JPH04352181A - Power source circuit for image forming device - Google Patents

Abstract

PURPOSE:To obtain the power source circuit for image forming devices which can generate and supply a bias power source for a developing device without having the converter transformer to be exclusively used for generating AC biases and can control output. CONSTITUTION:This power source circuit has the high-frequency converter transformer T1 having a high-voltage winding L2 for electrification for supplying electricity to a developer which is load, a winding L6 for developing biases, and windings exclusive of the above-mentioned windings on a secondary side, a 1st switch S1 for shorting one end of the winding for developing biases at a prescribed low frequency to the ground, a current rectifying element D2 for rectifying the output at the other end of the winding for developing biases, and a 2nd switch S2 for shorting the output of the above-mentioned current rectifying element D2 to the ground at the low frequency of the antiphase of the phase of the switch S1. The output from the current rectifying element D2 modulated by the on and off of the 1st switch S1 and the 2nd switch S2 is supplied to the developing device which is the load.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for an image forming apparatus such as an electrophotographic printer or a copying machine, which supplies a developing bias AC to a developing unit of the image forming apparatus.

0002

2. Description of the Related Art Conventionally, a high-voltage power source for charging and a power source for developing bias in an image forming apparatus have been constructed of converter circuits that receive a low-voltage power source (usually 24 V) for sequence control. Additionally, the number of peripheral circuits such as a converter transformer and its drive circuit increased, leading to an increase in the cost, size, and weight of the entire copying machine or printer.

For this reason, the applicant et al. installed a low voltage winding (24V) for sequence control on the secondary side of one converter transformer.
We proposed a composite power supply system that controls all of the windings at once, including a high-voltage charging winding, a developing bias winding, and a fluorescent lamp drive winding for exposure. We have been working to reduce costs.

0004

[Problems to be Solved by the Invention] Even in the conventional composite power supply system, the AC power supply for developing bias can only be generated by a DC-AC converter from a low-voltage power supply for sequence control, and low frequency (1 KHz to 3KHz) and high pressure (1
(KVpp to 3KVpp), this leads to an increase in the size of the converter transformer and the increase in the power of the drive circuit.

The present invention has been made to solve the problems of the prior art described above, and it is possible to generate and supply bias power for a developing device without having a dedicated converter transformer for generating AC bias. Another object of the present invention is to provide a power supply circuit for an image forming apparatus that can control output.

[0006]

[Means for Solving the Problems] Therefore, the power supply circuit of the image forming apparatus according to the present invention is a high-frequency power supply circuit having a high-voltage winding for charging, a winding for developing bias, and a winding other than the above-mentioned winding on the secondary side. a converter transformer, a first switch that short-circuits one end of the developing bias winding to ground at a predetermined low frequency, a rectifying element that rectifies the output of the other end of the developing bias winding, and the first switch. and a second switch that short-circuits the output from the rectifying element to ground at an opposite phase low frequency, the rectified output modulated by turning on and off the first switch and the second switch to supply power to the developing device of the load. The purpose of the present invention is to achieve the above object by a configuration characterized by the following.

[0007]

[Operation] With the above configuration, the high frequency converter transformer generates a high frequency output for generating charging and developing bias power supplies to be supplied to the image forming apparatus load from the secondary side charging high voltage winding and developing bias winding. Occur. Further, low voltage output for sequence control, output to an exposure fluorescent lamp, etc. are generated from windings other than the above-mentioned windings.

The first switch short-circuits one end of the developing bias winding to ground at a predetermined low frequency, and the second switch short-circuits the output from the rectifying element that rectifies the output from the other end of the developing bias winding. Short-circuited to ground at the opposite phase low frequency to the first switch. Then, the rectified output modulated by turning on and off the first switch and the second switch is supplied to the developing device as a load.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A power supply circuit for an image forming apparatus according to the present invention will be described below with reference to embodiments. FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention, and FIG. 2 is a voltage waveform diagram of the first embodiment.

T1 is a voltage resonance type high frequency converter transformer (hereinafter referred to as converter transformer), and the secondary side includes a high voltage winding L2 for charging, a 5V winding L3 for sequence control, a 24V winding L5 for sequence control, and an exposure fluorescent lamp. winding L4
, a developing bias winding L6. On the primary side of the high frequency converter transformer T1, the commercial line input is rectified by a rectifier stack D11 and a switching element (FET) Q
1, apply while switching high frequency. The rectified output of the 24V winding L3 is voltage-divided to a predetermined value by resistors R1 and R2, and then compared with a reference power source E2 by a comparator 6. The output of the comparator 6 is electrically isolated and signal-coupled by a photocoupler 5, and then input to a switching element drive circuit 2 via a control means 1 having a shunt regulator.

