JP2004328869A - Zero cross signal output device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate and output a precise zero cross signal by removing the effect of noise when generating and outputting a zero cross signal, based on an AC signal obtained from an AC power source. <P>SOLUTION: This zero cross signal output device is provided with a capacitor 406 on the secondary side of a photocoupler PC3 which outputs a secondary zero cross signal FW, and a control circuit 500 executes interruption with the timing of ON of a secondary zero cross signal FW. Furthermore, this is provided with a constant current element 601 on the power source side of the voltage dividing point between resistor elements R1 and R2 provided in series for dividing the voltage of an AC signal, and this suppresses the effect of an induced noise current while suppressing a current consumption by lowering the impedance at ON of a primary zero cross signal. Or, this gives hysteresis properties and prevents a malfunction due to noise, by providing three or more resistor elements which divide the voltage of an AC signal and connecting the junction between the resistor elements on the grounding side more than the voltage dividing point and the line of a primary zero cross signal with each other via a resistor element or a diode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a zero-cross signal output device that generates and outputs a zero-cross signal based on an AC signal obtained from an AC power supply, and an image forming apparatus including the same.
[0002]
[Prior art]
The image forming apparatus generates a zero-cross signal based on the full-wave rectified AC signal obtained from the AC power supply, and interrupts the control CPU using the zero-cross signal (executes interrupt processing), thereby monitoring the power failure. And power control of the fixing device, detection of a power supply frequency (50 Hz / 60 Hz), and the like. Therefore, when noise occurs in the zero-cross signal, unnecessary interrupt processing occurs and the device malfunctions.
Conventionally, in order to prevent malfunction of interrupt processing due to noise generated in a zero-cross signal, Patent Document 1 discloses that interrupt is prohibited for a predetermined time after an interrupt is generated by a zero-cross signal. Accordingly, it is possible to prevent a malfunction in which a zero-cross signal is continuously turned ON / OFF and an unnecessary interrupt process is generated due to generation of noise near a zero-cross detection voltage in the AC signal.
[0003]
[Patent Document 1]
JP-A-2002-27089
[0004]
[Problems to be solved by the invention]
However, as shown in Patent Literature 1, there is a problem in that when a time zone in which interrupts are prohibited is provided, the pulse width (time from ON to OFF) of the zero-cross signal, which is a relatively short time width, cannot be detected.
When the voltage of the AC signal fluctuates due to the voltage fluctuation of the AC power supply, this changes the zero-cross detection timing (timing at which the voltage of the AC signal becomes the zero-cross detection voltage). As a result, the phase of the AC signal changes. Despite the absence, the phase of the zero-cross signal changes. In order to cope with this, conventionally, the influence of the power supply voltage has been removed by detecting the pulse width of the zero-cross signal and detecting, for example, a center point (a half point) thereof. If the pulse width cannot be detected, the influence of the phase change of the zero-cross signal due to the power supply voltage change cannot be removed.
On the other hand, it is known that it is effective to reduce the impedance of the AC signal path in order to prevent malfunction due to the induced noise current in the AC signal. However, if the impedance is simply reduced, the flowing current increases and the consumption increases. Since the power is increased, there is a problem that it is actually difficult to reduce the impedance and remove the influence of noise (inductive noise).
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate the influence of noise when generating and outputting a zero-cross signal based on an AC signal obtained from an AC power supply. An object of the present invention is to provide a zero-cross signal output device capable of generating and outputting a high-precision zero-cross signal and an image forming apparatus including the same.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention provides a zero-cross signal generating means for generating a primary-side zero-cross signal based on a full-wave rectified AC signal obtained from an AC power supply, and an input of the primary-side zero-cross signal. A zero-cross signal output means for outputting a secondary-side zero-cross signal via a photocoupler, wherein the zero-cross signal output means is connected from a collector terminal to an emitter terminal on the secondary side of the photocoupler. And a capacitor connected in parallel with the path.
