Power supply device, electronic apparatus, image formation device, power supply control method of power supply device and power supply control program of power supply device

Abstract

To suppress the application of overvoltage to a circuit in a power supply device while supply of power to a load is maintained when overvoltage is inputted to the power supply device.SOLUTION: A power supply device includes: a phase control circuit capable of generating second AC voltage by controlling a phase of first AC voltage; a rectifier circuit for rectifying second AC voltage and generating first voltage; a voltage detection circuit for detecting a voltage level of first voltage; a zero cross detection circuit for detecting a zero cross point of first AC voltage; and a power supply control circuit for receiving a detection result of the voltage detection circuit and the zero cross detection circuit and outputting a trigger signal to the phase control circuit after the phase of first AC voltage advances 90 degrees or more from the zero cross point at every half wave period of first AC voltage when the voltage level exceeds a first threshold. The phase control circuit stops output of second AC voltage to the rectifier circuit before the trigger signal is received and outputs second AC voltage to the rectifier circuit until the next zero cross point from reception of the trigger signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power supply device, an electronic device, an image forming apparatus, a power supply control method for a power supply device, and a power supply control program for a power supply device. [Background technology]

[0002] In an image forming apparatus having a load such as a fixing device, when the voltage from a commercial AC power source exceeds a rated value, a technique is known in which the AC voltage waveform is phase-controlled to shorten the time that current is passed through the load, thereby suppressing the application of an overvoltage to the load (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0003] However, when the time that current is applied to the load is shortened by phase control, there is a risk that sufficient power may not be supplied to the load. For example, if a predetermined amount of power cannot be supplied to a fixing device that fixes toner or the like to a medium, the toner or the like may not be fixed sufficiently to the medium, and print quality may deteriorate.

[0004] In view of the above problems, an object of the present invention is to prevent an overvoltage from being applied to a circuit within a power supply device while maintaining the supply of power to a load when an overvoltage is input to the power supply device. [Means for solving the problem]

[0005] In order to solve the above technical problem, a power supply device of one embodiment of the present invention is a power supply device that generates a DC voltage from a first AC voltage, the power supply device comprising: a phase control circuit capable of generating a second AC voltage by controlling a phase of the first AC voltage; a rectifier circuit that rectifies the second AC voltage to generate a first voltage; a voltage detection circuit that detects a voltage level of the first voltage; a zero-cross detection circuit that detects a zero-cross point of the first AC voltage; and a power supply control circuit that receives a detection result of the voltage detection circuit and a detection result of the zero-cross detection circuit, and when the voltage level exceeds a first threshold value, performs phase control to output a trigger signal to the phase control circuit after the phase of the first AC voltage advances by 90 degrees or more from a zero-cross point for each half-wave period of the first AC voltage, wherein the phase control circuit stops outputting the second AC voltage to the rectifier circuit before receiving the trigger signal during the implementation of the phase control, and outputs the second AC voltage to the rectifier circuit after receiving the trigger signal until the next zero-cross point. Effect of the Invention

[0006] When an overvoltage is input to the power supply device, it is possible to prevent the overvoltage from being applied to a circuit within the power supply device while maintaining the supply of power to a load. [Brief description of the drawings]

[0007] [Figure 1] 1 is a block diagram showing an example of a power supply device according to a first embodiment of the present invention. [Diagram 2] 2 is a timing diagram showing an example of the operation of the power supply device of FIG. 1. [Diagram 3] 2 is a flow diagram showing an example of the operation of the power supply device of FIG. 1. [Figure 4] FIG. 11 is a block diagram showing an example of a power supply device according to a second embodiment of the present invention. [Diagram 5] 5 is an overall configuration diagram showing an example of an image forming apparatus in which the power supply device of FIG. 4 is mounted. [Figure 6] 5 is a block diagram showing an example of a hardware configuration of a control board in FIG. 4. [Figure 7]FIG. 11 is a block diagram showing an example of a power supply device according to a third embodiment of the present invention. [Figure 8] 8 is a timing diagram showing an example of the operation of the power supply device of FIG. 7. [Figure 9] 8 is a flow diagram showing an example of the operation of the power supply device of FIG. 7. [Figure 10] FIG. 10 is a flow chart showing a continuation of the operation of FIG. 9. [Figure 11] FIG. 11 is a block diagram showing an example of a power supply device according to a fourth embodiment of the present invention. [Figure 12] 12 is a timing diagram showing an example of the operation of the power supply device of FIG. 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated descriptions may be omitted. In the following, the voltage lines through which voltages are transmitted are designated by the same reference numerals as the voltage names, and the signal lines through which signals are transmitted are designated by the same reference numerals as the signal names.

[0009] (First embodiment) Fig. 1 is a block diagram showing an example of a power supply device according to a first embodiment of the present invention. For example, the power supply device 100 shown in Fig. 1 is a switching power supply that generates, for example, DC voltages V24 and V5 by smoothing and voltage converting an input voltage ACIN supplied from a commercial AC power supply AC through phase control. The input voltage ACIN is an example of a first AC voltage. Although not particularly limited, the effective value of the input voltage ACIN when normal is assumed to be 100 Vrms.

[0010] The DC voltage V24 is supplied to a load 290 such as a motor or a fan to operate the load 290. The DC voltage V5 is supplied to the control board 200 and the like and is used as an operating power source for the control board 200. Although not particularly limited, the DC voltages V24 and V5 may be 24 V and 5 V, respectively. The power supply device 100, together with the control board 200 and the load 290, may be mounted in an electronic device 300 such as an image forming apparatus, a projector, an electronic whiteboard, a digital signage, an imaging device, a PC (Personal Computer), a server, or the like.

[0011] The power supply device 100 includes a phase control circuit 110, a rectifier circuit 120, a voltage detection circuit 130, a zero-cross detection circuit 140, a DC / DC converter 150, a power supply control circuit 160, a current fuse 170, and electrolytic capacitors C1, C2, and C3.

[0012] The phase control circuit 110 has, for example, a triac (not shown) arranged on the supply path of the input voltage ACIN. The phase control circuit 110 can generate an AC voltage ACOUT by controlling the phase of the input voltage ACIN by turning on / off the triac based on a phase control signal PCNT from the power supply control circuit 160. The phase control circuit 110 outputs the generated AC voltage ACOUT to the rectifier circuit 120. A method of controlling the phase of the input voltage ACIN by the phase control circuit 110 is described in FIG. 2. The AC voltage ACOUT is an example of a second AC voltage. The phase control signal PCNT is an example of a trigger signal.

[0013] The rectifier circuit 120 is, for example, a full-wave rectifier circuit including a diode bridge, which rectifies the AC voltage ACOUT from the phase control circuit 110 and outputs it as a DC voltage (pulsating current). The electrolytic capacitor C1 is connected to the output of the rectifier circuit 120 and functions as a smoothing circuit. For example, the electrolytic capacitor C1 may be an aluminum block capacitor.

