JPS63128368A - High voltage generating device in electrostatic photographic-image forming device - Google Patents

Abstract

PURPOSE:To make a self-excited oscillation circuit or a dedicated oscillation circuit unnecessary, by providing a rectangular wave signal generating means which supplies a rectangular wave signal from its output port to a boosting circuit, in microcomputer for controlling image formation. CONSTITUTION:Since resistors R1 and R2 are connected to the base of a transistor Tr1, the Tr1 and a Tr4 are turned ON/OFF according to the rectangular wave signal generated from the output port fMC of the microcomputer 1, and a high voltage transformer T1 is excited. An A.C. high voltage is induced on a coil L2 by the above excitation, and it is recitfied by a double voltage rectifier circuit consisting of diodes D1 and D2, and capacitors C1 and C2, and a D.C. high voltage is generated at an output terminal MCout via a resistor R6. In such way, it is not necessary to provide the self-excited oscillation circuit or the dedicated oscillation circuit to excite the high voltage transformer consisting of the boosting circuit, and to simplify a circuit regarding the above part.

Description

DETAILED DESCRIPTION OF THE INVENTION (Al Industrial Field of Application) This invention relates to a high voltage generator used for charging, transfer, developing bias, etc. in an electrostatographic image forming apparatus.

(Bl. Prior Art) In an electrostatic electrophotographic copying machine, high voltage is required for a charger for charging a photoreceptor drum, a developing device, a charger for transfer, and the like.

Conventionally, the high voltage supplied to each part necessary for such image formation is generally performed by DC/DC conversion or DC/AC conversion from a low voltage power source. For this purpose, the high voltage generation circuit is comprised of an oscillation circuit section, a booster circuit section, and an output voltage (current) stabilization circuit section.

FIG. 4 shows an example of a conventional high voltage generating circuit. In the figure, T is a high voltage transformer, Ll is a primary coil, L2 is a secondary coil, and L3 is a positive feedback coil. 3 is an excitation circuit for the coil L1, and 4 is a positive feedback circuit for the excitation circuit 3, which performs positive feedback to the excitation circuit 3 according to the voltage induced in the coil L3. This constitutes an automatic oscillation circuit, and an AC high voltage is generated in the coil L2 of the high voltage transformer T. Diode D1. D2 is a rectifying diode, which together with capacitors C1 and C2 constitutes a voltage doubler rectifier circuit. A voltage dividing circuit is constituted by resistors R7 and R8 and variable resistor VR, and its output voltage is supplied to output voltage stabilizing circuit section 5. Output voltage stabilization circuit 5
acts to reduce the output of the excitation circuit 3 when the output voltage rises, and also performs control so that the output voltage is stabilized even with voltage fluctuations of the DC power supply voltage (2). Note that the resistor R6 is inserted to limit the output current, and the capacitor C3 is inserted to remove high frequency components.

(C) Problems to be Solved by the Invention The high voltage generation circuit in such a conventional electrostatic photographic image forming apparatus performs self-sustaining oscillation based on the input DC voltage and boosts the voltage using a high voltage transformer. However, the circuit configuration was relatively complicated. Therefore, the present invention uses the functions of a microcomputer to perform various controls regarding image formation in an electrostatic image forming apparatus to simplify the configuration of a high voltage generation circuit, reduce the number of overall components, and reduce costs. It is an object of the present invention to provide a high-voltage generating device for an electrostatographic image forming apparatus that makes it possible to achieve the following.

Means for Solving the Fd1 Problem The high voltage generator in the electrostatographic image forming apparatus of the present invention includes a booster circuit that inputs an alternating voltage and outputs a high voltage, and a microcomputer for controlling image formation. The present invention is characterized in that a rectangular wave signal generating means is provided for supplying a rectangular wave signal from the output port to the booster circuit.

(e) Effect With the above configuration, a rectangular wave signal is generated from the output port of the microcomputer that controls image formation, and the booster circuit is activated by this rectangular wave signal to generate a high voltage. Therefore, there is no need for an automatic oscillation circuit or a dedicated oscillation circuit for exciting the high-voltage transformer constituting the booster circuit, and the circuit for that part can be simplified.

(f) Embodiment FIG. 1 shows a circuit of a high voltage generator in a copying machine to which the present invention is applied. In the figure, numeral 1 represents a microcomputer, which includes a ROM that stores in advance a control program for performing various controls related to image formation, and a RAM that is used as a working area when executing the control program. This microcomputer 1 includes a key human power device 61 and a display device 7. Various sensors8. Various drive control circuits 9 are connected and used for executing the control program. In a microcomputer, fMC + fTC + fBA are 3 of the output ports.
represents a bit. 2a, 2b, and 2'c represent booster circuits, and in the figure, only 2a is shown as a specific circuit. As will be described later, for example, a rectangular wave signal having a predetermined frequency is generated from fMc, and the booster circuit is driven by this rectangular wave signal, and the output terminal MCo is driven by the rectangular wave signal.
Outputs DC high voltage from ut.

