JPH01108578A - Power source unit - Google Patents

Abstract

PURPOSE:To decrease the power consumption, to miniaturized the title unit and to reduce its cost by inserting a high breakdown strength transistor into a ground and controlling a current of the high breakdown strength transistor through an isolation circuit. CONSTITUTION:A high breakdown strength transistor Q3 is inserted into the ground in order to apply a bias voltage to a housing shield or a grid wire 6 of a primary electrifier 5. Subsequently, the detecting a current flowing between a collector and an emitter of this high breakdown strength transistor Q3, or a voltage of the housing shield or the grid wire 6, a base current of the high breakdown strength transistor Q3 is controlled through an isolation circuit. In such a way, it does not occur that about 10 times of the necessary power is consumed for a bleeder resistance, said unit is miniaturized and the cost is reduced, and also, the variable range can be selected widely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device, and particularly to a power supply device for an image forming apparatus such as an electronic copying machine or a printer.

[Conventional technology]

Conventionally, as this type of device, the one shown in FIG. 5 is known. FIG. 6 is an explanatory diagram showing the voltage-current characteristics of the grid wire.

In the figure, 1 is a photosensitive drum, which is a photosensitive member, and 2 is a photosensitive drum 1, after cleaning the photosensitive drum 1 and charging it with a primary charger 5, which is a charging means, which will be described later. An optical system forms an electrostatic latent image on the photosensitive drum 1 by an exposure light source 2 for exposing an image of a document or the like.

3 is a developing device, and this developing device 3 allows the photosensitive drum 1 to be
After developing the upper electrostatic latent image and transferring the developed image onto the transfer paper 4, an image is formed by a process such as fixing.

5 is the charging wire of the primary charger 5; 6 is a grid wire provided between the charging wire 5a and the photosensitive drum 1; the grid wire 6 and the charging wire 5a are connected to each other; Close to the primary charger 5 consisting of
When passing through the photosensitive drum 1, the surface of the photosensitive drum 1 is charged.

7 is a transfer charger, 10 is a high voltage power supply for this transfer charger 7, 9 is a developing bias power supply for the developer 3, and 11 is the -
This is a grid power source for the grid wire 6 of the charger 5.

Reference numeral 8 denotes a high-voltage power supply that supplies power to the charging wire 5a of the negative charger 5, which supplies a negative high voltage of approximately -6 kV to the charging wire 5a of the primary charger 5, which is the charging means. A grid wire 6 is provided between the charging wire 5a and the photosensitive drum 1, which is a drum of the image forming apparatus, in order to stabilize charging. It is configured to supply a constant voltage power supply of 900V.

In the above configuration, when looking at the grid wire 6 as a load from the grid power supply 11 side, it is noted that current flows in the positive direction despite the negative voltage output.

That is, since the charging wire 5 has negative polarity, power flows from the grid power source 11 toward the grid wire 6, which is the primary grid. In the conventional device shown in FIG. 5, the grid voltage is formed by a DC-DC converter, and the output voltage is divided into a predetermined ratio by resistors R2, R22 connected in parallel with a smoothing capacitor C21. , the switching transformer Q2 on the primary side of the inverter transformer T2I is compared with the reference voltage connected to the terminal P21 by the operational amplifier Q21 by the PWM circuit 21.
By changing the energization ratio of 2, the output voltage was kept constant.

[Problem that the invention seeks to solve]

In this way, conventional equipment was configured,
Since the grid current is directed to cut off the diode D21, it will flow through the resistors R2□ and R22. For example, the upper limit data and lower limit data in the grid wire voltage/current characteristic diagram shown in FIG. Even if we take intermediate standard data, for example, grid voltage -200V
In order to ensure this, it is necessary to set the series resistance of resistors R2+ and R22 to 1 MΩ or less.

Furthermore, if the output voltage is set to -900V by changing the reference voltage supplied to the terminal P21, the resistors R2, , R2
2, it is understood that the power consumed alone is 0.81W.

For this reason, in the conventional device, compared to the power consumed by the load (900 V x 120 x 10 -6 A = 0.108 W), a very wasteful amount of power is consumed on the power source side, resulting in an increase in the size of the power source.

There was a problem that the cost would increase.

[Purpose of the invention]

This invention was made in order to solve such problems, and by inserting a high voltage transistor between the grounds,
It is an object of the present invention to provide a power supply device that consumes less power, is smaller in size, and can be reduced in cost by controlling the base current of a high voltage transistor through an isolation circuit.

[Means for Solving Problem C] For this reason, in the power supply device of the present invention, a high voltage transistor is inserted between the grounds, and the current flowing between the collector and emitter of this high voltage transistor is connected to the case shield or the grid. The above object is achieved by detecting the voltage of the wire and controlling the current of the high voltage transistor through an isolation circuit.

[Effect]

With the above configuration, the power supply device of the present invention reduces the current flowing between the collector and emitter of the high voltage transistor.
or detect the voltage on the enclosure shield or grid,
This is used to control the current of the high voltage transistor via the isolation circuit.

〔Example〕

An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is an explanatory diagram of a power supply device according to an embodiment of the present invention.

Identical (equivalent) components in the conventional apparatus shown in FIG. 5 are indicated by the same reference numerals to avoid redundant explanation.

In the conventional example, the grid power supply is configured by a DC-DC converter, whereas in one embodiment of the present invention, a high voltage transistor (hereinafter referred to as "high voltage transistor") is used.

