JP2892438B2 - Development bias circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing bias circuit that applies a required AC bias to a developing device used in an electrophotographic or electrostatic recording type image forming apparatus.

2. Description of the Related Art For example, in an image forming apparatus such as an electrophotographic copying machine or a printer, an appropriate developing bias is supplied to a developing device that develops an electrostatic latent image formed on a photoconductor as an image carrier. For this purpose, a developing bias circuit is used. Conventionally, as shown in FIG. 7, a developing bias circuit for supplying an AC bias to a developing device is provided with an oscillation output from an oscillation circuit 31 having a predetermined frequency (for example, about 2 KHz) to a step-up transformer 33 via a DC blocking circuit 32. The boosting transformer 33 boosts the voltage to a predetermined high voltage, and supplies a required AC bias to the developing device through an output terminal 34 connected to the secondary side of the transformer 33. Therefore, when a predetermined frequency, for example, a rectangular wave is generated from the oscillation circuit 31 and supplied to the step-up transformer 33, the high voltage AC bias generated at the output terminal 34 has a duty cycle of 50% as shown in FIG. , And the waveform becomes dull.

Problems to be Solved by the Invention As described above, when the output of the oscillation circuit is boosted by the transformer to obtain the required AC bias, the output waveform of the AC bias supplied to the developing device becomes blunt,
There is a disadvantage that the rise of the waveform is delayed. It has also been difficult to change the duty cycle of the output waveform.

Therefore, an object of the present invention is to reduce the rounding of the output waveform of the AC bias supplied to the developing device as much as possible,
An object of the present invention is to provide a developing bias circuit capable of easily changing a duty cycle of an output waveform.

Means for Solving the Problems The above object is achieved by a developing bias circuit according to the present invention. In summary, the present invention relates to a developing bias circuit that supplies an AC bias to a developing device used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system. Starting, generating a first oscillation output having a frequency corresponding to the frequency of the AC bias, and a frequency higher than the oscillation frequency of the first oscillation means, operating simultaneously with the operation of the image forming apparatus. Second oscillating means for generating a second oscillating output, and boosting means for boosting a second oscillating output from the second oscillating means;
Rectifying means for rectifying the high-voltage AC output from the boosting means;
Detecting means for detecting a rectified output from the rectifying means; at least one comparison control means for controlling inputs of the second oscillating means and the boosting means in accordance with a detected voltage from the detecting means; And a means for synchronizing the second oscillating means and a first oscillating output from the first oscillating means, and switching the rectified output from the rectifying means to a frequency corresponding to the frequency of the AC bias. A developing bias circuit, comprising: switching means for generating a high-voltage AC output; and DC blocking means for blocking a DC voltage component of the high-voltage AC output and providing a required AC bias.

According to another aspect of the present invention, an ON signal is supplied to an input in a developing bias circuit that supplies an AC bias to a developing device used in an image forming apparatus such as an electrophotographic method or an electrostatic recording method. The first oscillating means for generating a first oscillating output having a frequency corresponding to the frequency of the AC bias, and operating simultaneously with the operation of the image forming apparatus. Second oscillating means for generating a second oscillating output having a frequency higher than the frequency;
Boosting means for boosting the second oscillation output from the oscillating means, rectifying means for rectifying the high-voltage AC output from the boosting means, detecting means for detecting the rectified output from the rectifying means,
A central processing unit for setting a reference voltage for determining the peak-to-peak voltage of the AC bias; a digital-analog converter for converting digital data from the central processing unit into an analog signal; At least one comparison control unit that controls inputs of the second oscillation unit and the boosting unit in accordance with an output signal and a detection voltage from the detection unit; and a unit that synchronizes the first and second oscillation units. A switching unit that is operated by a first oscillation output from the first oscillation unit and that switches a rectified output from the rectification unit to generate a high-voltage AC output having a frequency corresponding to the frequency of the AC bias; DC blocking means for blocking a DC voltage component of the high-voltage AC output and providing a required AC bias. Developing bias circuit is provided that.

In a preferred aspect of the present invention, the first oscillating means is configured to have a variable duty cycle.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of a developing bias circuit according to the present invention. The first oscillation circuit 2 is activated when an ON signal is input to the remote terminal 1 and generates an oscillation output having a frequency corresponding to the AC bias supplied to the developing device (shown as a load 16). In addition, when the off signal is input, the device is brought into an inoperative state. These ON and OFF signals are supplied to the remote terminal 1 from the control circuit of the image forming apparatus when the operation of the developing device starts and when the operation of the developing device ends, for example. The oscillation output of the first oscillation circuit 2 is supplied to a high-voltage switch circuit 3, which generates a switching pulse having a pulse repetition frequency corresponding to the frequency of the oscillation output.