Thus, when the secondary-side zero-cross signal is turned on, a discharge circuit including the ON resistance of the secondary-side transistor (phototransistor) of the photocoupler and the capacitor is formed, and the time constant is sufficiently small. When the charge level instantaneously falls and turns off, a charging circuit composed of the collector load resistance of the secondary transistor of the photocoupler and a capacitor is formed, and the time constant of the charging circuit changes from the Low level to the High level. The rise is first-order lag. Therefore, in the case of switching between ON and OFF in the primary-side zero-cross signal, when the ON / OFF switching occurs instantaneously continuously due to noise, the influence of the noise in the secondary-side zero-cross signal is reduced. . For this reason, if the capacitance of the capacitor is set to an appropriate value assuming the magnitude of noise, it is possible to generate and output a highly accurate zero-cross signal by eliminating the influence of noise. It is possible to prevent the malfunction of the interrupt control using the signal which makes the switching of OFF slow) due to noise.
[0006]
Further, a second invention provides a zero-cross signal generating means for generating a primary-side zero-cross signal based on a full-wave rectified AC signal obtained from an AC power supply, and a means for inputting the primary-side zero-cross signal and receiving the signal via a photocoupler. And a zero-cross signal output means for outputting a secondary-side zero-cross signal. The zero-cross signal generation means comprises a plurality of resistance elements provided in series to divide the AC signal. A zero-cross signal output device comprising a voltage dividing circuit and a constant current element provided on a power supply side of a voltage dividing point in the voltage dividing circuit.
As a result, the current flowing through the voltage dividing circuit is limited by the constant current element, so that an increase in power consumption is suppressed, and the impedance of the voltage dividing circuit near the zero-crossing detection timing is reduced to cause a malfunction due to an induced noise current. Can be prevented.
[0007]
According to a third aspect of the present invention, there is provided a zero-crossing signal generating means for generating a primary-side zero-crossing signal based on a full-wave rectified AC signal obtained from an AC power supply, and the primary-side zero-crossing signal being input and passed through a photocoupler. A zero-cross signal output means for outputting a secondary-side zero-cross signal, wherein the zero-cross signal generation means comprises three or more resistive elements provided in series for dividing the AC signal. And a power-supply-side connection point of one of the resistive elements further located on the ground side than the resistive element connected from the ground side to the voltage-dividing point of the voltage-divider circuit. It is configured as a zero-cross signal output device, wherein a line of a next-side zero-cross signal is connected via a resistance element or a diode.
Thus, when the voltage at the voltage dividing point falls below a predetermined reference voltage and the primary-side zero-crossing signal is ON, the ground-side voltage dividing resistor element is turned on by a diode or a resistor. Therefore, the voltage dividing ratio (voltage at the voltage dividing point) is set to be smaller than a predetermined value determined by the voltage dividing resistor. When the voltage at the voltage dividing point is higher than a predetermined reference voltage and the primary-side zero-cross signal is OFF, when a diode is used, the diode causes the ground-side voltage-dividing resistance element to generate a zero-cross detection signal. Since the isolation is performed, the voltage dividing ratio becomes a predetermined voltage dividing ratio determined by the voltage dividing resistor. If a resistance element is used, the voltage is pulled up to an OFF state of the zero cross signal, so that the voltage dividing ratio is the predetermined voltage dividing determined by the voltage dividing resistor. It will be set larger than the partial pressure ratio. By switching the voltage division ratio in accordance with the output state of the zero-cross signal in this manner, a hysteresis characteristic is obtained, and malfunction due to noise can be prevented.
[0008]
Further, the present invention includes the zero-cross signal output device according to the first invention, and control means for performing an interrupt process based on the timing at which the secondary-side zero-cross signal output thereby is turned on. The image forming apparatus may be regarded as an image forming apparatus characterized by the above.
Similarly, the present invention includes the zero-cross signal output device according to the second or third invention, and control means for performing interrupt processing using the secondary-side zero-cross signal output thereby. Alternatively, the image forming apparatus may be regarded as an image forming apparatus.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments and examples are mere examples embodying the present invention, and do not limit the technical scope of the present invention.
