Power supply device and image forming apparatus

Abstract

To achieve transition to a safe state before a power source device breaks down and to notify a user of the occurrence of an abnormality.SOLUTION: A power supply unit 120 converts AC voltage to DC voltage and at least can switch between a first mode outputting first DC voltage and a second mode outputting second DC voltage lower than the first DC voltage. The power supply unit 120 has a CPU 223 which switches between the first mode and the second mode and determines an over-current state where an overcurrent is generated. When the CPU 223 determined the over-current state, it controls so as to switch to the second mode and report that the power supply unit 120 is in the over-current state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power supply device and an image forming apparatus, and more particularly to a configuration for protecting a power supply device mounted in an image forming apparatus such as a copying machine, a facsimile machine, or a printer from an overload / overcurrent state. [Background technology]

[0002] Image forming devices, such as copiers, facsimiles, and printers, that form images on recording materials using electrophotographic processes and other processes are equipped with power supplies that generate DC voltages from AC power sources and supply the power necessary for transporting recording materials and forming images. These power supplies often output at least two DC voltages, one of which outputs a relatively low voltage necessary for control elements such as CPUs and ASICs and control circuits. The other outputs a relatively high voltage necessary for the electrophotographic process and for actuators such as motors and solenoids. Power supply configurations include those with multiple AC-DC converters and those with a single AC-DC converter that outputs a relatively high voltage, which is then used to generate a relatively low voltage necessary for the control circuitry via a DC-DC converter. Given the current demand for cost reduction, power supply configurations that use only a single, costly AC-DC converter are widely adopted, and further simplification and cost reduction are required.

[0003] Such power supply devices have traditionally been provided with a protection circuit that stops operation of the power supply device when the output reaches an overcurrent state, thereby protecting the power supply device from failure. The power supply device enters an overcurrent state when a device to which the power supply device supplies power consumes more power than expected, or when a short circuit or other fault occurs in the power supply path. In this case, the power supply device detects the overcurrent state and stops output to prevent failure or other faults from occurring. For example, Patent Document 1 proposes a power supply device with a protection function that stops switching control of a switching element by a primary-side control circuit when an abnormality occurs, such as an excessive current flowing in the output due to a load short or other fault. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-058166 Summary of the Invention [Problem to be solved by the invention]

[0005] However, especially in a power supply device with only one AC-DC converter, if the AC-DC converter enters an overload state and the protection circuit activates, shutting down the output, the following situation occurs: The DC-DC converter connected to that output also shuts down, causing the device equipped with the power supply device, such as an image forming device, to shut down completely. In this case, the user may not understand why the image forming device suddenly shut down. Furthermore, if the power supply device is in an overload state but an excessive current continues to flow to the extent that the overcurrent protection function does not activate, the overload may cause the internal components of the power supply to overheat and potentially be destroyed. In this case, the power supply device will also suddenly shut down due to damage caused by the overcurrent. This leaves the user confused as to why the image forming device suddenly shut down, and they may end up exacerbating the damage by turning the power switch back on again.

[0006] The present invention has been made under these circumstances, and has as its object to transition the power supply device to a safe state before it is destroyed, and to notify the user that an abnormality has occurred. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention has the following configuration. (1) A power supply device including a conversion means for converting AC voltage to DC voltage, and capable of switching at least between a first mode for outputting a first DC voltage and a second mode for outputting a second DC voltage lower than the first DC voltage, the power supply device including: a switching means for switching between the first mode and the second mode; and a determination means for determining that an overcurrent state has occurred in the conversion means. a display means for displaying information; When the determining means determines that the overcurrent state exists, the switching means switches to the second mode, The display unit displays information about the overcurrent state in the conversion means. and a control means. (2) An image forming apparatus including a power supply device that includes a conversion means for converting AC voltage to DC voltage and that can switch between at least a first mode for outputting a first DC voltage and a second mode for outputting a second DC voltage lower than the first DC voltage, the image forming apparatus including: a switching means for switching between the first mode and the second mode; and a determination means for determining that an overcurrent state has occurred in the conversion means. a display means for displaying information; When the determining means determines that the overcurrent state exists, the switching means switches to the second mode, The display unit displays information about the overcurrent state in the conversion means. and a control unit. [Effects of the Invention]

[0008] According to the present invention, the power supply device can be transitioned to a safe state before it is destroyed, and the user can be notified that an abnormality has occurred. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a diagram showing a configuration of an image forming apparatus according to a first embodiment; [Figure 2] FIG. 1 is a diagram showing the configuration of a power supply unit and an engine controller according to a first embodiment. [Figure 3] Flowchart showing the control of the first embodiment [Figure 4] FIG. 10 is a diagram showing the configuration of a power supply unit and an engine controller according to a second embodiment. [Figure 5] Flowchart showing the control of the second embodiment DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail by way of examples with reference to the accompanying drawings. [Example]