[0014] The voltage (pulsating current) output from the rectifier circuit 120 is smoothed by the electrolytic capacitor C1, and a voltage V1 that depends on the amplitude of the input voltage ACIN is generated. The voltage V1 is an example of a first voltage. For example, when the effective value of the input voltage ACIN is 100 Vrms, a voltage V1 (pulsating current) with a maximum value of √2×100 V (approximately 141.4 V) is generated.

[0015] The voltage detection circuit 130 detects the maximum value of the voltage V1 (pulsating current) as a voltage level, and outputs the detected voltage level as a voltage detection signal VDET to the power supply control circuit 160. The voltage detection circuit 130 may detect the maximum value of the voltage V1 for each half-wave period of the AC input voltage ACIN. Hereinafter, the maximum value of the voltage V1 (pulsating current) for each half-wave period is denoted by the symbol V1(max).

[0016] For example, the voltage detection signal VDET has multiple bits and represents a voltage value as, for example, a digital value. The zero-cross detection circuit 140 outputs a zero-cross signal ZCRS having a pulse synchronized with a zero-cross point, which is the timing at which the input voltage ACIN crosses 0 V, to the power supply control circuit 160.

[0017] The power supply control circuit 160 includes a controller such as a CPU. The power supply control circuit 160 outputs a phase control signal PCNT to the phase control circuit 110, which controls the phase control circuit 110, based on a voltage detection signal VDET that is a detection result of the voltage detection circuit 130 and a zero-cross signal ZCRS that is a detection result of the zero-cross detection circuit 140.

[0018] The DC / DC converter 150 generates DC voltages V24 and V5 based on the voltage V1. Although not particularly limited, the DC voltage V24 may be 24 V, and the DC voltage V5 may be 5 V. The current fuse 170 is disposed between the input terminal of the input voltage ACIN of the power supply device 100 and the phase control circuit 110, and protects the power supply device 100 from an overcurrent.

[0019] If the voltage smoothed by the electrolytic capacitor C1 is Vs (Vrms), the maximum value of the voltage input from the rectifier circuit 120 to the electrolytic capacitor C1 is √2×Vs. For example, if the voltage V1 is 100 Vrms, the maximum value is √2×100 V (approximately 141.4 V).

[0020] Considering the fluctuation of the input voltage ACIN, for example, when an electrolytic capacitor C1 with a withstand voltage of 200 V is used, if the smoothed voltage V1 rises to 141.4 Vrms (=200 / √2) or more, the maximum value of the voltage input to the electrolytic capacitor C1 exceeds 200 V. Therefore, when there is a risk that a voltage exceeding the withstand voltage of each of the electrolytic capacitor C1 and the DC / DC converter 150 may be applied to the power supply control circuit 160, the power supply control circuit 160 controls the phase control circuit 110 to turn the triac on / off. This makes it possible to make the maximum voltage supplied to the rectifier circuit 120 equal to or lower than the withstand voltage.

[0021] However, even when the voltage supplied to the rectifier circuit 120 is lowered, the power supply control circuit 160 performs phase control so that the voltage V1 is maintained at a high voltage that does not become an overvoltage, so that normal DC voltages V24, V5 are output from the DC / DC converter 150.

[0022] Fig. 2 is a timing diagram showing an example of the operation of power supply device 100 in Fig. 1. That is, Fig. 2 shows an example of a power control method for power supply device 100. For example, the operation shown in Fig. 2 may be realized by a power control program executed by the CPU of power supply control circuit 160.

[0023] For example, after power is applied to the power supply device 100, the power supply control circuit 160 constantly outputs a high-level phase control signal PCNT to the phase control circuit 110 until the voltage V1(max) per half-wave cycle of the input voltage ACIN exceeds the threshold voltage VT1 (FIG. 2(a)). The threshold voltage VT1 is an example of a first threshold. The zero-cross detection circuit 140 outputs a zero-cross signal ZCRS every time the input voltage ACIN becomes 0V (FIG. 2(b)).

[0024] While the phase control signal PCNT is at a high level, the triac of the phase control circuit 110 is maintained in an on state, and the phase control circuit 110 outputs the input voltage ACIN as the AC voltage ACOUT without performing phase control (FIG. 2(c)).

[0025] In the AC voltage ACOUT, the solid line waveform indicates that a voltage is supplied to the rectifier circuit 120, and the dashed line waveform indicates that no voltage is supplied to the rectifier circuit 120 due to phase control. The shaded area of ​​the AC voltage ACOUT visually indicates the power supplied to the electrolytic capacitor C1 and the DC / DC converter 150 via the rectifier circuit 120.

[0026] For example, suppose that the input voltage ACIN rises and the voltage V1(max) exceeds the threshold voltage VT1 due to a neutral phase loss in a single-wire three-wire power supply, erroneous connection of the power supply device 100 to a 200V power supply, or use of the power supply device 100 in an area where the commercial AC power supply AC is unstable. The power supply control circuit 160 detects that the voltage V1(max) has exceeded the threshold voltage VT1 based on the voltage detection signal VDET (FIG. 2(d)).

[0027] When the voltage V1(max) exceeds the threshold voltage VT1, the power supply control circuit 160 outputs a phase control signal PCNT to the triac of the phase control circuit 110 to set the phase angle of the AC voltage ACOUT to 90 deg, and starts phase control (FIG. 2(e)). During phase control, the phase control circuit 110 stops outputting the AC voltage ACOUT to the rectifier circuit 120 before receiving the phase control signal PCNT, and outputs the AC voltage ACOUT to the rectifier circuit 120 after receiving the phase control signal PCNT until the next zero cross point. The triac is turned off while receiving a low-level phase control signal PCNT, turned on in response to a high-level phase control signal PCNT, and then turned off when the input voltage ACIN becomes 0V, i.e., when the polarity of the input voltage ACIN changes.

[0028] The power supply control circuit 160 adjusts the time from the edge of the zero-cross signal ZCRS to the output of the phase control signal PCNT according to the value of the voltage V1(max) indicated by the voltage detection signal VDET so that the voltage V1(max) does not exceed the withstand voltage of the electrolytic capacitor C1. The power supply control circuit 160 outputs the phase control signal PCNT as a trigger signal after the phase of the input voltage ACIN advances by 90 deg or more from the zero-cross point. Then, the power supply control circuit 160 sets the phase angle to 90 deg or more and performs control so that the voltage V1(max) is equal to the threshold voltage VT1 (FIG. 2(f)).

