JP6241428B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present disclosure relates to a power supply device and an image forming apparatus that use a switching element to supply power from a power supply unit to a load.

  In a power supply device including a switching element typified by a flyback method, it is important to reduce switching loss during standby and light load. Therefore, in such a power supply device, at the time of standby and light load, the switching element can be operated in an intermittent operation mode in which a continuous period in which the switching operation is continuously executed and a pause period in which the switching operation is paused are repeated. (For example, patent document 1). As a result, the number of switching operations per unit time is reduced, and the switching loss is reduced.

  In such a power supply device, an inrush current is generated from the switching element when the switching element is turned on after the suspension period ends due to the influence of the charge stored in the parasitic capacitance of the switching element during the suspension period, and the unnecessary radiation is deteriorated. There is a possibility that a roaring sound (vibration sound) may occur due to the vibration of the transformer.

  In order to solve the above problems, the following Patent Documents 2 to 4 are disclosed.

  Patent Document 2 discloses a technique for preventing vibration noise of a coil or a transformer under intermittent oscillation control by changing the peak value of the drain current and performing PWM control of the switching element (paragraph [0020]).

  In Patent Document 3, when the cycle of the intermittent switching operation is detected and the detected cycle reaches a predetermined threshold, the detected cycle is switched so that the detected cycle does not become a cycle within a predetermined range. A technique for preventing the vibration noise of the above is disclosed (claim 1).

  In Patent Document 4, the first switching element (Q1) and the second switching element (Q2) are driven with the voltage from the same first drive winding (Lb1), so that the on period is obtained while synchronizing. Is separately controlled to suppress an increase in the switching frequency of the first switching element (Q1) and prevent vibration noise of the transformer (paragraph [0037]).

JP 2005-027472 A Japanese Patent Laying-Open No. 2005-065481 JP2013-1888083A International Publication No. 2009/025157

  Here, when the resistance value of the resistor connected to the control terminal of the switching element is increased, the switching speed is reduced, and the inrush current generated when the switching element is turned on can be suppressed.

  However, in this case, since the switching loss increases due to the increase in the resistance value, the switching element generates heat and the efficiency deteriorates in the normal operation mode.

  In addition, since all of Patent Documents 1 to 4 do not pay attention to switching the resistance value of the control terminal of the switching element, the basic configuration is different from the present disclosure.

  An object of the present disclosure is to provide a technique for suppressing an excessive inrush current in a switching element when switching from a pause period to a continuous period in an intermittent operation mode while suppressing switching loss in a normal operation mode. To do.

A power supply device according to an aspect of the present disclosure includes a primary winding and a secondary winding, and a transformer that transmits primary power to the secondary side;
A first switching element having a first conduction terminal connected to the primary winding;
A current detector connected to the second conduction terminal of the first switching element and detecting a current flowing through the second conduction terminal;
When the current detected by the current detection unit is greater than a predetermined threshold, the first switching element is driven in a normal operation mode in which a switching operation is continuously performed, and when the detected current is less than the threshold, A first controller that drives the first switching element in an intermittent operation mode that repeats a continuous period in which the switching operation is continuously performed and a pause period in which the switching operation is suspended;
A resistance switching unit including first and second resistors connected in series between the control terminal of the first switching element and the first control unit; and a second switching element connected in parallel to the second resistor;
A first diode having an anode connected to the second conduction terminal, a base resistor having one end connected to the cathode of the first diode and connected to a control terminal of the second switching element, and in parallel with the base resistance And a second control unit that turns off the second switching element by lowering the charging voltage of the first capacitor below the on-voltage of the second switching element during the idle period. ing.

  According to this aspect, the second switching element and the second control unit that bypass the second resistance that is a part of the gate resistance of the first switching element are provided. Accordingly, in the intermittent operation mode, the voltage at the control terminal of the second switching element is lower than the on-voltage during the idle period, and the second switching element is in the off state. As a result, the first resistor and the second resistor are connected to the control terminal of the first switching element, and the switching speed when the first switching element is turned on at the start of the continuous period after the end of the pause period can be reduced. As a result, it is possible to suppress the occurrence of an excessive inrush current at the start of the continuous period.

  On the other hand, in the normal operation mode, since the second switching element is turned on by the second controller, the second resistor is bypassed, and the first resistor is connected to the control terminal of the first switching element. As a result, since the switching speed of the first switching element is increased, the switching loss is improved, heat generation of the first switching element and deterioration of efficiency are prevented, and vibration noise can be prevented from being generated in the transformer.