[0011] [Image forming equipment] Hereinafter, an embodiment of the power supply device of the present invention implemented in an image forming apparatus will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the schematic configuration of an image forming apparatus using an electrophotographic process. In the first embodiment, a laser beam printer will be described as an example of the image forming apparatus. However, the image forming apparatus may also be a copier, a facsimile, or a combination machine thereof. Furthermore, the power supply device of the present invention may be installed in other electronic devices. A laser beam printer main body 101 (hereinafter referred to as the main body 101) shown in FIG. 1 includes a paper feed cassette 104 that stores recording material S, a paper feed roller 141 that feeds the recording material S from the paper feed cassette 104, and a pair of conveying rollers 142. Furthermore, the main body 101 includes, downstream of the pair of conveying rollers 142, a top sensor 143 that detects the leading edge of the recording material S and a pair of registration rollers (hereinafter referred to as registration rollers) 144 that synchronously convey the recording material S. Furthermore, the main body 101 includes, downstream thereof, a cartridge unit 105 that forms a toner image on the recording material S based on laser light emitted from a laser scanner 106. The cartridge unit 105 has a photosensitive drum 148, a primary charging roller 147, a developing roller 146, and the like, which are necessary for a known electrophotographic process, and together with a transfer roller 145, forms a toner image on the recording material S. The main body 101 has a heat fixing device 103 downstream thereof for thermally fixing the unfixed toner image formed on the recording material S. The heat fixing device 103 has a fixing film 149, a pressure roller 150, and a heater 102 arranged inside the fixing film 149. The heat fixing device 103 has a thermistor 109 arranged near the heater 102 so as to detect the temperature of the heater 102 within the fixing film 149. The main body 101 also has a pair of discharge rollers 151 downstream thereof, and discharges the recording material S after the toner image has been formed and thermally fixed.

[0012] The power supply unit 120 (details to be described later) is a power supply device that can switch between outputting a voltage of 24V or 5V as needed, generating a 24V voltage in print mode or standby mode. Here, print mode refers to a state in which an image can be formed on a recording material S, and standby mode refers to a state in which the printer is on standby and consumes less power than print mode, waiting for a print instruction to transition to print mode. There is also a sleep mode in which the printer operates the minimum functions of the main body 101 to further conserve power. The power supply unit 120 supplies a 24V voltage as a drive system voltage via an engine controller 123 (details to be described later). The drive system voltage is a voltage supplied to, for example, drive units such as motors and clutches (not shown), a high-voltage power supply (not shown) for supplying high voltage to the cartridge unit 105, and a drive unit (not shown) for the rotating polygon mirror of the laser scanner 106.

[0013] The engine controller 123 controls the main body 101 and controls the drive unit (not shown) to operate each roller and control the conveyance of the recording material S. The engine controller 123 also controls the laser scanner 106, cartridge unit 105, heat fixing unit 103, etc. to perform an image formation (hereinafter referred to as printing) operation. The engine controller 123 also includes a DC-DC converter 121 (described later), which generates a voltage of 3.3V, which is mainly used in the control system, based on the voltage supplied from the power supply unit 120. The DC-DC converter 121 may be provided outside the engine controller 123. The 3.3V voltage generated by the DC-DC converter 121 is supplied to a control circuit (not shown) inside the engine controller 123. The 3.3V voltage is further supplied to a control system circuit including a video controller 131 (described later), a laser light emitting unit (not shown) of the laser scanner 106, a top sensor 143, etc. The video controller 131 is connected to the engine controller 123 via an engine interface 133, and is also connected to an external device 132 such as a personal computer via a general-purpose interface 134 (for example, USB).

[0014] The power supply unit 120 detects the zero-cross timing of an AC power supply 201 (see FIG. 2), which will be described later, and transmits a zero-cross detection signal (not shown) to the engine controller 123. The engine controller 123 then controls a heater switching means (not shown) so that the power from the AC power supply 201 is synchronized with the zero-cross timing and has a predetermined phase angle or wave number duty ratio, thereby controlling the heater 102 to a predetermined temperature.

[0015] The video controller 131 receives print information (for example, the number of copies to be printed and various settings) and print data from the general-purpose interface 134. The video controller 131 is equipped with an internal image control unit (not shown) and converts the print data into image data that can actually be printed. Thereafter, the engine controller 123 receives the image data from the video controller 131 via the engine interface 133 at a predetermined timing and transmits it to the laser scanner 106. In the image forming operation, members that contribute to forming an image on the recording material S function as image forming means.

[0016] [Power supply unit] FIG. 2 is a diagram showing the configuration of a power supply unit 120 and an engine controller 123 (controller) that are the power supply device of the first embodiment. An AC power supply 201 is connected to the power supply unit 120, which generates a DC voltage Vo2 from an input AC voltage and outputs it to the secondary side. Herein, the DC voltage Vo2 has at least two output voltage values: a first DC voltage of 24 V and a second DC voltage of 5 V that is lower than the first DC voltage. For example, when the main body 101 is in print mode or standby mode (a standby state in which immediate printing is possible), the DC voltage Vo2 is output at 24 V. Hereinafter, the state in which the DC voltage Vo2 is 24 V is referred to as a first voltage output mode (first mode). On the other hand, when the main body 101 is in sleep mode (power-saving mode), the DC voltage Vo2 is output at 5 V. Hereinafter, the state in which the DC voltage Vo2 is 5 V is referred to as a second voltage output mode (second mode). The engine controller 123 has a CPU 223 as a control means, and the CPU 223 switches the DC voltage Vo2. The CPU 223 functions as a switching means for switching between the first mode and the second mode. Note that the CPU 223 provided in the printer main body 101 may be integrated into a power supply board (not shown), so that the power supply unit 120 has the CPU 223.

