JPH05173433A - High voltage generation circuit for electrophotographic copying device - Google Patents

Abstract

PURPOSE:To make external size small, to reduce a cost and to enhance reliability. CONSTITUTION:Boosting transformers for positive output and negative output 41 and 45 are provided and control circuits 51 and 53 are connected to coils on the primary sides of the respective transformers 41 and 45. Then, a current on the primary side is outputted with respect to the respective transformers 41 and 45 by a switching action. Besides, rectifier diodes 42, 46 and smoothing capacitors 43, 47 are connected to coils on the secondary sides of the respective transformers 41, 45 and resistors 44, 48 are connected to the respective capacitors 43, 47 in parallel. The respective resistor 44, 48 are mutually serially connected. Then, a load output is connected to one of them and the other is grounded. By the control circuits 51, 53, the current on the primary side is outputted with respect to the respective transformers 41, 45 in timing corresponding to the load output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage generating circuit for an electrophotographic apparatus.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic apparatus, the surface of a photosensitive drum uniformly charged by a primary charging process is exposed corresponding to image data read by an optical means to form an electrostatic latent image. To be done. Then, the electrostatic latent image is developed in a developing process and then transferred to a recording medium in a transfer process to form an image. In the electrophotographic apparatus, a charging roller is charged to charge the surface of the photosensitive drum by a primary charging process, a developing roller is used to develop the surface of the photosensitive drum, and a toner image obtained by the development is transferred. To this end, a transfer roller is provided, and a voltage is applied to each roller.

FIG. 2 is a conceptual diagram of a high voltage generating circuit of a conventional electrophotographic apparatus. In the figure, 11 is a cylindrical photosensitive drum, 12 is a charging roller, 13 is a developing roller, 14 is a toner conveying roller for supplying toner to the developing roller 13 smoothly, and 15 is a transfer roller. Further, 16 is a negative power source for applying a negative voltage to the charging roller 12, and 17 is a negative power source for applying a negative voltage to the developing roller 13. Also,
Reference numeral 18 denotes a positive power source that applies a positive voltage to the transfer roller 15 to transfer the toner image onto a recording medium (not shown), and 19 applies a reverse bias to return the toner attached to the transfer roller 15 to the photosensitive drum 11 and transfer the toner. It is a negative power source for cleaning the roller 15. The positive power source 18 and the negative power source 19 are selectively connected via the changeover switch 20, and the positive power source 18 and the negative power source 19 are not simultaneously connected to the transfer roller 15.

FIG. 3 is a time chart of a high voltage application sequence in the high voltage generating circuit of the conventional electrophotographic apparatus. Here, the signal for controlling the primary charging output is CH (Ch
signal), a signal for controlling the positive output for transfer is TR1
(Transfer), and a signal for controlling the negative output for transfer is TR2. First, after the power supply _Vcc is turned on, the signal C
H is turned on, and the high-voltage primary charging output is applied to the charging roller 12. Next, when the recording medium passes over the photosensitive drum 11, the signal TR1 is turned on, and a high voltage positive output is applied to the transfer roller 15.

After repeating the predetermined printing operation, the signal CH is turned off, the signal TR2 is turned on, and the transfer roller 15 is turned on.
A negative high-voltage output is applied to the transfer roller 15 to clean it, and then the photosensitive drum 11 is stopped. Next, a specific configuration of the high voltage generating circuit will be described. FIG. 4 is a schematic diagram of a high voltage generating circuit that generates a transfer output applied to the transfer roller.

In the figure, a step-up transformer 21, a rectifying diode 22 and a smoothing capacitor 23 are provided for positive output, and a step-up transformer 24, a rectifying diode 25 and a smoothing capacitor 26 are provided for negative output.
Reference numeral 27 is a high voltage relay for switching the positive output or the negative output, which is operated by turning on / off the signals TR1 and TR2.

