Power supply device and image processing apparatus

Abstract

To provide a power supply device and an image processing apparatus that can easily avoid a reduction in the operation quality of electric loads.SOLUTION: A power supply device 3 comprises a switching power supply unit 31, and a mode control unit. The switching power supply unit 31 can switch between a PWM mode in which an oscillatory frequency is constant and a PFM mode in which an oscillatory frequency varies, and outputs output voltage to electric loads L1-L8. The mode control unit fixes the control mode of the switching power supply unit 31 to the PWM mode when a specific condition is satisfied.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a power supply device and an image processing device. [Background technology]

[0002] As a related art, a power supply device configured to control a switching power supply unit (DC-DC converter) using a DC-DC converter control IC is known (see, for example, Patent Document 1). In the power supply device of the related art, the switching power supply unit can switch between a PWM mode and a PFM mode (intermittent operation mode).

[0003] In this power supply, the DC-DC converter control IC switches the switching power supply unit to PWM mode when the voltage generated by the additional circuit (second coil) exceeds a threshold voltage, and switches the switching power supply unit to PFM mode when the voltage is below the threshold voltage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-14219 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the power supply device according to the above-mentioned related art, the switching power supply unit automatically switches to PFM mode when the load is light, which increases the ripple of the output voltage output to the electrical load, and may result in a decrease in the operating quality depending on the electrical load, such as an analog circuit.

[0006] An object of the present invention is to provide a power supply device and an image processing device that can easily avoid a decrease in the operational quality of an electric load. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a power supply device including a switching power supply unit and a mode control unit. The switching power supply unit is switchable between a PWM mode in which the oscillation frequency is constant and a PFM mode in which the oscillation frequency varies, and outputs an output voltage to an electrical load. The mode control unit fixes the control mode of the switching power supply unit to the PWM mode when certain conditions are met.

[0008] An image processing apparatus according to another aspect of the present invention includes the power supply apparatus described above and a main body having an image processing function. The electrical load includes the main body. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a power supply device and an image processing device that can easily avoid a decrease in the operational quality of an electrical load. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic block diagram of an image processing device according to the first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the appearance of the image processing device according to the first embodiment. [Figure 3] FIG. 3 is a schematic block diagram illustrating an example of a power supply device of the image processing apparatus according to the first embodiment. [Figure 4] FIG. 4 is a schematic block diagram showing an example of the operation of the power supply device of the image processing apparatus according to the first embodiment. [Figure 5] FIG. 5 is a schematic block diagram showing an example of the operation of the power supply device of the image processing apparatus according to the first embodiment. [Figure 6] FIG. 6 is a schematic block diagram showing an example of the operation of the power supply device of the image processing apparatus according to the first embodiment. [Figure 7] FIG. 7 is a schematic diagram showing an example of the operation of the power supply device of the image processing apparatus according to the first embodiment. [Figure 8] FIG. 8 is a schematic diagram showing an example of the operation of the power supply device of the image processing apparatus according to the first embodiment. [Figure 9] FIG. 9 is a schematic block diagram illustrating an example of a power supply device of the image processing apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description will discuss preferred embodiments of the present invention with reference to the accompanying drawings. The preferred embodiments are merely examples of the present invention and are not intended to limit the technical scope of the present invention.

[0012] (Embodiment 1) [1] Overall configuration of image processing device First, the overall configuration of an image processing device 10 according to this embodiment will be described with reference to FIGS.

[0013] The image processing device 10 according to this embodiment is, for example, a multifunction peripheral having multiple functions, such as a scanning function for acquiring image data from an original, a printing function for forming an image based on the image data, a facsimile function, and a copying function. The image processing device 10 may be a printer, scanner, facsimile machine, copier, etc., as long as it has an image processing function including at least one of the function for forming an image and the function for acquiring image data.

[0014] As shown in Fig. 1, the image processing device 10 includes an automatic document feeder 11, an image reading unit 12, an image forming unit 13, a paper feeder 14, an operation and display unit 15, a main body control unit 16, and a power supply unit 3. The automatic document feeder 11 is an ADF (Auto Document Feeder), and is therefore represented as "ADF" in Fig. 1, and will also be referred to as "ADF 11" in the following description. In this embodiment, as shown in Fig. 2, the image processing device 10 includes a housing 101. The ADF 11, the image reading unit 12, the image forming unit 13, the paper feeder 14, the operation and display unit 15, the main body control unit 16, and the power supply unit 3 are provided in the housing 101.