[0017] The AC voltage of the AC power supply 201 input to the power supply unit 120 is rectified by a bridge diode 204 and then smoothed by a capacitor 210 to become a DC voltage with the DCL line as the negative polarity and the DCH line as the positive polarity. The DCH line is connected to one of two terminals of a primary winding 205a of a power transformer 205 (hereinafter referred to as a transformer), and is also connected to a VH terminal of a power supply IC 222 via a resistor 230, to supply voltage. The power supply IC 222 starts operating when a voltage is applied to the VH terminal. In FIG. 2, the side of the primary winding 205a and primary auxiliary winding 205b of the transformer 205 is referred to as the primary side, and the side of the secondary winding 205c is referred to as the secondary side.

[0018] A field effect transistor (hereinafter referred to as FET) 243, which is a switching element, has its drain terminal connected in series to the other terminal of the primary winding 205a and its source terminal connected to the DCL line via a current detection resistor 241. The gate terminal of the FET 243 is connected to an OUT terminal of the power supply IC 222 via a gate resistor 242. The power supply IC 222 controls the on / off (hereinafter referred to as ON / OFF) of the FET 243, causing a current to flow through the primary winding 205a. The current flowing through the primary winding 205a is converted into a voltage by the current detection resistor 241 and input to an IS terminal of the power supply IC 222. The power supply IC 222 monitors the voltage of the IS terminal and controls the current flowing through the primary winding 205a and the FET 243 so that it falls within a predetermined current range.

[0019] When a current flows through the primary winding 205a, a flyback voltage of opposite polarity is induced in the primary auxiliary winding 205b and the secondary winding 205c. The voltage induced in the primary auxiliary winding 205b is rectified and smoothed via a resistor 233, a diode 234, and a capacitor 235 to output a voltage Vcc. This voltage Vcc is then supplied to a Vcc terminal as a power supply for the power supply IC 222. The voltage induced in the secondary winding 205c is rectified by a secondary-side rectifier diode 251, which serves as a rectifier element, and then smoothed by a secondary-side smoothing capacitor 252, which serves as smoothing means, to be output as a DC voltage Vo2. The bridge diode 204, the capacitor 210, the transformer 205, the FET 243, the power supply IC 222, the secondary-side rectifier diode 251, and the secondary-side smoothing capacitor 252 function as a conversion means for converting an AC voltage into a DC voltage.

[0020] (feedback circuit) Next, the feedback circuit 224 will be described. The feedback circuit 224 is composed of resistors 253, 254, 255, 256, 257, a shunt regulator 258, an FET 259, a photocoupler 206, and a capacitor 207. The feedback circuit 224 monitors the DC voltage Vo2 and feeds back the DC voltage Vo2 as an FB signal from the secondary-side circuit to the FB terminal of the power supply IC 222 on the primary side via the photocoupler 206 so that the DC voltage Vo2 is 5 V or 24 V. The power supply IC 222 controls the ON / OFF of the FET 243 based on the voltage corresponding to the FB signal input to the FB terminal so that the DC voltage Vo2 is a predetermined voltage. In addition, a 5V / 24V signal is input to the feedback circuit 224 from the engine controller 123, and the output voltage is switched by the 5V / 24V signal so that the DC voltage Vo2 is 5 V or 24 V. The feedback circuit 224 performs feedback so that the DC voltage Vo2 becomes 5V when the 5V / 24V signal is at a high level, and becomes 24V when the 5V / 24V signal is at a low level, for example.

[0021] Resistors 253, 254, and 256 are connected in series between the DC voltage Vo2 and ground (hereinafter referred to as Gnd), and a FET 259 is connected in parallel to the resistor 256. That is, the drain terminal of the FET 259 is connected to the connection point between the resistors 254 and 256, and the source terminal is connected to Gnd on the secondary side. Furthermore, a 5V / 24V signal is input from the engine controller 123 to the gate terminal of the FET 259.

[0022] The anode terminal of the photodiode 206a of the photocoupler 206 is connected to the DC voltage Vo2 via a resistor 255, and the cathode terminal is connected to the cathode terminal of the shunt regulator 258. The resistor 257 connected in parallel with the photodiode 206a of the photocoupler 206 is a resistor for bypassing leakage current from the shunt regulator 258. The anode terminal of the shunt regulator 258 is connected to the Gnd of the DC voltage Vo2, and the reference terminal is connected to the junction of the resistors 253 and 254. The collector terminal of the phototransistor 206b of the photocoupler 206 is connected to the FB terminal of the power supply IC 222 as the FB signal, and the emitter terminal is connected to the DCL line. The capacitor 207 is a noise-absorbing capacitor provided for the FB signal and is connected between the FB terminal of the power supply IC 222 and the DCL line.

