JP2014057435A - Booster circuit, light source drive unit, image reading device, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a booster circuit, light source drive unit, image reading device, and image forming device, capable of suppressing generation of an output ripple voltage with a simple configuration.SOLUTION: The booster circuit 100 includes a booster section 10 and a control section 20. The booster section 10 includes a switching element 12 that switches on-off operations according to a driving signal, and boosts an input voltage Vin by on-off operations of the switching element 12. The control section 20 controls a driving signal according to the input voltage Vin. The control section 20 controls the driving signal so that a switching frequency of the switching element 12 is switched according to the input voltage.

Description

  The present invention relates to a booster circuit, a light source driving device, an image reading device, and an image forming apparatus.

  As a scanner light source, a method of using a chip LED (Light Emitting Diode) having a greater energy saving effect than a conventional Xe lamp or the like is known. When many chip LEDs are driven, the number of driveable circuits per drive circuit is more than double that of a non-boost circuit by boosting and supplying power. Also, in other general circuit systems, the usable power supply voltage is often limited, and boosting is an effective means when a high voltage is required for driving the load. Already put into practical use.

  In addition, in a switching type booster circuit that boosts an input voltage by switching a current flowing through an inductor, a ripple is generated in principle in output. In order to suppress this ripple, there are methods such as (1) increasing the switching frequency, (2) increasing the inductance of the inductor, and (3) using a high-performance output capacitor. However, the method (1) has a demerit of a decrease in conversion efficiency, and the methods (2) and (3) have a demerit of an increase in cost. Therefore, an appropriate balance considering these merits / disadvantages. Design with. However, for example, when the input voltage decreases due to variations due to individual differences or changes over time, output ripple increases, causing problems such as output instability and increased input / output line stress.

  For example, in Patent Document 1, for the purpose of obtaining a stable output voltage by suppressing the output ripple voltage of a DC-DC converter, the switching frequency is controlled according to the detection result and the output ripple voltage is detected. A technique for suppressing the voltage is disclosed.

  However, the technique disclosed in Patent Document 1 requires a large number of peripheral circuits in order to detect the output ripple voltage, resulting in a problem that the configuration becomes complicated and the manufacturing cost increases.

  The present invention has been made in view of the above, and an object of the present invention is to provide a booster circuit, a light source driving device, an image reading device, and an image forming device that can suppress an output ripple voltage with a simple configuration.

  In order to solve the above-described problems and achieve the object, the present invention includes a switching element that switches on and off according to a drive signal, and boosts an input voltage by an on / off operation of the switching element, and the input voltage And a control unit that controls the drive signal in accordance with the boosting circuit.

  According to the present invention, the output ripple voltage can be suppressed with a simple configuration.

FIG. 1 is a conceptual diagram showing a conventional booster circuit and an image of ripple change. FIG. 2 is a conceptual diagram illustrating a booster circuit according to the embodiment and an image of a ripple change. FIG. 3 is a diagram illustrating a configuration example of the LED driving device according to the first embodiment. FIG. 4 is a diagram illustrating a configuration example of the LED driving device according to the second embodiment. FIG. 5 is a diagram illustrating a configuration example of an LED drive device according to a modification of the second embodiment. FIG. 6 is a diagram illustrating a configuration example of the LED drive device according to the third embodiment. FIG. 7 is a diagram illustrating a configuration example of an LED drive device according to a modification of the third embodiment. FIG. 8 is a diagram illustrating a configuration example of an LED drive device according to a modification of the third embodiment. FIG. 9 is a diagram illustrating a mechanical configuration example of an image reading apparatus to which the present invention can be applied. FIG. 10 is a block diagram illustrating a functional configuration example of the image reading apparatus. FIG. 11 is a diagram illustrating a configuration example of an image forming apparatus to which the present invention is applicable.