[0015] The image processing device 10 includes a main body 1 having an image processing function. The main body 1 is provided with an ADF 11, an image reading unit 12, an image forming unit 13, a paper feed unit 14, an operation display unit 15, and a main body control unit 16. In other words, the image processing device 10 includes the main body 1 having an image processing function and a power supply device 3.

[0016] The ADF 11 transports a document whose image is to be read by the image reading unit 12. The ADF 11 includes a document setting unit, a plurality of transport rollers, a document holder, a paper discharge unit, and the like.

[0017] The image reading unit 12 reads an image from a document and outputs image data corresponding to the read image. The image reading unit 12 includes a document table, a light source, a plurality of mirrors, an optical lens, a CCD (Charge Coupled Device), and the like.

[0018] The image forming unit 13 forms an image on a sheet by electrophotography based on image data output from the image reading unit 12. The image forming unit 13 also forms an image on a sheet based on image data input from an information processing device external to the image processing device 10, such as a personal computer.

[0019] Image forming section 13 has four image forming units corresponding to the four colors of C (cyan), M (magenta), Y (yellow), and K (black), an optical scanning device, an intermediate transfer belt, a secondary transfer roller, a fixing device, a developing device, etc. Each image forming unit has a photosensitive drum, a charging roller, a primary transfer roller, a drum cleaning unit, etc. Image forming section 13 may be configured to form an image on a sheet by an image forming method other than the electrophotographic method, such as an inkjet method.

[0020] The image forming unit 13 forms an image on a sheet using toner as a developer. Specifically, the surface of the photosensitive drum, which has been charged by a charging roller, is irradiated with laser light based on image data from an optical scanning device. This forms an electrostatic latent image on the surface of the photosensitive drum. The developing device has a developing roller, a magnet roller, etc., and performs a developing process to develop the electrostatic latent image formed on the surface of the photosensitive drum. When the image forming unit 13 forms an image using an inkjet method, ink (another example of a developer) is supplied instead of toner. After the image formation in the image forming unit 13, the sheet is discharged (supplied) to an auxiliary device or the like for post-processing.

[0021] The paper feed unit 14 supplies sheets to the image forming unit 13. The paper feed unit 14 has a paper feed cassette, a manual feed tray, a sheet transport path, a plurality of transport rollers, etc. The image forming unit 13 forms an image on the sheets supplied from the paper feed unit 14. The sheets supplied to the image forming unit 13 are, for example, paper, but are not limited to paper and may be, for example, a resin film, etc.

[0022] The operation display unit 15 is a user interface in the image processing device 10. The operation display unit 15 has a display unit such as a liquid crystal display that displays various information in response to control instructions from the control unit of the main body, and an operation unit such as a switch or touch panel that inputs various information to the control unit of the main body in response to user operations. Furthermore, the image processing device 10 may also have, in addition to or instead of the operation display unit 15, an audio output unit, an audio input unit, etc. as a user interface.

[0023] The main body control unit 16 mainly comprises a computer system having one or more processors and one or more memories, and performs overall control of the image processing device 10. In the image processing device 10, the one or more processors execute programs to realize the functions of the main body control unit 16. In this embodiment, as an example, the main body control unit 16 includes a CPU (Central Processing Unit).

[0024] The power supply device 3 is a device that generates (outputs) power for the operation of the image processing device 10. The power supply device 3 is electrically connected to one or more electrical loads and supplies power to the one or more electrical loads. In this embodiment, the main body 1 of the image processing device 10 is the "electrical load," and the power supply device 3 supplies power to each part of the main body 1 as the electrical load. In other words, the one or more electrical loads that receive power from the power supply device 3 include the ADF 11, image reading unit 12, image forming unit 13, paper feed unit 14, operation display unit 15, and main body control unit 16. In this way, the image processing device 10 includes the power supply device 3 for electrical devices and the main body 1 having an image processing function. The electrical load includes the main body 1.

[0025] In this embodiment, the power supply device 3 is electrically connected to an AC plug and converts an AC voltage of 100 V (or 200 V) applied to the AC plug into a DC voltage of 24 V, for example, and further converts the DC voltage of 24 V into a DC voltage of 5.0 V, 3.3 V, or 1.5 V. In other words, when the AC plug is connected to an outlet (power socket), AC power is applied to the power supply device 3 from an AC power source such as a system power supply, and the power supply device 3 generates DC power from this AC power.