Here, FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus provided with a zero-cross signal output device X according to an embodiment of the present invention, and FIG. 2 is a sectional view of the zero-cross signal output device X according to the embodiment of the present invention. FIG. 3 is a circuit diagram showing a configuration, FIG. 3 is a diagram showing voltage waveforms of an AC signal and a zero-cross signal in a zero-cross signal output device X according to an embodiment of the present invention, and FIG. 4 is a zero-cross signal according to a first embodiment of the present invention. FIG. 5 is a circuit diagram illustrating a configuration of the output device X1, FIG. 5 is a diagram illustrating voltage waveforms of an AC signal and a zero-cross signal in the zero-cross signal output device X1 according to the first embodiment of the present invention, and FIG. FIG. 7 is a circuit diagram illustrating a configuration of a zero-cross signal output device X2 according to an embodiment. FIG. 7 is a circuit diagram illustrating a configuration of a zero-cross signal output device X3 according to a third embodiment of the present invention.
[0010]
First, a schematic configuration of a copying machine 1 which is an example of an image forming apparatus including a zero-cross signal output device X according to an embodiment of the present invention will be described with reference to FIG.
The upper part of the copying machine 1 is a document reading unit 110. The automatic document feeder 112 provided in the document reading unit 110 automatically forms a plurality of documents set on a document set tray on the upper surface of the automatic document feeder 112 one by one on a glass plate. This is a device that feeds the original onto a document table 111.
The reading optical system of the document reading unit 110 scans an image of a document placed on the document table 111 or fed by the automatic document feeder 112 onto the document table 11 to read the image. , A first scanning unit 113, a second scanning unit 114, an optical lens 115 for forming reflected light from a document on a CCD line sensor 116, a CCD line sensor 116 as a photoelectric conversion element, and the like. It is configured. The first scanning unit 113 includes an exposure lamp unit 113a for exposing the surface of the original, a first mirror 113b for reflecting a reflected light image from the original in a predetermined direction, and the like. Further, the second scanning unit 114 includes second and third mirrors 114a and 114b for guiding the reflected light from the document reflected from the first mirror to the CCD line sensor 116.
The document image read by the document reading unit 110 is sent as image data to an image data input unit (not shown), and after the image data is subjected to predetermined image processing, the image processing The image forming unit 210 is temporarily stored in a memory of the image forming unit, and the image data in the memory is read out after the image processing is completed or in response to a predetermined output instruction from the outside to constitute an image forming unit 210 disposed below the document reading unit. Is transferred to the writing unit 227.
[0011]
The writing unit 227 includes a semiconductor laser light source (not shown) that emits a laser beam in accordance with the content of image data transferred from the image processing unit or an external device, and a polygon mirror that deflects the laser beam at an equal angular velocity. (Not shown), and comprises an f-θ lens (not shown) that corrects the laser beam deflected at a constant angular velocity on the photosensitive drum 2 so as to be deflected at a constant velocity. In the present embodiment, a laser writing unit is used as the writing unit 227, but a solid-scanning optical writing head unit using a light emitting element array such as an LED or an EL may be used. As the photosensitive drum 2, for example, a photoconductive layer such as amorphous silicon (a-Si), selenium (Se), or an organic optical semiconductor (OPC) is formed on an outer peripheral surface of a conductive substrate (metal drum) made of aluminum or the like. Is formed in the form of a thin film, but is not particularly limited.
Further, the image forming unit 210 includes a charger 223 around the photosensitive drum 2 for charging the photosensitive drum 2 to a predetermined potential, and a toner on the electrostatic latent image formed on the photosensitive drum 2. And a corona discharge type transfer device 225 (the transfer device) for transferring a toner image formed on the surface of the photosensitive drum 2 to a recording sheet (paper, an example of the material to be transferred). An example of the means), a static eliminator 229 for neutralizing the photosensitive drum 2, a cleaning device 226 for collecting excess toner on the photosensitive drum, and the like are also provided. The recording sheet on which the image has been transferred by the image forming unit 210 is then sent to the fixing unit 217, where the image is fixed on the recording sheet.
