JP2014007817A - Power supply device, and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent burning damage to a resistance of an inrush current prevention circuit after restoration from repeated instantaneous interruptions.SOLUTION: A power supply device 1 comprises a monitor circuit 11 that detects at least turning-off of an input AC voltage in order to convert the input AC voltage into DC currents V1 and V2, and outputs detection signals, a resistance 121, and a switch connected in parallel while being capable of bypassing the resistance 121. The power supply device 1 further includes an inrush current prevention circuit 12 that is connected with a subsequent stage of the monitor circuit 11, and delay means 17 that turns on the switch after the lapse of a predetermined time from the time of input of a detection signal S1 of the monitor circuit 11.

Description

  The present invention relates to a power supply device including an inrush current prevention circuit and an image forming apparatus including the power supply device.

  Conventionally, an electronic device such as an image forming apparatus is equipped with the power supply device as described above. An example of this type of power supply device is disclosed in Patent Document 1. In the conventional power supply device, a current larger than the rated value flows to charge the capacitor at the time of starting. In order to protect the electronic components from this large inrush current, the power supply device is provided with an inrush current prevention circuit and the like. The switch of the inrush current prevention circuit is closed when it is delayed for a predetermined period from when the external AC power supply is turned on, thereby bypassing the resistance of the inrush current prevention circuit. On the other hand, when the external AC voltage is turned off, the switch of the inrush current prevention circuit is opened.

JP 2002-78344 A

  In general, in order to satisfy the safety standards of each country, an electronic device equipped with a power supply device has an input interruption test (that is, an input voltage of one cycle (if the input frequency is 50 [Hz], the instantaneous interruption time is 20 [ ms]) may be subjected to a test to confirm that there is no functional degradation or breakage of the electronic equipment. However, in the conventional power supply device, since the inrush current prevention circuit repeatedly operates in the input instantaneous interruption test, the temperature of the resistance rises. In this state, if the electronic device recovers from the momentary interruption and the electronic device requires a large amount of power, an inrush current flows through the resistor of the inrush current prevention circuit. As a result, the resistance may burn out.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply device capable of preventing burnout of the resistance of an inrush current prevention circuit after returning from repeated instantaneous interruption, and an image forming apparatus provided therein.

  In order to achieve the above object, a first aspect of the present invention is a power supply device that converts an input AC voltage to a DC voltage supplied to an electronic device, and detects at least the OFF of the input AC voltage. A monitor circuit for outputting a signal; a resistor; a switch connected in parallel so that the resistor can be bypassed; and an inrush current preventing circuit connected to a subsequent stage of the monitor circuit; and when a detection signal of the monitor circuit is input Delay means for turning on the switch after a predetermined time has elapsed.

  A second aspect of the present invention is an image forming apparatus including the power supply device.

  According to each aspect described above, it is possible to provide a power supply device capable of preventing the burnout of the resistance provided in the inrush current prevention circuit and the image forming apparatus provided therein.

1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus including a power supply device according to each embodiment of the present invention. It is a block diagram which shows the detailed structure of the power supply device which concerns on 1st embodiment. It is a flowchart which shows operation | movement of the power supply device of FIG. It is a block diagram which shows the detailed structure of the power supply device which concerns on 2nd embodiment. It is a flowchart which shows operation | movement of the power supply device of FIG. It is a block diagram which shows the detailed structure of the power supply device which concerns on 3rd embodiment. It is a flowchart which shows operation | movement of the power supply device of FIG.

(First embodiment)
FIG. 1 is a schematic diagram illustrating a detailed configuration of an image forming apparatus including a power supply device according to the first embodiment of the present invention. FIG. 1 is also used in the second and third embodiments. FIG. 2 is a block diagram illustrating a detailed configuration of the power supply device according to the first embodiment and a connection relationship with the image forming apparatus.

  The following words are defined before the description of the power supply device and the like. First, the horizontal direction and vertical direction of the image forming apparatus are the horizontal direction and vertical direction of the paper surface of FIG. In some configurations shown in FIG. 1, suffixes a, b, c, and d are added to the right side of the reference number. a, b, c, and d mean yellow (Y), magenta (M), cyan (C), and black (Bk). For example, the photosensitive drum 87a means a yellow photosensitive drum 87. Reference numbers without subscripts mean Y, M, C, and Bk colors. For example, the photosensitive drum 87 means Y, M, C, or Bk photosensitive drums.