  Hereinafter, embodiments of a booster circuit, a light source driving device, an image reading device, and an image forming device according to the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a conceptual diagram showing a conventional booster circuit 1 and an image of a ripple change. The booster circuit 1 boosts the input voltage Vin and outputs the boosted voltage Vout to the load side. Normally, the output is fed back to perform boost control. Here, when the input voltage Vin is small and the boost rate is large, the ripple of the boost voltage Vout increases.

  FIG. 2 is a conceptual diagram showing the booster circuit 100 of the present embodiment and an image diagram of ripple change. The booster circuit 100 of the present embodiment is configured not only to perform boost control by feeding back the output, but also to control (switch) the PWM signal frequency of the boost control by monitoring the input voltage Vin, and the input voltage Vin is large. When the input voltage Vin is small, the frequency is increased to suppress the ripple.

  Although the detailed configuration will be described later, as shown in FIG. 2, the booster circuit 100 includes a booster 10 and a controller 20. The boosting unit 10 includes a switching element that is switched on and off in accordance with a drive signal, and boosts the input voltage Vin by an on / off operation of the switching element. In this example, the configuration of the booster 10 is the same as that of the booster circuit 1 of FIG.

  The control unit 20 controls the drive signal according to the input voltage Vin. More specifically, the control unit 20 feeds back the output voltage Vout output from the boosting unit 10 to control a duty ratio indicating a ratio between a period during which the switching element is turned on and a period during which the switching element is turned off. The drive signal is controlled so that the switching frequency of the switching element is switched according to the input voltage Vin. As will be described later, in the present embodiment, the control unit 20 is driven so that the switching frequency of the switching element is higher when the input voltage Vin is lower than the threshold, compared to when the input voltage Vin is higher than the threshold. Control the signal. Here, the drive signal is a voltage signal for controlling on / off of the switching element, and is represented by a periodic pulse wave. In the following description, the drive signal may be referred to as a PWM signal.

  FIG. 3 is a diagram illustrating an example of an LED driving device (light source driving device) using the booster circuit 100 and the constant current circuit 30 of the present embodiment. The booster circuit 100 includes a booster 10 and a controller 20. The step-up unit 10 includes an inductor 11, a switching element 12, a diode 13 as a rectifier, and a capacitor 14 as a smoother. The switching element 12 is switched on and off according to the PWM signal output from the control unit 20. The switching element 12 is composed of, for example, an FET, and a PWM signal is input to its gate. In this example, the inductor 11, the switching element 12, and the diode 13 constitute a step-up converter, and the switching element 12 switches at high speed according to the PWM signal from the control unit 20 (repeats the on / off operation). As a result, the input voltage Vin is boosted and supplied to the capacitor 14. The boosted voltage (output voltage Vout) is supplied from the capacitor 14 to the load (LED).

  The control unit 20 includes a generation unit 21 and an output unit 22. The generation unit 21 generates a triangular wave signal corresponding to the input voltage Vin. In the present embodiment, the generation unit 21 generates a triangular wave signal having a higher frequency when the input voltage Vin is smaller than the threshold as compared to when the input voltage Vin is larger than the threshold. More specifically, the generation unit 21 includes a comparator 23 and a triangular wave generation circuit 24. The comparator 23 receives the input voltage Vin and a predetermined voltage Vref2 (corresponding to “threshold”), generates a signal corresponding to the comparison result between the input voltage Vin and the predetermined voltage Vref2, and outputs the signal to the triangular wave generation circuit 24. To do. In this example, when the input voltage Vin is larger than the predetermined voltage Vref2, the comparator 23 generates a high level signal and outputs it to the triangular wave generation circuit 24. On the other hand, when the input voltage Vin is smaller than the predetermined voltage Vref2, the comparator 23 generates a low level signal and outputs it to the triangular wave generation circuit 24.

  The triangular wave generation circuit 24 generates a low-frequency triangular wave signal when the input voltage Vin is larger than the predetermined voltage Vref2, and generates a high-frequency triangular wave signal when the input voltage Vin is smaller than the predetermined voltage Vref2. . In this example, the triangular wave generation circuit 24 generates a low-frequency triangular wave signal when the output signal from the comparator 23 is high level, and generates a high-frequency triangular wave signal when the output signal from the comparator 23 is low level. Generate.

