Power supply circuit, and image forming apparatus

Abstract

To prevent occurrence of conduction abnormality resulting from repetition of input and interruption of AC voltage in short time with a simple configuration.SOLUTION: A power supply circuit 6 comprises a full-wave rectification circuit 62, a smoothing circuit 63, a first half-wave rectification circuit 66a, a second half-wave rectification circuit 66b, a third half-wave rectification circuit 66c, a voltage conversion circuit 64 and a control circuit 68. The voltage conversion circuit 64 operates when a voltage level of an AC detection line L3 as an output line of the third half-wave rectification circuit exceeds a first reference level and converts primary voltage as output voltage of the smoothing circuit 63 into DC secondary voltage. The control circuit 68 transmits output voltage of the first half-wave rectification circuit 66a to the AC detection line L3 when the secondary voltage is less than a second reference level based on the voltage level of the AC detection line L3 and stops transmission of the output voltage of the first half-wave rectification circuit 66a to the AC detection line L3 when the secondary voltage is less than the second reference level.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power supply circuit that converts an input AC voltage into a DC voltage, and an image forming apparatus including the same. [Background technology]

[0002] An image forming apparatus such as a printer, copier, or multifunction peripheral includes a printing device that forms an image on a sheet. The image forming apparatus further includes a power supply circuit that converts an input AC voltage into a DC voltage. The printing device operates using power supplied by the power supply circuit.

[0003] The power supply circuit includes a full-wave rectifier circuit, a smoothing circuit, and a voltage conversion circuit. The full-wave rectifier circuit full-wave rectifies an AC voltage input from an external source. The smoothing circuit smoothes the output voltage of the full-wave rectifier circuit. The voltage conversion circuit converts a primary voltage, which is the output voltage of the smoothing circuit, into a DC secondary voltage.

[0004] In some cases, the power supply circuit includes a zero-cross detection circuit that generates a zero-cross signal from the AC voltage. For example, the zero-cross signal is used to control a heater included in a fixing device of the printing device.

[0005] It is also known that the power supply circuit determines the state of the AC voltage using the level of the output voltage of the voltage conversion circuit and the level of the zero-cross signal (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-041949 Summary of the Invention [Problem to be solved by the invention]

[0007] However, if the AC voltage is repeatedly input and cut off within a short period of time, the output voltage of the smoothing circuit may exceed the level of the AC voltage, causing an abnormal current flow in the full-wave rectifier circuit.

[0008] An object of the present invention is to provide a power supply circuit and an image forming apparatus that can prevent, with a simple configuration, the occurrence of abnormalities in electrical conduction caused by repeated input and interruption of AC voltage within a short period of time. [Means for solving the problem]

[0009] A power supply circuit according to one aspect of the present invention includes a full-wave rectifier circuit, a smoothing circuit, a first half-wave rectifier circuit, a second half-wave rectifier circuit, a third half-wave rectifier circuit, a zero-crossing signal generation circuit, a voltage conversion circuit, and a control circuit. The full-wave rectifier circuit full-wave rectifies an AC voltage input from an external source. The smoothing circuit smoothes the output voltage of the full-wave rectifier circuit. The first half-wave rectifier circuit rectifies a voltage transmitted by a first single-side transmission line, which is one of a neutral-side transmission line and a live-side transmission line that constitute a pair of AC transmission lines that transmit the AC voltage to the full-wave rectifier circuit. The second half-wave rectifier circuit and the third half-wave rectifier circuit each rectify a voltage transmitted by a second single-side transmission line, which is the other of the neutral-side transmission line and the live-side transmission line. The zero-cross signal generation circuit generates a zero-cross signal indicating zero-cross timing of the AC voltage from the output voltages of the first half-wave rectifier circuit and the second half-wave rectifier circuit. The voltage conversion circuit operates when the voltage level of an AC detection line, which is the output line of the third half-wave rectifier circuit, exceeds a first reference level and converts the primary voltage, which is the output voltage of the smoothing circuit, into a DC secondary voltage. The control circuit transmits the output voltage of the first half-wave rectifier circuit to the AC detection line when the secondary voltage falls below a second reference level based on the voltage level of the AC detection line, and stops transmitting the output voltage of the first half-wave rectifier circuit to the AC detection line when the secondary voltage falls below the second reference level.