(Configuration of image forming apparatus)
1 and 2, the image forming apparatus is an MFP (Multifunction Peripheral) or the like that employs an electrophotographic method, and is configured to be able to create a full-color printed material by a tandem method, for example. Specifically, the image forming apparatus includes a power supply device 1, an AC input terminal 2, a main switch 3, an engine load 4, a control board 5, a supply device 6, and a printing unit 7.

  The power supply device 1 is supplied with an AC voltage from a commercial power supply via an AC input terminal 2. The power supply device 1 converts the input AC voltage into a desired DC voltage. In the present embodiment, two types of DC voltages, that is, a DC voltage V1 of 24 [V] and a DC voltage V2 of 5 [V] are generated. The DC voltage V1 is typically provided to the engine load 4 and the DC voltage V2 is typically provided to the control board 5.

  The main switch 3 is provided between the L terminal of the AC input terminal 2 and the power supply device 1 and is turned on / off by, for example, a user's manual operation.

  The engine load 4 typically includes a drive motor, a cooling fan, and a high-voltage power supply, and is driven by the DC voltage V1. The drive motor rotates and drives each rotating body (for example, the photosensitive drum 87) provided in the image forming apparatus. The cooling fan cools a heat generating component (such as a fixing device) provided in the image forming apparatus. The high-voltage power supply generates a DC bias voltage or the like supplied to a charger, a developer, or the like provided in the image forming apparatus.

  A CPU 51 and a control load 52 are mounted on the control board 5. The CPU 51 controls each component of the image forming apparatus. The control load 52 includes a cooling fan for cooling the CPU 51, for example. Other examples of the control load 52 include a liquid crystal display.

  In FIG. 1, in the supply device 6, the sheet material S stacked on the supply tray 61 is taken out by a pickup roller 62. The taken sheet material S is sent out one by one to the transport path R1 (see dotted line) by the supply roller 63 and the separation roller 64.

  In the printing unit 7, the registration roller pair 71 forms a registration nip. The sheet material S sent from the supply device 6 and transported through the transport path R1 is abutted against the registration nip, and is temporarily stopped. The registration roller pair 71 sends the temporarily stopped sheet material S to the downstream side of the conveyance path R1 at a timing suitable for secondary transfer described later.

  In the printing unit 7, the imaging unit 72 is provided immediately downstream of the conveyance path R 1 with respect to the registration roller pair 71, and includes an optical scanning device 81, an intermediate transfer belt 82, a driving roller 83, a driven roller 84, and a secondary roller 84. A transfer roller 85 and an image forming unit 86 for each color are included. Each color image forming unit 86 includes a photosensitive drum 87 configured to be rotatable.

  When the image data is input, the optical scanning device 81 generates a light beam γ for each color and scans the outer peripheral surface of the rotating photosensitive drum 87. Thereby, an electrostatic latent image of a corresponding color is generated on each outer peripheral surface. Thereafter, the electrostatic latent image is developed by a developing device (not shown) for each color, and a toner image is generated.

  The intermediate transfer belt 82 is stretched endlessly between the rollers 83 and 84 and rotates in the direction of the arrow α. In the predetermined area of the intermediate transfer belt 82, the toner images carried on the photosensitive drum 87 are sequentially transferred (primary transfer), and a full-color composite toner image in which the toner images of the respective colors overlap is formed. The composite toner image is conveyed toward the secondary transfer roller 85 by driving the intermediate transfer belt 82.

  The secondary transfer roller 85 contacts the intermediate transfer belt 82 to form a secondary transfer nip. The sheet material S is introduced from the registration roller pair 71 into the secondary transfer nip. A transfer voltage is applied to the secondary transfer roller 85, and the composite toner image on the intermediate transfer belt 82 is secondarily transferred to the sheet material S passing through the secondary transfer nip. The secondary transfer roller 85 and the intermediate transfer belt 82 send the sheet material S after the secondary transfer to the downstream side of the conveyance path R1.

  The fixing device 73 has a fixing nip formed by a heating roller and a pressure roller. As the sheet material S from the secondary transfer nip passes through the fixing nip, the fixing device 73 fixes the composite toner image on the sheet material S. Thereafter, the fixing device 73 sends the sheet material S to the reversing / discharging roller pair 74 provided downstream of the transport path R1.

  The reverse / discharge roller pair 74 performs printing on the second surface (back surface) when the sheet material S that has been subjected to fixing processing on the first surface (front surface) is introduced from the fixing device 73 during double-sided printing of the sheet material S. Therefore, the sheet material S is switched back and sent out to the reversing path R2 (see the alternate long and short dash line). The sheet material S is conveyed toward the registration roller pair 71 by the double-sided conveyance roller pair 75 and 76 disposed on the reversing path R2. Thereafter, the sheet material S is temporarily stopped at a predetermined refeeding position, and after the timing adjustment with the other sheet material S passing through the joining point of the conveyance path R1 and the reversing path R2, the sheet material S is reversed. In this state, it is abutted against the resist nip. Thereafter, in the same manner as described above, secondary transfer and fixing processing are performed on the second surface.

