Power supply unit, image forming apparatus, and method for detecting abnormalities in a power supply unit

Abstract

To detect high voltage supplied to a transformer mounted in a power supply device even when the characteristics of the transformer vary before the transformer is damaged without narrowing a working voltage range.SOLUTION: A power supply device has: a transformer steps down a first AC voltage supplied from an AC power supply to generate a second AC voltage; a rectification circuit that rectifies the second AC voltage to generate a pulsating current; a smoothing circuit that smooths the pulsating current to generate a DC voltage; a zero-cross signal circuit that generates a zero-cross signal of the pulsating current; and an abnormality detection unit that detects an abnormality in the first AC voltage when the DC voltage exceeds a voltage threshold and the duty ratio of the zero-cross signal exceeds a ratio threshold.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a power supply device, an image forming apparatus, and a method for detecting an abnormality in the power supply device.

Background Art

[0002] In a power supply device mounted in an image forming apparatus, a method is known in which a high voltage of an input voltage is detected based on a duty ratio of a zero-cross signal of the input voltage, and when the high voltage is detected, the supply of power to a fixing device is stopped (see, for example, Patent Document 1).

Summary of the Invention

Problems to be Solved by the Invention

[0003] For example, although the output voltage of a transformer included in a power supply device changes following the input voltage, when the input voltage is higher than a predetermined value, distortion may occur in the waveform of the output voltage of the transformer. Therefore, when detecting a high voltage of the input voltage based on the duty ratio of the zero-cross signal of the output voltage of the transformer and stopping the supply of power to the transformer, the detection point of the high voltage varies due to variations in the characteristics of individual transformers.

[0004] In order to avoid the detection point of the high voltage being included in a breakdown voltage range where the transformer may be damaged, for example, it is set to a voltage lower than the breakdown voltage range by a predetermined margin. As a result, the usable voltage range of the input voltage to the power supply device may become narrow. In order not to narrow the usable voltage range, for example, it is necessary to increase the capacity of the transformer and raise the minimum voltage of the breakdown voltage range. However, when increasing the capacity of the transformer, the size of the transformer increases. As a result, the cost of the transformer increases, and the mounting area of the substrate increases, so the cost of the power supply device increases.

[0005] In view of the above problems, an object of the present invention is to detect a high voltage supplied to a transformer before the transformer is damaged without narrowing the usable voltage range even when the characteristics of the transformer mounted in the power supply device vary. [Means for solving the problem]

[0006] To solve the above technical problems, one embodiment of the present invention provides a power supply device comprising: a transformer that steps down a first AC voltage supplied from an AC power source to generate a second AC voltage; a rectifier circuit that rectifies the second AC voltage to generate a pulsating current; a smoothing circuit that smooths the pulsating current to generate a DC voltage; a zero-crossing signal circuit that generates a zero-crossing signal of the pulsating current; and an abnormality detection unit that detects an abnormality in the first AC voltage when the DC voltage exceeds a voltage threshold and the duty cycle of the zero-crossing signal exceeds a ratio threshold. [Effects of the Invention]

[0007] Even when the characteristics of the transformers installed in the power supply unit vary, it is possible to detect the high voltage supplied to the transformer before it is damaged, without narrowing the operating voltage range. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an example of an image forming apparatus equipped with a power supply device according to one embodiment of the present invention. [Figure 2] This is a block diagram showing an example of a power supply unit in Figure 1. [Figure 3] Figure 2 is a block diagram showing an example of a transformer protection function provided within the AC power supply section. [Figure 4] Figure 3 is a circuit block diagram showing an example of a smoothing circuit, a zero-crossing signal circuit, and an anomaly detection unit. [Figure 5] This block diagram shows another example of a transformer protection function provided within the AC power supply section shown in Figure 2. [Figure 6] This figure shows an example of the waveform of the zero-crossing signal generated by the zero-crossing signal circuit shown in Figure 4. [Figure 7] This is a characteristic diagram showing the relationship between the input voltage and the duty cycle of the zero-crossing signal. [Figure 8]This diagram illustrates an example of detecting high input voltages using DC voltage and the duty cycle of the zero-crossing signal, respectively. [Figure 9] This figure shows an example of detecting high input voltages by combining voltage threshold settings and ratio threshold settings. [Figure 10] This figure shows an example of variation in the magnetic saturation region of the transformer shown in Figure 3. [Figure 11] Figure 3 is a flowchart showing an example of a method for detecting abnormalities in the input voltage using the abnormality detection unit. [Modes for carrying out the invention]

[0009] Embodiments will be described below with reference to the drawings. In the following, voltage lines through which voltage is transmitted will be denoted by the same reference numeral as the voltage name, and signal lines through which signals are transmitted will be denoted by the same reference numeral as the signal name. In each drawing, identical components will be denoted by the same reference numeral, and redundant explanations may be omitted.