The switching element drive circuit 2 has a repetition frequency F1 centered around 200 KHz, and its frequency is controlled in accordance with the input level while keeping the off time constant. This frequency control keeps the 24V output stable even if there are fluctuations in the commercial line input or load. The off-time is determined by the inductance on the primary side of the converter transformer T1, the equivalent distributed capacitance, and the resonant capacitor C4.

The polarities of the secondary windings, except for the fluorescent lamp winding L4, are selected so that the rectifier diode D3 is turned on when the switching element Q1 is turned off, so that each rectified output is stabilized in the same way as the 24V output. be done.

One end of the developing bias winding L6 is short-circuited to ground by the first switch S1, and the other end of the developing bias winding L6 is rectified by a diode D2 constituting a rectifier circuit and connected to a coupling capacitor C3. Output terminal P
2 to a load developing device (not shown). Further, the rectifier circuit output is configured to be short-circuited to ground by the second switch S2.

The low frequency oscillation circuit 21 outputs a square wave having a repetition frequency of 1200 Hz, which is the optimum frequency for development. This output controls the switch S1, and the inverted output of the same output controls the switch S2.

Next, the operation of the first embodiment will be explained with reference to FIG. Note that (A) in FIG. 2 shows the output waveform of the switching element drive circuit 2, (B) shows the output waveform of the low-frequency oscillation circuit 21, and (C) shows the output waveform of the rectifier circuit (diode D).
2 cathode) shows the output waveform.

During the timing period when the switch S1 is turned on and the switch S2 is turned off, as shown in FIG. 2, the load capacitance connected to the output terminal P2 is charged via the capacitor C3. And conversely, during the timing period when switch S1 is off and switch S2 is on,
Discharge the load capacitance.

A DC bias E1 is connected to the output terminal P2 via a high resistance R3, and is superimposed on the AC bias obtained at the cathode of the diode D2 of the rectifier circuit.

With the above configuration and control, the AC bias is not supplied from a dedicated transformer, but from the developing bias winding L6 of the converter transformer T1, which has multiple types of secondary windings.
AC bias can be formed from the output of Further, the control device 1 and the low frequency oscillation circuit 21 can control the output to a predetermined output waveform.

Next, a second embodiment of the invention will be described. FIG. 3 is a block diagram of the second embodiment, and FIG. 4 is a voltage waveform diagram of the same, which is an example in which the AC amplitude of the developing bias is stabilized. Note that the same or equivalent parts as in the first embodiment are denoted by the same reference numerals and redundant explanation will be omitted.

Reference numeral 1 denotes a control means, which internally includes a microcomputer (hereinafter referred to as CPU) and peripheral devices such as memory. In addition to controlling the power supply device of the embodiment, it is also connected to a sequence controller of a printer (copying machine) body (not shown) through a bus line or communication port, and sends and receives sequence signals.

A first counter 6 counts down the reference clock of the CPU of the control means 1 to F1 (200 Kz). The second counter 7 inputs the output of the first counter 6 and generates a low frequency signal with a repetition frequency F2 (1.2 Kz) and a duty ratio of 1:1. Switching element Q1 (F
ET) is controlled by the switching element drive circuit 2. The output of the switching element drive circuit 2 has a repetition frequency F1, and its pulse width is controlled by the control means 1.

When the diode Q3 that short-circuits one end of the winding L6 to the ground is turned on, the output of the AC bias winding L6 of the converter transformer T1 is rectified by the diode D2 of the rectifier circuit, and is then rectified by the diode D2 in the rectifier circuit. ), the load capacitor connected to the output terminal P2 is charged. The output voltage of the output terminal P2 is divided into a predetermined ratio by a voltage detection circuit 4 made up of resistors R21 and R22, and then input to the comparator 3. The comparator 3 compares the voltage detection output with the reference voltage E3 and outputs the comparison result to the control means 1. When the output of output terminal P2 reaches a predetermined level V1, transistor Q3 is cut off. When the transistor Q3 is turned off and the output of the output terminal P2 falls below the threshold due to discharge, the comparator 3 is inverted, the transistor Q3 is turned on again, and charging of the load capacitance is started.