[0010] An image forming apparatus according to another aspect of the present invention includes the power supply circuit described above, and a printing device that operates using power supplied by the power supply circuit and forms an image on a sheet. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a power supply circuit and an image forming apparatus that can prevent, with a simple configuration, the occurrence of abnormalities in electrical conduction caused by repeated input and interruption of AC voltage within a short period of time. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus including a power supply circuit according to an embodiment. [Figure 2] FIG. 2 is a configuration diagram of a main part of the power supply circuit according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following embodiment is an example of the present invention, and does not limit the technical scope of the present invention.

[0014] The power supply circuit 6 according to the embodiment constitutes a part of the image forming apparatus 10. The image forming apparatus 10 is capable of executing a print process for forming an image on a sheet 9.

[0015] [Configuration of image forming apparatus 10] 1, the image forming apparatus 10 includes a sheet transport mechanism 3 and a printing device 4. In this embodiment, the image forming apparatus 10 also includes an image reading device 2 that reads an image from a document 9x.

[0016] The sheet transport mechanism 3 transports the sheet 9 stored in the sheet storage unit 30 along a transport path 300. The sheet transport mechanism 3 includes a sheet feeding mechanism 31 and a plurality of pairs of transport rollers 32.

[0017] The sheet feeding mechanism 31 sends out the sheet 9 from the sheet storage unit 30 to the conveying path 300. A plurality of pairs of conveying rollers 32 convey the sheet 9 along the conveying path 300.

[0018] The printing device 4 forms an image on a sheet 9 transported along a transport path 300. One of the plurality of transport roller pairs 32 ejects the sheet 9 with the image formed thereon from the transport path 300.

[0019] 1, the printing device 4 performs the printing process by electrophotography. In this case, the printing device 4 includes an optical scanning device 40, one or more image forming units 4x, a transfer device 44, and a fixing device 45.

[0020] The image forming unit 4x includes a photoconductor 41, a charging device 42, and a developing device 43. The charging device 42 charges the surface of the photoconductor 41. The optical scanning device 40 forms an electrostatic latent image on the surface of the photoconductor 41 by scanning a beam of light across the charged surface of the photoconductor 41.

[0021] The developing device 43 develops the electrostatic latent image into a toner image by supplying toner to the surface of the photoreceptor 41. The photoreceptor 41 is an image carrier that carries the toner image.

[0022] The transfer device 44 transfers the toner image on the surface of the photoreceptor 41 to a sheet 9. The fixing device 45 fixes the toner image to the sheet 9 by applying heat and pressure to the toner image transferred to the sheet 9. The fixing device 45 includes a heater 450 that heats the toner image.

[0023] 1, the printing apparatus 4 is a tandem color printing apparatus, and therefore includes a plurality of image forming units 4x corresponding to a plurality of developing colors.

[0024] The transfer device 44 includes an intermediate transfer belt 441, a plurality of primary transfer devices 442 and a secondary transfer device 443 corresponding to the plurality of image forming units 4x.

[0025] Each primary transfer device 442 transfers the toner image on the photoconductor 41 of each image forming unit 4x onto the surface of the intermediate transfer belt 441. The secondary transfer device 443 transfers the toner image on the surface of the intermediate transfer belt 441 onto the sheet 9.

[0026] The printing device 4 may be a device that forms an image on the sheet 9 by a method other than the electrophotographic method. For example, the printing device 4 may be a device that forms an image on the sheet 9 by an inkjet method.

[0027] The image forming apparatus 10 further includes a control device 5 that controls the image reading device 2, the sheet conveying mechanism 3, and the printing device 4. The control device 5 executes various data processing operations and controls various devices in the image forming apparatus 10.

[0028] The control device 5 includes a power supply board 60 on which a power supply circuit 6 is mounted. The power supply circuit 6 converts an input AC voltage VA1 into a DC voltage. The AC voltage VA1 is supplied from an AC power supply 100 such as a commercial power supply.

[0029] The image reading device 2, the sheet transport mechanism 3, and the printing device 4 are operated by power supplied from a power supply circuit 6.