[0010] Figure 1 is an overall configuration diagram showing an example of an image forming apparatus equipped with a power supply device according to one embodiment of the present invention. The image forming apparatus 1 shown in Figure 1 is, for example, a digital multifunction printer (MFP: Multi-Function Printer) having functions such as copying, printing, scanning, and facsimile. The image forming apparatus 1 can switch between operating modes that realize the copying, printing, scanning, and facsimile functions, respectively, using application switching keys on the operation unit of the image forming apparatus 1. When the copying function is selected, the image forming apparatus 1 enters copying mode; when the printing function is selected, it enters printing mode; when the scanning function is selected, it enters scanner mode; and when the facsimile function is selected, it enters facsimile mode.

[0011] Furthermore, the image forming apparatus 1 switches its internal state to a normal mode or an energy-saving mode (power-saving mode) depending on the state of its internal circuitry. For example, the normal mode has an operating mode (operating state) and a standby mode (standby state).

[0012] For example, the operating mode includes a copy mode or print mode for printing images or text data onto paper media. The print mode includes the operation of printing received data onto paper media in facsimile mode. The operating mode also includes a scanner mode for scanning documents or the transmission / reception operation in facsimile mode. The state of the internal circuitry is switched by the user's operation of the control panel of the image forming apparatus 1 or by control within the image forming apparatus 1.

[0013] For example, the image forming apparatus 1 includes an automatic document feeder (ADF) 2, an image reading device 3, a writing unit 4, a printer unit 5, an operation unit 11, a control device 12, and a power supply unit 20. The printer unit 5 includes a photoreceptor drum 6, a developing device 7, a transport belt 8, a fixing device 9, and a storage space in which a paper tray 10 is housed.

[0014] The power supply unit 20 is connected to the commercial power supply 40 via the power cable 30 and has the function of generating, for example, AC voltage and DC voltage using the AC voltage supplied from the commercial power supply 40 and supplying it as power to the load. The commercial power supply 40 is an example of an AC power supply. For example, loads to which power is supplied include the automatic document feeder 2, the image reading device 3, the writing unit 4, the printer unit 5, and the operation unit 11.

[0015] The printer unit 5 creates a toner image to be transferred to paper or other media based on the image information. The printer unit 5 is an example of an image forming unit that forms an image. Below, we will briefly explain an example of the image formation process in the image forming apparatus 1, specifically when the operating mode is set to copy mode.

[0016] In the copying mode, a stack of originals (multiple originals) to be copied is set on the automatic document feeder 2, or an original to be copied is set on the image reading device 3. When the start button displayed on the operation unit 11 is pressed, the automatic document feeder 2 feeds the originals one by one to the image reading device 3. The image reading device 3 reads the image information of each of the originals sequentially sent from the automatic document feeder 2 or the original set on the image reading device 3. The image information read by the image reading device 3 is processed by, for example, an image processing unit mounted on the control device 12.

[0017] The writing unit 4 converts the image information processed by the image processing unit into optical information. The photosensitive drum 6 is uniformly charged by a charger disposed at a position facing the photosensitive drum 6 and then exposed by a laser beam including the optical information converted by the writing unit 4. An electrostatic latent image is formed on the photosensitive drum 6 by the exposure. The developing device 7 develops the electrostatic latent image on the photosensitive drum 6 to form a toner image on the photosensitive drum 6. The transfer belt 8 transfers the toner image onto a paper medium or the like. The fixing device 9 fixes the toner image onto a paper medium or the like. Then, the transfer paper on which the image of the original is copied is discharged from the discharge unit.

[0018] The operation unit 11 receives various inputs according to the user's operations and displays various information on the display unit of the operation unit 11. For example, the information displayed on the operation unit 11 is information indicating the operation that has received the input, information indicating the operation status of the image forming apparatus 1, or information indicating the setting state of the image forming apparatus 1. For example, the control board of the operation unit 11 operates constantly by receiving a DC voltage from the power supply device. Therefore, the operation unit 11 can receive various inputs not only during the normal mode but also during the energy saving mode.

[0019] The control device 12 controls the overall operation of the image forming apparatus 1, such as controlling the printer unit 5, controlling communication, and controlling input to the operation unit 11, by causing a controller such as a built-in CPU to execute a control program. Then, the control device 12 performs image processing or data processing by executing an image processing program or a data processing program, and forms an image to be transferred onto a paper medium or the like. The control device 12, for example, operates upon receiving a DC voltage during normal mode and stops operating during power saving mode.

[0020] Note that in FIG. 1, an example where the power supply device 20 is mounted on the image forming apparatus 1 is shown. However, the power supply device 20 may be mounted on an image forming apparatus having a single function such as a scanner, a printer, or a facsimile. Alternatively, the power supply device 20 may be mounted on an electronic device such as a projector, an electronic blackboard, a digital signage, an imaging device, or a PC (Personal Computer).

[0021] FIG. 2 is a block diagram showing an example of the power supply device 20 in FIG. 1. The power supply device 20 has an AC power supply unit 200 and a DC power supply unit 300. The AC power supply unit 200 generates an AC voltage AC to be supplied to the fixing device 9 in FIG. 1 and the like based on the AC voltage supplied from the commercial power supply 40 via the power cable 30. The DC power supply unit 300 generates a DC voltage DC based on the AC voltage supplied from the commercial power supply 40. For example, the DC voltage DC is supplied to the printer unit 5 in FIG. 1, the operation unit 11, the automatic document feeder 2, the image reading device 3, the writing unit 4, and the like.