Reference numeral 31 is a control circuit which is connected to the primary winding of the step-up transformer 21 and outputs a primary current by switching operation and outputs a relay signal to the high voltage relay 27. A transistor 32 is connected to the control circuit 31. When a control signal is sent to the transistor 32 to turn it on and off, the primary side current of the step-up transformer 21 is controlled.

A control circuit 33 is connected to the primary side winding of the step-up transformer 24 and outputs a primary side current by a switching operation and outputs a relay signal to the high voltage relay 27. A transistor 34 is connected to the control circuit 33. When a control signal is sent to the transistor 34 to turn it on and off, the primary side current of the step-up transformer 24 is controlled.

That is, when the signal TR1 is turned on, the switch 27a on the positive output side of the high voltage relay 27 is closed,
A high voltage positive output is applied to the transfer roller 15. When the signal TR2 is turned on, the switch 27b on the negative output side in the high voltage relay 27 is closed and the high voltage negative output is applied to the transfer roller 15. In this way, the positive output and the negative output can be obtained from one contact constituted by the shaft of the transfer roller 15 by changing the time. If positive output and negative output are generated at the same time, a current flows into the other circuit, which causes an abnormal state. Therefore, the control circuits 31 and 33 side prohibit it.

[0010]

However, in the high voltage generating circuit of the above-mentioned conventional electrophotographic apparatus, since the high voltage relay 27 that performs a mechanical switching operation is used, not only it lacks reliability, but also As the external size increases, the high-voltage relay 27 is a special component, which increases the cost.

The present invention solves the above-mentioned problems of the high voltage generating circuit of the conventional electrophotographic apparatus, has high reliability, has a small external dimension, and can reduce the cost of the electrophotographic apparatus. An object is to provide a voltage generating circuit.

[0012]

Therefore, in the high voltage generating circuit of the electrophotographic apparatus of the present invention, a positive output step-up transformer and a negative output step-up transformer are provided respectively, and the primary winding of each step-up transformer is provided. A control circuit is connected, and a primary side current is output to each step-up transformer by switching operation. Further, a rectifier and a smoother are connected to the respective secondary windings of the respective step-up transformers, and resistors are connected in parallel to the respective smoothers.

The two resistors are connected in series with each other,
The load output is connected to either one and the other is grounded. The control circuit outputs the primary side current to each of the positive and negative output step-up transformers at a timing corresponding to the load output.

[0014]

According to the present invention, the step-up transformers for positive output and negative output are respectively provided as described above, the control circuit is connected to the primary side winding of each step-up transformer, and each step-up transformer is switched by the switching operation. On the other hand, the primary side current is output. Therefore, a high voltage is obtained on the secondary side of each step-up transformer.

Further, since a rectifier and a smoother are connected to the secondary windings of each step-up transformer, the secondary current is rectified and smoothed. A resistor is connected in parallel to each of the smoothers, the two resistors are connected in series with each other, and the load output is connected to one of the resistors and the other is grounded. Therefore, the current output from the secondary winding of one of the step-up transformers flows to the load output, and then returns to the secondary side winding through the resistance connected from the GND to the other step-up transformer. In addition, the current output from the secondary winding of the other step-up transformer is GND
To the load output, and returns to the secondary winding through a resistor connected to one step-up transformer.

Each of the control circuits outputs the primary side current to the positive output booster transformer and the negative output booster transformer at a timing corresponding to the load output. A positive output and a negative output can be selectively obtained from one terminal according to the required timing.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a high voltage generating circuit of an electrophotographic apparatus of the present invention. In the figure, a step-up transformer 41, a rectifier or rectifier diode 42, and a smoother or smoothing capacitor 43 are provided for positive output, and a resistor 44 having a high resistance value of several tens of MΩ or more is provided in parallel with the smoothing capacitor 43. Connected. Also,
Step-up transformer 45 and rectifier diode 46 for negative output
And a smoothing capacitor 47 is provided, and the smoothing capacitor 47 has a resistor 48 having a high resistance value of several tens of MΩ or more.
Are connected.