[0029] Then, the power supply control circuit 160 outputs a phase control signal PCNT to the triac of the phase control circuit 110, which sets the phase angle of the AC voltage ACOUT to 90 deg or more, thereby preventing an overvoltage exceeding the withstand voltage from being input to the electrolytic capacitor C1 and the DC / DC converter 150. When the overvoltage state of the input voltage ACIN is resolved, the voltage V1(max) becomes equal to or less than the threshold voltage VT2 by continuing the phase control at a phase angle of 90 deg (FIG. 2(g)). In this case, even if the phase control is stopped, an overvoltage will not be applied to the electrolytic capacitor C1, etc. The threshold voltage VT2 is an example of a second threshold.

[0030] In phase control using a triac, switching loss occurs when the triac is turned on. Therefore, if phase control of 90 degrees or more is continued even after the maximum voltage of the input voltage ACIN drops and returns to a normal waveform, not only will the voltage V1(max) drop, but the efficiency of the power supply device 100 will also deteriorate compared to when phase control is not used.

[0031] Therefore, the power supply control circuit 160 detects that the voltage V1(max) has become lower than a threshold voltage VT2, which is a threshold voltage VT1 with hysteresis (FIG. 2(h)). Based on the detection, the power supply control circuit 160 sets the phase control signal PCNT to a high level from the next control period of the triac (a half-wave period of the input voltage ACIN) (FIG. 2(i)).

[0032] As a result, the triac is fixed in the on state, phase control is stopped, and the phase control circuit 110 can output the input voltage ACIN as the AC voltage ACOUT to the rectifier circuit 120. The rectifier circuit 120 can generate the voltage V1 by fully using the input voltage ACIN. As a result, it is possible to prevent the efficiency of the power supply device 100 from deteriorating (FIG. 2(j)). The decrease in the voltage V1(max) is stopped, and the voltage V1(max) becomes approximately the same value as the maximum value of the input voltage ACIN (FIG. 2(k)).

[0033] Although not particularly limited, for example, when an electrolytic capacitor C1 with a withstand voltage of 200 V is used, 180 V is determined to be an input overvoltage state with a margin. In this case, in order to perform phase control at a phase angle of 90 deg or more when the voltage V1(max) exceeds 180 V, the threshold voltage VT1 is set to 180 V. Then, the power supply control circuit 160 starts phase control when the voltage V1(max) exceeds 180 V.

[0034] Although not particularly limited, the threshold voltage VT2 is set to about 140 V to 170 V. The threshold voltage VT2 of about 140 V to 170 V corresponds to an effective value of the input voltage ACIN of about 100 V to 120 V.

[0035] For example, if the input voltage ACIN rises and its effective value becomes 150Vrms, the maximum value of the input voltage ACIN and the AC voltage ACOUT will be approximately 212V. In this case, by setting the phase angle θ to 122deg, which is greater than or equal to 90deg, the voltage V1(max) can be set to the threshold voltage VT1. 122deg can be calculated from 180V / (√2×150Vrms)=sinθ=≒0.849.

[0036] Even if the input voltage ACIN becomes even larger, by further increasing the phase angle, it is possible to control the voltage V1(max) so that it does not exceed the threshold voltage VT1, and it is possible to control so that a voltage higher than 180 V is not applied to the electrolytic capacitor C1.

[0037] Fig. 3 is a flow diagram showing an example of the operation of power supply device 100 in Fig. 1. That is, Fig. 3 shows an example of a power control method for power supply device 100. For example, the flow shown in Fig. 3 may be realized by a power control program executed by a CPU mounted on power supply control circuit 160. An example in which the CPU executes the power control program will be described below. The flow shown in Fig. 3 is started when power supply device 100 is connected to an alternating current power supply AC (AC power is turned on) and power supply device 100 is started.

[0038] First, in step S102, the CPU of the power supply control circuit 160 starts monitoring the voltage V1(max) upon receiving the voltage detection signal VDET from the voltage detection circuit 130 upon being started. Next, in step S104, the CPU continues to output a high-level phase control signal PCNT to the phase control circuit 110 to keep the triac on all the time.

[0039] Next, in step S106, if the voltage V1(max) exceeds the threshold voltage VT1, the CPU executes step S108. In step S108, the CPU starts phase control of the AC voltage by the triac at a phase angle φ=90 deg. The phase angle φ=90 deg corresponds to the timing at which the phase control signal PCNT is set to a high level after a half-wave period of the input voltage ACIN from the timing at which the zero-cross signal ZCRS is received.

[0040] Next, in step S110, if the voltage V1(max) exceeds the threshold voltage VT1, the CPU performs step S112, and if the voltage V1(max) is equal to or less than the threshold voltage VT1, the CPU performs step S114. In step S112, the CPU increases the phase angle φ by one unit and returns to step S110. Although not particularly limited, one unit may be 1 deg. The maximum value φmax of the phase angle φ is 180 deg.

[0041] In step S114, the CPU decreases the phase angle φ by one unit and executes step S116. The minimum value φmin of the phase angle φ is 90 deg. In step S116, if the voltage V1(max) is less than the threshold voltage VT2, the CPU executes step S118, and if the voltage V1(max) is equal to or greater than the threshold voltage VT2, the CPU returns to step S110. In step S118, the CPU stops the phase control by keeping the triac always on, and returns to step S106.

[0042] As described above, in the first embodiment, when the voltage V1(max) exceeds the threshold voltage VT1, the power supply control circuit 160 performs phase control at a phase angle φ=90 deg or more to bring the voltage V1(max) closer to the threshold voltage VT1. This makes it possible to prevent the voltage V1(max) from becoming an overvoltage while allowing the DC / DC converter 150 to operate normally, even when an overvoltage close to the withstand voltage of the electrolytic capacitor C1 or the like is input to the power supply device 100. As a result, it is possible to prevent the application of an overvoltage to the electrolytic capacitor C1 or the like while maintaining the supply of power to the load 290 mounted in the electronic device 300 together with the power supply device 100.

[0043] When the voltage V1(max) falls below the threshold voltage VT2, the power supply control circuit 160 constantly sets the phase control signal PCNT to a high level, fixes the triac in an on state, and stops phase control. This allows the phase control circuit 110 to output the input voltage ACIN as an AC voltage ACOUT to the rectifier circuit 120, and the rectifier circuit 120 can generate the voltage V1 by fully using the input voltage ACIN. As a result, it is possible to prevent the efficiency of the power supply device 100 from deteriorating.

[0044] Second Embodiment FIG. 4 is a block diagram showing an example of a power supply device according to a second embodiment of the present invention. The same elements as those in FIG. 1 are given the same reference numerals, and detailed description thereof will be omitted. The power supply device 100A shown in FIG. 4 has the same configuration and function as the power supply device 100 in FIG. 1, except that it does not have the power supply control circuit 160 in FIG. 1. The power supply device 100A is a switching power supply that generates DC voltages V24 and V5. The power supply device 100A may be mounted, together with a control board 200 and a load 290, in an electronic device 300 such as an image forming device, a projector, an electronic whiteboard, a digital signage, an imaging device, a PC (Personal Computer), or a server. The control board 200 is an example of a power supply control device that controls the power supply device 100A.