[0030] [Power circuit 6] As shown in FIG. 2, the power supply circuit 6 includes a noise filter circuit 61, a full-wave rectifier circuit 62, and a smoothing circuit 63.

[0031] The noise filter circuit 61 includes a first noise filter circuit 61a and a second noise filter circuit 61b connected in series. The second noise filter circuit 61b is connected after the first noise filter circuit 61a.

[0032] An AC voltage VA1 input from the outside is supplied to a full-wave rectifier circuit 62 via a noise filter circuit 61. The full-wave rectifier circuit 62 full-wave rectifies the AC voltage VA1. For example, the full-wave rectifier circuit 62 is a bridge diode.

[0033] The smoothing circuit 63 smoothes the output voltage of the full-wave rectifier circuit 62. For example, the smoothing circuit 63 is a smoothing capacitor. The power supply circuit 6 also includes a circuit that converts the output voltage of the smoothing circuit 63 into various DC voltages.

[0034] However, if the input and interruption of the AC voltage VA1 are repeated within a short period of time, the output voltage of the smoothing circuit 63 may exceed the level of the AC voltage VA1, resulting in an abnormal current flow in the full-wave rectifier circuit 62.

[0035] The power supply circuit 6 has a configuration for preventing the occurrence of the above-mentioned abnormal current flow caused by the AC voltage VA1 being repeatedly turned on and off within a short period of time. The configuration will be described below.

[0036] The power supply circuit 6 includes a noise filter circuit 61, a full-wave rectifier circuit 62, and a smoothing circuit 63, as well as three half-wave rectifier circuits 66a, 66b, and 66c, a zero-cross signal generating circuit 67, a boost circuit 64, one or more voltage generating circuits 65, and a control circuit 68 (see FIG. 2).

[0037] Each of the half-wave rectifier circuits 66a, 66b, and 66c is a diode. The three half-wave rectifier circuits 66a, 66b, and 66c include a first half-wave rectifier circuit 66a, a second half-wave rectifier circuit 66b, and a third half-wave rectifier circuit 66c.

[0038] The AC voltage VA1 is transmitted by a pair of AC transmission lines L1, L2 to the full-wave rectifier circuit 62. The pair of AC transmission lines L1, L2 that transmit the AC voltage VA1 is made up of a neutral-side transmission line L1 and a live-side transmission line L2.

[0039] The first half-wave rectifier circuit 66a rectifies the voltage transmitted through the neutral-side transmission line L1. The second half-wave rectifier circuit 66b rectifies the voltage transmitted through the live-side transmission line L2. The third half-wave rectifier circuit 66c also rectifies the voltage transmitted through the live-side transmission line L2.

[0040] In this embodiment, the neutral side transmission line L1 is an example of a first single-sided transmission line corresponding to the first half-wave rectifier circuit 66a, and the live side transmission line L2 is an example of a second single-sided transmission line corresponding to the second half-wave rectifier circuit 66b and the third half-wave rectifier circuit 66c.

[0041] 2, the first half-wave rectifier circuit 66a is connected to a line branching off from a portion of the neutral-side transmission line L1 between the first noise filter circuit 61a and the second noise filter circuit 61b, and the second half-wave rectifier circuit 66b is connected to a line branching off from a portion of the live-side transmission line L2 between the first noise filter circuit 61a and the second noise filter circuit 61b.

[0042] On the other hand, the third half-wave rectifier circuit 66c is connected to a line branching off from a portion between the second noise filter circuit 61b and the full-wave rectifier circuit 62 in the Live-side transmission line L2.

[0043] In the following description, the output voltage of the first half-wave rectifier circuit 66a will be referred to as the first rectified voltage Vx1, the output voltage of the second half-wave rectifier circuit 66b will be referred to as the second rectified voltage Vx2, and the output voltage of the third half-wave rectifier circuit 66c will be referred to as the third rectified voltage Vx3.

[0044] The output line of the third half-wave rectifier circuit 66c is referred to as the AC detection line L3. The AC detection line L3 is a transmission line for the third rectified voltage Vx3 that extends from the third half-wave rectifier circuit 66c to the boost circuit 64.