The high-voltage transistor Q2, which is an electronic switch that short-circuits the output of the rectifier circuit to the ground, is shown in FIG.
As shown in (b) and (c), it is turned on and off in synchronization with the second counter output. When electronic switch Q2 is on, Q3 is turned off.

The frequencies F1 and F2, the pulse width modulation of the switching element drive circuit, the pulse width of the electronic switch drive signal, etc. are determined in advance based on data stored in the storage device ROM in the CPU constituting the control means 1. ,
It has a controlled configuration.

[0025] The above configuration and control have the same effects as the first embodiment, and can more easily perform output control that matches the load situation.

Next, a third embodiment of the present invention will be described. FIG. 5 is a block diagram of the third embodiment, in which the same or equivalent parts as in the second embodiment are denoted by the same reference numerals and redundant explanation will be omitted.

The third embodiment is characterized by the reference voltage E2 for detecting the sequence power supply (+24V) of the first embodiment and the reference voltage E2 for detecting the developing AC bias amplitude of the second embodiment.
3 is controlled by the CPU of the control means 1. That is, output signals corresponding to the reference voltages E2 and E3 are alternately output from the CPU, converted into analog signals by the D/A converter 5, and input to the comparator 3.

The error input of the comparator 3 includes the rectified output of the sequence control winding L5, that is, the detection output from the voltage detection circuit composed of the sequence power output and resistors R23 and R24, and the AC bias winding L6. The rectified output, that is, the detection output from the developing AC bias voltage detection circuit 4 is time-divisionally switched and inputted by the analog switch 8 in synchronization with the input switching of the reference voltages E2 and E3. The comparison output of the comparator 3 is input to the control means 1, and the control means 1 controls the switching element drive circuit, the electronic switch Q2, and the transistor Q3 based on the input and the control program.

With the above configuration and control, one comparator 3 can control the primary side (sequence power supply control) of the converter transformer T1 and the rectified output (developing AC bias) on the secondary side. Although not shown, 5V output, high voltage output for charging, fluorescent lamp drive output, etc.
By switching the detection output in a time division manner using an analog switch and inputting it to a comparator, it becomes possible to individually stabilize and control each output independently of the primary side.

In the third embodiment, since the electronic switch Q3 is a PNP transistor with a high breakdown voltage, the breakdown voltage between the collector and emitter is considerably lower than that of an NPN transistor. In order to solve this problem, in the embodiment, the developing bias winding L
6 is voltage-doubled and rectified by a capacitor C6 and diodes D1 and D2.

[0031] Also, to save cost and space,
Individual control of switching element drive circuit 2 on the primary side of the converter transformer, high voltage for charging on the secondary side, developing bias, etc.
Various functions such as sequence control of motors, solenoids, etc. of the image forming apparatus are integrated into a single chip as a control means 1.

[0032]

As described above, according to the present invention, it is possible to provide a power supply circuit for an image forming apparatus having the following effects.

1. Because high voltage output is required at low frequency,
There is no need for a relatively large dedicated developing AC bias step-up transformer, and the AC bias voltage can be output from a transformer that is shared with the power supply for charging, sequence control, and exposure fluorescent lamps.

2. By digitizing the control circuit, excluding the minimum circuits such as comparators and switching element drive PWM circuits, the circuit scale can be reduced. Various functions such as individual control of bias, sequence control of motors and solenoids, etc. can be integrated on a single chip, maximizing the effects of integration in terms of cost and space.

3. The frequency, amplitude, output DC level, duty of each output on the secondary side of the converter including the developing AC bias output, the driving frequency of the converter transformer, the threshold value of the load current limiter, etc. can be easily changed by programming the control means CPU. can.

4. Highly accurate and complex control to reduce overshoot and ripple in each control output can be achieved with almost no increase in cost or space.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is a voltage waveform diagram of the first embodiment.

FIG. 3 is a block diagram of a second embodiment.

FIG. 4 is a voltage waveform diagram of the second embodiment.

FIG. 5 is a block diagram of a third embodiment.