[0023] Next, a method in which the feedback circuit 224 switches the DC voltage Vo2 between 24V and 5V will be described. When the 5V / 24V signal output from the engine controller 123 is at a high level, the FET 259 is turned ON. At this time, the voltage obtained by dividing the DC voltage Vo2 by resistors 253 and 254 is input to the reference terminal of the shunt regulator 258. Then, feedback is provided to the FB terminal of the power supply IC 222 via the photocoupler 206 so that the voltage at the reference terminal of the shunt regulator 258 becomes the same as the internal reference voltage. As a result, the DC voltage Vo2 is controlled to 5V. Furthermore, when the 5V / 24V signal is at a low level, the FET 259 is turned OFF. At this time, the voltage obtained by dividing the DC voltage Vo2 by resistors 253, 254, and 256 is input to the shunt regulator 258. Then, feedback is provided to the FB terminal of the power supply IC 222 via the photocoupler 206 so that the reference terminal of the shunt regulator 258 becomes the same voltage as the internal reference voltage, and as a result, the DC voltage Vo2 is controlled to 24V.

[0024] (engine controller, etc.) The engine controller 123 is equipped with a CPU 223 and a DC-DC converter 121. The DC voltage Vo2 output from the power supply unit 120 is connected from the engine controller 123 to the aforementioned drive unit, high-voltage power supply (both not shown), etc., together with a control signal (not shown) output from the CPU 223. In the sleep mode, the DC voltage Vo2 becomes 5V. Therefore, in order to prevent 5V from being unnecessarily supplied to the drive unit, etc., a switch or the like for blocking the supply of the DC voltage Vo2 in the sleep mode may be provided.

[0025] A 5V / 24V signal is output from the engine controller 123 to the power supply unit 120. The 5V / 24V signal is output from the Port201 terminal of the CPU 223 via a resistor 264, and the high level / low level is input to the power supply unit 120. The CPU 223 switches the DC voltage Vo2 to 5V or 24V by switching the Port201 terminal between high level and low level.

[0026] The DC voltage Vo2 output from the power supply unit 120 is input to the engine controller 123. The DC voltage Vo2 is also input to the DC-DC converter 121 which is a generating means. The DC-DC converter 121 outputs a voltage Vo which is a third DC voltage lower than the DC voltage Vo2 (Vo < Vo2). Here, the DC-DC converter 121 operates to output a predetermined voltage Vo (for example, 3.3V) regardless of whether the input DC voltage Vo2 is 24V or 5V. And the voltage Vo is supplied to the control system circuits including the CPU 223, control circuit (not shown), video controller 131, laser emitting part of the laser scanner 106 (not shown), top sensor 143, etc. inside the engine controller 123 as described above.

[0027] Thermistor 208 (temperature detection means), which is a temperature detection element, is located in power supply unit 120 and is disposed near transformer 205 (here, secondary winding 205c of transformer 205), which is an element that generates heat due to an increase in load current, and secondary-side rectifier diode 251. One terminal of thermistor 208 is connected to Gnd on the secondary side, and the other terminal is input as a TH signal to A / D 201 terminal, which is an A / D port of CPU 223 on engine controller 123. The TH signal is then pulled up by pull-up resistor 209 on engine controller 123.

[0028] When the main body 101 is in standby mode or print mode (when the 5V / 24V signal is at a low level), the CPU 223 monitors the TH signal and determines whether the temperature detected by the thermistor 208 is within a normal range. If the temperature detected by the thermistor 208 is equal to or lower than a predetermined temperature, the CPU 223 determines that the transformer 205 and secondary-side rectifier diode 251 are operating normally. The predetermined temperature is a temperature threshold value used by the CPU 223 to determine whether the CPU 223 is normal or abnormal. In this case, the CPU 223 determines that the load current of the power supply unit 120 is within a normal value.

[0029] On the other hand, if the temperature detected by the thermistor 208 is higher than a predetermined temperature, the CPU 223 determines that the load current of the power supply unit 120 has become abnormally high, causing the transformer 205 and the secondary-side rectifier diode 251 to reach an abnormal temperature. If the temperature detected by the thermistor 208 is higher than a predetermined threshold, the CPU 223 determines that an overcurrent state has occurred. The CPU 223 functions as a determination unit for determining that an overcurrent state has occurred. In this case, the CPU 223 transitions the 5V / 24V signal from low level to high level. The CPU 223 then notifies the video controller 131 that the load state of the main body 101 is abnormal. The video controller 131 displays, on the display panel 160 of the main body 101, information that the load state is abnormal (overload state), for example, information that the power supply unit 120 has an error. Furthermore, the video controller 131 may notify the external device 132 via the general-purpose interface 134 of information that the power supply unit 120 is in an overload state, and may cause a message indicating this to be displayed on the screen of the external device 132. Furthermore, the main body 101 may output a message indicating that the power supply unit 120 is in an overload state by printing it on the recording material S. This allows the CPU 223 to notify the user that the power supply unit 120 is in an abnormal state. In this way, in the first embodiment, when the CPU 223 determines that an overcurrent state exists, it switches to the second mode and controls to notify the user that the power supply unit 120 is in an overcurrent state.

[0030] [Abnormality detection and notification processing] Next, the control of the first embodiment will be described with reference to FIG. 3. When the power supply of the main body 101 is turned on, the processes from step (hereinafter referred to as S) 102 onward are executed. In S102, the power supply unit 120 starts up when a voltage is applied to the VH terminal of the power supply IC 222 in the power supply unit 120. At this time, the 5V / 24V signal is in a low level state. Therefore, the power supply unit 120 first enters a state in which the DC voltage Vo2 outputs 24V (first voltage output mode), and supplies the DC voltage Vo2 of 24V to the engine controller 123.