On the other hand, a second oscillation circuit 5 for generating a high-frequency output having a higher frequency than that of the first oscillation circuit 2 is provided, and the oscillation output of the second oscillation circuit 5 is supplied to a booster circuit 6 to be boosted. After that, it is supplied to the rectifier circuit 7 where it is rectified and becomes a DC output. The high-voltage DC output from the rectifier circuit 7 is switched by the switching pulse from the high-voltage switch circuit 3, and is output via a DC cutoff circuit 14 to an output terminal 15.
And supplied to the developing device as a required AC bias. At the same time, the high-voltage DC output is supplied to the detection circuit 8 and its voltage is detected.
Are compared with the voltage from the first reference voltage source 9 in the first comparison circuit 11, and are compared with the voltage from the second reference voltage source 10 in the second comparison circuit 12. Be compared. The comparison result from the first comparison circuit 11 is supplied to the booster circuit 6, and the comparison result from the second comparison circuit 12 is input to the pulse width limiting circuit 13. 2 controls the duty cycle of the oscillation output of the oscillation circuit 5. In this embodiment, the first oscillation circuit 2 and the second oscillation circuit 5 are connected to each other through the synchronization circuit 4. The other circuits except the first oscillation circuit 2 are configured to operate when the image forming apparatus is operated.

In the above configuration, when the power of the circuit (the power of the image forming apparatus) is turned on, the first oscillation circuit 5 does not operate unless an ON signal is supplied to the remote terminal 1, but the other circuits are in the operating state, and the second oscillation circuit is in the operating state. The oscillation circuit 5 starts oscillating,
The high frequency output is supplied to the booster circuit 6. In the present embodiment, the second oscillation circuit 5 generates a pulse output, and its oscillation frequency, that is, the pulse repetition frequency is higher than the oscillation frequency of the first oscillation circuit 2, for example, 10 times or more (in this embodiment,
32 times). The pulse output boosted by the booster circuit 6 is rectified by the rectifier circuit 7 to become a high-voltage DC output corresponding to the peak-to-peak voltage of the AC bias supplied to the developing device, and the output side of the high-voltage switch circuit 3 and the detection circuit 8 Supplied to At this time, since the first oscillation circuit 2 is not operated, no switching pulse is generated from the high voltage switch circuit 3 and the high voltage DC output from the rectifier circuit 7 is not switched. Therefore, this DC output is blocked by the DC cutoff circuit 14 and is not supplied to the output terminal 15, so that it is not applied to the developing device.

The DC voltage detected by the detection circuit 8 is input to first and second comparison circuits 11 and 12, where the first comparison circuit 11 compares the DC voltage with the voltage of the first reference voltage source 9. When the detected voltage is higher than the first reference voltage, the oscillation input to the booster circuit 6 is stopped.
In the second comparison circuit 12, the second reference voltage source 10
The pulse width limiting circuit 13
And limits the pulse width of the oscillation pulse of the second oscillation circuit 5 according to the difference between the detection voltage and the second reference voltage. The voltage of the second reference voltage source 10 is the first
Is set lower than the voltage of the reference voltage source 9 of the first
The configuration is such that the ripple of control by the comparison circuit 11 is reduced.

Next, when an ON signal is input to the remote terminal 1 by, for example, operating the developing device, the first oscillation circuit 2
Is activated and starts oscillating. At this time, the first oscillating circuit 2 performs an oscillating operation in synchronization with the second oscillating circuit 5 by the synchronizing circuit 4, so that it operates stably without causing jitter. In this embodiment, the oscillation output from the first oscillation circuit 2 is a pulse output having a frequency (pulse repetition frequency) of an AC bias applied to the developing device and a duty cycle. Supplied. As a result, the high voltage switch circuit 3 operates to generate a switching pulse having a pulse repetition frequency and a duty cycle corresponding to the frequency of the AC bias applied to the developing device, and the high voltage from the rectifier circuit 7 supplied to its output side. On / off switching of DC output,
Generate a high voltage pulse output of the required pulse repetition frequency and duty cycle. The DC component of the high-voltage pulse output is cut off by the DC cut-off circuit 14. As a result, a rectangular wave AC output having a required pulse repetition frequency and duty cycle is generated at the output terminal 15 and supplied to the developing device as an AC bias. Will be. FIG. 2 shows an output waveform of the rectifier circuit 7 when an ON signal is supplied to the remote terminal 1. FIG. 3 shows a waveform of a rectangular wave AC output appearing at the output terminal 15 at that time.