[0045] The voltage detection signal VDET from the voltage detection circuit 130 and the zero cross signal ZCRS from the zero cross detection circuit 140 are supplied to a control board 200A connected to the power supply device 100A. The phase control circuit 110 receives a phase control signal PCNT from the control board 200A. The control board 200A has a CPU 210 that operates by receiving a DC voltage V5 generated by the DC / DC converter 150. The CPU 210 controls the power supply device 100A by carrying out the flow shown in Fig. 3, thereby realizing the same operation as that shown in Fig. 2. The CPU 210 is an example of a power supply control circuit.

[0046] Fig. 5 is an overall configuration diagram showing an example of an image forming apparatus in which the power supply device 100A of Fig. 4 is installed. The image forming apparatus 1 shown in Fig. 5 is, for example, a digital multifunction peripheral (MFP: Multi-Function Printer) having a copy function, a print function, a scanner function, a facsimile function, etc. The image forming apparatus 1 can mutually switch between operation modes that respectively realize the copy function, the print function, the scanner function, and the facsimile function by using an application switching key or the like on the operation unit of the image forming apparatus 1. The image forming apparatus 1 goes into a copy mode when the copy function is selected, goes into a print mode when the print function is selected, goes into a scanner mode when the scanner function is selected, and goes into a facsimile mode when the facsimile function is selected.

[0047] In addition, the image forming apparatus 1 switches its internal state to a normal mode, an energy saving mode (power saving mode), etc., depending on the state of the internal circuit. For example, the normal mode includes an operating mode (operating state) and a standby mode (standby state).

[0048] For example, the operating mode includes a copy mode or a print mode in which an image or text data is printed on a paper medium. The print mode includes an operation in a facsimile mode in which received data is printed on a paper medium. The operating mode also includes a transmission / reception operation in a scanner mode in which an original document is scanned or a facsimile mode. The state of the internal circuitry is switched by the user of the image forming apparatus 1 operating the operation unit or by control within the image forming apparatus 1.

[0049] For example, the image forming apparatus 1 includes an automatic document feeder 2 (ADF: Auto Document Feeder), an image reading device 3, a writing unit 4, a printer unit 5, an operation unit 11, a control board 200A, and a power supply device 100A. The printer unit 5 includes a photoconductor drum 6, a developing device 7, a transfer belt 8, a fixing device 9, and a storage space for storing a paper feed tray 10.

[0050] The power supply device 100A is connected to a commercial AC power source AC via a power cable, and has a function of generating, for example, DC voltages V24 and V5 shown in Fig. 4 using AC voltage supplied from the commercial AC power source AC, and supplying the DC voltages V24 and V5 as power to a load 290 and a control board 200A shown in Fig. 4. The load 290 to which power is supplied includes the automatic document feeder 2, the image reader 3, the writing unit 4, the printer unit 5, the operation unit 11, etc.

[0051] The printer unit 5 creates a toner image to be transferred to a paper medium or the like based on image information. The printer unit 5 is an example of an image forming section that forms an image. Below, as an example of the flow of image formation in the image forming apparatus 1, a case where the operation mode is set to the copy mode will be briefly described.

[0052] In the copy mode, a stack of documents (multiple documents) to be copied is set in the automatic document feeder 2, or a document to be copied is set on the image reading device 3. When a start button displayed on the operation unit 11 is pressed, the automatic document feeder 2 feeds the documents one by one to the image reading device 3. The image reading device 3 reads image information of each of the documents sent in sequence from the automatic document feeder 2 or the document set on the image reading device 3. The image information read by the image reading device 3 is processed, for example, by an image processing unit mounted on the control device 12.

[0053] The writing unit 4 converts the image information processed by the image processing unit into optical information. The photoconductor drum 6 is uniformly charged by a charger disposed opposite the photoconductor drum 6, and then exposed to laser light containing the optical information converted by the writing unit 4. An electrostatic latent image is formed on the photoconductor drum 6 by the exposure. The developing device 7 develops the electrostatic latent image on the photoconductor drum 6 to form a toner image on the photoconductor drum 6. The transfer belt 8 transfers the toner image to a paper medium or the like. The fixing device 9 fixes the toner image to the paper medium or the like. The transfer paper on which the image of the original has been copied is then discharged from the discharge section.

[0054] The operation unit 11 accepts various inputs according to user 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 for which the input was accepted, information indicating the operating 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 receives a DC voltage from a power supply device and operates at all times. Therefore, the operation unit 11 can accept various inputs not only in the normal mode but also in the energy saving mode.

[0055] The CPU 210 (FIG. 4) mounted on the control board 200A executes an operation control program to control the overall operation of the image forming apparatus 1, including control of the printer unit 5, control of communication, and control of input to the operation unit 11. The CPU 210 also executes an image processing program or a data processing program to perform image processing or data processing, and form an image to be transferred onto a paper medium or the like. Furthermore, the CPU 210 executes a power supply control program to perform the same phase control as in FIGS. 2 and 3.

[0056] 5 shows an example in which the power supply device 100A is installed in an image forming apparatus 1 such as a digital multifunction peripheral. However, the power supply device 100A may also be installed in an image forming apparatus having a single function such as a scanner, printer, or facsimile.

[0057] Fig. 6 is a block diagram showing an example of a hardware configuration of the control board 200A of Fig. 4. The control board 200A is equipped with a CPU 210, a ROM (Read Only Memory) 220, and a RAM (Random Access Memory) 230. The control board 200A is also equipped with an input interface unit 240, an output interface unit 250, an input / output interface unit 260, and a communication interface unit 270.

[0058] For example, the CPU 210, the ROM 220, the RAM 230, the input interface unit 240, the output interface unit 250, the input / output interface unit 260, and the communication interface unit 270 are connected to one another via a bus BUS. Note that a plurality of the CPU 210, the ROM 220, the RAM 230, the input interface unit 240, the output interface unit 250, the input / output interface unit 260, and the communication interface unit 270 may be integrated on one chip.

[0059] The control board 200A may be mounted on a computer device such as a PC or a server. The power supply control circuit 160 shown in Fig. 1 may be designed as a microcomputer having the CPU 210, ROM 220, and RAM 230 of Fig. 6, an input port, and an output port. For example, the microcomputer receives the voltage detection signal VDET and the zero cross signal ZCRS at the input ports, and outputs the phase control signal PCNT from the output port.

[0060] The CPU 210 executes various programs such as an OS (Operating System) and applications. The ROM 220 holds basic programs and various parameters for enabling the CPU 210 to execute the various programs. The RAM 230 stores the various programs executed by the CPU 210 and data used by the programs. For example, the various programs may include a power supply control program for controlling the power supply device of FIG. 4. The various programs may also include an image processing program for performing image processing of a document image read by the image reading device 3 of FIG. 1.