  The output unit 22 generates and outputs a PWM signal according to a comparison result between the triangular wave signal generated by the generation unit 21 and the output that is fed back. In this example, the output unit 22 includes a comparator, and receives the triangular wave signal generated by the generation unit 21 and the voltage Vb (output voltage Vout after being supplied to the load) returned from the load. Note that the form of the output that is fed back is not limited to this, and may be, for example, a form in which the output voltage Vout is input to the output unit 22 as it is.

  When the triangular wave signal is larger than the feedback output, the output unit 22 generates and outputs a PWM signal that causes the switching element 12 to be turned on. On the other hand, when the triangular wave signal is smaller than the feedback output, , Generate and output a PWM signal for switching off the switching element. In the example of FIG. 3, the output unit 22 generates and outputs a high level signal (a PWM signal set to a high level) when the triangular wave signal is greater than the feedback output. Then, when the high level signal is supplied to the gate of the switching element 12, the switching element 12 is turned on. That is, a high level signal is continuously output from the output unit 22 over a period in which the triangular wave signal is larger than the feedback output, and the switching element 12 is maintained in the ON state. Further, when the triangular wave signal is smaller than the feedback output, the output unit 22 generates and outputs a low level signal (a PWM signal set to a low level). Then, when the low level signal is supplied to the gate of the switching element 12, the switching element 12 is turned off. That is, a low level signal continues to be output from the output unit 22 over a period in which the triangular wave signal is smaller than the feedback output, and the switching element 12 is maintained in the OFF state.

  Note that the constant current circuit 30 shown in FIG. 3 can be realized by various known configurations.

  As described above, the booster circuit 100 according to the present embodiment includes the control unit 20 that controls the PWM signal according to the input voltage Vin, in addition to the booster unit 10 having the same configuration as that of the conventional booster circuit 1. . The control unit 20 not only performs the boost control by feeding back the output, but when the input voltage Vin is smaller than the threshold, the switching frequency of the switching element 12 is larger than when the input voltage Vin is higher than the threshold. The ripple is suppressed by controlling the PWM signal so as to be high. According to the present embodiment, since a large number of peripheral circuits for detecting the output ripple voltage are not necessary, there is an advantageous effect that the output ripple voltage can be suppressed with a simple configuration.

(Second Embodiment)
Next, a second embodiment will be described. Description of parts common to the first embodiment described above will be omitted as appropriate. FIG. 4 is a diagram illustrating an example of the LED driving device according to the second embodiment. In the example of FIG. 4, the control unit 200 is configured to include a generation unit 210 and an output unit 22. The generation unit 210 includes an inverting circuit 211 and a V / F converter 212. In this example, the input voltage Vin is input to the V / F converter 212 through the inverting circuit 211, so that a triangular wave signal having a different frequency is generated according to the input voltage Vin. More specifically, a triangular wave signal having a higher frequency is generated as the input voltage Vin is smaller. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.

(Modification of the second embodiment)
FIG. 5 is a diagram illustrating an example of an LED drive device according to a modification of the second embodiment. In the example of FIG. 5, the control unit 201 further includes a voltage dividing unit 213 in addition to the generating unit 210 and the output unit 22. The voltage dividing unit 213 is a unit that divides the input voltage Vin and inputs the divided voltage to the generating unit 210. In the example of FIG. 5, the voltage dividing unit 213 includes two resistors connected in series, and a node between the two resistors is connected to the input side of the inverting circuit 211. Since the input voltage Vin is resistance-divided and then input to the generation unit 210, there is an advantage that the rating of the V / F converter 212 (inversion circuit 211) can be reduced. The above example can be similarly applied to other embodiments.