[0022] The AC power supply unit 200 has a power control unit 210 including a triac for controlling the AC voltage supplied to the fixing device 9 and a transformer protection function to be described later. The power control unit 210 is connected to the commercial power supply 40 via a switch SW such as a relay provided in the supply path of the AC voltage from the commercial power supply 40 to the power control unit 210, and controls the supply of the AC voltage AC to the load.

[0023] The switch SW is turned on when the power supply unit 20 is turned on and turned off when the power supply unit 20 is turned off. In addition, to ensure the safety of the user of the image forming apparatus 1, the switch SW is turned off when the cover of the main body of the image forming apparatus 1, which houses the printer unit 5, is opened and turned on when the cover is closed. The DC power supply unit 300 generates a DC voltage DC while receiving an AC voltage from the commercial power supply 40, regardless of whether the switch SW is on or off.

[0024] Figure 3 is a block diagram showing an example of a transformer protection function provided within the AC power supply unit 200 in Figure 2. The power control unit 210 includes a transformer 211, a rectifier circuit 212, a smoothing circuit 213, a zero-crossing signal circuit 214, and an abnormality detection unit 215. The transformer protection function is realized by the smoothing circuit 213, the zero-crossing signal circuit 214, the abnormality detection unit 215, and the switch SW. Furthermore, the smoothing circuit 213, the zero-crossing signal circuit 214, and the abnormality detection unit 215 function as a transformer protection circuit.

[0025] Transformer 211 steps down the AC voltage ACIN from the commercial power supply 40 according to the ratio of the number of input turns to the number of output turns, and outputs it as AC voltage AC1. For example, AC voltage AC1 is supplied as the transformer output to a fixing device 9, etc. AC voltage ACIN is an example of a first AC voltage, and AC voltage AC1 is an example of a second AC voltage. Hereinafter, the AC voltage ACIN supplied from the commercial power supply 40 will also be referred to as the input voltage ACIN, and the AC voltage AC1 output by transformer 211 will also be referred to as the transformer output voltage AC1.

[0026] The rectifier circuit 212 is, for example, a full-wave rectifier circuit including a diode bridge, which rectifies the transformer output voltage AC1 and outputs it as an AC voltage AC2. The AC voltage AC2 output from the rectifier circuit 212 is a pulsating current obtained by inverting the negative voltage side of the transformer output voltage AC1 to the positive voltage side.

[0027] The smoothing circuit 213 smooths the AC voltage AC2 to generate a DC voltage ACV. The zero-crossing signal circuit 214 generates a zero-crossing signal ZCRS, in which the voltage value inverts each time the AC voltage AC2 passes through voltage α (Figure 6).

[0028] The abnormality detection unit 215, based on the value of the DC voltage ACV output from the smoothing circuit 213 and the zero-crossing signal ZCRS output from the zero-crossing signal circuit 214, outputs an error signal ERR to the switch SW if it detects an abnormality in the input voltage ACIN. In addition, if the abnormality detection unit 215 detects an abnormality in the input voltage ACIN, it may also display error information indicating an abnormality in the transformer 211 on the display unit provided on the operation unit 11 in Figure 2.

[0029] Furthermore, the abnormality detection unit 215 may calculate the voltage value of the input voltage ACIN input to the transformer 211 from the DC voltage ACV based on the characteristics of the transformer 211, the rectifier circuit 212, and the smoothing circuit 213. If the calculated voltage value of the input voltage ACIN is abnormal, the abnormality detection unit 215 may display error information indicating the abnormal voltage value along with the voltage value on the display unit of the operation unit 11. In addition, the abnormality detection unit 215 may also display the voltage value of the input voltage ACIN on the display unit of the operation unit 11 even if the voltage value of the input voltage ACIN is not abnormal. This allows the user of the image forming apparatus 1 to recognize that the input voltage ACIN is normal.

[0030] Figure 4 is a circuit block diagram showing an example of the smoothing circuit 213, zero-crossing signal circuit 214, and anomaly detection unit 215 shown in Figure 3. The smoothing circuit 213 includes resistors R3, R4, R5, R6, R7, R8, capacitives C11, C12, C13, C14, C15, and operational amplifiers OP1 and OP2. The smoothing circuit 213 generates a DC voltage ACV by cutting the high-frequency components of the AC voltage AC2 and smoothing the ripple of the pulsating components. The value of the DC voltage ACV increases in accordance with the increase in the input voltage ACIN from the commercial power supply 40.

[0031] The zero-crossing signal circuit 214 has resistors R9 and R10 and a transistor Tr, and operates as a common-emitter circuit. Resistors R9 and R10 supply a voltage obtained by dividing the voltage value of the AC voltage AC2 to the base of transistor Tr. Transistor Tr turns on when it receives a voltage at its base that is equal to or greater than the on voltage. This causes conduction between the collector and emitter, and the voltage of the zero-crossing signal ZCRS becomes the ground voltage GND (low level). Transistor Tr turns off when it receives a voltage at its base that is less than the on voltage. This blocks the collector and emitter, and the voltage of the zero-crossing signal ZCRS becomes the power supply voltage Vcc (high level) connected to the pull-up resistor R20 of the anomaly detection unit 215. For example, the power supply voltage Vcc is generated by the DC power supply unit 300 shown in Figure 2.