On the discharge side of the image forming unit 210, in addition to the fixing unit 217, a switchback path 221 for reversing the direction (front and rear) of the recording sheet in order to form an image again on the back surface of the recording sheet is provided. A post-processing device 260 that performs a stapling process and the like on the formed recording sheet and has a lifting tray 261 is provided. The recording sheet on which the toner image is fixed by the fixing unit 217 is guided to the post-processing device 260 by the discharge roller 219 through the switchback path 221 as necessary, where a predetermined post-processing is performed. After that, it is discharged onto the elevating tray 261.
The copier 1 supplies the recording sheet to the image forming unit 210 and communicates with the paper tray 251 and the switchback path 221 provided below the image forming unit 210 to supply the recording sheet to both sides of the recording sheet. In addition to a double-sided unit 255 for temporarily retreating recording sheets when performing image formation, a multi-stage paper feed unit 270 having a plurality of paper feed trays 252 and 253, a manual feed tray 254 protruding from the side of the copying machine 1 is provided. Is provided. The image forming apparatus further includes a conveying unit 250 that conveys the recording sheets set on each of the trays 251, 252, 253, and 254 to a transfer position of the image forming unit 210 by the transfer device 225. The duplex unit 255 can be replaced with a normal paper cassette, and the duplex unit 255 can be replaced with a normal paper cassette.
[0012]
Next, the circuit configuration of the zero-cross signal output device X provided in the copying machine 1 will be described with reference to FIG.
The zero-cross signal output device X includes a primary circuit section A on the AC power supply 301 side, and a secondary circuit section insulated from the primary circuit section A via the switching regulator 304 and the photocouplers PC1, PC2, and PC3. B.
The output of the AC power supply 301 is subjected to full-wave rectification by the full-wave rectifier circuit 303 after passing through the main switch 302 (manual switch) in the primary circuit section A, and the signal after the full-wave rectification is output to the switching regulator 304. At the same time, the voltage is made constant by the switching FET 309 and the smoothing circuit 310 and output to the DC line 311.
On the other hand, the signal via the signal output to the switching regulator 304 is smoothed by the smoothing circuits 404 and 405 in the secondary side circuit section B, and the driving system constant voltage power supply output V _M , And circuit system constant voltage power supply output V _CC Is generated. Drive system constant voltage power supply output V _M Is supplied to a drive circuit such as a drum motor, and at the same time, is divided and input to an inversion shunt regulator SRG1. The shuntator SRG1 compares an input voltage with an internal reference voltage, and when the input voltage is high, its output is turned on. When this output is in the ON state, it is transmitted to the primary side via the photocoupler PC1, forcibly grounding the gate of the switching FET 309, and stopping the switching oscillation. When the input voltage is low, the output of the shunt regulator SRG1 is turned off, the forcible grounding of the gate of the switching FET 309 is released, the primary side performs switching oscillation, and the driving system output voltage V _M Is a constant voltage. Also, the smoothed voltage V obtained from the secondary coil middle tap of the switching regulator 304 (transformer) _L Is stabilized by a voltage drop type constant voltage power supply element VRG, and its output is _cc Is supplied to a control circuit or the like.
The output of the AC power supply 301 is subjected to full-wave rectification by another full-wave rectification circuit 307 in the primary side circuit section A, and a signal after the full-wave rectification (hereinafter referred to as an AC signal 314) is supplied from the power supply side. The voltage is divided by a first resistance element R1 and a second resistance element R2 (voltage dividing circuit) connected in series to the ground side. The voltage dividing point 308 is connected to the input terminal of the shunt regulator (SRG2) connected to the DC line 311. When the voltage at the voltage dividing point 308 (divided voltage) becomes lower than a predetermined reference voltage, the output of the SRG2 is output. In the ON state, a current flows from the DC line 311 through the resistor and the photocoupler PC3 to the SRG2, and the photodiode 312a constituting the photocoupler PC3 emits light. The connected phototransistor 312b is turned on.