(Third embodiment)
Next, a third embodiment will be described. Description of parts common to the above-described embodiments will be omitted as appropriate. The booster circuit according to the third embodiment further includes an input circuit that generates a voltage signal input to the V / F converter 212 described above. The input circuit includes a constant current source, a plurality of resistors, and a selection unit that selects at least one resistor connected to the constant current source from the plurality of resistors according to the input voltage Vin. In addition, the voltage signal generated by the input circuit has a value proportional to the resistance value of the path through which the current from the constant current source flows. Further, the frequency of the triangular wave signal generated by the V / F converter 212 changes according to the voltage signal generated by the input circuit, and the V / F converter 212 increases as the value of the voltage signal generated by the input circuit increases. The frequency of the triangular wave signal generated at is increased. In this embodiment, at least one resistor connected to the constant current source is selected so that the resistance value of the path through which the current from the constant current source flows increases as the input voltage Vin decreases. The specific contents of this embodiment will be described below.

  FIG. 6 is a diagram illustrating an example of the LED driving device according to the fourth embodiment. In the example of FIG. 6, the control unit 202 includes a generation unit 220 and an output unit 22. The generation unit 220 includes an input circuit 230 and a V / F converter 212.

  The input circuit 230 includes a constant current source 231, a plurality of resistors R1 to R4 (R1 <R2 <R3 <R4; in the following description, simply referred to as “resistor R” if they are not distinguished from each other), a multiplexer 232 and a conversion unit 233. The input voltage Vin is input to the conversion unit 233. The conversion unit 233 is means for converting analog data into digital data, and converts an analog value of the input voltage Vin that has been input into a digital value. The digital value of the input voltage Vin converted by the conversion unit 233 is input to the multiplexer 232.

  The multiplexer 232 selects at least one resistor R connected to the constant current source 231 according to the input digital value. Since a constant current flows through the selected resistor R by the constant current source 231, a voltage signal proportional to the resistance value is generated and input to the V / F converter 212. The frequency of the triangular wave signal generated by the V / F converter 212 changes according to the voltage signal (voltage signal generated by the input circuit 230) input to the V / F converter 212, and as a result, the frequency of the PWM signal. Changes. In this example, the multiplexer 232 corresponds to a “selection unit” in the claims.

  Now, assuming that the digital value input to the multiplexer 232 is 2 bits, an operation example of the multiplexer 232 will be described. First, in the first case where the input voltage Vin is large, it is assumed that the 2-bit digital value input to the multiplexer 232 is “11”. In this case, the resistor R1 having the smallest resistance value is selected and connected to the constant current source 231.

  In the second case where the input voltage Vin is slightly smaller than that in the first case, it is assumed that the 2-bit digital value input to the multiplexer 232 is “10”. In this case, the resistor R2 having a resistance value larger than that of the resistor R1 is selected and connected to the constant current source 231. As a result, the voltage signal input to the V / F converter 212 (the voltage signal generated by the input circuit 230) is larger than that in the first case, and a triangular wave signal having a higher frequency than that in the first case is generated. Since it is generated by the V / F converter 212, a PWM signal having a higher frequency is obtained as a result.

  Further, in the third case where the input voltage Vin is smaller than that in the second case, it is assumed that the 2-bit digital value input to the multiplexer 232 is “01” or “00”. In this case, the resistor R3 or the resistor R4 having a resistance value larger than that of the resistor R2 is selected and connected to the constant current source 231. As a result, the voltage signal input to the V / F converter 212 (the voltage signal generated by the input circuit 230) is larger than that in the second case, and a triangular wave signal having a higher frequency than that in the second case is generated. Since it is generated by the V / F converter 212, a PWM signal having a higher frequency is obtained as a result.

  In short, the multiplexer 232 selects one of the resistors R1 to R4 so that the resistance value of the path through which the current from the constant current source 231 flows increases as the input voltage Vin decreases. As a result, the smaller the input voltage Vin is, the larger the voltage signal generated by the input circuit 230 is. Therefore, the frequency of the triangular wave signal generated by the V / F converter 212 is increased. As a result, a PWM signal having a higher frequency is generated. can get.