) Consists of a series regulator using Q3. That is, in this case, since the load current itself is extremely small, a series regulator is inserted into the route of the load current flowing from the ground to the high voltage, and its output is connected to the grid wire 6.

A high voltage transistor Q3 is connected between the grid wire 6 and the ground. In order to protect this high voltage transistor Q3, a resistor is actually inserted on the collector side or the emitter side.

R3 and R4 are resistors, and the resistors R3 and R4 divide the grid voltage into a predetermined ratio, and the operational amplifier Q divides the grid voltage into a predetermined ratio.
It is designed to be compared with a reference voltage applied to terminal P1.

T1 is a pulse transformer for controlling the base current of the high voltage transistor Q3, and this pulse transformer T1
plays the role of isolation.

The output of the operational amplifier Q1 is applied as a collector bias to the transistor Q2. The base of this transistor Q2 is connected/supplied with an AC signal of a predetermined frequency by the oscillation circuit 12, and is driven in a switching mode. That is, the AC amplitude on the primary side of the pulse transformer T1 is changed according to the output of the operational amplifier Q1. The AC signal isolated by the pulse transformer T1 is rectified by the diode D2 to control the base current of the high voltage transistor Q3.

In addition, C1 is a smoothing capacitor, R,, R2゜R5, R
6, R7, and Ra are resistors, and D is a varistor for protecting the high voltage transistor Q3 from overvoltage.

According to one embodiment of the present invention, in order to apply a bias voltage to the case shield of the negative charger 5 or the grid wire 6, a high voltage transistor Q3 is inserted between the ground, and the collector of the high voltage transistor Q3 is connected to the ground. By detecting the current flowing between the emitters or the voltage of the case shield or grid wire 6, and controlling the base current of the high voltage transistor Q3 through the isolation circuit, the power is approximately 10 times higher than that required for the bleeder resistor. There is no need to consume anything, and it is compact.

This has the effect of reducing costs, allowing a wide variable range to be selected, and providing a power supply device with improved reliability.

Further, according to the embodiment, since NPN transistors can be used, various types of high voltage transistors can be selected.

Furthermore, according to one embodiment of the present invention, since the pulse transformer T is used only to control the base current of the high voltage transistor Q3, it is only necessary to consider and satisfy the dielectric strength voltage between the primary and secondary transistors. Therefore, it is easy to downsize.

[Other Examples]

Other embodiments of the invention will be described below with reference to FIGS. 2 to 4.

In addition, in the figure, P 411 P 51 are terminals, Q 3+
+ Q 411Q 5+ is operational amplifier, Q42 is PNP
transistor, Q S2 is a high voltage transistor, Q5
3 is a photocoupler, R3,, R32, R4, ~R44,
R5□ to R56 are resistors, and Z D + is a Zener diode.

In the power supply device according to one embodiment of the present invention, the case where the charging voltage is a negative voltage has been explained, but as shown in FIG. 2, even if the charging voltage is a positive voltage and the grid voltage is fixed, It has a great effect.

Further, in the power supply device according to one embodiment of the present invention, the charging means is negatively charged and uses an NPN high voltage transistor. However, as shown in FIG. 3, it is possible to use a PNP transistor Q42 as a series regulator. Since there is no need for isolation, there is no need for a pulse transformer, making it possible to further simplify the embodiment compared to the previous embodiment.

Further, in the above embodiment, a pulse transformer was used as the isolation means, but if a photocoupler Q53 is used instead of the pulse transformer as shown in FIG. 4, the circuit can be simplified and miniaturized.

Cost can be easily reduced.

〔Effect of the invention〕

As described above, according to the present invention, a high voltage transistor is inserted between the grounds and the current of the high voltage transistor is controlled via an isolation circuit, thereby reducing power consumption, miniaturization, and This has the effect of providing a power supply device that can reduce costs.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a power supply device according to an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of another embodiment of the present invention in the case of positive charging, FIG. 3 is an explanatory diagram of an example using the same PNPI-transistor, and FIG. 4 is an explanatory diagram of an example using a photocoupler as the isolation means. An explanatory diagram, FIG. 5 is an explanatory diagram of a conventional device, and FIG. 6 is a voltage/current characteristic diagram of a grid wire. In the figure 5...Charger 5a...Charging wire 6...Grid wire 11...Grid power supply 13--Isolation circuit ri, -...
- Varistor Q3 - High voltage transistor Q53 Photocoupler T, Pulse transformer In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (6)

[Claims] (1) In an electrophotographic image forming apparatus, a high voltage transistor is inserted between the ground in order to apply a bias voltage to the case shield or grid wire of the charging means, and the voltage flows between the collector and emitter of this high voltage transistor. A power supply device characterized in that the base current of the high-voltage transistor is controlled via an isolation circuit by detecting a current or a voltage of a case shield or a grid wire. (2) The power supply device according to claim 1, wherein the isolation circuit comprises a DC-DC converter circuit, and controls the DC voltage on the primary side using a detected voltage or a detected current. (3) Claim 1, characterized in that the high voltage transistor has a varistor inserted between its collector and emitter.
Power supplies listed in section. (4) The charging means applies a load to the charged wire, and the emitter of the NPN high voltage transistor is connected directly or via a resistor to the case shield or grid wire, and the collector is connected to the ground directly or via a resistor. A power supply device according to claim 1, characterized in that: (5) The power supply device according to claim 1, wherein the high voltage transistor is a high voltage FET. (6) The power supply device according to claim 1, wherein the isolation circuit uses a photocoupler.