Thus, according to the configuration of the present embodiment, the first and second
By simply changing the reference voltages of the reference voltage sources 9 and 10, the peak-peak voltage of the rectangular wave AC output generated at the output terminal 15 can be changed. In addition, since an AC output corresponding to the frequency and the duty cycle of the first oscillation circuit 2 is obtained at the output terminal 15, it is easy to change the frequency and / or the duty cycle. In addition, by changing the limit value of the pulse width limiting circuit 13, the rise and rounding of the waveform can be improved.

Further, in the present embodiment, the second oscillation circuit 5 is activated at the same time when the power supply of the circuit is turned on. Therefore, when the ON signal is applied to the remote terminal 1 as in the prior art, the second oscillation circuit 5 is turned on. 5 does not overshoot the oscillation circuit 5 at the time of remote-on compared with the case where the terminal 5 is operated, and a stable AC output is obtained at the output terminal 15. FIG. 4 shows an AC output waveform at the output terminal 15 when an ON signal is applied to the remote terminal 1. FIG. 4A shows an AC output waveform obtained at the output terminal 15 by the configuration of the present embodiment. FIG. 2B shows the AC signal obtained at the output terminal 15 when the first and second oscillation circuits 2 and 5 are operated when an ON signal is applied to the remote terminal 1 as in the prior art. The output waveform is shown.

The second embodiment of the developing bias circuit according to the present invention is the fifth embodiment.
Shown in the figure. In this embodiment, the first oscillation circuit 1 is omitted from the configuration of the first embodiment, and the second oscillation circuit 5
And a frequency dividing circuit 17 which divides the oscillation output from the second oscillation circuit 5 into an oscillation output having a frequency corresponding to the AC bias supplied to the developing device (load 16). A pulse output having a frequency (pulse repetition frequency) and a duty cycle of an AC bias applied to the developing device is generated from the duty cycle variable circuit 18 and supplied to the high voltage switch circuit 3. It is what was constituted. The duty cycle variable circuit 18 changes the duty cycle of the divided oscillation output as necessary.
As long as the off signal is applied to the remote terminal 1 connected to the input, no output is generated. When an ON signal is applied to the remote terminal 1, the duty cycle variable circuit 18 is operated, and applies a divided oscillation output of a predetermined frequency and duty cycle, for example, a pulse output, to the high-voltage switch circuit 3. As a result, the high voltage switch circuit 3 operates to generate a switching pulse having a pulse repetition frequency and a duty cycle corresponding to the frequency of the AC bias applied to the developing device, and the high voltage from the rectifier circuit 7 supplied to its output side. The DC output is switched on and off to generate a high voltage pulse output with a required pulse repetition frequency and duty cycle. It is apparent that the same operation and effect as those of the first embodiment can be obtained also in the present embodiment. Therefore, corresponding portions are denoted by the same reference numerals and description thereof will be omitted.

FIG. 6 shows a third embodiment of the present invention. In this embodiment, the first and second reference voltage sources 9 and 10 are deleted from the configuration of the first embodiment, and a CPU (central processing unit) 19 is used instead.
And a digital-to-analog converter 20 for converting digital data from the CPU 19 into an analog signal. The digital-to-analog converter 20 supplies reference voltages to the first and second comparison circuits 11 and 12, respectively. It is composed. According to this embodiment, it is needless to say that the same operation and effect as those of the above-described first embodiment can be obtained. Analog converter 20
Has the advantage that the settings can be changed freely. In addition, since a stable output can be obtained by feeding back changes in the state of the output terminal 15 and the load (developing device) 16 to the CPU 19, it is possible to cope with complicated control. There are advantages too.

In addition, each said Example is only a mere illustration of this invention,
Accordingly, the configuration, elements used, and the like can be variously changed as necessary. In addition, the oscillation frequency of the second oscillation circuit is set to be at least ten times higher than the oscillation frequency of the first oscillation circuit (accordingly, the frequency of the AC bias). Furthermore, the oscillation output of the oscillation circuit may be an AC output, and is not limited to a rectangular wave output.