(Modification 1 of 3rd Embodiment)
FIG. 7 is a diagram illustrating an example of an LED drive device according to Modification 1 of the third embodiment. The control unit 203 illustrated in FIG. 7 includes a generation unit 240 and an output unit 22. The generation unit 240 includes an input circuit 250 and a V / F converter 212. The input circuit 250 includes a constant current source 231, a plurality of resistors R <b> 5, a selection unit 251, and a voltage dividing unit 252.

  The voltage dividing unit 252 is a unit that divides the input voltage Vin and inputs it to the selection unit 251. In the example of FIG. 7, the voltage divider 252 includes three resistors connected in series. A node between the resistors corresponds to the plurality of FETs included in the selection unit 251 on a one-to-one basis, and is connected to the gate of the corresponding FET.

  In the example of FIG. 7, four resistors R5 connected in parallel with each other are provided. Here, a plurality of resistors R5 having the same resistance value are provided, but the present invention is not limited to this. In the example of FIG. 7, three resistors R5 out of the four resistors R5 can be selected by the selection unit 251, and one resistor R5 is a default resistor.

  Each of the selection units 251 receives a divided input voltage Vin and can select at least one resistor R5 connected to the constant current source 231 in accordance with each on / off state. Includes FET3. Note that the number of FETs included in the selection unit 251 is not limited to three, and can be arbitrarily changed.

  For example, in the fourth case where the input voltage Vin is sufficiently large, it is assumed that all of the FET1 to FET3 are turned on. In this case, three resistors R5 are selected, and four resistors R5 including the default resistor R5 are connected to the constant current source 231. Since the four resistors R5 are connected in parallel to each other, the resistance value of the path through which the current from the constant current source 231 flows is R5 × 1/4.

  In the fifth case where the input voltage Vin is slightly smaller than the fourth case, it is assumed that only the FET 1 is turned off and the FET 2 and the FET 3 are turned on. In this case, two resistors R5 are selected, and three resistors R5 including the default resistor R5 are connected to the constant current source 231. Since the three resistors R5 are connected in parallel to each other, the resistance value of the path through which the current from the constant current source 231 flows is R5 × 1/3, which is larger than that in the fourth case. Therefore, the voltage signal input to the V / F converter 212 (voltage signal generated by the input circuit 250) is larger than that in the fourth case, and a triangular wave signal having a higher frequency than that in the fourth case is V. As a result, a higher frequency PWM signal is obtained.

  Further, in the sixth case where the input voltage Vin is smaller than that in the fifth case, it is assumed that FET2 or FET3 is turned off in addition to FET1. In this case, one resistor R5 is selected, and two resistors R5 including the default resistor R5 are connected to the constant current source 231. Since the two resistors R5 are connected in parallel to each other, the resistance value of the path through which the current from the constant current source 231 flows is R5 × 1/2, which is larger than that in the fifth case. Therefore, the voltage signal input to the V / F converter 212 (the voltage signal generated by the input circuit 250) is larger than that in the fifth case, and a triangular wave signal having a higher frequency than that in the fifth case is V. As a result, a higher frequency PWM signal is obtained.

(Modification 2 of 3rd Embodiment)
FIG. 8 is a diagram illustrating an example of an LED drive device according to Modification 2 of the third embodiment. The control unit 204 illustrated in FIG. 8 includes a generation unit 260 and an output unit 22. The generation unit 260 includes an input circuit 270 and a V / F converter 212. The input circuit 270 includes a constant current source 231, a plurality of resistors R 6, a selection unit 271, and a voltage dividing unit 252.

  The voltage dividing unit 252 is a unit that divides the input voltage Vin and inputs it to the selection unit 271 and has the same configuration as that of FIG.

  In the example of FIG. 8, three resistors R6 connected in parallel with each other are provided. Here, a plurality of resistors R6 having the same resistance value are provided, but the present invention is not limited to this. In the example of FIG. 8, two of the three resistors R6, R6, can be selected by the selection unit 271, and one resistor R6 is a default resistor.