In addition, a power supply device according to another aspect of the present disclosure includes a primary winding and a secondary winding, and transmits a primary side power to the secondary side,
A first switching element having a first conduction terminal connected to the primary winding;
A current detector connected to the second conduction terminal of the first switching element and detecting a current flowing through the second conduction terminal;
When the current detected by the current detection unit is greater than a predetermined threshold, the first switching element is driven in a normal operation mode in which a switching operation is continuously performed, and when the detected current is less than the threshold, A first controller that drives the first switching element in an intermittent operation mode that repeats a continuous period in which the switching operation is continuously performed and a pause period in which the switching operation is suspended;
A resistance switching unit including first and second resistors connected in series between the control terminal of the first switching element and the first control unit; and a second switching element connected in parallel to the second resistor. Prepared,
The first control unit turns off the second switching element until the first on-period of the first switching element ends after the continuous period is started.

  In this aspect, the 2nd switching element which bypasses the 2nd resistance connected to the control terminal of the 1st switching element is provided. In the intermittent operation mode, the first switching unit turns off the second switching element until the first on-period of the first switching element ends after the continuous period starts. As a result, the first resistor and the second resistor are connected to the control terminal of the first switching element, and the switching speed when the first switching element is turned on at the start of the continuous period can be reduced. As a result, it is possible to suppress the occurrence of an excessive inrush current at the start of the continuous period.

  On the other hand, in the normal operation mode, since the first switching element is turned on by the first control unit, the second resistance is bypassed, and the first resistance is connected to the control terminal of the first switching element. As a result, since the switching speed of the first switching element is increased, the switching loss is improved, heat generation of the first switching element and deterioration of efficiency are prevented, and vibration noise can be prevented from being generated in the transformer.

In the above aspect, the resistance value switching unit is
A first series circuit including the first resistor connected to the control terminal of the first switching element, and a second diode having an anode connected to the first resistor and a cathode connected to the first control unit. When,
A second series circuit including a third resistor connected to the anode of the second diode, and the second resistor having one end connected to the third resistor and the other end connected to the first controller. May be included.

  According to this aspect, the resistance value switching unit includes the first resistor connected to the control terminal of the first switching element and the anode connected to the first resistor, and the cathode connected to the first control unit. A second series circuit including a first resistor including a third resistor connected to the anode of the second diode and one end connected to the third resistor and the other resistor connected to the first controller. And.

  Therefore, when the first switching element is turned off, the charge is drawn from the gate capacitance of the first switching element not through the second series circuit but through the first series circuit, so that the switching speed when the first switching element is turned off. Can be made higher than the switching speed at the time of turn-on, and the switching loss can be reduced.

In the above aspect, the current detection unit is connected between a Zener diode having a cathode connected to the second conduction terminal of the first switching element, and between the cathode of the Zener diode and the first control unit. A fourth resistor, a fifth resistor connected in parallel to the Zener diode, a second capacitor having one end connected to the first control unit and the other end connected to the anode of the Zener diode,
The second control unit may be configured such that the anode of the first diode is connected to the cathode of the Zener diode, and the terminal of the first capacitor opposite to the first diode is connected to the anode of the Zener diode. Good.

  According to this aspect, when the first switching element is turned on, the second capacitor is charged by the current flowing through the second conduction terminal of the first switching element, the charging voltage of the second capacitor is input to the first control unit, One control unit can measure the current of the second conduction terminal by this charging voltage. The cathode of the Zener diode is connected to one end of the second capacitor via a fourth resistor, the anode of the Zener diode is connected to the other end of the second capacitor, and the fifth resistor is connected in parallel to the Zener diode. ing. Therefore, when the voltage of the fifth resistor exceeds the breakdown voltage of the Zener diode due to an increase in the current flowing through the second conduction terminal, the Zener diode is turned on and the voltage increase between the fifth resistors is suppressed. This prevents the charging voltage of the second capacitor from exceeding the breakdown voltage of the Zener diode, and prevents the first control unit from being damaged by an excessive voltage input.

  Furthermore, since the second control unit is connected in parallel with the Zener diode, an excessive voltage is applied to the circuit elements of the second control unit, and the circuit elements constituting the second control unit can be prevented from being damaged. .

  Still another image forming apparatus according to this aspect includes the power supply device described above.

  According to this aspect, it is possible to provide an image forming apparatus that suppresses switching loss in the normal operation mode and at the same time suppresses occurrence of an inrush current in the switching element when switching from the pause period to the continuous period in the intermittent operation mode.

  According to the present disclosure, at the same time as suppressing switching loss in the normal operation mode, it is possible to suppress an excessive inrush current from being generated in the switching element when switching from the pause period to the continuous period in the intermittent operation mode.

