Display device feeder circuit and image forming apparatus

Abstract

To avoid a situation where a back face light emitting unit of a display device emits light after power supply is stopped.SOLUTION: A bypass capacitor 115 is connected to a voltage output line of a DC power supply circuit 111. A light emission voltage generation circuit 112 converts output voltage of the DC power supply circuit 111 into light emission voltage of DC to be supplied to a back face light emission unit 21b of a display device 21. A control element 13 operates with output voltage of a rectifier circuit 12, and controls the light emission voltage generation circuit 112. A first load 16 is electrically connected to the first bypass capacitor 115. A switch circuit 17 cuts off current from the bypass capacitor 115 to th first load 16 when AC voltage is input, and permits the current from the first bypass capacitor 115 to the first load 16 when the AC voltage is not input.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a display device power supply circuit that outputs a voltage to a rear light-emitting portion of a display device, and an image forming device including the same. [Background technology]

[0002] The image forming apparatus includes a display device such as a liquid crystal display device, and a display device power supply circuit that outputs a voltage to a rear light emitting portion of the display device.

[0003] It is also known that the display device includes a circuit that discharges residual charges in a plurality of light-emitting diodes arranged in a matrix (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-46088 Summary of the Invention [Problem to be solved by the invention]

[0005] The display device power supply circuit includes a plurality of bypass capacitors for stabilizing the output voltage.

[0006] When the power supply from the AC power source to the display device power supply circuit is unintentionally stopped due to a power outage or the like, some of the accumulated charges in the multiple bypass capacitors may flow into the circuit, causing the backlight emitting unit to emit light. If the backlight emitting unit continues to emit light after the power supply to the display device power supply circuit is stopped, this may cause anxiety or distrust in the user.

[0007] An object of the present invention is to provide a display device power supply circuit and an image forming device that can prevent the backlight emitting portion of the display device from emitting light after the power supply is stopped. [Means for solving the problem]

[0008] A display device power supply circuit according to one aspect of the present invention includes a DC power supply circuit, a rectifier circuit, a first bypass capacitor, a light-emitting voltage generation circuit, a control element, a first load, and a first switch circuit. The DC power supply circuit converts an input AC voltage into a DC voltage. The rectifier circuit rectifies the AC voltage. The first bypass capacitor is connected to a voltage output line of the DC power supply circuit. The light-emitting voltage generation circuit converts an output voltage of the DC power supply circuit into a DC light-emitting voltage supplied to a backlight-emitting portion of the display device. The control element operates according to the output voltage of the rectifier circuit and controls the light-emitting voltage generation circuit. The first load is electrically connected to the first bypass capacitor. The first switch circuit is electrically connected to the first bypass capacitor and blocks current from the first bypass capacitor to the first load when the AC voltage is input and allows current from the first bypass capacitor to the first load when the AC voltage is not input.

[0009] According to another aspect of the present invention, an image forming apparatus includes a printing device, a display device, and the display device power supply circuit. The printing device forms an image on a sheet. The display device has a backlight-emitting unit and is capable of displaying information related to the printing device. The display device power supply circuit outputs a light-emitting voltage to the backlight-emitting unit of the display device. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a display device power supply circuit and an image forming device that can prevent the backlight emitting portion of the display device from emitting light after the power supply is stopped. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus including a display device power supply circuit according to an embodiment. [Figure 2]FIG. 2 is a block diagram showing the configuration of the display device power supply circuit according to the embodiment. [Figure 3] FIG. 3 is a circuit diagram of a main part of a display device power supply circuit according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] [Configuration of image forming apparatus 10] The display device power supply circuit 100 according to the embodiment constitutes a part of the image forming device 10.

[0014] The image forming apparatus 10 includes a power supply 1, a human interface 2, a printing device 3, a communication device 4, and a control device 5 (see FIG. 1).

[0015] The power supply 1 converts the AC voltage supplied from the AC power supply 1000 into a DC voltage and supplies the DC voltage to the devices in the image forming apparatus 10. That is, the human interface 2, the printing device 3, the communication device 4, and the control device 5 operate using the power supplied from the power supply 1.

[0016] For example, the power supply 1 converts AC voltage supplied from an AC power supply 1000 into various DC voltages required by the printing device 3, the communication device 4, and the control device 5. The AC power supply 1000 is a commercial power supply.