  The selection unit 271 receives a divided input voltage Vin, and a plurality of bipolar transistors that can select at least one resistor R6 connected to the constant current source 231 according to each on / off state. Includes T1-T3. Note that the number of FETs included in the selection unit 251 is not limited to three, and can be arbitrarily changed.

  For example, in the seventh case where the input voltage Vin is sufficiently large, it is assumed that all of T1 to T3 are turned on. In this case, two resistors R6 are selected, and three resistors R6 including the default resistor R6 are connected to the constant current source 231. Since the three resistors R6 are connected in parallel to each other, the resistance value of the path through which the current from the constant current source 231 flows is R6 × 1/3.

  In the eighth case where the input voltage Vin is slightly smaller than that in the seventh case, it is assumed that only T1 is turned off and T2 and T3 are turned on. In this case, one resistor R6 is selected, and two resistors R6 including the default resistor R6 are connected to the constant current source 231. Since the two resistors R6 are connected in parallel to each other, the resistance value of the path through which the current from the constant current source 231 flows is R6 × 1/2, which is larger than in the seventh case. Therefore, the voltage signal input to the V / F converter 212 (the voltage signal generated by the input circuit 250) is larger than that in the seventh case, and a triangular wave signal having a higher frequency than that in the seventh case is V. As a result, a higher frequency PWM signal is obtained.

  Furthermore, in the ninth case where the input voltage Vin is smaller than the eighth case, it is assumed that T2 or T3 is turned off in addition to T1. In this case, neither of the two selectable resistors R6 is selected, and only the default resistor R6 is connected to the constant current source 231. Therefore, the resistance value of the path through which the current from the constant current source 231 flows is R6, which is larger than in the eighth case. Therefore, the voltage signal input to the V / F converter 212 (the voltage signal generated by the input circuit 250) is larger than that in the eighth case, and a triangular wave signal having a higher frequency than that in the eighth case is V. As a result, a higher frequency PWM signal is obtained.

(Image reading device)
Next, an image reading apparatus capable of mounting the LED driving device (light source driving circuit) of each of the above embodiments will be described. As shown in FIG. 9, an image reading apparatus such as a scanner in a digital copying machine that reads an original image with a CCD and converts an image signal into a digital signal is processed. A first carriage 106 composed of a light source 102 for document exposure and a first reflecting mirror 103, a second carriage 107 composed of a second reflecting mirror 104 and a third reflecting mirror 105, and a CCD linear image sensor 109 (hereinafter referred to as CCD). ), And a white reference plate 113 for correcting various distortions caused by the reading optical system or the like. During scanning, the first carriage 106 and the second carriage 107 are moved in the sub-scanning direction A by a stepping motor (not shown). In document reading by sheet-through, after the first carriage 106 and the second carriage 107 move below the sheet-through reading slit 115, the document 112 placed on the automatic document feeder 114 is moved in the direction B by the roller 116. By guiding, reading is performed at the position of the sheet-through reading slit 115.

  As shown in the scanner block diagram of FIG. 10, the analog image data photoelectrically converted by the CCD 119 is output to the analog processing circuit unit 120. The analog processing circuit unit 120 performs various image processing such as sample hold processing and black level correction on the analog image data, and then outputs the analog image data to the A / D conversion circuit unit 121. The A / D conversion circuit unit 121 converts the input analog image data into digital image data, and outputs it to the subsequent stage (image processing circuit unit or the like) via the LVDS interface 122. Various timing clocks of the CCD 119, the analog processing circuit unit 120, the A / D conversion circuit unit 121, the stepping motor, and the light source (both not shown) in the scanner device are generated and supplied by the timing clock generation circuit unit 123. The CPU or timing clock generation circuit unit 123 in the system can also generate a drive signal for the light source 102 and a PWM signal for driving the constant current source. By generating and outputting the light source driving signal synchronized with the reading line and the signal, it is possible to minimize adverse effects on the image such as light amount unevenness and fluctuation. In the digital image reading apparatus, by applying the present invention to the drive circuit system of the light source 102, a light source drive system capable of stable boosting operation can be realized.