[0061] The input interface unit 240 is connected to an input device 410 such as the image reading device 3 and the operation unit of the image forming device 1. The output interface unit 250 is connected to an output device 420 such as a display unit of the operation unit 11. The input / output interface unit 260 is connected to an input / output device 430 such as an auxiliary storage device and a recording medium.

[0062] When various programs such as an image processing program or a power supply control program are stored in the recording medium, the programs may be transferred from the recording medium to the RAM 230 or the like via the input / output interface unit 260. The communication interface unit 270 is capable of connecting the image forming apparatus 1 to a network or the like.

[0063] As described above, in the second embodiment, similarly to the first embodiment, when the voltage V1(max) exceeds the threshold voltage VT1, the CPU 210 performs phase control at a phase angle φ=90 deg or more to bring the voltage V1(max) closer to the threshold voltage VT1. This makes it possible to prevent overvoltage from being applied to the electrolytic capacitor C1, etc., while maintaining the supply of power to the load 290 mounted on the electronic device 300 together with the power supply device 100A.

[0064] When the voltage V1(max) falls below the threshold voltage VT2, the CPU 210 constantly sets the phase control signal PCNT to a high level, fixes the triac in an on state, and stops phase control. This makes it possible to prevent the efficiency of the power supply device 100A from deteriorating.

[0065] Furthermore, in the second embodiment, by installing the power supply device 100A in the image forming apparatus 1, it is possible to prevent overvoltage from being applied to internal circuits such as the electrolytic capacitor C1 in the power supply device 100A while maintaining the supply of power to the load 290 of the image forming apparatus 1.

[0066] (Third embodiment) Fig. 7 is a block diagram showing an example of a power supply device according to a third embodiment of the present invention. Elements similar to those in Fig. 1 and Fig. 4 are given the same reference numerals and detailed description will be omitted.

[0067] 7 is a switching power supply that generates, for example, DC voltages V24, V5 by phase-controlling and smoothing an input voltage ACIN supplied from a commercial AC power supply AC, similar to the power supply device 100 shown in Fig. 1. The power supply device 100B may be mounted, together with a control board 200A and a load 290, in an electronic device 300 such as an image forming apparatus, a projector, an electronic whiteboard, a digital signage, an imaging device, a PC (Personal Computer), or a server.

[0068] Power supply device 100B has the same configuration and function as power supply device 100A in Fig. 4, except that it has a phase control circuit 110B and a zero-cross detection circuit 140B instead of the phase control circuit 110 and the zero-cross detection circuit 140 in Fig. 4. Electronic device 300 has the same configuration and function as electronic device 300 in Fig. 4, except that it has power supply device 100B instead of power supply device 100A in Fig. 4.

[0069] For example, the power supply device 100B includes a phase control circuit 110B, a rectifier circuit 120, a voltage detection circuit 130, a zero-cross detection circuit 140B, a DC / DC converter 150, a current fuse 170, and electrolytic capacitors C1, C2, and C3. The phase control circuit 110B includes a triac 111, a phototriac coupler 112, a relay 113, and resistors R1, R2, and R3. The zero-cross detection circuit 140B includes a rectifier circuit 141, a phototransistor coupler 142, a capacitor C4, and resistors R4 and R5.

[0070] In the phase control circuit 110B, one end of the triac 111 is connected to the input voltage line ACIN via a current fuse 170, and the other end of the triac 111 is connected to the rectifier circuit 120 via an AC voltage line ACOUT. In addition, one end of the triac 111 is connected to one end of the triac of the phototriac coupler 112 via a resistor R1. The other end of the triac 111 is connected to one end of the triac of the phototriac coupler 112 via a resistor R1.

[0071] The control terminal of the triac 111 is connected to the other end of the phototriac coupler 112. The light emitting diode of the phototriac coupler 112 has an anode connected to the phase control signal line PCNT via a resistor R3, and a cathode grounded.

[0072] When the phase control signal PCNT is at a low level, the triac of the phototriac coupler 112 is turned off, and the triac 111 is turned off. When the phase control signal PCNT is at a high level, the triac of the phototriac coupler 112 is turned on, and the triac 111 is turned on. If the triac 111 is temporarily turned on, the on state of the triac 111 is maintained until the input voltage ACIN becomes 0 V, even if the phase control signal PCNT becomes a low level.

[0073] One end of the relay 113 is connected to the input voltage line ACIN via a current fuse 170, and the other end of the relay 113 is connected to the rectifier circuit 120 via an AC voltage line ACOUT. That is, the relay 113 is connected in parallel with the triac 111.

[0074] For example, relay 113 is a normally closed type, and is turned on even when relay control signal RCNT output from control board 200A is in a floating state. This allows input voltage ACIN to be supplied to rectifier circuit 120 via relay 113 immediately after power supply to power supply device 100B is started, and before CPU 210 is started. Therefore, compared to a case in which relay 113 is not provided, the time from when input voltage ACIN is supplied to power supply device 100B until DC / DC converter 150 generates voltages V24 and V5 can be shortened.

[0075] The relay 113 is turned on when the relay control signal RCNT is at a high level, and supplies the input voltage ACIN to the rectifier circuit 120 without passing through the triac 111. The relay 113 is turned off when the relay control signal RCNT is at a low level.

[0076] In the zero-cross detection circuit 140B, resistors R4 and R5 are connected in series between one end of the current fuse 170 and the input of the rectifier circuit 141. The connection node of the resistors R4 and R5 is grounded via a capacitor C4. The light-emitting diode of the phototransistor coupler 142 has an anode connected to the output of the rectifier circuit 141 and a cathode grounded. The transistor of the phototransistor coupler 142 has a collector connected to the zero-cross signal line ZCRS and an emitter grounded.

[0077] For example, the rectifier circuit 141 is a diode bridge, and supplies a voltage obtained by full-wave rectifying the input voltage ACIN to the phototransistor coupler 142. Then, the phototransistor coupler 142 outputs a zero-cross signal ZCRS for each half-wave period of the input voltage ACIN.

[0078] 1, the power supply device 100B may have a power supply control circuit 160 that receives the voltage detection signal VDET and the zero cross signal ZCRS and outputs a phase control signal PCNT. In this case, the CPU 210 of the control board 200A of the electronic device 300 does not control the power supply device 100B.

[0079] FIG. 8 is a timing diagram showing an example of the operation of the power supply device 100B of FIG. 7. That is, FIG. 8 shows an example of a power supply control method of the power supply device 100B. For example, the operation shown in FIG. 8 may be realized by a power supply control program executed by the CPU 210 of the control board 200A. Detailed description of the same operation as in FIG. 2 will be omitted. FIG. 8 is similar to the waveform of FIG. 2, except that the waveform of the phase control signal PCNT when the voltage V1(max), which is the maximum value per half-wave cycle of the voltage V1 (pulsating current), is lower than the threshold voltage VT2, is different from that in FIG. 2.