[0032] Voltage α is the AC voltage AC2 when an ON voltage is applied to the base of transistor Tr. That is, transistor Tr turns on when the rectifier circuit 212 outputs an AC voltage AC2 greater than or equal to voltage α, and turns off when the rectifier circuit 212 outputs an AC voltage AC2 less than voltage α. Therefore, the zero-crossing signal circuit 214 can generate a zero-crossing signal ZCRS with voltage α as the zero-crossing point, in synchronization with the change in the waveform of the AC2 output from the rectifier circuit 212.

[0033] The abnormality detection unit 215 includes a pull-up resistor R20 and a control IC 216. Based on the value of the DC voltage ACV and the duty cycle of the zero-crossing signal ZCRS, IC 216 detects an abnormality in the input voltage ACIN and outputs an error signal ERR to switch SW, turning off switch SW. This stops the supply of the input voltage ACIN to transformer 211, thereby preventing failure or destruction of transformer 211. IC 216 also includes a timer as a time measurement means for acquiring the duty cycle of the zero-crossing signal ZCRS.

[0034] Figure 5 is a block diagram showing another example of the transformer protection function provided within the AC power supply unit of Figure 2. Elements identical to those in Figure 3 are given the same reference numerals, and detailed explanations are omitted. The power control unit 210A shown in Figure 5 is provided in the AC power supply unit 200 instead of the power control unit 210 in Figure 2.

[0035] The power control unit 210A includes a transformer 211, a rectifier circuit 212, a zero-crossing signal circuit 214, and an abnormality detection unit 215A. In other words, the power control unit 210 does not have the smoothing circuit 213 shown in Figure 3, and instead of the abnormality detection unit 215 shown in Figure 3, it has an abnormality detection unit 215A.

[0036] The transformer protection function is implemented by the zero-crossing signal circuit 214, the anomaly detection unit 215A, and the switch SW. The zero-crossing signal circuit 214 and the anomaly detection unit 215A also function as a transformer protection circuit. The anomaly detection unit 215A detects an anomaly in the transformer 211 based on the frequency of the zero-crossing signal ZCRS output from the zero-crossing signal circuit 214, and outputs an error signal ERR to the switch SW.

[0037] Figure 6 shows an example of the waveform of the zero-crossing signal ZCRS generated by the zero-crossing signal circuit 214 in Figure 4. In the waveform of the zero-crossing signal ZCRS, the time t1 corresponding to the pulse width and the pulse period are measured by a timer provided inside IC 216. The duty cycle of the zero-crossing signal ZCRS is expressed by equation (1). Duty cycle of ZCRS = t1 / period …(1)

[0038] The waveform of the transformer output voltage AC1 is proportional to the waveform of the input voltage ACIN from the commercial power supply 40 within the operating voltage range (Figures 6(a), (b)). When the input voltage ACIN increases and the transformer output voltage AC1 exceeds the operating voltage range, the magnetic flux in the core of the transformer 211 saturates and the inductance decreases. As a result, the amount of change in the transformer output voltage AC1 becomes small near the zero-crossing point where the voltage crosses the zero point, causing distortion (Figure 6(c)).

[0039] The AC voltage AC2 output from the rectifier circuit 212 is a pulsating voltage obtained by inverting the negative voltage side of the transformer output voltage AC1 waveform output from the transformer 211. The zero-crossing signal ZCRS becomes the ground voltage GND when the AC voltage AC2 is greater than or equal to voltage α, and becomes the power supply voltage Vcc when the AC voltage AC2 is less than voltage α.

[0040] Within the operating voltage range of the transformer output voltage AC1, the higher the transformer output voltage AC1, the greater the rate of change per unit time around the zero-crossing point of the AC voltage AC2. As a result, the time during which the AC voltage AC2 is below voltage α is shortened, the time t1 which is the high-level period of the zero-crossing signal ZCRS is shortened, and the duty cycle of the zero-crossing signal ZCRS is reduced.

[0041] If the transformer output voltage AC1 becomes even larger and exceeds the operating voltage range (Figure 6(c)), the waveform of the transformer output voltage AC1 becomes distorted. Consequently, the waveform of the AC voltage AC2 also becomes distorted, and the amount of change in the AC voltage AC2 near the zero-crossing point becomes smaller. As a result, the time t1, which is the high-level period of the zero-crossing signal ZCRS, becomes longer, and the duty cycle of the zero-crossing signal ZCRS increases.

[0042] Figure 7 is a characteristic diagram showing the relationship between the input voltage ACIN and the duty cycle of the zero-crossing signal ZCRS. For example, the region of input voltage ACIN in which magnetic saturation of transformer 211 does not occur is called the linear region. The region of input voltage ACIN in which magnetic saturation of transformer 211 occurs is called the magnetic saturation region. In the magnetic saturation region, distortion occurs in the waveforms of the transformer output voltage AC1 and AC voltage AC2, as shown in Figure 6(c). In the magnetic saturation region, the region in which the input voltage ACIN is even higher and there is a risk of damage to transformer 211 due to use for a certain period of time or longer is called the transformer damage region.