(Image forming device)
Next, an image forming apparatus capable of mounting an image reading apparatus capable of mounting the LED driving device (light source driving circuit) of each of the above embodiments will be described. FIG. 11 is a schematic configuration diagram of the digital copying machine 1000. This configuration is a copying machine 1000 as an image forming apparatus, and a contact glass 280 is provided on the upper surface of the copying machine 1000. Further, an automatic document feeder (hereinafter simply referred to as ADF) 2010 is provided at the upper part of the copying machine 100, and this ADF 2010 is connected to the copying machine 1000 via a hinge (not shown) so as to open and close the contact glass 280. Has been. The ADF 2010 separates documents one by one from a document tray 2020 as a document placing table on which a document bundle composed of a plurality of documents can be placed, and faces the contact glass 280 from the document bundle placed on the document tray 2020. Separating / conveying means that conveys the original and the original conveyed to the contact glass 280 by the separating / conveying means is conveyed / stopped to a reading position on the contact glass 280, and a book disposed below the contact glass 280. An original that has been read by the image reading apparatus 400 (known exposure lamp 290, mirrors 300, 301, 302, lens 350, CCD 360, etc.) 400 of the invention is carried out from the contact glass 280. The paper feed motor is driven by an output signal from the controller. When the paper feed start signal is input from the copying machine 1000, the controller drives the paper feed motor in the forward and reverse directions. When the paper feed motor is driven in the forward direction, the feed roller 2030 rotates in the clockwise direction so that the uppermost original is fed from the original bundle and conveyed toward the contact glass 280. When the leading edge of the document is detected by the document set detection sensor 2070, the controller rotates the paper feed motor in reverse based on the output signal from the document set detection sensor 2070. This prevents subsequent documents from entering and prevents separation.

  Further, when the document set detection sensor 2070 detects the trailing edge of the document, the controller counts the rotation pulse of the conveyance belt motor from this detection time point, and when the rotation pulse reaches a predetermined value, the controller By stopping the driving and stopping the feeding belt 2040, the document is stopped at the reading position of the contact glass 280. Also, when the trailing edge of the document is detected by the document set detection sensor 2070, the controller drives the paper feed motor again, separates the subsequent document as described above, and conveys the document toward the contact glass 280. When the pulse of the paper feed motor from when the original is detected by the original set detection sensor 2070 reaches a predetermined pulse, the paper feed motor is stopped and the next original is awaited first. When the original stops at the reading position on the contact glass 280, the copying machine 1000 reads and exposes the original. When the reading and exposure are completed, a signal is input from the copier 1000 to the controller. When this signal is input, the controller drives the conveyor belt motor to rotate forward, and the document is transferred from the contact glass 280 by the conveyor belt 2160. It is carried out to the discharge roller 2050.

  As described above, a document bundle placed on the document tray 2020 in the ADF 2010 with the image surface of the document on the contact glass 280 from the top document when the print key on the operation unit is pressed. It is fed to a predetermined position. The fed original is read by the reading unit 2500 from the image data of the original on the contact glass 280, and is then discharged to the discharge port A (discharge port at the time of reverse document discharge) by the feeding belt 2040 and the reverse driving roller. Further, when it is detected that there is a next document on the document tray 2020, it is fed onto the contact glass 280 in the same manner as the previous document.