[0031] In S103, the engine controller 123 is started up in response to the supply of DC voltage Vo2 in S102, and the DC-DC converter 121 starts operating and outputs voltage Vo. As a result, voltage Vo is supplied to the CPU 223, and the CPU 223 starts operating. In S104, in response to the supply of voltage Vo in S103, the CPU 223 sets the 5V / 24V signal to low level and continues operation in print mode or standby mode (shown as standby / print mode). In S105, the CPU 223 monitors the state of the thermistor 208 and determines whether the temperature detected by the thermistor 208 is within a normal range. Specifically, the CPU 223 determines that the detected temperature is normal if it is equal to or lower than a predetermined temperature, and that the detected temperature is abnormal if it is higher than the predetermined temperature.

[0032] If the CPU 223 determines in S105 that the detected temperature is within a normal range, the process proceeds to S106; if it determines that the detected temperature is not within the normal range, the process proceeds to S108. In S106, the CPU 223 determines whether or not transition to sleep mode is possible. If the CPU 223 determines in S106 that transition to sleep mode is not possible, the process returns to S104. If the CPU 223 determines in S106 that transition to sleep mode is possible, the process proceeds to S107. In S107, the CPU 223 transitions the 5V / 24V signal to a high level to transition to sleep mode, and the process returns to S106.

[0033] In S108, the CPU 223 transitions the 5V / 24V signal to high level, switching the DC voltage Vo2 from 24V to 5V (5V output). The drop in DC voltage Vo2 significantly reduces the load current and the temperature. As a result, damage to the elements of the power supply unit 120 is avoided, and the DC voltage Vo2 can continue to be safely output. In S109, the CPU 223 displays information on a user interface, such as the display panel 160, that an abnormality has occurred in the output line of the power supply unit 120, including the main body 101, i.e., that an overload state has occurred, to notify the user. The CPU 223 then stops the operation of the power supply unit 120 and terminates the process. Note that before stopping the operation of the power supply unit 120, the state of the thermistor 208 may be monitored, and if the temperature returns to a normal range, the power supply unit 120 may continue to operate.

[0034] In the first embodiment, the thermistor 208 is disposed near elements that are likely to generate heat when an overcurrent load occurs on the secondary side, such as the secondary winding 205c of the transformer 205 and the secondary-side rectifier diode 251. However, the configuration is not limited to that shown in FIG. 2 . For example, the thermistor 208 may be disposed near elements that are more likely to increase in temperature in response to a load current, such as the primary-side FET 243 and the primary winding 205a of the transformer 205. However, when detecting elements on the primary side, it is necessary to consider insulation between the primary and secondary sides for safety. That is, the detection result by the temperature detection means on the primary side needs to be transmitted to the engine controller 123 on the secondary side using an insulated transmission means such as a photocoupler. In this way, the thermistor 208 may detect the temperature of at least one of the primary winding 205a, the secondary winding 205c, the FET 243, and the secondary-side rectifier diode 251. Furthermore, the elements whose temperatures are detected are not limited to the above-mentioned elements, and may be any elements that generate heat when a current flows through them (hereinafter referred to as heat-generating elements). For example, a load switch (not shown) provided on the secondary side, a resistor for current detection, and the like are also included in the heat generating elements.

[0035] In the first embodiment, the DC voltage Vo2 has two modes, 24 V and 5 V. However, the present invention is not limited to this. Depending on the configuration and application of the device, the present invention can be applied to systems with more than two different output voltage modes. That is, the power supply device may output two or more different voltages. In this case, the operation of switching to a lower voltage may be repeated multiple times depending on the amount of heat generated by the device, or the voltage to be switched to may be selected depending on the amount of heat generated. Furthermore, the threshold value for determining an abnormality (such as the normal temperature range) may be changed depending on the value of the DC voltage Vo2 to be switched to. For example, an abnormality may be determined at a lower temperature when the DC voltage Vo2 is 5 V than when it is 24 V. In this case, the CPU 223 may monitor the status of the thermistor 208 even when the power supply unit 120 is outputting 5 V as the DC voltage Vo2 (e.g., after the process of S107 in FIG. 3).

[0036] As described above, in the first embodiment, the load state of the power supply unit 120 is monitored by the thermistor 208, and whether or not an abnormal load has occurred is determined based on the detection result of the thermistor 208. If it is determined that an abnormal load has occurred, it is possible to prevent the elements of the power supply unit 120 from being destroyed and to switch to a voltage that is safe, thereby transitioning the mode. It is also possible to notify the user that the load state of the power supply unit 120 is abnormal. In this way, even if an abnormality occurs in the image forming apparatus or a device connected to it and the load current of the power supply unit becomes excessive, it is possible to keep the elements in the power supply unit safe and notify the user that an abnormality has occurred, while utilizing an existing configuration. As described above, according to the first embodiment, the power supply device can be transitioned to a safe state before it is destroyed, and the user can be notified that an abnormality has occurred. [Example]

[0037] [Power supply unit] Next, a second embodiment will be described with reference to the drawings. In the first embodiment described above, an example was described in which an overcurrent in the power supply unit 120 is detected by the thermistor 208, which is a temperature detection element. In the second embodiment, an example is described in which an overcurrent in the power supply unit 420 is detected by an overcurrent detection circuit 424 (current detection means) that detects a current flowing on the secondary side of the transformer 205. Note that the main configuration and operation are the same as those described in the first embodiment, so the same reference numerals are used and the description here will be omitted. Similarly, the power supply unit 120 and the engine controller 123 will be described as the power supply unit 420 and the engine controller 423, respectively. These will be described in detail below.