On the other hand, when the divided voltage of the AC signal 314 becomes higher than the reference voltage, the output of the SRG2 is turned off, the light emission of the photodiode 312a constituting the photocoupler PC3 stops (turns off), and the secondary side The phototransistor 312b on the circuit section B side is turned off.
As a result, the signal flowing through the SRG2 becomes a zero-cross signal (primary-side zero-cross signal 315) which becomes a low level when the AC signal 314 is lower than a predetermined voltage. Here, the full-wave rectifier circuit 307, the resistance elements R1, R2, SRG2, etc. constitute an example of the zero-cross signal output means.
[0013]
On the other hand, in the secondary side circuit section B, the constant voltage power supply output V _M Is supplied to the collector of the phototransistor 312b (photocoupler PC3) via the resistor R, and the phototransistor 312b (photocoupler PC2) is turned on (that is, the AC signal 314 is divided). When the voltage at the voltage dividing point 308 is lower than the reference voltage), the secondary-side zero-cross signal FW becomes Low level, and the phototransistor 312b is turned off (the voltage at the voltage dividing point 308 is higher than the reference voltage). The secondary-side zero-cross signal FW becomes a high level.
With such a configuration, the primary-side zero-cross signal 315 is generated from the AC signal 314 that has been full-wave rectified by the rectifier circuit 307, and is isolated through the photocoupler PC2. Is output as
3A to 3D show the output signal (a) of the AC power supply 301 obtained by the zero-cross signal output device X, the AC signal 314 (b), the primary-side zero-cross signal 315 (c), FIG. 6 shows voltage waveforms of the secondary-side zero-cross signal FW (d).
[0014]
The secondary side circuit section B is provided with an input terminal for a power save signal PS. When the power save signal PS is turned on (High level), the photocoupler PC1 is turned on, and the switching oscillation of the switching FET 309 is stopped. It is forcibly stopped and enters the power save state.
Further, an input terminal of a power relay signal PR is provided in the secondary circuit section B, and when the power relay signal PR is turned on (High level), the relay coil RL is operated, thereby causing the primary circuit section A to operate. The relay contact 305 is turned off, and the AC signal 314 is stopped (Low level).
The power save signal PS and the power relay signal PR are turned on by the predetermined control circuit 500 when the copier 1 has not been operated for a predetermined time or longer and a print request from an external device has not been received. Is controlled.
The secondary circuit section B is provided with an input terminal for a heater lamp signal HL, and the control circuit 500 turns on / off the heater lamp signal HL during the printing operation of the copying apparatus 1, whereby the photocoupler is operated. When the PC 2 is operated / stopped, the fixing temperature of the heater lamp 306a such as a halogen lamp is controlled by the phase angle in the fixing temperature control circuit 306 provided in the primary circuit section A.
The control circuit 500 includes a CPU, and interrupts the CPU using the secondary-side zero-cross signal FW (performs interrupt processing) to monitor a power failure, control the power of the fixing device, and control the power frequency (50 Hz). / 60 Hz).
The push switch 401 is for the control circuit 500 to detect that a request for a copy operation has been made by a user operation.
The configuration described above is the same as the configuration of a conventional zero-cross signal output circuit provided in a general image forming apparatus.
[0015]
A feature of the zero cross signal output device X according to the present invention is that a capacitor 406 connected in parallel with a path from the collector terminal to the emitter terminal (collector to emitter of the phototransistor 312b) on the secondary side of the photocoupler PC3 is provided. It is being done.
As a result, as shown in FIG. 3E, when the secondary-side zero-cross signal FW is turned on, it instantaneously falls from a high level to a low level, and when it is turned off, the capacitor 406 operates from the low level. The rise to the High level becomes dull like a first-order lag. Therefore, as shown by a broken line in FIG. 3F, when the primary zero-cross signal 315 is switched between OFF and ON, a continuous OFF / ON switching occurs instantaneously due to noise. As shown by the solid line in FIG. 3 (f), the influence of noise on the secondary-side zero-cross signal FW also becomes dull and is suppressed below the threshold voltage for interrupt detection, so that the control circuit 500 operates normally without malfunction. Become.