It is a figure which shows the outline of the internal structure of the image forming apparatus to which the power supply device which concerns on Embodiment 1 of this indication was applied. 1 is a block diagram illustrating a configuration of an image forming apparatus. It is a figure which shows an example of the circuit structure of the power supply device in Embodiment 1 of this indication. It is a figure which shows an example of the waveform of the power supply device in normal operation mode. It is a figure which shows an example of the waveform of the power supply device in intermittent operation mode. It is a figure which shows an example of the circuit structure of the power supply device in the comparative example of this indication. It is a figure which shows an example of the waveform of the power supply device of the comparative example in normal operation mode. It is a figure which shows an example of the waveform of the power supply device of the comparative example in intermittent operation mode. It is a figure which shows an example of the circuit structure of the power supply device in Embodiment 2 of this indication. It is a figure which shows an example of the waveform of the intermittent operation mode in the power supply device of Embodiment 2 of this indication.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating an outline of an internal structure of an image forming apparatus 1 to which a power supply device according to Embodiment 1 of the present disclosure is applied. The image forming apparatus 1 can be applied to, for example, a digital multi-function peripheral having a copy, printer, scanner, and facsimile function. The image forming apparatus 1 includes an apparatus main body 100, a document reading unit 200 disposed on the apparatus main body 100, a document feeding unit 300 disposed on the document reading unit 200, and an operation disposed on the upper front of the apparatus main body 100. Part 400 is provided.

  The document feeder 300 functions as an automatic document feeder, and transports a plurality of documents placed on the document placement unit 301 to the document reading unit 200 so that the document reading unit 200 continuously reads the document.

  The document reading unit 200 includes a carriage 201 on which an exposure lamp and the like are mounted, a document table 203 made of a transparent member such as glass, a CCD (Charge Coupled Device) sensor (not shown), and a document reading slit 205. When reading a document placed on the document table 203, the document is read by the CCD sensor while moving the carriage 201 in the longitudinal direction of the document table 203. On the other hand, when reading a document fed from the document feeding unit 300, the carriage 201 is moved to a position facing the document reading slit 205, and the document fed from the document feeding unit 300 is scanned. Reading is performed by the CCD sensor through the reading slit 205. The CCD sensor outputs the read original as image data.

  The apparatus main body 100 includes a sheet storage unit 101, an image forming unit 103, and a fixing unit 105. The sheet storage unit 101 is disposed at the lowermost part of the apparatus main body 100 and includes a sheet tray 107 that stores a bundle of sheets. In the stack of sheets stored in the sheet tray 107, the uppermost sheet is sent out toward the sheet conveyance path 111 by the pickup roller 109. The sheet is conveyed to the image forming unit 103 through the sheet conveyance path 111.

  The image forming unit 103 forms a toner image on the conveyed paper. The image forming unit 103 includes a photosensitive drum 113, an exposure unit 115, a developing unit 117, and a transfer unit 119. The exposure unit 115 generates light modulated according to image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.), and is uniformly charged. Irradiate the circumferential surface of the photosensitive drum 113. As a result, an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 113. In this state, toner is supplied from the developing unit 117 to the peripheral surface of the photosensitive drum 113, and a toner image corresponding to the image data is formed on the peripheral surface. This toner image is transferred to the sheet conveyed from the sheet storage unit 101 by the transfer unit 119.

  The sheet on which the toner image is transferred is sent to the fixing unit 105. In the fixing unit 105, heat and pressure are applied to the toner image and the paper, and the toner image is fixed to the paper. The paper is discharged to the stack tray 121 or the paper discharge tray 123. As described above, the image forming apparatus 1 prints a monochrome image.

  The operation unit 400 includes an operation key unit 401 and a display unit 403. The display unit 403 has a touch panel function and displays a screen including soft keys. The user operates the soft keys while viewing the screen to make settings necessary for executing functions such as copying.

  The operation key unit 401 is provided with operation keys including hard keys. Specifically, the operation key unit 401 is provided with a start key 405, a numeric keypad 407, a stop key 409, a reset key 411, a function switching key 413 for switching between copy, printer, scanner, and facsimile.

  A start key 405 is a key for starting operations such as copying and facsimile transmission. A numeric keypad 407 is a key for inputting numbers such as the number of copies and a facsimile number. A stop key 409 is a key for stopping a copying operation or the like halfway. A reset key 411 is a key for returning the set contents to the initial setting state.

  The function switching key 413 includes a copy key, a transmission key, and the like, and is a key for switching between a copy function and a transmission function. When the copy key is operated, an initial copy screen is displayed on the display unit 403. When the transmission key is operated, an initial screen for facsimile transmission and mail transmission is displayed on the display unit 403.

  FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus 1. The image forming apparatus 1 has a configuration in which an apparatus main body 100, a document reading unit 200, a document feeding unit 300, an operation unit 400, an overall control unit 500, and a power supply device 700 are connected to each other by a bus. Since the apparatus main body 100, the document reading unit 200, the document feeding unit 300, and the operation unit 400 have already been described, description thereof will be omitted.

  The power supply device 700 is constituted by, for example, a DC / DC converter, converts AC power supplied from a system power supply into DC power, and supplies the DC power to each unit of the image forming apparatus 1. Details of the power supply device 700 will be described later.