[0038] FIG. 4 is a diagram showing the configuration of a power supply unit 420 and an engine controller 423 of the second embodiment. Compared to FIG. 2, the power supply unit 120, engine controller 123, power supply IC 222, and CPU 223 are replaced with a power supply unit 420, engine controller 423, and a power supply CPU 422 and CPU 323, which are power supply control units. However, the main operations are almost the same. On the other hand, the thermistor 208 and pull-up resistor 209 are deleted, and an overcurrent detection circuit 424 is added, which are differences from the first embodiment. The following description will focus on these differences.

[0039] The power supply unit 420 generates a DC voltage Vo2 from the input AC voltage and outputs it to the secondary side. In the second embodiment, the DC voltage Vo2 is controlled by a power supply CPU 422 on the primary side. The DC voltage Vo2 is switched between 5V and 24V by a CPU 323 (control means) mounted on the engine controller 423. The AC voltage input to the power supply unit 420 is rectified and smoothed by a bridge diode 204 and a capacitor 210 to become a DC voltage for the DCL line / DCH line. This voltage is then divided by resistors 430, 431, and 432. A Zener diode 436 is connected in parallel to the resistor 432, and the voltage is clamped to a voltage Vcc and supplied to a Vcc terminal of the power supply CPU 422. The power supply CPU 422 starts operating when a voltage is applied to the Vcc terminal.

[0040] The power supply CPU 422 has a Port 403 terminal connected to the gate terminal of the FET 243 via a gate resistor 242, and controls the ON / OFF of the FET 243 by setting the Port 403 terminal to a high level or a low level. When a current flows through the primary winding 205a, the current is converted to a voltage by a current detection resistor 241 and input to an A / D 401 terminal, which is an A / D port of the power supply CPU 422. The power supply CPU 422 monitors the voltage of the A / D 401 terminal and controls the current flowing through the primary winding 205a and the FET 243 to fall within a predetermined current range. When the power supply CPU 422 starts up and the FET 243 begins switching operation, a voltage is induced in the primary auxiliary winding 205b, and when the voltage begins to be output to the capacitor 235, the voltage Vcc is switched to be supplied from the primary auxiliary winding 205b. The FB signal output from the feedback circuit 224 is input to the A / D 402 terminal, which is an A / D port of the power supply CPU 422 .

[0041] (Overcurrent detection circuit) Next, the overcurrent detection circuit 424 will be described. The output stage of the DC voltage Vo2 is provided with a current detection resistor 408 for detecting the current flowing to the engine controller 423. The input side of the current detection resistor 408 is divided by resistors 410 and 411 on the engine controller 423, and the divided voltage Vc is input to the inverting input terminal (- terminal) of a comparator 412 also on the engine controller 423. The output side (DC voltage Vo2) of the current detection resistor 408 is input to the non-inverting input terminal (+ terminal) of the comparator 412 via resistor 413 also on the engine controller 423. The output terminal of the comparator 412 is input to the Port 401 terminal of the CPU 323 and is pulled up to the voltage Vo by a resistor 409.

[0042] When the current flowing through the engine controller 423 is within the normal range, the voltage drop due to the resistor 408 is small, and the DC voltage Vo2 is higher than the voltage Vc divided by the resistors 410 and 411 (Vo2 > Vc). Therefore, the output of the comparator 412 becomes high level and is input to the CPU 323. If the current flowing through the engine controller 423 is large beyond the normal range, the voltage drop due to the resistor 408 becomes large, and the DC voltage Vo2 becomes lower than the voltage Vc (Vo2 < Vc). Therefore, the output of the comparator 412 is inverted to the low level and is input to the Port 401 terminal of the CPU 323. The CPU 323 determines that it is in an overcurrent state when the DC voltage Vo2 is lower than the voltage Vc, that is, when the current detected by the overcurrent detection circuit 424 is larger than a predetermined threshold value. The CPU 323 determines whether the current value is normal or abnormal by monitoring the level of the Port 401 terminal.

[0043] When the DC voltage Vo2 is 5V, the difference ΔV between the voltage Vc divided by the resistors 410 and 411 and the DC voltage Vo2 5V is smaller than the difference ΔV when it is 24V 24V (ΔV 5V < ΔV 24V ). That is, when the DC voltage Vo2 is 5V, the output of the comparator 412 is inverted with a smaller output current than when it is 24V, and an abnormality is notified to the CPU 323. When the DC voltage Vo2 is 24V and a low level is input to the Port 401 terminal, the CPU 323 changes the Port 201 terminal from the low level to the high level and switches the DC voltage Vo2 from 24V to 5V. Also, when the DC voltage Vo2 is 5V and a low level is input to the Port 401 terminal, the CPU 323 switches the Port 402 terminal from the low level to the high level and changes the level of the Pstop signal.