Reference numeral 51 is a control circuit which is connected to the primary winding of the step-up transformer 41 and outputs a primary current by a switching operation. A transistor 52 is provided in the control circuit 51. When a control signal is sent to the transistor 52 to turn it on and off, the boosting transformer 41
The primary side current flows to. Reference numeral 53 is a control circuit which is connected to the primary winding of the step-up transformer 45 and outputs a primary current by a switching operation. A transistor 54 is provided in the control circuit 53. When a control signal is sent to the transistor 54 to turn it on and off, a primary side current flows through the step-up transformer 45.

The resistors 44 and 48 are connected in series, the resistor 44 is connected to the TR output, and the resistor 4
8 is grounded (connected to GND). Thus, on the output side, the structure is such that no mechanical switching operation is performed. When the signal TR1 is turned on in the high voltage generating circuit of the electrophotographic apparatus having the above configuration, the secondary side current of the step-up transformer 41 is rectified by the rectifying diode 42, smoothed by the smoothing capacitor 43, and then passed through the TR output. Is sent to the transfer roller 15 (see FIG. 2), and the transfer roller 1
A high voltage positive output is applied to 5. After that, the secondary side current passes through a load (not shown) and returns from the GND to the step-up transformer 41 via the resistor 48. Similarly, in the case of a negative output, the secondary side current of the step-up transformer 45 passes from the GND to the transfer roller 15, returns to the step-up transformer 45 via the resistor 44 and the rectifying diode 46.

The generated voltage has a voltage division ratio of the resistors 44 and 48 for both positive output and negative output. For example, resistors 44 and 4
If the value of 8 is the same, the step-up transformer 41 at the time of positive output
The voltage of the value obtained by subtracting the drop voltage due to the resistor 48 from the voltage across the secondary winding of is the voltage of the value obtained by subtracting the drop voltage due to the resistor 44 from the voltage across the secondary winding of the step-up transformer 45 when TR is negative. Will be applied to the output.

In this way, a positive output and a negative output can be obtained from one TR output terminal at a required timing without using a high-voltage relay 27 (see FIG. 4) which performs a mechanical switching operation. it can. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0022]

As described above in detail, according to the present invention, the positive output booster transformer and the negative output booster transformer are provided, and the control circuit is connected to the primary winding of each booster transformer. Primary current is output to each step-up transformer by switching operation. A rectifier and a smoother are connected to each secondary winding of each step-up transformer, and a resistor is connected to the load. The load output is connected to one of the two resistors and the other is grounded. ..

Therefore, as the load output, the positive output and the negative output can be selectively obtained. Further, the control circuit is configured to output the primary side current to each of the positive output and negative output step-up transformers at the timing corresponding to the load output. Positive output and negative output can be selectively obtained from one terminal.

Since it is not necessary to use a high-voltage relay or the like that performs mechanical switching operation, reliability can be improved and the external dimensions can be reduced, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a high voltage generating circuit of an electrophotographic apparatus of the present invention.

FIG. 2 is a conceptual diagram of a high voltage generation circuit of a conventional electrophotographic apparatus.

FIG. 3 is a time chart of a high voltage application sequence in a high voltage generation circuit of a conventional electrophotographic apparatus.

FIG. 4 is a schematic diagram of a high voltage generation circuit that generates a transfer output applied to a transfer roller.

[Explanation of symbols]

 41,45 Step-up transformer 42,46 Rectifying diode (rectifier) 43,47 Smoothing capacitor (smoothing device) 44,48 Resistance 51,53 Control circuit

Claims (2)

[Claims] 1. (a) Positive output and negative output booster transformers, and (b) primary booster transformer windings connected to the primary windings to output primary currents to the booster transformers. Control circuit, (c) rectifiers and smoothers connected to the respective secondary windings of the step-up transformer, and (d) each smoother connected in parallel and in series with each other. And a load output connected to one of the two resistors, and the other is grounded. 2. The control circuit has means for outputting a primary-side current to each of the positive and negative output step-up transformers at a timing corresponding to a load output.
A high-voltage generation circuit for the electrophotographic apparatus described.