Here, the threshold voltage of the interruption detection in the control circuit 500 which performs the interruption processing by using the secondary side zero cross signal FW as an input is V. _th , The voltage level (High level) when the signal FW is OFF is V _CC (When ON, 0 (zero) V), the time width of the noise is Tn, the capacitance of the capacitor 406 is C, and the photocoupler PC ₃ Assuming that the resistance value of the resistance element 407 connected to the collector is R, noise is not detected by the control circuit 500 in a range where the following equation (1) is satisfied, and the influence of noise is removed. Malfunction of the control circuit 500 can be prevented (Ln represents a natural logarithm of low e).
C · R> -Tn / Ln (1-V _th / V _CC …… (1)
Therefore, for example, the threshold voltage V _th = V _CC In the case of / 2, by selecting the capacitor 406 and the resistance element 407 such that the following equation (2) is satisfied, malfunction of the control circuit 500 due to noise can be prevented.
C · R = Tn / 0.693 (2)
Also, unlike the prior art, there is no need to provide a time zone in which interrupts are prohibited, so that the control circuit 500 can detect the pulse width (time from ON to OFF) of the secondary-side zero-cross signal FW. is there. As a result, the influence of the phase change of the secondary-side zero-cross signal FW due to the change of the power supply voltage can be removed, and the highly accurate zero-cross signal can be detected. Here, the rise time (ON → OFF) of the secondary-side zero-cross signal FW can be estimated in advance by the resistance value of the resistance element 407 and the capacitance of the capacitor 406, so that the pulse width of the secondary-side zero-cross signal FW At the time of detection, if the rise time is taken into consideration, the pulse width can be obtained with higher accuracy.
Further, if the control circuit 500 executes the interrupt processing at the timing when the secondary-side zero-cross signal FW is turned on (High → Low), the interrupt processing is executed at an accurate timing with no delay due to the instantaneous falling signal. can do.
[0016]
【Example】
(Second invention)
Next, with reference to FIG. 4, a description will be given of a zero-cross signal output device X1 according to a first embodiment (an embodiment of the second invention) in which a configuration for further improving noise removal performance is added to the zero-cross signal output device X. I do.
The zero-cross signal output device X1 is different from the zero-cross signal output device X in that the first resistance element R1 and the second resistance element are provided in series from the power supply side to the ground side in order to divide the AC signal 314. A constant current diode 601 (an example of the constant current element) is provided between a voltage dividing point 308 of R2 and the first resistance element R1.
FIG. 5 shows the respective current waveforms of the AC signal 314 (full-wave rectified signal), the signal at the voltage dividing point 308 (voltage dividing circuit current), and the secondary zero-cross signal FW in the zero-cross signal output device X1. Represent.
As shown in FIG. 5, the current waveform of the signal at the voltage dividing point 308 is limited by the pinch-off current Ip of the constant current diode 601 due to the provision of the constant current diode 601. If this pinch-off current Ip is a current obtained by adding a margin to the current Iref flowing when the voltage at the voltage dividing point 308 becomes the reference voltage of the SRG2, it is necessary to operate (ON / OFF) the SRG2. Will be enough.
Generally, it is known that it is effective to reduce the impedance of the circuit (signal path) (here, the resistance values of the resistance elements R1 and R2) in order to prevent a malfunction due to an induced noise current in an AC signal. I have. However, when the impedance of the circuit is reduced, the flowing current increases, so that the power consumption increases.
For example, in FIG. 5, the reference voltage of SRG2 is 2.5 V, the resistance values of the first and second resistance elements R1 and R2 are 4.7 KΩ and 47 KΩ, respectively, and the timing is 11.2 degrees in each phase. When zero-cross detection is performed, the current flowing through the resistance elements R1 and R2 (voltage dividing circuit) at each phase of 11.2 degrees is 0.53 A, the peak current is 2.7 mA, and the power consumption is 0.193 W.