  The reverse / discharge roller pair 74 discharges the sheet material S to the discharge tray 77 when the sheet material S that has been subjected to the fixing process on the second surface is introduced. Further, in the case of single-sided printing, the sheet material S that has been subjected to the fixing process on the first surface is discharged from the reverse / discharge roller pair 74 to the discharge tray 77 without being switched back.

(Configuration of power supply)
In FIG. 2, a power supply device 1 includes a monitor circuit 11, an inrush current prevention circuit (hereinafter simply referred to as a prevention circuit) 12, a diode bridge 13, a capacitor 14, a large load DC / DC converter 15, and a small load. DC / DC converter 16 for delay, delay means 17, and switching element 18 are included.

  The monitor circuit 11 is provided at the front end of the power supply device 1, more specifically, on the power supply line and between the AC input terminal 2 and the inrush current prevention circuit 12. The monitor circuit 11 detects at least whether the AC voltage is input off, and outputs a detection signal S1 indicating that to the delay means 17 described later. In the present embodiment, the detection signal S1 is a Lo level signal to indicate that the AC voltage is input off. Note that the monitor circuit 11 can actually detect that the input of the AC voltage is turned on, and outputs the Hi-level detection signal S1 when it is detected.

  The prevention circuit 12 is provided between the monitor circuit 11 and the diode bridge 13 on the power supply line. The prevention circuit 12 includes a resistor 121, a bypass line 122, and a relay 123. The resistor 121 is provided on the ground side of the power supply line. The bypass line 122 is a line that is connected in parallel to the resistor 121 and bypasses the resistor 121. The relay 123 has a switch and a coil. The switch is provided on the bypass line 122. The coil is supplied with the DC voltage V1 of the DC / DC converter 15. In the present embodiment, the switch is closed while a current flows through the coil, thereby short-circuiting the bypass line 122. Conversely, the switch opens while no current is flowing through the coil.

  The diode bridge 13 is provided between the prevention circuit 12 and the DC / DC converter 15 on the power supply line, and generates a DC voltage by half-wave rectifying the input AC voltage.

  The capacitor 14 is connected in parallel to the subsequent stage of the diode bridge 13 and smoothes the input DC voltage.

  The DC / DC converter 15 converts the DC voltage smoothed by the capacitor 14 into a DC voltage V1 of 24 [V], and supplies it to the engine load 4. The DC / DC converter 15 is turned on / off by a control signal S2 transmitted from the CPU 51. As a result, the image forming apparatus enters the standby mode (power saving mode) or returns from the standby mode.

  The DC / DC converter 16 converts the DC voltage smoothed by the capacitor 14 into a DC voltage V2 of 5 [V] smaller than the DC voltage V1, and supplies the DC voltage V2 to the control board 5. Unlike the DC / DC converter 15, the DC / DC converter 16 operates while the main switch 3 is on.

  The delay means 17 is an electronic circuit connected to the monitor circuit 11 through a signal line and having a predetermined time constant τ. Here, the time constant τ is preferably selected to be about 100 [ms]. Here, it is assumed that at least 1 [s] is required to switch the main switch 3 from OFF to ON by the user's manual operation, and it is substantially not less than 100 [ms]. Based on this assumption, the time constant τ is selected to be about 100 [ms].

  When the delay means 17 receives the Lo level detection signal S1 from the monitor circuit 11, the delay means 17 outputs the control signal S3 to the switching element 18 after the time constant has elapsed with reference to the reception time.

  The switching element 18 is, for example, an FET. The coil of the relay 123 is connected to the source, the drain is grounded, and the output terminal of the delay means 17 is connected to the gate. When the Lo level control signal S3 is input to the gate of the switching element 18, a current flows from the source to the drain. That is, the switching element 18 is turned on. Conversely, in the Hi level, no current flows between the source and the drain, and the switching element 18 is turned off. That is, the relay 123 is open between the coil and the ground.