The configuration and operation of the booster circuit 2a are as follows. T1 is a high voltage transformer, Ll is a primary coil, and R2 is a secondary coil. The transistor Tr4 is a transistor that excites the coil L1, and forms a Darlington circuit together with the transistor Trl. Note that R5 is Tr
4 bias resistance. There is a resistor R1 at the base of Tri.
, R2 are connected as shown in the figure, the output port f of the microcomputer 1. Tri and Tr4 are turned on according to the rectangular wave signal generated from. Excitation of the high-voltage transformer T1 induces an AC high voltage in the coil L2, which is rectified by a voltage doubler rectifier circuit including a diode Di, D2° capacitors CI and C2, and output to an output terminal MC via a resistor R6.

A high DC voltage is generated at ut. The output voltage of the voltage divider circuit configured by R7, VR, and R8 is the transistor Tr.
It is supplied to the base of 2. If the output voltage decreases, the base potential of Tr2 decreases, the collector current increases, and the base potential of transistor Tr3 decreases. As a result, at the on-timing of Tr4, L
The excitation current flowing through I increases and acts to raise the output voltage. In this way, the output voltage is stabilized. Also, if the voltage of the DC power supply voltage VB decreases,
The current flowing through the voltage detection circuit consisting of R3, ZD, and R4 decreases, and the base potential of Tr3 decreases. This acts to increase the output voltage in the same way as in the previous case,
Efforts are made to stabilize the output voltage.

Next, the operation of generating a rectangular wave signal from the output port of the microcomputer 1 will be explained.

FIGS. 2(A) to 2(C) are flowcharts showing the processing procedure of the microcomputer 1. As shown in (A) of the same figure, when the power of the apparatus is first turned on, each part is initialized and the fixing device etc. are warmed up (n'l→n2
). After that, the content of the operated key is read from the key-powered device (n3). If the operated key is not the print key, copy conditions are set in accordance with the operations of keys after the print key, that is, various key operations for setting copy conditions. (n4). When the print key is operated, first, paper feeding is started, and the paper is conveyed until a microsinch (not shown) MSI provided at a predetermined position is turned on (n6-'n?).After that, Clear the timing counter TC to be used later and start the process (n8=n9
). Thereafter, a rectangular wave signal is output from a predetermined output port (n10).

FIG. 2(B) shows step nl in FIG. 2(A).

represents the processing of In this process, first, a "'H" level is output to a predetermined output port, and the process waits for a certain period of time (n20-n21). Then set the output port to “
Wait for a certain amount of time as L”Lehel (n22
-=n23). As a result, a rectangular wave signal is generated from the output port. FIG. 3 shows the waveform of the signal.

Due to the time wait at n21 shown in FIG. 2(B), the time output port from tl to t2 becomes "H" level, and n
Due to the waiting time at 23, the output port goes to the "L" level from t2 to t3. In this way, a square wave signal of a constant frequency is generated.

FIG. 2(C) shows processing performed when an interrupt signal is generated while a rectangular wave signal is generated by the processing shown in FIG. 2(B). The interrupt signal is generated by an output pulse of a timing pulse disk that detects the rotation angle of the photoreceptor drum as it rotates. First, in the interrupt processing, the timing counter TC is incremented (n30), and it is determined whether the value has reached a predetermined value N1 (n31). When TC=N 1, the sheet stopped at the position of the microsinch MSI starts to be conveyed toward the photosensitive drum (n 32
). During interrupt processing, the TC value is set to a predetermined value N2.
If it is detected that the process required for image formation has been completed, the process is terminated and the process returns to the key reading routine (n33-n34→■-n3).
. As described above, a rectangular wave signal is generated from a predetermined output port, a high voltage is generated by the booster circuit, and processing is performed according to a predetermined timing by interrupt processing.

(g1 Effects of the Invention As described above, according to the present invention, the functions of the microcomputer used for various controls of image formation are utilized to generate a rectangular wave signal from the microcomputer, so that the high voltage generation circuit can does not require a self-help oscillation circuit or a dedicated oscillation circuit, and can simplify the entire circuit, reduce the number of required parts, and reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a control section of a copying machine according to the present invention, and FIG.
Figures (A), (B), and (C) are flowcharts showing the processing procedure of the ``ficrocomputer'' in the same device.
FIG. 3 is a diagram showing a rectangular wave signal output from a microcomputer, and FIG. 4 is a diagram showing a conventional high voltage generation circuit. 1-microcomputer, 2a, 2b, 2c-boost circuit. Figure 2 (A) Figure 2 (B)

Claims (1)

[Claims] (1) A high voltage generator used in an electrostatographic image forming apparatus, comprising a step-up circuit that inputs an alternating current voltage and outputs a high voltage, and connects the microcomputer for controlling image formation from its output port to the 1. A high voltage generator for an electrostatographic image forming apparatus, comprising a rectangular wave signal generating means for supplying a rectangular wave signal to a booster circuit.