the embodiment shown in 1- is a positive charger system, the concept for negative charging is basically the same, and an example of the circuit is shown in FIG.

That is, the polarity of the high voltage diode ZD is reversed from the above example,
The collector of transistor TRI is connected to ground G via adjustment resistor R4. ZD constant voltage resistor R6
Connect between D and resistor R3.

In this configuration, the voltage across resistor R3 is Zener voltage +
Pace emitter voltage of TRI and TR2, that is, V2+
2VBB, and from this the current flowing through R3 can be found. Considering that the current flowing through R6 is almost the same as that flowing through R3, the shield or ground voltage V, becomes.

In the examples of FIGS. 2 and 3, a specific voltage is used, but FIG. 4 shows an embodiment in which the shield/grid voltage can be set to an arbitrary value.

That is, for example, in substantially the same configuration as in FIG. 2, the constant voltage diode ZD is used as a variable power source to control its voltage. With this configuration, the shield grid voltage V is equal to the shield grid voltage, which is the input voltage V cont
is determined uniquely.

C. As described in detail of the invention, it is possible to maintain the shield or grid potential at a predetermined value, and therefore it is also possible to eliminate its adjustment, and the shield or grid voltage can be easily controlled with a compact device. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a charging system of an electrophotographic apparatus to which the present invention is applied, FIGS. 2 to 4 are embodiments of the present invention, and FIG. 5 is a circuit diagram of a conventional shield adjustment device for a charger. 1... High voltage power supply, 2... Charger, 2a... Shield, 2b... Grid, 2c... Charging wire, G...
Ground, TR2... High voltage transistor, 7...
Varistor, R1-R2/R3...Resistance for voltage division, TRI
...Transistor.

Claims (1)

[Claims] (1) A means for maintaining the shield potential or grid potential of a charger at a predetermined value in an electrophotographic device such as a copying machine or printer, which includes a high withstand voltage transistor and a varistor in parallel between the shield or grid and the ground. A charger characterized in that a potential is detected by resistor division between the voltage detection means and the ground, and a current amplification means is provided between the voltage detection means and the high voltage transistor.