[0080] 8, when power is not being supplied to the power supply device 100B and the control board 200A, the normally-closed type relay 113 is on. Therefore, the power supply terminal ACIN of the power supply device 100B that receives the input voltage ACIN is connected to the input of the rectifier circuit 120 via the relay 113 and the AC voltage line ACOUT.

[0081] Thereafter, when the power supply device 100B is powered on, the input voltage ACIN is supplied to the rectifier circuit 120 without passing through the turned-off triac 111, and voltage V1 in Fig. 7 is generated by smooth rectification. The DC / DC converter 150 uses the voltage V1 to generate DC voltages V24 and V5. The voltage detection circuit 130 outputs the value of voltage V1(max) to the control board 200A as a voltage detection signal VDET.

[0082] When the CPU 210, which is started by receiving the DC voltage V5, detects based on the voltage detection signal VDET that the voltage V1(max) is lower than the threshold voltage VT2, it sets the phase control signal PCNT to a low level and sets the relay control signal RCNT to a high level (FIG. 8(a)). After this, the operation until the voltage V1(max) reaches the threshold voltage VT2 is the same as that in FIG. 2 (FIG. 8(b)). However, the input voltage ACIN is supplied to the power supply device 100B via the relay 113.

[0083] When the CPU 210 detects that the voltage V1(max) has reached the threshold voltage VT2, it sets the phase control signal PCNT to a high level and sets the relay control signal RCNT to a low level (FIGS. 8(c) and (d)). This turns on the triac 111, and the input voltage ACIN is supplied to the rectifier circuit 120 via the triac 111, making it possible to control the phase of the input voltage ACIN. The operation when the voltage V1(max) is equal to or higher than the threshold voltage VT2 is the same as that in FIG. 2.

[0084] 2, when the CPU 210 detects that the voltage V1(max) is lower than the threshold voltage VT2, it sets the phase control signal PCNT to a high level from the next control cycle of the triac (FIGS. 8(e) and (f)). Also, when the CPU 210 detects that the voltage V1(max) is lower than the threshold voltage VT2, it sets the relay control signal RCNT to a high level, thereby turning on the relay 113 (FIG. 8(g)).

[0085] The CPU 210 sets the phase control signal PCNT to a low level after time T1, which is the time from when the relay control signal RCNT is output until the relay 113 actually turns on (FIG. 8(h)). By waiting for the passage of time T1, it is possible to prevent both the triac 111 and the relay 113 from turning off, and to prevent malfunction of the power supply device 100B. Furthermore, by turning off the triac 111, it is possible to prevent switching loss when the triac 111 is on, similar to when the voltage V1(max) becomes lower than the threshold voltage VT2 in FIG. 2, and to prevent deterioration in the efficiency of the power supply device 100B.

[0086] Fig. 9 is a flow diagram showing an example of the operation of the power supply device 100B of Fig. 7. That is, Fig. 9 shows an example of a power control method of the power supply device 100B. The flow shown in Fig. 9 may be realized by a power control program executed by the CPU 210 mounted on the control board 200A. Detailed description of the same operations as those in Fig. 3 will be omitted.

[0087] 9 is started when the power supply device 100B is connected to an AC power source AC (AC power-on) and the power supply device 100B is started. When the AC power source is turned on, the rectifier circuit 120 receives the input voltage ACIN from the relay 113 as the AC voltage ACOUT and operates to operate the DC / DC converter 150.

[0088] First, in step S202, the CPU 210 is started by a power-on reset and starts monitoring the voltage V1(max) by the voltage detection signal VDET. Next, in step S204, the CPU 210 compares the voltage V1(max) with a threshold voltage VT2, and if the voltage V1(max) exceeds the threshold voltage VT2, the CPU 210 executes step S206.

[0089] In step S206, the CPU 210 sets the phase control signal PCNT to a high level to keep the triac 111 always on, and sets the relay control signal RCNT to a low level to turn off the relay 113. Next, in step S208, the CPU 210 determines whether or not the voltage V1(max) exceeds the threshold voltage VT2, and if it does, executes step S210, and if it does not, executes step S212.

[0090] In step S210, the CPU 210 compares the voltage V1(max) with a threshold voltage VT1, and if the voltage V1(max) exceeds the threshold voltage VT1, executes step S214 in Fig. 10. In step S212, the CPU 210 sets the relay control signal RCNT to a high level to turn on the relay 113. Furthermore, the CPU 210 sets the phase control signal PCNT to a low level after a time T1 has elapsed since the high-level relay control signal RCNT was output to the relay 113 until the relay 113 actually turns on, thereby turning off the triac 111. Then, the CPU 210 returns the process to step S204.

[0091] 10, the CPU 210 sets the phase angle φ to an initial value of 90 deg. For example, the CPU 210 sets a value corresponding to 90 deg in a register for phase control. The phase angle φ=90 deg corresponds to the timing at which the phase control signal PCNT is set to a high level after a half-wave period of the input voltage ACIN from the timing at which the zero-cross signal ZCRS is received.

[0092] Next, in step S216, the CPU 210 performs phase control of the triac 111 with the currently set phase angle φ. Next, in step S218, the CPU 210 determines whether or not the voltage V1(max) exceeds the threshold voltage VT1, and if it does, performs step S220, and if it does not, performs step S222.

[0093] In step S220, the CPU 210 increases the phase angle φ by one unit, and returns the process to step S216. The maximum value φmax of the phase angle φ is 180 deg. In step S222, the CPU 210 decreases the phase angle φ by one unit, and moves the process to step S222. The minimum value φmin of the phase angle φ is 90 deg. Although not particularly limited, one unit may be 1 deg.

[0094] In step S224, the CPU 210 determines whether the voltage V1(max) is lower than the threshold voltage VT2, and if it is lower, executes step S226, and if it is equal to or higher than the threshold voltage VT2, returns the process to step S216. In step S226, the CPU 210 sets the relay control signal RCNT to a high level, as in step S212, to turn on the relay 113. Furthermore, the CPU 210 turns off the triac 111 after a time T1 has elapsed since the relay control signal RCNT was set to a high level, and returns the process to step S204 in FIG.

[0095] As described above, in the third embodiment, similarly to the first and second embodiments, when the voltage V1(max) exceeds the threshold voltage VT1, the CPU 210 performs phase control at a phase angle φ=90 deg or more to bring the voltage V1(max) closer to the threshold voltage VT1. This makes it possible to prevent overvoltage from being applied to the electrolytic capacitor C1, etc., while maintaining the supply of power to the load 290 mounted on the electronic device 300 together with the power supply device 100B.