(Power supply operation)
Next, with reference to FIG. 3, the operation of the power supply device 1 when the AC power supply transitions from OFF to ON in a short time (for example, during an input interruption test) will be described. First, when the AC voltage is turned off (S31), the monitor circuit 11 outputs the detection signal S1 (Lo level) to the delay means 17 (S32). When the time constant τ elapses from the time when the detection signal S1 is received, the delay means 17 outputs the control signal S3 (Lo level) to the switching element 18 and turns off the switching element 18 (S33). As a result of S33, since the coil of the relay 123 and the ground are open, no current flows through the coil. As a result, the switch of the relay 123 is turned off (S34). Thereafter, when the AC power supply is turned on, the inrush current flows through the resistance of the prevention circuit 12 (S35).

(Operation and effect of power supply)
As described above, in the power supply device 1, the relay 123 is turned off after the elapse of the time constant τ from the reception of the Lo level detection signal S1. As a result, a current flows through the resistor 121. Here, since the time constant is set to 5 cycles (100 [ms]) as the tolerance of the input instantaneous interruption test, the relay 123 does not operate during the input instantaneous interruption test. As a result, it is possible to prevent the resistor 121 from being burned out after returning from repeated OFF to ON (that is, instantaneous interruption). Since the switching of the main switch 3 is substantially impossible at 100 [ms], the prevention circuit 12 correctly resists the inrush current by turning off the relay 123 at 100 [ms] after the AC voltage is detected to be off. 121 can be made to flow.

(Second embodiment)
Next, a power supply device and an image forming apparatus according to the second embodiment will be described with reference to FIGS. 1, 4, and 5.

(Configuration of image forming apparatus)
The image forming apparatus according to the second embodiment is different from that according to the first embodiment in that a power supply apparatus 1a and a control board 5a are provided instead of the power supply apparatus 1 and the control board 5 (see FIG. 1). Further, in FIG. 4, the power supply device 1 a is different from the power supply device 1 in that the delay unit 17 and the switching element 18 are not provided. Since it is common except the above, in 2nd embodiment, the description of what is corresponded to the structure of 1st embodiment is abbreviate | omitted.

  A CPU 51a, a control load 52, and a memory 53a are mounted on the control board 5a. The CPU 51 a controls each part of the image forming apparatus in the same manner as the CPU 51. In addition, the CPU 51a executes a program stored in the memory 53a in response to the detection signal S1 of the monitor circuit 11, and controls on / off of the heavy load DC / DC converter 15. Since the control load 52 has already been described, the description thereof is omitted.

(Power supply operation)
Next, the operation of the power supply device 1a of FIG. 4 will be described with reference to FIG. The flow chart of FIG. 5 differs from that of FIG. 3 in that S51 to S56 are provided instead of S33 and S34. Since the rest is common, in FIG. 5, the same step numbers are assigned to the steps corresponding to the steps in FIG.

  When S31 and S32 are executed, a Lo level detection signal S1 is transmitted from the monitor circuit 11 to the CPU 51a. When this detection signal S1 is received, the CPU 51a starts executing the program stored in the memory 53a.

  First, the CPU 51a determines whether or not the image forming apparatus enters a standby mode (S51). If NO, the main power supply is turned off (S52).

  On the other hand, in the case of YES, the CPU 51a starts a timer (not shown) and starts measuring a predetermined time (100 [ms] as in the first embodiment) in order to perform the delay process (S53). Thereafter, when 100 [ms] elapses (S54), the CPU 51a gives a control signal S2 to the heavy load DC / DC converter 15 (S55). Here, the large load DC / DC converter 15 is provided with a main relay for turning on / off the operation of the converter 15. The control signal S2 is given to the main relay and is a signal for turning off the operation of the large load DC / DC converter 15.

  As a result, the DC voltage V1 droops, and the energization of the coil provided in the relay 123 is eventually stopped. As a result, the switch of the relay 123 is turned off (S56). Thereafter, when the AC power supply is turned on, the inrush current flows through the resistance of the prevention circuit 12 (S35).

(Operation and effect of power supply)
As described above, in the power supply device 1a, the relay 123 is turned off after a predetermined time has elapsed since the reception of the Lo level detection signal S1. Therefore, the same effect as that of the first embodiment is obtained. In addition, since the power supply device 1a turns off the relay 123 by software control, a hardware configuration such as the delay unit 17 and the switching element 18 required in the first embodiment is not required. Therefore, the power supply device 1a can be reduced in size at a low cost.

(Third embodiment)
Next, a power supply device and an image forming apparatus according to the third embodiment will be described with reference to FIG. 1, FIG. 6, and FIG.

(Configuration of image forming apparatus)
The image forming apparatus according to the third embodiment is different from that according to the first embodiment in that a power supply apparatus 1b and a control board 5b are provided instead of the power supply apparatus 1 and the control board 5 (see FIG. 1). 6 is different from the power supply device 1a of FIG. 4 in that the power supply device 1b further includes a delay means 17 and a switching element 18. Since it is common except the above, in 3rd embodiment, the description of what is corresponded to the structure of 2nd embodiment is abbreviate | omitted.