[Explanation of symbols]

D2 Diode L2 forming a rectifier circuit
Charging high voltage winding L6 Developing bias winding P2 Output terminal Q2 Electronic switch S1 Switch S forming the first switch circuit
2 Switch T1 constituting the second switch circuit
High frequency converter transformer 1 Control means 2 Switching element drive circuit 3 Comparator 4 Voltage detection circuit 6 First counter 7 Second counter Note that in the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (11)

[Claims] 1. A high-frequency converter transformer having a high-voltage winding for charging, a winding for developing bias, and a winding other than the above-mentioned winding on the secondary side, and a predetermined low-frequency converter transformer with one end of the winding for developing bias being grounded. a first switch that short-circuits the developing bias winding; a rectifying element that rectifies the output of the other end of the developing bias winding;
A second switch short-circuits the output from the rectifying element to ground at a low frequency in opposite phase to the first switch, and the rectified output modulated by turning on and off the first switch and the second switch is used to develop a load. A power supply circuit for an image forming apparatus, characterized in that it supplies power to an image forming apparatus. 2. The high frequency converter transformer is a voltage resonance type high frequency converter transformer, and has a voltage detection circuit that detects a flyback output voltage of a secondary winding, and the detected value of the voltage detection circuit is constant. 2. The power supply circuit for an image forming apparatus according to claim 1, further comprising a control means for controlling the amount of current supplied to the primary side so that the power supply circuit of the image forming apparatus has the following characteristics. 3. A voltage detection circuit for detecting the rectified output of the developing bias winding, a comparator for comparing the detection output of the voltage detection circuit with a predetermined value, and a first switch circuit based on the output from the comparator. The power supply circuit for an image forming apparatus according to claim 1, further comprising a control means for controlling the image forming apparatus. 4. The power supply circuit for an image forming apparatus according to claim 1, wherein the rectifier circuit for the developing bias winding includes a voltage doubler rectifier circuit or a multistage booster rectifier circuit. 5. The AC bias output obtained by modulating and rectifying the developing bias winding output of the high frequency converter transformer is superimposed on the DC bias output obtained from the charging high voltage winding output of the high frequency converter transformer. 2. The power supply circuit for an image forming apparatus according to claim 1, wherein the power supply circuit supplies power to the developing device of the load. 6. A first counter that counts down the reference clock frequency to frequency F1, and a second counter that counts down the output of the first counter to frequency F2 and generates a low frequency signal having a predetermined duty ratio. and a pulse width modulation drive circuit whose fundamental frequency is the first counter output frequency F1, and a primary side driven by the pulse width modulation drive circuit, and a secondary side at least a low voltage winding for sequence control and a load developing device. a high-frequency converter transformer having a high-voltage winding for charging and a winding for developing bias; a rectifying circuit for rectifying the output of the developing bias winding; an electronic switch for short-circuiting the output of the rectifying circuit to ground; a voltage detection circuit for detecting the output of the circuit; a comparator for comparing the output of the voltage detection circuit with a reference voltage; A power supply circuit for an image forming apparatus, comprising: a control means for controlling a switch. 7. The control means according to claim 1, wherein the control means determines the frequencies F1, F2 and the duty ratio of the frequency F2 and controls the pulse width modulation drive circuit and the electronic switch according to a built-in program. 6
A power supply circuit of the image forming apparatus described above. 8. The control means has a built-in program for determining a reference voltage value to be input to the comparator, and converts the determined value into an analog value by a D/A converter and inputs it to the comparator for control. The power supply circuit for an image forming apparatus according to claim 6. 9. Peripherals such as a microcomputer and storage devices RAM and ROM constituting the control means;
Pulse width modulation drive circuit, comparator, counter circuit,
9. A power supply circuit for an image forming apparatus according to claim 6, wherein a D/A converter and the like are integrated and formed on the same chip. 10. A load current detection circuit is provided on the secondary side of the high frequency converter transformer, the detected output of the load current is compared with a second reference voltage by a second comparator, and the output of the second comparator is 10. The power supply circuit for an image forming apparatus according to claim 6, wherein the power supply circuit controls the output of the pulse width modulation drive circuit by inputting the signal into the control means to limit or stop the output of the pulse width modulation drive circuit. 11. An analog switch that time-divides the output of a load current detection circuit provided on the secondary side of the high-frequency converter transformer and the output of a voltage detection circuit that detects the output of the rectifier circuit and inputs the time-divided signals to a switching comparator. At the same time as the input to the comparator is switched, the reference voltage data is also switched and input to the comparator via the D/A converter, and the comparison result is input to the control device to output voltage for the pulse width modulation drive circuit and developing bias. 11. The power supply circuit for an image forming apparatus according to claim 6, wherein the power supply circuit controls the image forming apparatus.