[0017] The human interface 2 includes a display device 21 and an operation device 22. Each of the display device 21 and the operation device 22 operates using power supplied from a power source 1. The display device 21 is a liquid crystal display device having a liquid crystal display panel 21a and a rear light emitting unit 21b.

[0018] The power supply 1 includes a display device power supply circuit 100 that outputs a DC voltage to each of the liquid crystal display panel 21a and the backlight emission unit 21b (see FIG. 2). The display device power supply circuit 100 is mounted on a substrate 1x that constitutes a part of the power supply 1.

[0019] The display device 21 displays information relating to the printing device 3 and the communication device 4. For example, the display device 21 can display information relating to various printing parameters in the printing device 3, the progress of the printing process, various errors, and the like.

[0020] The operation device 22 is a device that accepts human operations. For example, the operation device 22 includes one or both of a touch panel and one or more operation buttons that are configured integrally with the display device 21. For example, the operation device 22 accepts an operation to specify information to be displayed on the display device 21, an operation to set the print parameters, and the like.

[0021] The printing device 3 feeds a sheet 9 from a sheet storage unit (not shown), and forms an image on the sheet 9 while further transporting the sheet 9 .

[0022] For example, the printing device 3 forms an image on the sheet 9 by electrophotography or inkjet printing. The sheet 9 is an image forming medium such as paper or a resin sheet.

[0023] The communication device 4 executes communication with other devices. For example, the communication device 4 receives print job data from a host device (not shown) via a network such as a LAN (Local Area Network), and transmits the print job data to the control device 5.

[0024] The control device 5 controls various devices within the image forming apparatus 10, including the display device 21, the printing device 3, and the communication device 4.

[0025] The control device 5 includes a CPU (Central Processing Unit) 5a, a secondary storage device 5b, a signal interface 5c, etc. The CPU 5a executes computer programs stored in the secondary storage device 5b to perform various controls and data processing.

[0026] The secondary storage device 5b is a computer-readable non-volatile storage device. The secondary storage device 5b stores various data such as the computer program and the print job data. For example, a flash memory or a hard disk drive, or both, may be used as the secondary storage device 5b.

[0027] The signal interface 5c converts the detection signals of various sensors into digital detection data. The detection data is transmitted to the CPU 5a. Furthermore, the signal interface 5c converts various control commands output from the CPU 5a into control signals and transmits the control signals to the controlled devices.

[0028] Incidentally, the display device power supply circuit 100 includes a plurality of bypass capacitors for stabilizing the output voltage.

[0029] When the power supply from the AC power source 1000 to the display device power supply circuit 100 is stopped unintentionally due to a power outage or the like, some of the accumulated charges in the multiple bypass capacitors flow to the backlight-emitting unit 21b. If the backlight-emitting unit 21b continues to emit light after the power supply to the display device power supply circuit 100 is stopped, this may cause anxiety or distrust in the user.

[0030] The display device power supply circuit 100 has a configuration for preventing the rear light emitting section 21b of the display device 21 from emitting light after the power supply is stopped. This configuration will be described below.

[0031] The display device power supply circuit 100 includes a constant voltage circuit 11, a rectifier circuit 12, and a control element 13 (see FIG. 2). The constant voltage circuit 11 includes a DC power supply circuit 111, a light-emitting voltage generating circuit 112, and a first bypass capacitor 115.

[0032] Furthermore, the display device power supply circuit 100 includes a second bypass capacitor 14 , and the constant voltage circuit 11 includes a control voltage generating circuit 113 .

[0033] The DC power supply circuit 111 converts an AC voltage input via the voltage input line 101 into a DC voltage and outputs the DC voltage. The first bypass capacitor 115 is connected to the voltage output line 102 of the DC power supply circuit 111 and a ground. The first bypass capacitor 115 stabilizes the output voltage of the DC power supply circuit 111.

[0034] The light-emitting voltage generating circuit 112 converts the output voltage of the DC power supply circuit 111 into a light-emitting voltage. The light-emitting voltage is a DC voltage supplied to the rear light-emitting unit 21b of the display device 21. For example, the light-emitting voltage is a voltage of 24 volts.

[0035] The control voltage generation circuit 113 converts the output voltage of the DC power supply circuit 111 into a control voltage. The control voltage is a DC voltage supplied to various control circuits including the control element 13. The control voltage is a voltage lower than the light-emitting voltage. For example, the control voltage is a voltage of 5 volts.