As described above, according to the present invention, the peak-to-peak voltage of the AC output generated at the output terminal can be changed only by changing the reference voltages of the first and second reference voltage sources. Becomes Further, since an AC output corresponding to the frequency and the duty cycle of the first oscillation circuit is obtained at the output terminal, it is easy to change the frequency and the duty cycle.
Further, the rising and rounding of the waveform can be improved by changing the limit value of the pulse width limiting circuit.
In addition, since the second oscillation circuit is activated at the same time when the power supply of the circuit is turned on, there is no overshoot of the oscillation circuit which occurs when an ON signal is applied to the remote terminal.
There is a remarkable effect that a stable AC output is obtained at the output terminal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a developing bias circuit according to the present invention. FIG. 2 is a waveform diagram showing an output of the rectifier circuit when an ON signal is applied to the remote terminal in the first embodiment. FIG. 3 is a waveform diagram of an AC output appearing at an output terminal when an ON signal is applied to a remote terminal in the first embodiment. FIG. 4 is a waveform diagram showing a comparison between an AC output obtained by the developing bias circuit according to the present invention and an AC output obtained by a conventional developing bias circuit. FIG. 5 is a circuit diagram showing a second embodiment of the developing bias circuit according to the present invention. FIG. 6 is a circuit diagram showing a third embodiment of the developing bias circuit according to the present invention. FIG. 7 is a circuit diagram showing an example of a conventional developing bias circuit. FIG. 8 is a waveform diagram showing a rectangular wave output obtained by a conventional developing bias circuit. 1: Remote terminal 2: First oscillator circuit 3: High voltage switch circuit 4: Synchronous circuit 5: Second oscillator circuit 6: Boost circuit 7: Rectifier circuit 8: Detection circuit 9, 10: Reference voltage sources 11, 12: Comparison circuit 13: Pulse width limiting circuit 14: DC cutoff circuit 15: Output terminal 16: Load (developing device) 17: Divider circuit 18: Duty cycle variable circuit 19: Central processing unit (CPU) 20: Digital-analog converter

Claims (2)

(57) [Claims] 1. A developing bias circuit for supplying an AC bias to a developing device used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, wherein oscillation is started when an ON signal is supplied to an input. ,
A first oscillating means for generating a first oscillating output having a frequency corresponding to the frequency of the AC bias, and a second oscillating means which operates simultaneously with the operation of the image forming apparatus and has a higher frequency than the oscillating frequency of the first oscillating means. Second oscillating means for generating an oscillating output, boosting means for boosting a second oscillating output from the second oscillating means, rectifying means for rectifying a high-voltage AC output from the boosting means, and rectifying means Detecting means for detecting a rectified output from the control means, at least one comparison control means for controlling inputs of the second oscillating means and the boosting means in accordance with a detected voltage from the detecting means, and the first and second control means Means for synchronizing the oscillating means with the first oscillating means, and rectified output from the rectifying means is switched to perform high-voltage switching of a frequency corresponding to the frequency of the AC bias. A developing bias circuit, comprising: switching means for generating a current output; and DC blocking means for blocking a DC voltage component of the high-voltage AC output to provide a required AC bias. 2. A developing bias circuit for supplying an AC bias to a developing device used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, wherein oscillation is started when an ON signal is supplied to an input. ,
A first oscillating means for generating a first oscillating output having a frequency corresponding to the frequency of the AC bias, and a second oscillating means which operates simultaneously with the operation of the image forming apparatus and has a higher frequency than the oscillating frequency of the first oscillating means. Second oscillating means for generating an oscillating output, boosting means for boosting a second oscillating output from the second oscillating means, rectifying means for rectifying a high-voltage AC output from the boosting means, and rectifying means Detecting means for detecting a rectified output from the CPU, a central processing unit for setting a reference voltage for determining the peak-to-peak voltage of the AC bias, and a digital-analog conversion for converting digital data from the central processing unit into an analog signal. A control unit for controlling inputs of the second oscillating means and the boosting means in accordance with an output signal from the digital-analog converter and a detection voltage from the detecting means. A comparison control unit, a unit for synchronizing the first and second oscillating units, and a first oscillating output from the first oscillating unit that is operated to switch a rectified output from the rectifying unit. Switching means for generating a high-voltage AC output having a frequency corresponding to the frequency of the AC bias, and DC blocking means for providing a required AC bias by blocking a DC voltage component of the high-voltage AC output. Developing bias circuit.