[0044] (Pstop signal) The Pstop signal output from Port 402 of CPU 323 is input from engine controller 423 to power supply unit 420 and input to the anode terminal of photodiode 406a of photocoupler 406 via resistor 455. The cathode terminal of photodiode 406a is connected to the secondary side Gnd. The collector terminal of phototransistor 406b of photocoupler 406 is input to Port 404 terminal of power supply CPU 422 and is pulled up to voltage Vcc by resistor 456. The emitter terminal is connected to the DCL line. When the Pstop signal is at a low level, photodiode 406a of photocoupler 406 is turned off. The collector terminal of phototransistor 406b of photocoupler 406 becomes a high level, and Port 404 terminal of power supply CPU 422 becomes a high level. Since Port 404 terminal is at a high level, power supply CPU 422 determines that the power supply is normal and continues operating as is.

[0045] On the other hand, when the Pstop signal goes high, the photodiode 406a of the photocoupler 406 turns on, and the collector terminal of the phototransistor 406b of the photocoupler 406 goes low. When the power supply CPU 422 detects that the Port 404 terminal has transitioned to low, it determines that some abnormality has occurred and stops operation. In the second embodiment, when the CPU 323 determines that an overcurrent state exists in the second mode, it stops the power supply CPU 422.

[0046] [Abnormality detection and notification processing] Next, the control of the second embodiment will be described with reference to FIG. 5. When the power supply of the main body 101 is turned on, the processes from S202 onward are executed. In S202, the power supply unit 420 is started by applying a voltage to the Vcc terminal of the power supply CPU 422 in the power supply unit 420. At this time, since the 5V / 24V signal is in a low level state, the DC voltage Vo2, which is the output voltage of the power supply unit 420, becomes 24V and supplies the DC voltage Vo2 to the engine controller 423. In S203, the engine controller 423 is started by the supply of the DC voltage Vo2 in S202, the DC-DC converter 121 starts operating and outputs the voltage Vo, and the CPU 323 starts operating. In S204, the CPU 323 sets the 5V / 24V signal to a low level and continues operating in the print mode or standby mode.

[0047] In S205, the CPU 323 monitors the state of the overcurrent detection circuit 424 and determines whether the current is within a normal range. Specifically, the CPU 323 determines that the current is normal if the DC voltage Vo2 is equal to or higher than the voltage Vc, and determines that the current is abnormal if the DC voltage Vo2 is lower than the voltage Vc. If the CPU 323 determines that the current is within the normal range in S205, the process proceeds to S206. If the CPU 323 determines that the current is not within the normal range, the process proceeds to S209. In S206, the CPU 323 determines whether transition to sleep mode is possible. If the CPU 323 determines that transition to sleep mode is not possible in S206, the process returns to S204. If the CPU 323 determines that transition to sleep mode is possible, the process proceeds to S207. In S207, the CPU 323 transitions the 5V / 24V signal to a high level to transition to sleep mode. In S208, the CPU 323 monitors the state of the overcurrent detection circuit 424 and determines whether the current is within a normal range. If the CPU 323 determines in S208 that the current is within the normal range, it returns the process to S206, and if it determines that the current is not within the normal range, it advances the process to S209.

[0048] If the determination in S205 or S208 determines that the current exceeds the normal range and is abnormal, then in S209 the CPU 323 transitions the 5V / 24V signal to high level to switch the DC voltage Vo2 from 24V to 5V (5V output). The drop in DC voltage Vo2 from 24V to 5V significantly reduces the load current. In S210, the CPU 323 displays on a user interface, such as the display panel 160, that an abnormality has occurred in the output line of the power supply unit 420, including the main body 101, thereby notifying the user of an overload state. In S211, the CPU 323 monitors the status of the overcurrent detection circuit 424 and determines whether the current is within the normal range. If the CPU 323 determines that the current is within the normal range in S211, the process returns to S211; if the CPU 323 determines that the current exceeds the normal range and is abnormal, the process proceeds to S212. In S212, since the overcurrent condition is not resolved even though the DC voltage Vo2 is set to 5V output, the CPU 323 changes the Pstop signal from low level to high level to stop the operation of the power supply CPU 422, thereby stopping the power supply unit 420.

[0049] As described above, in the second embodiment, the two-stage protection function prevents damage to the elements of the power supply unit 420 and safely stops the DC voltage Vo2. In step S209 of FIG. 5, if an overcurrent is detected when the DC voltage Vo2 is outputting 24 V, the DC voltage Vo2 is switched from 24 V to 5 V. However, the operation of the power supply CPU 422 may be stopped without switching to 5 V. In this case, the overcurrent threshold for stopping operation may be set lower when the DC voltage Vo2 is 5 V than when it is 24 V. In this way, in the second embodiment, the predetermined threshold for the second mode may be set lower than the predetermined threshold for the first mode.