[0036] The rectifier circuit 12 rectifies the output voltage of the DC power supply circuit 111 and supplies the rectified voltage as an operating voltage to the control element 13. The control element 13 operates when supplied with the operating voltage.

[0037] That is, the operating voltage output from the DC power supply circuit 111 and the control voltage generated by the control voltage generating circuit 113 are supplied to the control element 13 .

[0038] The control element 13 controls the light-emitting voltage generation circuit 112. Specifically, the control element 13 receives a feedback signal representing the level of the output voltage of the light-emitting voltage generation circuit 112. Furthermore, the control element 13 outputs a level control signal to the light-emitting voltage generation circuit 112 according to the difference between the level of the feedback signal and a target level.

[0039] The light-emitting voltage generating circuit 112 adjusts the level of the output voltage in accordance with the level control signal, thereby maintaining the light-emitting voltage at the target level. Furthermore, the control element 13 controls the light-emitting voltage generating circuit 112 to start and stop outputting the light-emitting voltage.

[0040] The second bypass capacitor 14 is connected to the input line of the control voltage to the control element 13 and to the ground. The second bypass capacitor 14 stabilizes the control voltage input to the control element 13.

[0041] If the power supply from the AC power supply 1000 is stopped and the accumulated charge in the first bypass capacitor 115 flows to the control element 13 through the rectifier circuit 12, the control element 13 may activate the light-emitting voltage generating circuit 112. In this case, the light-emitting voltage may be output to the backlight-emitting unit 21b, causing the backlight-emitting unit 21b to emit light.

[0042] Similarly, if the electric charge stored in the second bypass capacitor 14 flows to the control element 13 when the power supply from the AC power supply 1000 is stopped, the control element 13 may activate the light-emitting voltage generating circuit 112. In this case, the light-emitting voltage may be output to the backlight-emitting unit 21b, causing the backlight-emitting unit 21b to emit light.

[0043] Therefore, the display device power supply circuit 100 includes a discharge circuit 15. The discharge circuit 15 discharges the first bypass capacitor 115 and consumes the charge stored in the first bypass capacitor 115 when the power supply from the AC power source 1000 is stopped.

[0044] Furthermore, when the power supply from the AC power supply 1000 is stopped, the discharge circuit 15 causes the second bypass capacitor 14 to discharge, thereby consuming the charge stored in the second bypass capacitor 14.

[0045] Next, specific examples of the DC power supply circuit 111, the rectifier circuit 12, and the discharge circuit 15 will be described with reference to FIG.

[0046] The DC power supply circuit 111 includes a rectifier circuit 111a and a voltage stabilizing capacitor 111b. The rectifier circuit 111a rectifies the AC voltage input through the voltage input line 101.

[0047] The voltage output line 102 of the DC power supply circuit 111 includes a first DC output line 102a and a second DC output line 102b. The capacitor 111b is connected to the first DC output line 102a and the second DC output line 102b, and keeps the voltage rectified by the rectifier circuit 111a constant.

[0048] The first bypass capacitor 115 is connected to the second DC output line 102b and the ground.

[0049] The voltage input line 101 includes a first AC input line 101a and a second AC input line 101b. The second AC input line 101b is electrically connected to a second DC output line 102b.

[0050] The rectifier circuit 12 includes one or more first diodes 121 and one or more second diodes 122. In the example shown in FIG. 3, the rectifier circuit 12 includes one first diode 121 and two second diodes 122.

[0051] The input terminal of the first diode 121 is connected to the first AC input line 101a, and the input terminal of the second diode 122 is connected to the second AC input line 101b. The output terminals of the first diode 121 and the second diode 122 are electrically connected to the input terminal of the control element 13 for the operating voltage.

[0052] When the supply of the AC voltage from the AC power supply 1000 is stopped, if the accumulated charge in the first bypass capacitor 115 flows to the control element 13 through the second diode 122, the control element 13 may activate the light-emitting voltage generating circuit 112.

[0053] Similarly, if the charge stored in the second bypass capacitor 14 flows to the control element 13 when the power supply from the AC power supply 1000 is stopped, the control element 13 may activate the light-emitting voltage generating circuit 112.