[0043] Typically, the transformer 211 is used in a region where the transformer output voltage AC1 is not distorted. In this embodiment, the abnormality detection unit 215 uses the distortion of the AC voltage AC2 waveform associated with the distortion of the transformer output voltage AC1 waveform in the magnetic saturation region of the transformer 211 to detect high voltages in the input voltage ACIN before the transformer 211 is damaged. The region in which high voltages are to be detected is the input voltage ACIN region which is greater than the operating guarantee voltage and lower than the transformer damage region in which the transformer 211 may be damaged. Therefore, it is necessary to define the voltage detection point as shown in equation (2). Operating voltage < Voltage detection point < Transformer failure region ... (2)

[0044] For example, the ratio threshold of the zero-crossing signal ZCRS is set by utilizing the characteristic that the duty cycle of the zero-crossing signal ZCRS increases as the transformer output voltage AC1 increases within the magnetic saturation region of the transformer 211. This makes it possible to detect high voltages in the input voltage ACIN before the transformer 211 is damaged. On the other hand, in the linear region shown in Figure 7, the duty cycle of the zero-crossing signal ZCRS decreases as the input voltage ACIN increases. Hereafter, the ratio threshold of the zero-crossing signal ZCRS will also be simply referred to as the ratio threshold.

[0045] Therefore, if the ratio threshold is set so that high voltage is detected before transformer 211 is damaged, there is a region within the operating voltage range that is above the set ratio threshold. For this reason, high voltage in the input voltage ACIN may be falsely detected even within the operating voltage range. In other words, when detecting high voltage in the input voltage ACIN using the ratio threshold, high voltage may be detected not only on the high voltage side of the input voltage ACIN but also on the low voltage side of the input voltage ACIN.

[0046] Figure 8 shows an example of detecting a high voltage of input voltage ACIN using the duty cycles of the DC voltage ACV and the zero-crossing signal ZCRS, respectively. Figure 8(a) shows the relationship between the input voltage ACIN and the DC voltage ACV. Figure 8(b) shows the relationship between the input voltage ACIN and the duty cycle of the zero-crossing signal ZCRS, similar to Figure 7.

[0047] In Figure 8(a), the DC voltage ACV increases linearly in the linear region in response to an increase in the input voltage ACIN. In the magnetic saturation region, the change in the DC voltage ACV in response to an increase in the input voltage ACIN becomes smaller due to the distortion of the AC voltage AC1 output from the transformer 211. Furthermore, the characteristics of the DC voltage ACV vary within the range enclosed by the two dashed lines DL1a and DL2a due to variations in the characteristics of the transformer 211.

[0048] For example, suppose the voltage threshold of the DC voltage ACV is set to a voltage value V2 in accordance with the characteristics shown by the dashed line DL2a, where the input voltage ACIN exceeds the operating guarantee voltage. In this case, the abnormality detection unit 215 detects a high voltage in the input voltage ACIN when the input voltage ACIN is equal to or greater than the voltage value VLa, which exceeds the operating guarantee voltage. However, if the voltage threshold is set to the voltage value V2, then, according to the characteristics shown by the dashed line DL1a, the detection of a high voltage in the input voltage ACIN will occur when the voltage value VHa or higher falls within the transformer damage region. In this case, since the high voltage in the input voltage ACIN is detected only after it reaches the voltage value VHa, the transformer 211 cannot be protected.

[0049] Furthermore, in order to prevent the high voltage of the input voltage ACIN from being detected in the transformer failure region, the voltage threshold of the DC voltage ACV is set to a voltage value V1 that is lower than the voltage value V2. In this case, even when the input voltage ACIN is at the operating guarantee voltage, a high voltage will be detected under the characteristics shown by the dashed line DL2a. Voltage value V1 is an example of a voltage threshold, which is the voltage value of the DC voltage ACV corresponding to the input voltage ACIN before it rises into the failure region of the transformer 211 under the worst-case conditions of the transformer 211's characteristics.

[0050] Thus, simply setting a voltage threshold for the DC voltage ACV may not adequately protect the transformer 211. When detecting high voltages in the input voltage ACIN using only the voltage threshold of the DC voltage ACV, it is necessary to increase the capacity of the transformer 211 to raise the voltage in the transformer failure region. Alternatively, both the voltage threshold of the DC voltage ACV and the operating guarantee voltage may need to be lowered. In the following, the voltage threshold of the DC voltage ACV will also be simply referred to as the voltage threshold.

[0051] In Figure 8(b), the duty cycle characteristics of the zero-crossing signal ZCRS vary within the range enclosed by the two dashed lines DL1b and DL2b due to variations in the characteristics of the transformer 211. For example, in Figure 8(b), the ratio threshold for the duty cycle of the zero-crossing signal ZCRS is set to the duty cycle DR corresponding to the voltage VHb in which the input voltage ACIN does not fall within the transformer failure region, in accordance with the characteristics of the dashed line DL1b. The value DR is an example of a ratio threshold, which is the duty cycle of the zero-crossing signal ZCRS corresponding to the input voltage ACIN before it rises into the failure region of the transformer 211, under the worst-case conditions of the transformer 211's characteristics.