[0096] Furthermore, in the third embodiment, by connecting relay 113 in parallel with triac 111, CPU 210 can turn off the triac and turn on relay 113 when not performing phase control by triac 111. This makes it possible to suppress the occurrence of switching loss when triac 111 is turned on, and suppress deterioration in efficiency of power supply device 100B.

[0097] Furthermore, by providing normally-closed relay 113, it is possible to supply input voltage ACIN to rectifier circuit 120 via relay 113 immediately after power supply to power supply device 100B is started and before CPU 210 is started. Therefore, compared to a case in which relay 113 is not provided, it is possible to shorten the time from when supply of input voltage ACIN is started to power supply device 100B until DC / DC converter 150 generates voltages V24 and V5.

[0098] (Fourth embodiment) Fig. 11 is a block diagram showing an example of a power supply device according to a fourth embodiment of the present invention. The same elements as those in Figs. 1 and 4 are given the same reference numerals, and detailed description thereof will be omitted. The power supply device 100C shown in Fig. 11 is a switching power supply that generates, for example, DC voltages V24, V5 by phase-controlling and smoothing an input voltage ACIN supplied from a commercial AC power supply AC, similar to the power supply device 100 shown in Fig. 1. The power supply device 100C may be mounted, together with a control board 200A and a load 290, in an electronic device 300 such as an image forming device, a projector, an electronic whiteboard, a digital signage, an imaging device, a PC (Personal Computer), or a server.

[0099] The power supply device 100C has a phase control circuit 110C and a rectifier circuit 120C instead of the phase control circuit 110 and the rectifier circuit 120 of Fig. 4. The output of the rectifier circuit 120C is connected to the phase control circuit 110 via a voltage line Va. The power supply device 100C also has a diode D1 having an anode connected to a voltage line Vb which is the output of the phase control circuit 110 and a cathode connected to a voltage line V1.

[0100] The voltage detection circuit 130 detects the value of the voltage V1(max) which is the maximum value per half-wave period of the voltage V1 (pulsating current) output from the cathode of the diode D1 and smoothed by the electrolytic capacitor C1. The power supply device 100C has the same configuration and function as the power supply device 100A of FIG. 4, except that the rectifier circuit 120C directly receives the input voltage ACIN via the current fuse 170, and the phase control circuit 110C is connected to the output of the rectifier circuit 120C.

[0101] The rectifier circuit 120C is, for example, a full-wave rectifier circuit including a diode bridge, which rectifies the input voltage ACIN and outputs it as a voltage Va (pulsating current). The voltage Va is an example of a second AC voltage. The phase control circuit 110C has a thyristor (not shown) controlled by a phase control signal PCNT. For example, the thyristor is turned off while receiving a low-level phase control signal PCNT, turned on when receiving a high-level phase control signal PCNT, and then turned off when the voltage Va becomes 0V, i.e., when the polarity of the voltage Va changes.

[0102] Then, the phase control circuit 110C outputs a voltage Vb (pulsating current) whose phase is controlled in response to the phase control signal PCNT. The diode D1 functions as a reverse current prevention element that prevents a current from flowing from the voltage line V1 to the phase control circuit 110C.

[0103] 1, the voltage detection circuit 130 detects the value of the voltage V1(max), which is the maximum value of the voltage V1 (pulsating current) for each half-wave period, and outputs the detected value as a voltage detection signal VDET to the control board 200A. The CPU 210 of the control board 200A compares the value of the voltage V1(max) indicated by the voltage detection signal VDET with threshold voltages VT1 and VT2, and outputs a phase control signal PCNT to the phase control circuit 110 in accordance with the timing of the zero-cross signal ZCRS.

[0104] 1, the power supply device 100C may have a power supply control circuit 160 that receives the voltage detection signal VDET and the zero cross signal ZCRS and outputs a phase control signal PCNT. In this case, the CPU 210 of the control board 200A of the electronic device 300 does not control the power supply device 100C.

[0105] Fig. 12 is a timing diagram showing an example of the operation of the power supply device 100C of Fig. 11. That is, Fig. 12 shows an example of a power control method of the power supply device 100C. For example, the operation shown in Fig. 12 may be realized by a power control program executed by the CPU 210 of the control board 200A. Detailed description of the same operations as those in Fig. 2 will be omitted.

[0106] 12 is similar to the waveforms in FIG. 2, except that it uses a pulsating current after full-wave rectification. The waveforms of the input voltage ACIN, the voltage V1(max), the zero-cross signal ZCRS, and the phase control signal PCNT are the same as those in FIG.

[0107] The rectifier circuit 120C full-wave rectifies the input voltage ACIN to generate a voltage Va (pulsating current) (FIG. 12(a)). The CPU 210 outputs a high-level phase control signal PCNT to the phase control circuit 110C until the voltage V1(max) exceeds the threshold voltage VT1 (FIG. 12(b)). When the voltage V1(max) falls below the threshold voltage VT2, the CPU 210 outputs a high-level phase control signal PCNT to the phase control circuit 110C (FIG. 12(c)). While the phase control signal PCNT is at a high level, the phase control circuit 110C maintains the built-in thyristor in an on state and outputs a voltage Vb with the same waveform as the DC voltage Va (FIGS. 12(d) and (e)).

[0108] 2, when the voltage V1(max) exceeds the threshold voltage VT1, the CPU 210 outputs a phase control signal PCNT to the thyristor of the phase control circuit 110C to set the phase angle of the DC voltage Vb to 90 deg, and starts phase control (FIG. 12(f)). Then, the CPU 210 sets the phase angle to 90 deg or more, and performs control so that the voltage V1(max) is equal to the threshold voltage VT1 (FIG. 12(g)).

[0109] When the overvoltage state of the input voltage ACIN is resolved, the voltage V1(max) becomes equal to or lower than the threshold voltage VT2 by continuing the phase control at a phase angle of 90 deg (FIG. 12(h)). Then, the CPU 210 sets the phase control signal PCNT to a high level from the next control period of the thyristor (a half-wave period of the input voltage ACIN) (FIG. 12(i)).

[0110] The operation flow of the power supply device 100C is the same as that shown in Fig. 3, except that phase control is performed using a thyristor instead of a triac. Also, in the power supply device 100C, a normally closed type relay may be connected in parallel with the thyristor to perform control similar to that of the power supply device 100B in Fig. 7.

[0111] As described above, in the fourth embodiment, similarly to the first to third embodiments, when the voltage V1(max) exceeds the threshold voltage VT1, the CPU 210 performs phase control at a phase angle φ=90 deg or more to bring the voltage V1(max) closer to the threshold voltage VT1. This makes it possible to prevent overvoltage from being applied to the electrolytic capacitor C1, etc., while maintaining the supply of power to the load 290 mounted on the electronic device 300 together with the power supply device 100C.