[0054] The discharge circuit 15 includes a first load 16 and a first switch circuit 17. The discharge circuit 15 further includes a second load 18 and a second switch circuit 19.

[0055] The first load 16 is electrically connected to the first bypass capacitor 115 and the ground. In other words, the first load 16 is electrically connected to the second DC output line 102b and the ground.

[0056] The first load 16 is a load that consumes the charge stored in the first bypass capacitor 115. In this embodiment, the first load 16 is two resistive elements electrically connected in series.

[0057] The first switch circuit 17 is electrically connected to the voltage input line 101 of the DC power supply circuit 111. More specifically, the first switch circuit 17 is electrically connected to a first AC input line 101a of the voltage input line 101.

[0058] The first switch circuit 17 selectively switches between a first discharge prevention state and a first discharge permission state depending on whether the AC voltage is supplied to the voltage input line 101 or not.

[0059] The first discharge blocking state is a state in which current from the first bypass capacitor 115 to the first load 16 is blocked. The first discharge allowing state is a state in which current from the first bypass capacitor 115 to the first load 16 is allowed.

[0060] The current flowing from the first bypass capacitor 115 to the first load 16 is a current flowing due to the first bypass capacitor 115 discharging the accumulated charge.

[0061] First switch circuit 17 is in the first discharge-preventing state when the AC voltage is input to display power supply circuit 100 through voltage input line 101. On the other hand, first switch circuit 17 is in the first discharge-permitting state when the AC voltage is not input to display power supply circuit 100 through voltage input line 101.

[0062] In this embodiment, the first switch circuit 17 includes a voltage dividing circuit 171, a half-wave rectifying circuit 172, a field effect transistor 173, and the like.

[0063] Voltage divider circuit 171 divides the voltage of voltage input line 101 using two resistor elements. Half-wave rectifier circuit 172 half-wave rectifies the voltage at connection point 171a of the two resistor elements in voltage divider circuit 171. Field-effect transistor 173 operates when the output voltage of half-wave rectifier circuit 172 exceeds an operating level.

[0064] When the field-effect transistor 173 is in operation, it electrically connects the connection point 16a of the two resistor elements that make up the first load 16 to the ground, thereby blocking the current from the first bypass capacitor 115 to the first load 16.

[0065] On the other hand, when the field effect transistor 173 is not operating, it electrically disconnects the connection point 16a from the ground, thereby allowing a current to flow from the first bypass capacitor 115 to the first load 16.

[0066] That is, when the AC voltage is input to the DC power supply circuit 111, the charge stored in the first bypass capacitor 115 does not flow to the first load 16. On the other hand, when the AC voltage is not input to the DC power supply circuit 111, the charge stored in the first bypass capacitor 115 flows to the first load 16.

[0067] The second load 18 is electrically connected to the second bypass capacitor 14. Furthermore, the second load 18 is electrically connected to the ground via a second switch circuit 19. The second load 18 is a load that consumes the charge stored in the second bypass capacitor 14. In this embodiment, the second load 18 is a single resistive element.

[0068] The second switch circuit 19 selectively switches between a second discharge-preventing state and a second discharge-permitting state depending on whether or not a current flows from the first bypass capacitor 115 to the first load 16 .

[0069] The second discharge blocking state is a state in which current from the second bypass capacitor 14 to the second load 18 is blocked. The second discharge allowing state is a state in which current from the second bypass capacitor 14 to the second load 18 is allowed.

[0070] The second switch circuit 19 is in the second discharge element state when no current flows from the first bypass capacitor 115 to the first load 16. On the other hand, the second switch circuit 19 is in the second discharge-permitted state when a current flows from the first bypass capacitor 115 to the first load 16.

[0071] In this embodiment, the second switch circuit 19 is a photocoupler that operates with a current flowing from the first bypass capacitor 115 to the first load 16. The current flowing from the first bypass capacitor 115 to the first load 16 is the base current of the photocoupler.

[0072] When the photocoupler is in operation, it electrically connects the second load 18 to the ground, causing the charge stored in the second bypass capacitor 14 to flow to the second load 18.

[0073] On the other hand, when the photocoupler is not in operation, it electrically isolates the second load 18 from the ground, thereby preventing the charge stored in the second bypass capacitor 14 from flowing to the second load 18.