[0052] In this case, a high voltage of input voltage ACIN is detected when the input voltage ACIN exceeds the voltage value VHb just before the transformer failure region. Even in the characteristic shown by the dashed line DL2b, a high voltage of input voltage ACIN can be detected just before the transformer failure region. However, in the linear region, a high voltage of input voltage ACIN may also be detected when the input voltage ACIN is lower than the voltage value VLb. Therefore, simply setting a ratio threshold may lead to false detection of a high voltage of input voltage ACIN.

[0053] The detection method using either Figure 8(a) or Figure 8(b) alone has three problems. (1) When the duty cycle ratio threshold of the zero-crossing signal ZCRS is set to value DR, the starting voltage for detecting high voltages of the input voltage ACIN is included within the operating voltage range, resulting in false detection. (2) When the threshold voltage of the DC voltage ACV is set to the voltage value V2, the starting voltage for detecting high voltages of the input voltage ACIN falls within the transformer damage region, which may cause damage to the transformer 211. (3) When the threshold voltage of DC voltage ACV is set to the voltage value V1, the starting voltage for detecting high voltages of the input voltage ACIN is included in the operating voltage, which can lead to false detection.

[0054] Figure 9 shows an example of detecting high voltages in the input voltage ACIN by combining the setting of a voltage threshold and a ratio threshold. In Figure 9, the variation in the starting voltage for detecting high voltages in the input voltage ACIN when the voltage threshold and ratio threshold are set according to (1), (2), and (3) described above is shown by the arrows in the thick border.

[0055] In this embodiment, (1) and (3) are combined. In this case, as shown in equation (3), if both (1) and (3) are satisfied, the abnormality detection unit 215 detects a high voltage in the input voltage ACIN and outputs an error signal ERR to the switch SW. DC voltage ACV > V1 AND duty cycle of zero-crossing signal ZCRS > DR …(3)

[0056] In (1), if the input voltage ACIN is below the detection start voltage on the low-voltage side, the high-voltage detection condition is met. However, in this voltage range, the high-voltage detection ranges of (1) and (3) do not overlap, so the abnormality detection unit 215 does not detect the high voltage of the input voltage ACIN. In other words, the detection of the high voltage of the input voltage ACIN can be suppressed within the operating guarantee voltage range.

[0057] In (3), if the input voltage ACIN is equal to or greater than the detection start voltage, the high voltage detection condition is met. However, up to the high voltage side detection start voltage of (1), the high voltage detection ranges of (1) and (3) do not overlap, so the abnormality detection unit 215 does not detect the high voltage of the input voltage ACIN. When the input voltage ACIN becomes equal to or greater than the high voltage side detection start voltage of (1), the high voltage detection ranges of (1) and (3) overlap, and the condition of equation (3) is met, so the abnormality detection unit 215 detects the high voltage of the input voltage ACIN. The abnormality detection unit 215 then outputs an error signal ERR to the switch SW.

[0058] In this way, by combining the voltage threshold and the ratio threshold, the detection range for high voltages of the input voltage ACIN can be appropriately set. That is, the abnormality detection unit 215 can detect abnormalities in the input voltage ACIN within the range where the input voltage ACIN is above the operating guarantee voltage and below the transformer failure region. Therefore, there is no need to increase the capacity of the transformer 211 to raise the voltage in the transformer failure region, nor is there a need to lower both the voltage threshold and the operating guarantee voltage.

[0059] Figure 10 shows an example of variation in the magnetic saturation region of transformer 211 in Figure 3. The point at which magnetic saturation begins in transformer 211 (hereinafter referred to as the magnetic saturation point) varies from transformer 211 to transformer 211. Therefore, the starting voltage of the transformer failure region (hereinafter referred to as the transformer failure point), at which the transformer 211 may be damaged, also varies in accordance with the variation in the magnetic saturation point. In the high voltage detection method of the input voltage ACIN shown in Figure 9, the magnetic saturation of transformer 211 is detected, so the detected voltage changes in accordance with the variation in the magnetic saturation point of the transformer.

[0060] For example, if the magnetic saturation point is lower than the magnetic saturation point of a rated transformer (a) (variation (b)), the transformer failure point (b) will also be lower than the transformer failure point (a) of a rated transformer (a). Also, because the input voltage ACIN at which magnetic saturation begins is lower, the minimum detection point (b) of the high-voltage side detection start voltage using the ratio threshold DR in Figure 9(1) will also be lower than the minimum detection point (a) of a rated transformer (a).

[0061] For example, if the voltage detection point of the input voltage ACIN is set to a constant voltage regardless of the variation in the characteristics of the transformer 211, the transformer failure point (b) may be lower than the constant voltage detection point in a transformer 211 with a small magnetic saturation point. In this case, the transformer 211 may not be protected. Therefore, in order to detect high voltages in the input voltage ACIN and protect the transformer 211, it is necessary to increase the capacity of the transformer 211 or lower the upper limit of the operating guarantee voltage. In this embodiment, if the transformer failure point varies to the lower side of the input voltage ACIN, the detection point will also be lower, so high voltages (abnormalities) in the input voltage ACIN can be detected at an input voltage ACIN lower than the transformer failure point.