[0026] The power supply device 3, for example, receives a control signal from the main body control unit 16 and determines the state of power supply to one or more electrical loads (ADF 11, image reading unit 12, image forming unit 13, paper feed unit 14, operation display unit 15, main body control unit 16, etc.). Specifically, the main body 1 has multiple operating modes including a normal mode and an energy-saving mode. The energy-saving mode is a mode in which power consumption in the main body 1 is reduced compared to the normal mode. When the main body 1 operates in the normal mode, the power supply device 3 supplies power to multiple electrical loads. On the other hand, when the main body 1 operates in the energy-saving mode, the power supply device 3 supplies power to only some of the multiple electrical loads. Therefore, in the energy-saving mode, the main body control unit 16 outputs a control signal (sleep signal) to the power supply device 3 to switch the state of power supply from the power supply device 3.

[0027] The image processing device 10 further includes a storage unit, a communication unit, etc. The storage unit includes one or more non-volatile memories, and pre-stores information such as control programs for causing the main body control unit 16 to execute various processes. The communication unit is an interface that executes data communication between the image processing device 10 and an external device connected via a communication network such as the Internet or a LAN (Local Area Network).

[0028] Incidentally, a power supply device configured to control a switching power supply unit (DC-DC converter) using a DC-DC converter control IC is known as a related technology for a power supply device used in this type of image processing device 10. In the power supply device of the related technology, the switching power supply unit can switch between PWM mode and PFM mode (intermittent operation mode).

[0029] In this power supply, the DC-DC converter control IC switches the switching power supply unit to PWM mode when the voltage generated by the additional circuit (second coil) exceeds a threshold voltage, and switches the switching power supply unit to PFM mode when the voltage is below the threshold voltage.

[0030] However, in the power supply device according to the above-mentioned related art, the switching power supply unit automatically switches to PFM mode when the load is light, which increases the ripple of the output voltage output to the electrical load, and may result in a decrease in the operating quality depending on the electrical load, such as an analog circuit.

[0031] In contrast to this, this embodiment provides a power supply device 3 and an image processing device 10 that can easily avoid a decrease in the operational quality of the electrical load, using the configuration described below.

[0032] [2] Power supply configuration Next, the configuration of the power supply device 3 that supplies electric power (power source) to the electric loads L1 to L8 (see FIG. 3) will be described in more detail with reference to FIGS. 1 and 3 to 8. FIGS. 1 and 3 to 6 are block diagrams that schematically show the configuration of the power supply device 3. In this embodiment, the image processing device 10 is an example of an electric device that receives electric power from the power supply device 3.

[0033] As shown in FIG. 1, the power supply device 3 includes a switching power supply unit 31, a mode control unit 32, and an AC / DC converter 33.

[0034] The AC / DC converter 33 converts the AC voltage of 100V (or 200V) applied to the AC plug into a desired voltage, such as DC 24V, and outputs the voltage.

[0035] The switching power supply unit 31 is a switching-type power supply circuit that converts (steps down) the voltage output from the AC / DC converter 33 to a DC voltage of, for example, 5.0 V, 3.3 V, or 1.5 V and outputs the voltage. The switching power supply unit 31 outputs the output voltage to the electrical loads L1 to L8.

[0036] In this embodiment, as an example, the switching power supply unit 31 is a DC / DC converter that converts (steps down) a DC 24V voltage output from the AC / DC converter 33 into a DC 5.0V voltage and outputs it.

[0037] The switching power supply unit 31 has a switching element and converts the input voltage into a desired voltage by the switching operation of the switching element. Here, the switching power supply unit 31 has, for example, a signal generating unit that generates a PWM signal and is capable of adjusting the output voltage value (magnitude of the output voltage) in accordance with the PWM signal.

[0038] The "PWM signal" referred to here is a rectangular wave signal used for pulse width modulation (PWM) control. In other words, a PWM signal is a rectangular signal that alternates between H (High) level and L (Low) level, with one cycle being the sum of the time width of the H level and the time width of the L level. PWM control is possible by adjusting the duty ratio of the PWM signal. The "duty ratio" referred to here means the proportion of the H level period in the PWM signal, and is expressed by dividing the time width of the H level by the cycle.