  A CPU 51b, a control load 52, and a memory 53b are mounted on the control board 5b. In addition to controlling each part of the image forming apparatus, the CPU 51b executes a program stored in the memory 53b in response to the detection signal S1 of the monitor circuit 11, and transmits a control signal S3 to the delay means 17. Since the control load 52 is as described in the first embodiment, the description thereof is omitted.

(Power supply operation)
Next, the operation of the power supply device 1b of FIG. 6 will be described with reference to FIG. The flowchart in FIG. 7 includes S31 to S35 in FIG. 3 and S51 and S52 in FIG.

  When S31 and S32 are executed, a Lo level detection signal S1 is transmitted from the monitor circuit 11 to the CPU 51b. When this detection signal S1 is received, the CPU 51b starts executing the program stored in the memory 53b.

  First, the CPU 51b determines whether or not the image forming apparatus enters a standby mode (S51). If NO, the main power supply is turned off (S52).

  On the other hand, in the case of YES, the CPU 51b transmits a control signal S3 of Lo level to the delay means 17. When the time constant τ elapses from the reception time point of the control signal S3, the delay means 17 outputs the Lo level control signal S4 to the switching element 18 and turns off the switching element 18 (S33). As a result of S33, the coil of the relay 123 and the ground are opened, and as a result, the switch of the relay 123 is turned off (S34). Thereafter, when the AC power supply is turned on, the inrush current flows through the resistance of the prevention circuit 12 (S35).

(Operation and effect of power supply)
As described above, in the power supply device 1b, the relay 123 is turned off after approximately 100 [ms] has elapsed since the reception of the Lo level detection signal S1. Therefore, it is possible to achieve the same effect as in the first embodiment.

(Appendix)
In each of the above embodiments, the power supply devices 1, 1 a, and 1 b have been described as being provided in the image forming apparatus, but may be provided in other electrical devices.

  In the first and third embodiments, the delay means 17 has been described as an electronic circuit having a time constant τ. However, the present invention is not limited to this, and the delay means 17 may be a signal line that delays the detection signal S1 by a time constant τ in the first embodiment. In the third embodiment, the delay means 17 may be a signal line that delays the control signal S3 by a time constant τ.

  The power supply circuit and the image forming apparatus according to the present invention can prevent burning of the resistance provided in the inrush current prevention circuit, and can be applied not only to the MFP but also to various electric devices such as a copying machine, a facsimile machine, and a printer.

1, 1a, 1b Power supply device 11 Monitor circuit 12 Inrush current prevention circuit 13 Diode bridge 14 Capacitor 15 DC / DC converter for large load 16 DC / DC converter for small load 17 Delay means 18 Switching element 2 AC input terminal 3 Main switch 4 Engine load 5, 5a, 5b Control board 51, 51a, 51b CPU
52 Control load 53a, 53b Memory

Claims (5)

A power supply device that converts an input AC voltage to a DC voltage supplied to an electronic device,
At least a monitor circuit that detects the OFF of the input AC voltage and outputs a detection signal;
An inrush current prevention circuit including a resistor and a switch connected in parallel so that the resistor can be bypassed, and connected to a subsequent stage of the monitor circuit;
And a delay unit that turns on the switch after a predetermined time has elapsed since the detection signal was input to the monitor circuit.   2. The power supply device according to claim 1, wherein when the control unit determines that the electronic device is in a standby state, the control unit turns on the switch after a predetermined time has elapsed since the detection signal was input to the monitor circuit.   The electronic device includes a main switch that can be switched on / off by a user's manual operation, and the predetermined time does not exceed a time required for switching the main switch, and an AC voltage in an input interruption test is not exceeded. The power supply device according to claim 1, wherein the power supply device is longer than an instantaneous interruption time.   The power supply device according to claim 3, wherein the predetermined time is 100 [ms]. A power supply device that converts input AC voltage into DC voltage;
And at least one load connected to the power supply device and operated by a DC voltage generated by the power supply device,
The power supply device
At least a monitor circuit that detects the OFF of the input AC voltage and outputs a detection signal;
An inrush current prevention circuit including a resistor and a switch connected in parallel so that the resistor can be bypassed, and connected to a subsequent stage of the monitor circuit;
An image forming apparatus comprising: delay means for turning on the switch after a predetermined time has elapsed since the detection signal was input to the monitor circuit.

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