[0062] On the other hand, if the magnetic saturation point is higher than the magnetic saturation point of the rated transformer (a) (variation (c)), the transformer failure point (c) will also be higher than the transformer failure point (a) of the rated transformer 211. Furthermore, because the input voltage ACIN at which magnetic saturation begins is higher, the minimum detection point (c) of the high-voltage side detection start voltage using the ratio threshold DR will also be higher than the detection point (a) of the rated transformer (a).

[0063] For example, when setting the voltage detection point of the input voltage ACIN to a constant voltage, the detection point is set with a margin to account for variations in the characteristics of the transformer 211, for example, to match a variation (b) where the magnetic saturation point is low. In this case, for transformer 211 where the transformer failure point is higher than variation (b), a high voltage may be detected considerably earlier than the actual transformer failure point, and the supply of the input voltage ACIN to transformer 211 may be stopped. In other words, the image forming apparatus 1 may stop even though the input voltage ACIN has not reached an abnormal voltage.

[0064] In contrast, in this embodiment, the input voltage ACIN can be supplied to the transformers 211 up to the point just before the transformer failure point, according to the characteristics of each transformer 211, and the downtime of the image forming apparatus 1 can be shortened compared to when the voltage detection point is set to a constant voltage.

[0065] Thus, in this embodiment, the transformer 211 can be protected without increasing the capacity of the transformer 211 and without narrowing the operating voltage range in order to ensure a margin for detecting high voltages of the input voltage ACIN.

[0066] Figure 11 is a flowchart showing an example of an abnormality detection method for the input voltage ACIN by the abnormality detection unit 215 in Figure 3. For example, the flow shown in Figure 11 starts when the power to the image forming apparatus 1 is turned on.

[0067] First, in step S10, the abnormality detection unit 215 turns on the switch SW (relay). When the switch SW is turned on, the input voltage ACIN is supplied to the transformer 211, and the transformer 211 starts generating the transformer output voltage AC1. The smoothing circuit 213 starts outputting the DC voltage ACV, and the zero-crossing signal circuit 214 starts outputting the zero-crossing signal ZCRS.

[0068] Next, in step S12, the anomaly detection unit 215 acquires the zero-crossing signal ZCRS output from the zero-crossing signal circuit 214. Next, in step S14, the anomaly detection unit 215 acquires the DC voltage ACV output from the smoothing circuit 213.

[0069] Next, in step S16, the anomaly detection unit 215 uses a timer to measure the pulse width time t1 and pulse period of the zero-crossing signal ZCRS acquired in step S12. Then, the anomaly detection unit 215 uses equation (1) described above to calculate the duty cycle of the zero-crossing signal ZCRS.

[0070] Next, in step S18, the abnormality detection unit 215 determines whether the DC voltage ACV is greater than the voltage threshold V1. If the DC voltage ACV is greater than the voltage threshold V1, the input voltage ACIN may be high voltage, so the process proceeds to step S20. If the DC voltage ACV is less than or equal to the voltage threshold V1, the input voltage ACIN may not be high voltage, so the process returns to step S12.

[0071] In step S20, the anomaly detection unit 215 determines whether the duty cycle of the zero-crossing signal ZCRS is greater than the ratio threshold DR. If the duty cycle is greater than the ratio threshold DR, the input voltage ACIN is high voltage and there is a risk of damage to the transformer 211, so the process proceeds to step S22. If the duty cycle is less than or equal to the ratio threshold DR, the input voltage ACIN is not high voltage, so the process returns to step S12.

[0072] In step S22, the abnormality detection unit 215 detects an abnormality (high voltage) in the input voltage ACIN. That is, the abnormality detection unit 215 determines that a high voltage that could damage the transformer 211 is being input to the transformer 211 as the input voltage ACIN.

[0073] Next, in step S24, the abnormality detection unit 215 turns off the switch SW (relay), displays, for example, an abnormality in the input voltage ACIN on the display unit 11, and terminates the process shown in Figure 11. Turning off the switch SW stops the image forming operation by the image forming apparatus 1. Turning off the switch SW prevents abnormally high voltage from being input to the transformer 211, thus preventing failure or damage to the transformer 211. In addition, by displaying an abnormality on the display unit, the user of the image forming apparatus 1 can be made aware of abnormalities in the input voltage ACIN.

[0074] In this embodiment, the abnormality detection unit 215 can detect an abnormality (high voltage) in the input voltage ACIN based on the voltage threshold of the DC voltage ACV and the duty cycle ratio threshold of the zero-crossing signal ZCRS. This allows for the detection of high voltage supplied to the transformer 211 before it is damaged, even if the characteristics of the transformer 211 mounted on the power supply unit 20 vary, without narrowing the operating voltage range of the input voltage ACIN.

[0075] When the abnormality detection unit 215 detects an abnormality in the input voltage ACIN, it outputs an error signal ERR to the switch SW, turns off the switch SW, and stops the supply of the input voltage ACIN to the transformer 211. This prevents abnormally high voltage from being input to the transformer 211, thereby preventing failure or destruction of the transformer 211. As a result, failure of electronic equipment such as the image forming apparatus 1 on which the power supply unit 20 is installed can be prevented, and a decrease in the reliability of the image forming apparatus 1 can be suppressed.