[0039] Since switching power supply unit 31 is configured to be able to adjust the output voltage value (magnitude of output voltage) according to the PWM signal generated by the signal generating unit, a change in the PWM signal changes the magnitude of the output voltage of switching power supply unit 31. In other words, the magnitude of the output voltage of switching power supply unit 31 is not constant but is variable according to the duty ratio of the PWM signal generated by the signal generating unit.

[0040] The switching power supply unit 31 can switch between a PWM mode in which the oscillation frequency is constant and a PFM mode in which the oscillation frequency varies. The PWM mode is a mode in which the switching power supply unit 31 is driven by pulse width modulation (PWM) control using the above-mentioned PWM signal. The PFM mode is a mode in which the switching power supply unit 31 is driven by pulse frequency modulation (PFM) control using the PFM signal.

[0041] In PWM mode, the control signal (PWM signal) generated by the signal generation unit has a constant oscillation frequency (i.e., period), and the pulse width (i.e., the duration of the H level in one period) varies depending on the electrical loads L1 to L8. Compared to PFM mode, PWM mode has the advantage of being able to reduce output voltage ripple and has high responsiveness to load fluctuations, but it consumes more power and is less efficient under light loads (i.e., when power consumption in the electrical loads L1 to L8 is small).

[0042] In PFM mode, the control signal (PFM signal) generated by the signal generation unit has a constant pulse width (i.e., the duration of the H level in one cycle), but the oscillation frequency (i.e., the cycle) varies depending on the electrical loads L1 to L8. In PFM mode, the circuit function changes the oscillation frequency depending on the electrical loads L1 to L8, so the oscillation frequency tends to be lower under light loads. In PFM mode, the output voltage ripple is larger than in PWM mode, but because switching losses are proportional to the oscillation frequency, power consumption under light loads can be kept low, improving efficiency.

[0043] Because of this feature of improved efficiency under light loads, switching power supply unit 31 basically operates in PWM mode under heavy loads (i.e., when the power consumption of electrical loads L1 to L8 is large), and operates in PFM mode under light loads (i.e., when the power consumption of electrical loads L1 to L8 is small). In this way, switching power supply unit 31 is configured to switch between PWM mode and PFM mode depending on the state of electrical loads L1 to L8.

[0044] For example, as shown in FIG. 3, it is assumed that a plurality of electric loads L1 to L8 are connected to the output of the power supply device 3.

[0045] Here, power supply device 3 includes switching power supply unit 31, which includes first switching power supply unit 311 and second switching power supply unit 312. First switching power supply unit 311 and second switching power supply unit 312 operate independently. First switching power supply unit 311 and second switching power supply unit 312 each convert a DC 24V voltage output from AC / DC converter 33 into a DC 5.0V voltage and output the converted voltage.

[0046] Furthermore, power supply device 3 includes DC / DC converters 34 and 35 connected to the output of second switching power supply unit 312. DC / DC converter 34 converts the DC 5.0V voltage output from second switching power supply unit 312 to a DC 3.3V voltage and outputs it. DC / DC converter 35 converts the DC 5.0V voltage output from second switching power supply unit 312 to a DC 1.5V voltage and outputs it.

[0047] As an example, electrical load L1 is an APC (Automatic Power Control) that drives a semiconductor laser that outputs laser light in image forming unit 13, electrical load L2 is a control circuit for a CIS (Contact Image Sensor) in image reading unit 12, and electrical load L3 is a control circuit for a CCD in image reading unit 12. Electrical load L4 is a parallel communication unit conforming to the IEEE 1284 standard, electrical load L5 is a wireless communication unit that performs wireless communication such as Wi-Fi (registered trademark), and electrical load L6 is a USB host. Electrical load L7 is an ASIC (Application Specific Integrated Circuit), and electrical load L8 is a memory associated with the ASIC.

[0048] Of these electrical loads L1 to L8, electrical loads L1 to L6 are connected to the output of first switching power supply unit 311, electrical load L7 is connected to the output of DC / DC converter 34, and electrical load L8 is connected to the output of DC / DC converter 35. Of these electrical loads L1 to L8, electrical loads L1 to L3 are analog circuits, and the others are digital circuits.