[0074] By employing the display device power supply circuit 100, the accumulated charges in the first bypass capacitor 115 and the second bypass capacitor 14 are prevented from flowing to the control element 13 when the power supply from the AC power source 1000 is stopped.

[0075] That is, it is possible to prevent the rear light emitting portion 21b of the display device 21 from emitting light after the power supply is stopped.

[0076] [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.

[0077] <Appendix 1> a DC power supply circuit that converts an input AC voltage into a DC voltage; a rectifier circuit that rectifies the AC voltage; a first bypass capacitor connected to a voltage output line of the DC power supply circuit; a light-emitting voltage generating circuit that converts the output voltage of the DC power supply circuit into a DC light-emitting voltage that is supplied to a rear light-emitting unit of the display device; a control element that operates by the output voltage of the rectifier circuit and controls the light-emitting voltage generation circuit; a first load electrically connected to the first bypass capacitor; a first switch circuit electrically connected to the first bypass capacitor, blocking current from the first bypass capacitor to the first load when the AC voltage is being input, and allowing current to flow from the first bypass capacitor to the first load when the AC voltage is not being input.

[0078] <Appendix 2> a control voltage generating circuit that converts an output voltage of the DC power supply circuit into a control voltage that is supplied to the control element; a second bypass capacitor connected to an input line of the control voltage to the control element; a second load electrically connected to the second bypass capacitor; a second switch circuit that blocks current from the second bypass capacitor to the second load when no current is flowing from the first bypass capacitor to the first load, and allows current to flow from the second bypass capacitor to the second load when current is flowing from the first bypass capacitor to the first load.

[0079] <Appendix 3> 3. The display device power supply circuit according to claim 2, wherein the second switch circuit includes a photocoupler that operates in response to a current flowing from the first bypass capacitor to the first load.

[0080] <Appendix 4> a printing device for forming an image on a sheet; a display device having a rear light emitting portion and capable of displaying information about the printing device; An image forming apparatus comprising: a display device power supply circuit according to any one of Supplementary Note 1 to Supplementary Note 3, which outputs a light-emitting voltage to the rear light-emitting portion of the display device. [Explanation of symbols]

[0081] 1:Power supply 1x: PCB 3: Printing device 10: Image forming device 11: Constant voltage circuit 12: Rectifier circuit 13: Control element 14: Second bypass capacitor 16 :1st load 17: First switch circuit 18 :Second load 19: Second switch circuit 21:Display device 21a: Liquid crystal display panel 21b: Rear light emitting part 100: Display device power supply circuit 101: Voltage input line 102: Voltage output line 111:DC power supply circuit 112: Light-emitting voltage generation circuit 113: Control voltage generation circuit 115: First bypass capacitor 171: Voltage divider circuit 172: Half-wave rectifier circuit 173: Field effect transistor

Claims

1. a DC power supply circuit that converts an input AC voltage into a DC voltage; a rectifier circuit that rectifies the AC voltage; a first bypass capacitor connected to a voltage output line of the DC power supply circuit; a light-emitting voltage generating circuit that converts the output voltage of the DC power supply circuit into a DC light-emitting voltage that is supplied to a rear light-emitting unit of the display device; a control element that operates by the output voltage of the rectifier circuit and controls the light-emitting voltage generation circuit; a first load electrically connected to the first bypass capacitor; a first switch circuit electrically connected to the first bypass capacitor, blocking current from the first bypass capacitor to the first load when the AC voltage is being input, and allowing current to flow from the first bypass capacitor to the first load when the AC voltage is not being input.

2. a control voltage generating circuit that converts an output voltage of the DC power supply circuit into a control voltage that is supplied to the control element; a second bypass capacitor connected to an input line of the control voltage to the control element; a second load electrically connected to the second bypass capacitor; a second switch circuit that blocks current from the second bypass capacitor to the second load when no current is flowing from the first bypass capacitor to the first load, and that allows current to flow from the second bypass capacitor to the second load when current is flowing from the first bypass capacitor to the first load.

3. 3. The display device power supply circuit according to claim 2, wherein the second switch circuit includes a photocoupler that operates in response to a current flowing from the first bypass capacitor to the first load.

4. a printing device for forming an image on a sheet; a display device having a rear light emitting portion and capable of displaying information about the printing device; An image forming apparatus comprising: a display device power supply circuit according to claim 1 , which outputs a light-emitting voltage to the rear light-emitting portion of the display device.

Images