[0076] The duty cycle of the zero-crossing signal ZCRS decreases as the transformer output voltage AC1 increases within the operating voltage range (linear region) of the input voltage ACIN, and increases as the transformer output voltage AC1 increases within the magnetic saturation region of the transformer 211. However, by combining the voltage threshold V1 and the ratio threshold DR to detect high voltages in the input voltage ACIN, it is possible to suppress false detection of high voltages in the input voltage ACIN within the operating voltage range of the input voltage ACIN.

[0077] When the abnormality detection unit 215 detects an abnormality in the input voltage ACIN, it displays the abnormal voltage value on the display unit 11. This allows the user to recognize any abnormalities in the input voltage ACIN value.

[0078] The abnormality detection unit 215 displays the voltage value on the display unit 11 of the operation unit 11 even when the input voltage ACIN voltage value is not abnormal. This allows the user to recognize that there is no abnormality in the input voltage ACIN.

[0079] Although the present invention has been described above based on various embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be modified as long as they do not impair the spirit of the present invention, and can be appropriately determined according to their application. [Explanation of Symbols]

[0080] 1. Image forming apparatus 2. Automatic document feeder 3. Image reading device 4 Writing Unit 5. Printer Unit 6. Photoconductor drum 7. Developing device 8. Conveyor belt 9. Fixing device 10 Paper feed tray 11 Control section 12 Control device 20 Power supply 30 Power Cables 40 Commercial power supply 200 AC power supply section 210 Power supply control unit 211 Transformer 212 Rectifier circuit 213 Smoothing circuit 214 Zero-crossing signal circuit 215 Anomaly detection unit 216 IC 300 100, 110, 200 power supplies AC1 AC voltage (transformer output voltage) AC2 AC voltage ACIN AC voltage (input voltage) ACV DC Voltage DR ratio threshold ERR Error signal SW Switch V1, V1 voltage threshold ZCRS Zero Crossing Signal [Prior art documents] [Patent Documents]

[0081] [Patent Document 1] Japanese Patent Publication No. 2020-024315

Claims

1. A transformer that steps down the first AC voltage supplied from an AC power source to generate a second AC voltage, A rectifier circuit that rectifies the second AC voltage to generate a pulsating current, A smoothing circuit that smooths the pulsating current to generate a DC voltage, A zero-crossing signal circuit that generates the zero-crossing signal of the pulsating current, The system includes an abnormality detection unit that detects an abnormality in the first AC voltage when the DC voltage exceeds a voltage threshold and the duty cycle of the zero-crossing signal exceeds a ratio threshold. power supply.

2. The supply path for the first AC voltage from the AC power source to the transformer includes a switch which is turned off when the abnormality detection unit detects an abnormality in the first AC voltage. The power supply device according to claim 1.

3. The DC voltage increases in accordance with the increase in the first AC voltage. The duty cycle of the zero-crossing signal decreases in proportion to the increase in the first AC voltage, and increases in proportion to the increase in the first AC voltage after the magnetic saturation of the transformer begins due to a further increase in the first AC voltage. The voltage threshold is set to the voltage value of the DC voltage corresponding to the first AC voltage before it rises to the transformer failure region under the worst-case conditions of the transformer's characteristics. The ratio threshold is set to the duty cycle corresponding to the first AC voltage before it rises to the transformer failure region, under the worst-case conditions of the transformer's characteristics. The power supply device according to claim 1 or claim 2.

4. An image forming unit that forms an image, The system includes a power supply device that generates a voltage supplied to the image forming unit, The aforementioned power supply device is A transformer that steps down the first AC voltage supplied from an AC power source to generate a second AC voltage, A rectifier circuit that rectifies the second AC voltage to generate a pulsating current, A smoothing circuit that smooths the pulsating current to generate a DC voltage, A zero-crossing signal circuit that generates the zero-crossing signal of the pulsating current, The system includes an abnormality detection unit that detects an abnormality in the first AC voltage when the DC voltage exceeds a voltage threshold and the duty cycle of the zero-crossing signal exceeds a ratio threshold. Image forming apparatus.

5. The system further includes a display unit that displays information from the image forming unit, When the abnormality detection unit detects an abnormality in the first AC voltage, it causes the display unit to display error information. The image forming apparatus according to claim 4.

6. The abnormality detection unit calculates the voltage value of the first AC voltage based on the voltage value of the DC voltage and the characteristics of the transformer, the rectifier circuit, and the smoothing circuit, and displays the calculated voltage value on the display unit. The image forming apparatus according to claim 5.

7. An abnormality detection method for a power supply device having a transformer that steps down a first AC voltage supplied from an AC power source to generate a second AC voltage, The second AC voltage is rectified to generate a pulsating current. The aforementioned pulsating current is smoothed to generate a DC voltage, The zero-crossing signal of the pulsating flow is generated, An abnormality in the first AC voltage is detected when the DC voltage exceeds a voltage threshold and the duty cycle of the zero-crossing signal exceeds a ratio threshold. Method for detecting abnormalities in a power supply unit.

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