[0049] In the configuration shown in FIG. 3, for example, when main body 1 is in energy-saving mode, power supply device 3 supplies the minimum amount of power required to quickly start the system. Therefore, among electrical loads L1 to L8, only electrical load L8 (and a portion of electrical load L7) is powered on, while the rest are powered off. In this case, first switching power supply unit 311 is under a light load, and so the control mode of first switching power supply unit 311 is PFM mode. However, because electrical loads L1 to L3, which are analog circuits, are all powered off, ripples occurring in the output voltage of first switching power supply unit 311 do not affect these analog circuits. On the other hand, even if the control mode of second switching power supply unit 312 is PFM mode, ripples occurring in the output voltage of second switching power supply unit 312 are unlikely to affect electrical loads L7 and L8, which are digital circuits.

[0050] On the other hand, as shown in Fig. 4, in a situation where only the electric load L1 is powered on among the electric loads L1 to L6 connected to the output of the first switching power supply unit 311, the ripple generated in the output voltage of the first switching power supply unit 311 may affect the electric load L1, possibly leading to a deterioration in the operating quality of the electric load L1. In Figs. 4 to 6, the electric loads that are powered off among the electric loads L1 to L8 are indicated by hatching (diagonal lines) and dashed lines.

[0051] 4, first switching power supply unit 311 is under a light load, and therefore the control mode of first switching power supply unit 311 is PFM mode. At this time, among electrical loads L1 to L3, which are analog circuits, electrical load L1 is in a power-on state, and ripples occurring in the output voltage of first switching power supply unit 311 may affect the operation of electrical load L1, which is an analog circuit, and may lead to a degradation in the operating quality of electrical load L1. For example, voltage fluctuations (ripples) may cause analog values ​​to fluctuate, resulting in variations in sensor-acquired values, control values, etc., which may result in a degradation in the operating quality of electrical load L1.

[0052] Therefore, when a specific condition is satisfied, mode control unit 32 (see FIG. 1) fixes the control mode of switching power supply unit 31 to the PWM mode. Mode control unit 32 includes a processor such as a CPU, and has at least the function of fixing the control mode of switching power supply unit 31 to the PWM mode.

[0053] In other words, when the load becomes light, the control mode of switching power supply unit 31 is likely to switch (from PWM mode) to PFM mode, but if certain conditions are met, mode control unit 32 restricts the switching of the control mode of switching power supply unit 31 to PFM mode and forcibly sets the control mode to PWM mode. Therefore, even in the state shown in FIG. 4, the control mode of first switching power supply unit 311 can be set to PWM mode, and ripples occurring in the output voltage of first switching power supply unit 311 can be kept small. This prevents ripples occurring in the output voltage of first switching power supply unit 311 from affecting the operation of electrical load L1, which is an analog circuit, and reducing the operating quality of electrical load L1.

[0054] As described above, the power supply device 3 according to this embodiment includes a switching power supply unit 31 and a mode control unit 32. The switching power supply unit 31 is switchable between a PWM mode in which the oscillation frequency is constant and a PFM mode in which the oscillation frequency varies, and outputs an output voltage to the electrical loads L1 to L8. The mode control unit 32 fixes the control mode of the switching power supply unit 31 to the PWM mode when certain conditions are met.

[0055] According to this configuration, even when using switching power supply unit 31 that can switch between PWM mode and PFM mode, mode control unit 32 can fix the control mode of switching power supply unit 31 to PWM mode when specific conditions are met. Therefore, for example, by fixing the control mode of switching power supply unit 31 to PWM mode when electrical loads L1 to L3 made up of analog circuits are operating, it is possible to realize power supply device 3 and image processing device 10 that can easily avoid degradation in the operating quality of the electrical loads.

[0056] The operation of the mode control unit 32 will now be described in more detail.

[0057] First, a method (fixing means) for fixing the control mode to the PWM mode will be described.

[0058] 4, mode control unit 32 fixes the control mode to the PWM mode by inputting a signal to mode switching terminal 310 of switching power supply unit 31. That is, switching power supply unit 31 has mode switching terminal 310, and is configured so that the control mode is fixed to the PWM mode when mode switching terminal 310 is at L (Low) level. Therefore, when a specific condition is satisfied, mode control unit 32 maintains mode switching terminal 310 of switching power supply unit 31 (first switching power supply unit 311) at L level, and fixes the control mode to the PWM mode.