Here, assuming that the resistance values of the first and second resistance elements R1 and R2 are 470Ω and 4.7KΩ, respectively, which are 1/10 times the original values, while maintaining the phase angle of the zero-cross detection while taking measures against noise. The current flowing at the phase angle of 11.2 degrees is 5.3 mA, the peak current is 27 mA, and the power consumption is 1.93 W, which is ten times the original value. However, in this case, if a pinch-off current Ip of 5.3 mA is used as the constant current diode 601, the peak current flowing through the resistance elements R1 and R2 becomes 1/5 times, and the power consumption is 0.4753W. And about 1/4 times.
As described above, by making the pitch off current of the constant current element or less near the zero-cross detection timing, the impedance of the voltage dividing circuit is reduced to prevent a malfunction due to an induced noise current, and the voltage dividing circuit is controlled by the constant current element. Since the current flowing through the circuit is limited to the pinch-off current, power consumption can be suppressed.
As the constant current element, in addition to the constant current diode 601, a field effect transistor (FET) in which the drain and the gate are short-circuited, a current mirror circuit, or the like may be used.
[0017]
(Third invention)
Next, referring to FIG. 6, a description will be given of a zero-cross signal output device X2 which is a second embodiment (embodiment of the third invention) in which a configuration for further improving the noise removal performance is added to the zero-cross signal output device X. I do.
The zero-cross signal output device X1 is different from the zero-cross signal output device X in that the first and second resistance elements R1 and R2 are provided in series from the power supply side to the ground side in order to divide the AC signal 314. In addition, a third resistor R3 is provided in series on the ground side to form a voltage divider circuit with three resistors, and a connection point 602 (the voltage divider) between the second and third resistors R2 and R3 is provided. The power supply side connection point of the resistance element R3 further located on the ground side than the resistance element R2 connected from the ground side to the point 308) and the line of the primary side zero cross signal 315 are connected to the fourth resistance element R4. Are connected through a.
In FIG. 6, a very small-capacity capacitor C1 is provided between the voltage dividing point 308 and the primary side ground (GND). However, this does not particularly constitute the present invention, and is not particularly provided. Is also good.
With such a configuration, when the voltage at the voltage dividing point 308 falls below a predetermined reference voltage and the primary-side zero-cross signal is ON, the ground-side voltage dividing resistor R3 detects the zero-cross through the resistor R4. Since the signal is pulled into the ON state, the voltage dividing ratio is set to be smaller than a predetermined value ((R2 + R3) / (R1 + R2 + R3)) determined by the voltage dividing resistor. When the voltage at the voltage dividing point 308 rises above a predetermined reference voltage and the primary-side zero-crossing signal is OFF, the ground-side voltage-dividing resistor R3 is pulled up to the primary-side zero-crossing signal OFF state. Therefore, the partial pressure ratio is set to be larger than the predetermined partial pressure ratio. By switching the voltage division ratio in accordance with the output state of the zero-cross signal in this manner, a hysteresis characteristic is obtained, and malfunction due to noise can be prevented.
This effect is similarly exerted by the zero-cross signal output device X3 which is an embodiment in which the fourth resistance element R4 is replaced with a diode 603, as shown in FIG.
[0018]
【The invention's effect】
As described above, according to the first aspect, when generating and outputting a zero-cross signal based on an AC signal obtained from an AC power supply, a capacitor is provided on the secondary side of a photocoupler that outputs a secondary-side zero-cross signal. Is provided, noise is generated in the vicinity of the zero-cross detection voltage of the AC signal, whereby a malfunction in which the zero-cross signal is continuously turned on / off and unnecessary interrupt processing can be prevented can be prevented. At this time, since it is not necessary to provide a time zone in which interrupts are prohibited unlike the conventional case, it is possible to detect the pulse width of the zero-cross signal (secondary side), and the accuracy is improved without being affected by the power supply voltage change. It is possible to detect a high zero-cross signal. Furthermore, if an interrupt process is performed by the control unit at the timing when the secondary-side zero-cross signal is turned on, it is possible to execute the interrupt process at an accurate timing with no delay due to the instantaneously falling signal.