[0050] As described above, in the second embodiment, the load state of the power supply unit 420 is monitored, and if an abnormally increased load is detected, it is possible to prevent the elements of the power supply unit 420 from being destroyed and to transition the voltage to a safe state. Furthermore, when the DC voltage Vo2 of the power supply unit 420 reaches 5 V, which is the power saving (low voltage) mode, the overcurrent detection point (threshold) is set low. As a result, if the overcurrent value does not decrease even when the voltage is lowered, it is possible to safely stop operation and prevent element destruction. As described above, according to the second embodiment, the power supply device can be transitioned to a safe state before it is destroyed, and the user can be notified that an abnormality has occurred. [Explanation of symbols]

[0051] 120 Power Supply Unit 223 CPU

Claims

1. A power supply device including a conversion means for converting an AC voltage into a DC voltage, and capable of switching at least between a first mode in which a first DC voltage is output and a second mode in which a second DC voltage lower than the first DC voltage, a switching means for switching between the first mode and the second mode; a determination means for determining that an overcurrent state has occurred in the conversion means; a display means for displaying information; a control means for switching to the second mode by the switching means when the determining means determines that the overcurrent state exists, and for causing the display means to display information about the overcurrent state in the conversion means; A power supply device comprising:

2. a heating element that generates heat when a current flows through it; a temperature detection means for detecting the temperature of the heating element; Equipped with 2. The power supply device according to claim 1, wherein the determining means determines that the overcurrent state exists when the temperature detected by the temperature detecting means is higher than a predetermined threshold value.

3. The conversion means a transformer having a primary winding and a secondary winding; a switching element connected in series to the primary winding and performing an on / off switching operation; a power supply control unit that controls the switching operation of the switching element; a rectifying element that rectifies the voltage induced in the secondary winding; a smoothing means for smoothing the voltage rectified by the rectifying element into the DC voltage; and 3. The power supply device according to claim 2, wherein the heat generating element includes at least one of the primary winding, the secondary winding, the switching element, and the rectifying element.

4. The conversion means a transformer having a primary winding and a secondary winding; a switching element connected in series to the primary winding and performing an on / off switching operation; a power supply control unit that controls the switching operation of the switching element; a rectifying element that rectifies the voltage induced in the secondary winding; a smoothing means for smoothing the voltage rectified by the rectifying element into the DC voltage; and a current detection means for detecting a current flowing due to the DC voltage; 2. The power supply device according to claim 1, wherein the determining means determines that the overcurrent state exists when the current detected by the current detecting means is greater than a predetermined threshold value.

5. 5. The power supply device according to claim 4, wherein the control means stops the power supply control unit when the determination means determines that the overcurrent state exists in the second mode.

6. 6. The power supply device according to claim 5, wherein the predetermined threshold value in the second mode is set lower than the predetermined threshold value in the first mode.

7. generating means for generating a third DC voltage lower than the DC voltage output by the converting means, 7. The power supply device according to claim 1, wherein the generating means supplies the third DC voltage to the control means.

8. An image forming apparatus including a power supply device that includes a conversion unit that converts AC voltage into DC voltage, and that is switchable between at least a first mode in which a first DC voltage is output and a second mode in which a second DC voltage lower than the first DC voltage, a switching means for switching between the first mode and the second mode; a determination means for determining that an overcurrent state has occurred in the conversion means; a display means for displaying information; a control means for switching to the second mode by the switching means when the determining means determines that the overcurrent state exists, and for causing the display means to display information about the overcurrent state in the conversion means; An image forming apparatus comprising:

9. the power supply device has a heat generating element that generates heat when a current flows therethrough; temperature detection means for detecting the temperature of the heating element; 9. The image forming apparatus according to claim 8, wherein the determining unit determines that the overcurrent state occurs when the temperature detected by the temperature detecting unit is higher than a predetermined threshold value.

10. The conversion means a transformer having a primary winding and a secondary winding; a switching element connected in series to the primary winding and performing an on / off switching operation; a power supply control unit that controls the switching operation of the switching element; a rectifying element that rectifies the voltage induced in the secondary winding; a smoothing means for smoothing the voltage rectified by the rectifying element into the DC voltage; and 10. The image forming apparatus according to claim 9, wherein the heating element includes at least one of the primary winding, the secondary winding, the switching element, and the rectifying element.

11. The conversion means a transformer having a primary winding and a secondary winding; a switching element connected in series to the primary winding and performing an on / off switching operation; a power supply control unit that controls the switching operation of the switching element; a rectifying element that rectifies the voltage induced in the secondary winding; a smoothing means for smoothing the voltage rectified by the rectifying element into the DC voltage; and a current detection means for detecting a current flowing due to the DC voltage; 9. The image forming apparatus according to claim 8, wherein the determining unit determines that the overcurrent state occurs when the current detected by the current detecting unit is greater than a predetermined threshold value.

12. 12. The image forming apparatus according to claim 11, wherein the control unit stops the power supply control unit when the determination unit determines that the overcurrent state has occurred in the second mode.

13. 13. The image forming apparatus according to claim 12, wherein the predetermined threshold value in the second mode is set lower than the predetermined threshold value in the first mode.

14. generating means for generating a third DC voltage lower than the DC voltage output by the converting means, 14. The image forming apparatus according to claim 8, wherein the generating unit supplies the third DC voltage to the control unit.

Images