[0059] According to this configuration, the control mode can be fixed to the PWM mode by a simple configuration in which the signal input to the mode switching terminal 310 of the switching power supply unit 31 is controlled.

[0060] As another fixing means, the mode control unit 32 fixes the control mode to the PWM mode by operating a specific load among the electric loads L1 to L9, as shown in Figures 5 and 6. The "specific load" here refers to a load that generates the power consumption necessary to maintain the control mode of the switching power supply unit 31 in the PWM mode, and includes, for example, the dedicated load L9 shown in Figure 5 or the electric loads L5 and L6 shown in Figure 6 that have no effect on the system operation.

[0061] 5, when a specific condition is satisfied, the mode control unit 32 turns on the power of the dedicated load L9 and supplies power from the switching power supply unit 31 (first switching power supply unit 311) to the dedicated load L9. As a result, the output power (output current) of the switching power supply unit 31 (first switching power supply unit 311) exceeds a threshold, resulting in a heavy load, and the control mode is fixed to the PWM mode. Here, the dedicated load L9 is an electric load provided exclusively for fixing the control mode to the PWM mode, and is an electric load that is not essentially required for the image processing device 10. The dedicated load L9 is, for example, a resistor or a light-emitting element.

[0062] 6, when a specific condition is satisfied, the mode control unit 32 powers on the electrical loads L5 and L6, and supplies power to the electrical loads L5 and L6 from the switching power supply unit 31 (first switching power supply unit 311). As a result, the output power (output current) of the switching power supply unit 31 (first switching power supply unit 311) exceeds a threshold, resulting in a heavy load, and the control mode is fixed to the PWM mode. Here, the electrical loads L5 and L6 are electrical loads that are essentially necessary for the image processing device 10, but powering them on does not affect the system operation of the image processing device 10.

[0063] According to this configuration, even if the switching power supply unit 31 does not have the mode switching terminal 310, it is possible to fix the control mode to the PWM mode.

[0064] Next, the criteria (specific conditions) for determining whether or not to fix the control mode to the PWM mode will be described.

[0065] 7, the specific condition is determined based on the control timing of the electric loads L1 to L8. That is, the mode control unit 32, for example, communicates with the main body control unit 16, and determines whether or not to fix the control mode to the PWM mode based on the timing at which the main body control unit 16 controls the electric loads L1 to L8 of the respective units.

[0066] 7, the specific condition is that the electric load L1 consisting of the APC drives the semiconductor laser of the image forming unit 13 when the image forming unit 13 performs an image formation operation. In other words, when an image is formed based on image data, the electric load L1 consisting of the APC is turned on at the timing when laser light is output, and this timing is known by the main body control unit 16. Therefore, the mode control unit 32 communicates with the main body control unit 16 to know the period when the electric load L1 drives the semiconductor laser (denoted as "laser emission" in the figure), determines that the specific condition is met during that period, and fixes the control mode to the PWM mode.

[0067] According to this configuration, by monitoring the control timing of the electric loads L1 to L8, it is possible to reliably determine the timing at which the control mode should be fixed to the PWM mode.

[0068] Here, mode control unit 32 can determine whether switching power supply unit 31 is in PFM mode by determining in advance the threshold value of the output current (load current) of switching power supply unit 31 at which the mode switches from PWM mode to PFM mode and the current consumption of each electrical load L1-L9. Furthermore, mode control unit 32 can determine in advance which electrical load among electrical loads L1-L9 needs to be operated to cause the load current to exceed the threshold value. Therefore, only when switching power supply unit 31 is in PFM mode can mode control unit 32 operate a specific load and fix the control mode to PWM mode. However, as shown in FIG. 7, mode control unit 32 does not need to consider such a threshold value when forcibly fixing the control mode to PWM mode.

[0069] As another example, the specific condition is determined based on an evaluation of the operation of the electric loads L1 to L3. That is, by evaluating the operation of the electric loads L1 to L3, it is possible to determine, as a specific condition, that the operation quality of the electric loads L1 to L3 is actually degraded due to the influence of ripples occurring in the output voltage of the switching power supply unit 31.