According to the second aspect of the present invention, the constant current element is provided on the power supply side of the voltage dividing point of the resistance element provided in series to divide the AC signal, so that the current consumption can be reduced even if the impedance of the resistance element is reduced. And the effect of the induced noise current on the AC signal can be suppressed.
Further, according to the third aspect, of the three or more resistive elements provided in series to divide the AC signal, the connection point of the resistive element on the ground side with respect to the voltage dividing point and the primary-side zero-cross signal Is connected via a resistance element or a diode, the zero-cross detection operation has a hysteresis characteristic, and malfunction due to noise can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus including a zero-cross signal output device X according to an embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating a configuration of a zero-cross signal output device X according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating voltage waveforms of an AC signal and a zero-cross signal in the zero-cross signal output device X according to the embodiment of the present invention.
FIG. 4 is a circuit diagram illustrating a configuration of a zero-cross signal output device X1 according to the first embodiment of the present invention.
FIG. 5 is a diagram illustrating voltage waveforms of an AC signal and a zero-cross signal in the zero-cross signal output device X1 according to the first embodiment of the present invention.
FIG. 6 is a circuit diagram illustrating a configuration of a zero-cross signal output device X2 according to a second embodiment of the present invention.
FIG. 7 is a circuit diagram illustrating a configuration of a zero-cross signal output device X3 according to a third embodiment of the present invention.
[Explanation of symbols]
1. Image forming apparatus
2. Photoconductor drum (image carrier)
100: developing device
110 ... Image reading unit
210: Image forming unit
225 ... Transfer device
254: manual feed tray
280: Manual sheet feeding device
301 ... AC power supply
302: Main switch
303, 305: Full-wave rectifier circuit
304 Switching regulator
305… Relay contact
306: Fixing temperature control circuit
306a: heater lamp
308: partial pressure point
309 ... Switching FET
310,404,405 ... Smoothing circuit
311 ... DC line
312a ... photodiode (photocoupler)
312b: Phototransistor (photocoupler)
314 ... AC signal (full-wave rectified signal)
315: Primary zero-cross signal
406… Capacitor
407 ... resistance element
500 ... Control circuit
601 ... constant current diode (low current element)
603 ... diode

Claims (5)

Zero-cross signal generating means for generating a primary-side zero-cross signal based on a full-wave rectified AC signal obtained from an AC power supply; and inputting the primary-side zero-cross signal and outputting a secondary-side zero-cross signal via a photocoupler A zero-cross signal output device comprising:
The zero cross signal output device, wherein the zero cross signal output means includes a capacitor connected in parallel with a path from a collector terminal to an emitter terminal on the secondary side of the photocoupler. Zero-cross signal generating means for generating a primary-side zero-cross signal based on a full-wave rectified AC signal obtained from an AC power supply; and inputting the primary-side zero-cross signal and outputting a secondary-side zero-cross signal via a photocoupler A zero-cross signal output device comprising:
The zero-cross signal generating means includes a voltage dividing circuit including a plurality of resistance elements provided in series to divide the AC signal, and a constant current element provided on a power supply side of a voltage dividing point in the voltage dividing circuit. A zero-cross signal output device comprising: Zero-cross signal generating means for generating a primary-side zero-cross signal based on a full-wave rectified AC signal obtained from an AC power supply; and inputting the primary-side zero-cross signal and outputting a secondary-side zero-cross signal via a photocoupler A zero-cross signal output device comprising:
The zero-cross signal generating means includes a voltage dividing circuit including three or more resistive elements provided in series to divide the AC signal;
The connection point on the power supply side and the line of the primary-side zero-crossing signal in any one of the resistance elements located on the ground side more than the resistance element connected from the ground side to the voltage dividing point of the voltage divider circuit has a resistance. A zero-cross signal output device, which is connected via an element or a diode. 2. An image forming apparatus comprising: the zero-cross signal output device according to claim 1; and control means for performing an interrupt process based on a timing at which the secondary-side zero-cross signal output thereby is turned on. apparatus. 4. An image, comprising: the zero-cross signal output device according to claim 2; and control means for performing interrupt processing using the secondary-side zero-cross signal output thereby. Forming equipment.

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