[0045] The zero-cross signal generating circuit 67 generates a zero-cross signal SG1 from the first rectified voltage Vx1 and the second rectified voltage Vx2. The zero-cross signal SG1 is a signal that indicates the zero-cross timing of the AC voltage VA1. The zero-cross signal SG1 is used to control the heater 450 of the fixing device 45.

[0046] The boost circuit 64 operates when the voltage level of the AC detection line L3 exceeds a first reference level. Therefore, the boost circuit 64 operates when the level of the third rectified voltage Vx3 exceeds the first reference level. If the full-wave rectifier circuit 62 is in a normal conducting state, the level of the third rectified voltage Vx3 exceeds the first reference level.

[0047] The boost circuit 64 converts the primary voltage V1, which is the output voltage of the smoothing circuit 63, into a DC secondary voltage V2. In this embodiment, the secondary voltage V2 is higher than the primary voltage V1. For example, the primary voltage V1 is approximately 100 V, and the secondary voltage V2 is approximately 200 V. The boost circuit 64 is an example of a voltage conversion circuit that converts the primary voltage V1 into the secondary voltage V2.

[0048] When the voltage level of the AC detection line L3 is lower than the first reference level, the boost circuit 64 does not operate, and the primary voltage V1 is output as is as the secondary voltage V2.

[0049] The voltage generating circuit 65 converts the secondary voltage V2 into an equipment voltage that is lower than the secondary voltage V2. In this embodiment, the voltage generating circuit 65 includes a first voltage generating circuit 65a and a second voltage generating circuit 65b.

[0050] The first voltage generating circuit 65a converts the primary voltage V1 into a first device voltage V31. The second voltage generating circuit 65b converts the primary voltage V1 into a second device voltage V32 that is lower than the first device voltage V31. For example, the first device voltage V31 is 24 V and the second device voltage V32 is 5 V.

[0051] The control circuit 68 transmits the first rectified voltage Vx1 to the AC detection line L3 when the secondary voltage V2 is below a second reference level, and stops transmitting the first rectified voltage Vx1 to the AC detection line L3 when the secondary voltage V2 is above the second reference level.

[0052] The second reference level is a voltage determined based on the voltage level of the AC detection line L3, for example, the second reference level is equal to the voltage level of the AC detection line L3.

[0053] As described above, repeated input and interruption of AC voltage VA1 within a short period of time can cause primary voltage V1 to exceed the level of AC voltage VA1. In this case, some of the diodes constituting full-wave rectifier circuit 62 that are connected to live-side transmission line L2 enter a pseudo-open state, causing the above-mentioned electrical abnormality in which no current flows through full-wave rectifier circuit 62.

[0054] When the abnormal current flows, the level of the third rectified voltage Vx3 drops and the operation of the boost circuit 64 stops. When the operation of the boost circuit 64 stops, the level of the secondary voltage V2 drops, and the control circuit 68 transmits the first rectified voltage Vx1 to the AC detection line L3.

[0055] Therefore, even if the above-mentioned abnormality in the conduction of the full-wave rectifier circuit 62 temporarily occurs, the boost circuit 64 operates to resolve the abnormality. On the other hand, when the above-mentioned abnormality in the conduction of the full-wave rectifier circuit 62 does not occur, the boost circuit 64 operates using the first rectified voltage Vx1, and the transmission of the third rectified voltage Vx3 to the AC detection line L3 is stopped.

[0056] The three half-wave rectifier circuits 66a, 66b, and 66c are existing circuits, and the control circuit 68 added to the existing circuits is a simple switch circuit based on the secondary voltage V2 and the third rectified voltage Vx3.

[0057] As described above, by employing the power supply circuit 6, the occurrence of the above-mentioned electrical abnormality can be prevented with a simple configuration.

[0058] [Variations] In the power supply circuit 6, the first half-wave rectifier circuit 66a may half-wave rectify the voltage of the live-side transmission line L2, and the second half-wave rectifier circuit 66b and the third half-wave rectifier circuit 66c may half-wave rectify the voltage of the neutral-side transmission line L1.