[0112] When the voltage V1(max) falls below the threshold voltage VT2, the CPU 210 constantly sets the phase control signal PCNT to a high level, fixes the thyristor in an on state, and stops phase control. This makes it possible to prevent the efficiency of the power supply device 100C from deteriorating. In this way, even when a thyristor is mounted in the phase control circuit 110C and the phase control of the voltage Vb is performed by the thyristor, it is possible to obtain the same effects as those of the above-mentioned embodiment.

[0113] Although the present invention has been described above based on the embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0114] 1. Image forming device 2 Automatic document feeder 3. Image Scanning Device 4 Write Unit 5 Printer unit 6 Photoconductor drum 7. Developing device 8 Transfer belt 9 Fixing device 10 Paper feed tray 11 Control section 100, 100A, 100B, 100C power supplies 111 Triac 112 Phototriac coupler 113 Relay 110, 110B, 110C Phase control circuit 120 Rectifier circuit 130 Voltage detection circuit 140, 140B Zero-cross detection circuit 141 Rectifier circuit 142 Phototransistor coupler 150 DC / DC Converter 160 Power supply control circuit 170 Current fuse 200, 200A control board 210 CPU 220 ROM 230 RAM 240 Input Interface Section 250 Output interface section 260 Input / Output Interface Section 270 Communication Interface Section 290 Load 300 Electronic equipment 410 Input Device 420 Output Device 430 I / O device AC commercial alternating current power supply ACIN input voltage ACOUT AC voltage BUS C1, C2, C3 electrolytic capacitors C4 Capacitor PCNT Phase control signal R1, R2, R3, R4, R5 resistance V1 Voltage V5, V24 DC voltage Va, Vb voltage VDET Voltage detection signal VT1, VT2 threshold voltage ZCRS Zero cross signal [Prior art documents] [Patent documents]

[0115] [Patent Document 1] JP 2022-113325 A

Claims

1. A power supply device that generates a DC voltage from a first AC voltage, a phase control circuit capable of generating a second AC voltage by controlling a phase of the first AC voltage; a rectifier circuit that rectifies the second AC voltage to generate a first voltage; a voltage detection circuit that detects a voltage level of the first voltage; a zero-cross detection circuit that detects a zero-cross point of the first AC voltage; a power supply control circuit that receives a detection result of the voltage detection circuit and a detection result of the zero-cross detection circuit, and performs phase control when the voltage level exceeds a first threshold value by outputting a trigger signal to the phase control circuit after the phase of the first AC voltage advances by 90 degrees or more from a zero-cross point for each half-wave period of the first AC voltage, the phase control circuit stops outputting the second AC voltage to the rectifier circuit before receiving the trigger signal during the phase control, and outputs the second AC voltage to the rectifier circuit from receiving the trigger signal until a next zero crossing point; A power supply device comprising:

2. the power supply control circuit continues to output the trigger signal when the voltage level falls below a second threshold lower than the first threshold, thereby constantly outputting the first AC voltage to the rectifier circuit; 2. The power supply device according to claim 1 .

3. The phase control circuit includes: a triac that is turned on in response to the trigger signal and outputs the first AC voltage as the second AC voltage until the next zero crossing point; a normally-closed relay connected in parallel with the triac and operated under control of the power supply control circuit; the power supply control circuit turns off the relay and starts phase control by the triac when the voltage level exceeds the first threshold, and stops phase control by the triac and turns on the relay when the voltage level falls below the second threshold; 3. The power supply device according to claim 2 .

4. The phase control circuit includes: a thyristor that is turned on in response to the trigger signal and outputs the first AC voltage as the second AC voltage until the next zero crossing point; the power supply control circuit keeps the thyristor always on until the voltage level exceeds the first threshold, starts phase control by the thyristor when the voltage level exceeds the first threshold, and keeps the thyristor always on when the voltage level falls below the second threshold; 3. The power supply device according to claim 2 .

5. An electronic device having a power supply device that generates a DC voltage from a first AC voltage, and a power supply control device that controls the power supply device, The power supply device is a phase control circuit capable of generating a second AC voltage by controlling a phase of the first AC voltage; a rectifier circuit that rectifies the second AC voltage to generate a first voltage; a voltage detection circuit that detects a voltage level of the first voltage; a zero-cross detection circuit that detects a zero-cross point of the first AC voltage; the power supply control device receives a detection result of the voltage detection circuit and a detection result of the zero-cross detection circuit, and when the voltage level exceeds a first threshold value, outputs a trigger signal to the phase control circuit after the phase of the first AC voltage advances by 90 degrees or more from a zero-cross point for each half-wave period of the first AC voltage; the phase control circuit stops outputting the first AC voltage to the rectifier circuit before receiving the trigger signal, and outputs the first AC voltage to the rectifier circuit from receiving the trigger signal until a next zero crossing point; An electronic device characterized by:

6. The power supply device according to any one of claims 1 to 4, an image forming unit that forms an image using the DC voltage generated by the power supply device; An image forming apparatus comprising:

7. A power supply control method for a power supply device having a phase control circuit capable of generating a second AC voltage by controlling a phase of a first AC voltage, a rectifier circuit that rectifies the second AC voltage to generate a first voltage, a voltage detection circuit that detects a voltage level of the first voltage, and a zero-cross detection circuit that detects a zero-cross point of the first AC voltage, A power supply control device that controls the power supply device, receiving a detection result from the voltage detection circuit and a detection result from the zero-cross detection circuit, when the voltage level exceeds a first threshold value, outputting a trigger signal to the phase control circuit after the phase of the first AC voltage advances by 90 degrees or more from a zero cross point for each half wave period of the first AC voltage, causing the phase control circuit to stop outputting the first AC voltage to the rectifier circuit before receiving the trigger signal, and outputting the first AC voltage to the rectifier circuit from receiving the trigger signal until the next zero cross point; A power supply control method for a power supply device comprising the steps of:

8. A power supply control program for a power supply device having a phase control circuit capable of generating a second AC voltage by controlling a phase of a first AC voltage, a rectifier circuit that rectifies the second AC voltage to generate a first voltage, a voltage detection circuit that detects a voltage level of the first voltage, and a zero-cross detection circuit that detects a zero-cross point of the first AC voltage, A power supply control device for controlling the power supply device, receiving a detection result of the voltage detection circuit and a detection result of the zero-cross detection circuit; when the voltage level exceeds a first threshold value, outputting a trigger signal to the phase control circuit after the phase of the first AC voltage advances by 90 degrees or more from a zero cross point for each half wave period of the first AC voltage, causing the phase control circuit to stop outputting the first AC voltage to the rectifier circuit before receiving the trigger signal, and causing the phase control circuit to output the first AC voltage to the rectifier circuit from receiving the trigger signal until the next zero cross point; A power supply control program for a power supply device comprising:

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