[0070] 8, when the image forming unit 13 performs an image reading operation, if the evaluation of the operation of the electric load L3 consisting of the CCD control circuit of the image reading unit 12 is judged to be "reading quality: low," it is presumed that the operation quality of the electric load L3 has deteriorated. Therefore, when the operation quality of the electric loads L1 to L3 has actually deteriorated, the mode control unit 32 determines that a specific condition is satisfied, and fixes the control mode to the PWM mode.

[0071] According to this configuration, by monitoring and evaluating the operations of the electric loads L1 to L3, it is possible to reliably determine the timing when the control mode should be fixed to the PWM mode.

[0072] [3] Variation The multiple components included in the power supply device 3 may be distributed across multiple housings. For example, at least one of the switching power supply unit 31, the mode control unit 32, and the AC / DC converter 33 may be provided separately.

[0073] 3, the specific configuration of the power supply device 3 can be changed as appropriate as long as the same functions can be realized. For example, the DC / DC converters 34 and 35 can be omitted as appropriate.

[0074] (Embodiment 2) 9, the power supply device 3 according to this embodiment differs from the power supply device 3 according to the first embodiment in that it includes only one switching power supply unit 31. Hereinafter, the same components as those in the first embodiment will be denoted by the same reference numerals and descriptions thereof will be omitted as appropriate.

[0075] Switching power supply unit 31 converts the 24 V DC voltage output from AC / DC converter 33 into a 5.0 V DC voltage and outputs it. Of electrical loads L1 to L8, electrical loads L1 to L6 are connected directly to the output of switching power supply unit 31, electrical load L7 is connected via DC / DC converter 34, and electrical load L8 is connected via DC / DC converter 35 to the output of switching power supply unit 31.

[0076] In the power supply device 3 according to this embodiment, for example, in a situation where only the electric load L1 among the electric loads L1 to L6 is powered on, ripples occurring in the output voltage of the switching power supply unit 31 may affect the electric load L1 and reduce the operating quality of the electric load L1. Therefore, the mode control unit 32 (see FIG. 1) fixes the control mode of the switching power supply unit 31 to the PWM mode when certain conditions are met.

[0077] [Appendix to the invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0078] <Appendix 1> a switching power supply unit that can switch between a PWM mode in which the oscillation frequency is constant and a PFM mode in which the oscillation frequency varies, and outputs an output voltage to an electrical load; and a mode control unit that fixes the control mode of the switching power supply unit to the PWM mode when a specific condition is satisfied. power supply.

[0079] <Appendix 2> the mode control unit fixes the control mode to the PWM mode by inputting a signal to a mode switching terminal of the switching power supply unit. 1. The power supply device of claim 1.

[0080] <Appendix 3> The mode control unit fixes the control mode to the PWM mode by operating a specific load among the electric loads. 1. The power supply device of claim 1.

[0081] <Appendix 4> The specific condition is determined based on a control timing of the electric load. 4. The power supply device according to any one of Supplementary Notes 1 to 3.

[0082] <Appendix 5> The specific condition is determined based on an evaluation of the operation of the electrical load. 4. The power supply device according to any one of Supplementary Notes 1 to 3.

[0083] <Appendix 6> A power supply device according to any one of Supplementary Notes 1 to 5; a main body having an image processing function, the electrical load includes the main body; Image processing device. [Explanation of symbols]

[0084] 1 Main unit (electrical load) 3 Power supply 10 Image processing device 31 Switching power supply section 32 Mode control section 310 Mode switching terminal L1~L8 Electrical load L9 Dedicated load (specific load)

Claims

1. a switching power supply unit that can switch between a PWM mode in which the oscillation frequency is constant and a PFM mode in which the oscillation frequency varies, and outputs an output voltage to an electrical load; a mode control unit that fixes the control mode of the switching power supply unit to the PWM mode when a specific condition is satisfied; power supply.

2. the mode control unit fixes the control mode to the PWM mode by inputting a signal to a mode switching terminal of the switching power supply unit. The power supply device of claim 1 .

3. the mode control unit fixes the control mode to the PWM mode by operating a specific load among the electric loads. The power supply device of claim 1 .

4. The specific condition is determined based on a control timing of the electric load. The power supply device according to any one of claims 1 to 3.

5. The specific condition is determined based on an evaluation of the operation of the electrical load. The power supply device according to any one of claims 1 to 3.

6. The power supply device according to any one of claims 1 to 3; a main body having an image processing function, the electrical load includes the main body; Image processing device.

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