[0059] In this modified example, the live side transmission line L2 is an example of a first single-sided transmission line corresponding to the first half-wave rectifier circuit 66a, and the neutral side transmission line L1 is an example of a second single-sided transmission line corresponding to the second half-wave rectifier circuit 66b and the third half-wave rectifier circuit 66c.

[0060] [Notes on the Invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0061] <Appendix 1> a full-wave rectifier circuit that full-wave rectifies an AC voltage input from an external source; a smoothing circuit that smoothes the output voltage of the full-wave rectifier circuit; a first half-wave rectifier circuit that rectifies a voltage transmitted by a first single-side transmission line that is one of a neutral-side transmission line and a live-side transmission line that constitute a pair of AC transmission lines that transmit the AC voltage to the full-wave rectifier circuit; a second half-wave rectifier circuit and a third half-wave rectifier circuit that respectively rectify a voltage transmitted by a second single-side transmission line that is the other of the neutral-side transmission line and the live-side transmission line; a zero-cross signal generating circuit that generates a zero-cross signal representing a zero-cross timing of the AC voltage from the output voltages of the first half-wave rectifier circuit and the second half-wave rectifier circuit; a voltage conversion circuit that operates when the voltage level of an AC detection line that is an output line of the third half-wave rectifier circuit exceeds a first reference level, and converts a primary voltage that is an output voltage of the smoothing circuit into a DC secondary voltage; a control circuit that transmits the output voltage of the third half-wave rectifier circuit to the AC detection line when the secondary voltage falls below a second reference level based on a voltage level of the AC detection line, and stops transmission of the output voltage of the third half-wave rectifier circuit to the AC detection line when the secondary voltage falls below the second reference level.

[0062] <Appendix 2> 2. The power supply circuit according to claim 1, wherein the voltage conversion circuit is a boost circuit.

[0063] <Appendix 3> the power supply circuit according to Supplementary Note 1 or Supplementary Note 2; a printing device that operates using power supplied from the power supply circuit and forms an image on a sheet. [Explanation of symbols]

[0064] 4: Printing device 5: Control device 6:Power circuit 45: Fixing device 60: Power supply board 61: Noise filter circuit 62:Full wave rectifier circuit 63: Smoothing circuit 64: Boost circuit 65: Voltage generation circuit 65a: First voltage generating circuit 65b: Second voltage generating circuit 66a: 1st half-wave rectifier circuit 66b: Second half-wave rectifier circuit 66c: Third half-wave rectifier circuit 67: Zero-cross signal generation circuit 68: Control circuit 450: Heater L1: Neutral side transmission line L2: Live side transmission line L3: AC detection line

Claims

1. a full-wave rectifier circuit that full-wave rectifies an AC voltage input from an external source; a smoothing circuit that smoothes the output voltage of the full-wave rectifier circuit; a first half-wave rectifier circuit that rectifies a voltage transmitted by a first single-side transmission line that is one of a neutral-side transmission line and a live-side transmission line that constitute a pair of AC transmission lines that transmit the AC voltage to the full-wave rectifier circuit; a second half-wave rectifier circuit and a third half-wave rectifier circuit that respectively rectify a voltage transmitted by a second single-side transmission line that is the other of the neutral-side transmission line and the live-side transmission line; a zero-cross signal generating circuit that generates a zero-cross signal representing a zero-cross timing of the AC voltage from output voltages of the first half-wave rectifier circuit and the second half-wave rectifier circuit; a voltage conversion circuit that operates when a voltage level of an AC detection line that is an output line of the third half-wave rectifier circuit exceeds a first reference level, and converts a primary voltage that is an output voltage of the smoothing circuit into a DC secondary voltage; a control circuit that transmits the output voltage of the first half-wave rectifier circuit to the AC detection line when the secondary voltage falls below a second reference level based on a voltage level of the AC detection line, and stops transmitting the output voltage of the first half-wave rectifier circuit to the AC detection line when the secondary voltage falls below the second reference level.

2. 2. The power supply circuit according to claim 1, wherein said voltage conversion circuit is a boost circuit.

3. a power supply circuit according to claim 1 or 2; a printing device that operates using power supplied from the power supply circuit and forms an image on a sheet.

Images