  The transfer sheets stacked on the first tray 2080, the second tray 2090, and the third tray 2100 are fed by the first sheet feeding unit 2110, the second sheet feeding unit 2120, and the third sheet feeding unit 2130, respectively, and are conveyed vertically. The unit 2140 is transported to a position where it abuts on the photoreceptor 2150. The image data read by the image reading device 400 is written on the photosensitive member 2150 by a laser from the writing unit 2570 and passes through the developing unit 2270 to form a toner image. The toner image on the photosensitive member 2150 is transferred while the transfer paper is conveyed by the conveying belt 2160 at the same speed as the rotation of the photosensitive member 2150. Thereafter, the image is fixed by the fixing unit 2170 and conveyed to the paper discharge unit 2180. The transfer paper conveyed to the paper discharge unit 2180 is discharged to the paper discharge tray 2190 when the staple mode is not performed. In the copying machine 1000 (image forming apparatus), the booster circuit and the LED driving apparatus (light source driving apparatus) described in the above embodiments and the above-described image reading apparatus can be applied.

  As mentioned above, although embodiment of this invention was described, each above-mentioned embodiment was shown as an example and is not intending limiting the range of invention. The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments and modifications. For example, you may delete a some component from all the components shown by each embodiment and a modification.

DESCRIPTION OF SYMBOLS 10 Boosting part 11 Inductor 12 Switching element 14 Capacitor 20 Control part 21 Generation part 22 Output part 23 Comparator 24 Triangular wave generation circuit 30 Constant current circuit 100 Boosting circuit

JP 2006-149152 A

Claims (16)

Including a switching element that is switched on and off according to a drive signal, and a boosting unit that boosts an input voltage by an on / off operation of the switching element;
A control unit that controls the drive signal in accordance with the input voltage,
Boost circuit. The controller is
Feeding back the output voltage from the booster, and controlling the duty ratio indicating the ratio between the period when the switching element is turned on and the period when it is turned off,
Controlling the drive signal so that the switching frequency of the switching element is switched according to the input voltage;
The booster circuit according to claim 1. The control unit controls the drive signal such that when the input voltage is smaller than a threshold, the switching frequency of the switching element is higher than when the input voltage is higher than the threshold.
The booster circuit according to claim 2. The controller is
A generator for generating a triangular wave signal corresponding to the input voltage;
An output unit that generates and outputs the drive signal according to a comparison result between the triangular wave signal generated by the generation unit and the feedback output;
4. The booster circuit according to claim 2 or claim 3. When the input voltage is smaller than the threshold, the generator generates the triangular wave signal having a higher frequency than when the input voltage is larger than the threshold.
The booster circuit according to claim 4. When the triangular wave signal is larger than the feedback output, the output unit generates and outputs the drive signal for turning on the switching element, while the triangular wave signal is higher than the feedback output. If small, generate and output the drive signal to switch the switching element off,
The booster circuit according to claim 4. The generation unit includes a V / F converter.
The booster circuit according to claim 4. A voltage dividing unit that divides the input voltage and inputs the divided voltage to the generation unit;
The booster circuit according to claim 7. A constant current source;
Multiple resistors,
A selection unit that selects at least one resistor connected to the constant current source from the plurality of resistors according to the input voltage, and is a voltage signal input to the V / F converter An input circuit for generating
The voltage signal generated by the input circuit has a value proportional to a resistance value of a path through which a current from the constant current source flows.
The booster circuit according to claim 7. The selection unit selects at least one resistor connected to the constant current source so that the resistance value of the path increases as the input voltage decreases.
The booster circuit according to claim 9. A conversion unit for converting the input voltage from an analog value to a digital value;
The selection unit includes a multiplexer to which the digital value converted by the conversion unit is input, and selects at least one resistor connected to the constant current source according to the input digital value.
The booster circuit according to claim 10. Each of the selection units includes a plurality of FETs to which the divided input voltage is input and which can select at least one resistor connected to the constant current source according to each on / off. ,
The booster circuit according to claim 10. Each of the selection units includes a plurality of bipolar transistors that receive the divided input voltage and that can select at least one resistor connected to the constant current source in accordance with each ON / OFF. Including,
The booster circuit according to claim 10. The booster circuit according to claim 1.
Light source drive device. The light source driving device according to claim 14 is provided.
Image reading device. The image reading apparatus according to claim 15 is provided.
Image forming apparatus.

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