  The overall control unit 500 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The CPU executes control necessary for operating the image forming apparatus 1 on the above-described components of the image forming apparatus 1 such as the apparatus main body 100. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  FIG. 3 is a diagram illustrating an example of a circuit configuration of the power supply device 700 according to the first embodiment of the present disclosure. In the example of FIG. 3, a flyback DC / DC converter is shown as the power supply device 700, but the present disclosure is not limited to this, and a forward DC / DC converter may be employed.

  In the flyback method, power is stored in the transformer T during the ON period of the switching element Q11. When the switching element Q11 is switched OFF, the power stored in the transformer T is used using the counter electromotive force of the transformer T. This is a method of outputting to the secondary side. The forward method is a method in which power is transmitted from the primary side to the secondary side via the transformer T during the ON period of the switching element Q11.

  The transformer T includes a primary winding L1 and a tertiary winding L3 provided in the primary side circuit 7A, and a secondary winding L2 provided in the secondary side circuit 7B.

  The terminal T2 of the primary winding L1 is connected to the terminal T5 of the rectifier circuit 12 via the first potential line Ln1. The terminal T1 of the primary winding L1 is connected to the drain of the switching element Q11. The tertiary winding L3 has a terminal T3 connected to the first controller 71 and a terminal T4 connected to the second potential line Ln2. The first potential line Ln1 is a line that applies a first potential, and the second potential line Ln2 is a line that applies a second potential. For example, the second potential line Ln2 is grounded, and the first potential is higher than the second potential.

  The power supply device 700 includes a rectifier circuit 12, a primary side circuit 7 </ b> A, a secondary side circuit 7 </ b> B, and a detection unit 72. In the rectifier circuit 12, the terminal T5 is connected to the first potential line Ln1, and the terminal T6 is connected to the second potential line Ln2. The rectifier circuit 12 is constituted by, for example, a full-wave rectifier circuit including four diodes, and full-wave rectifies the AC power supplied from the system power supply 11 and outputs it to the capacitor CA.

  For example, the system power supply 11 supplies AC power with frequencies of 50 Hz and 60 Hz provided by an electric power company. However, this is only an example, and a power source that supplies AC power according to the region where the image forming apparatus 1 is used is employed as the system power source 11.

  The primary side circuit 7A and the secondary side circuit 7B are magnetically connected via a transformer T. The primary side circuit 7A includes a switching element Q11 (an example of a first switching element), a primary winding L1, a tertiary winding L3, a capacitor CA, a resistance value switching unit 13, a current detection unit 14, a first control unit 71, a second A control unit 15 and a capacitor CB are provided.

  Capacitor CA has one end connected to first potential line Ln1 and the other end connected to second potential line Ln2. Capacitor CA is formed of, for example, an electrolytic capacitor, and smoothes AC power that has been full-wave rectified by rectifier circuit 12. As a result, the first potential is applied to the first potential line Ln1.

  The switching element Q11 is configured by, for example, a field effect type MOSFET (Metal-Oxide-Semiconductor-Field-Effect-Transistor), and performs a switching operation under the control of the first control unit 71. In the example of FIG. 3, the switching element Q11 employs an n-type MOSFET, the drain is connected to the terminal T1 of the primary winding L1, and the gate is connected to the first control unit 71 via the resistance value switching unit 13. The source is connected to the current detector 14. Here, in the switching element Q11, the drain is an example of a first conduction terminal, the source is an example of a second conduction terminal, and the gate is an example of a control terminal.

  In the example of FIG. 3, an n-type MOSFET is used as the switching element Q11. However, a p-type MOSFET may be used, a bipolar transistor may be used, or an IGBT (Insulated Gate Bipolar Transistor). May be adopted.

  The resistance value switching unit 13 includes a first series circuit 13A, a second series circuit 13B, and a switching element Tr11 (an example of a second switching element). The first series circuit 13A includes a resistor R13 (an example of a first resistor) connected to the gate of the switching element Q11, a diode D2 (an anode connected to the resistor R13, and a cathode connected to the first controller 71). An example of a second diode).

  The second series circuit 13B includes a resistor R12 (an example of a third resistor) connected to the anode of the diode D2, and a resistor R11 (first resistor) having one end connected to the resistor R12 and the other end connected to the first controller 71. An example of two resistors).

  The switching element Tr11 is composed of, for example, an n-type bipolar transistor, the base is connected to the second potential line Ln2 via the base resistor Rb, and the collector and emitter are connected in parallel to the resistor R11. Note that a p-type bipolar transistor or a MOSFET may be employed as the switching element Tr11. The base of the switching element Tr11 is an example of a control terminal.

  When the switching element Q11 is turned on, since the diode D2 is present, charges are supplied from the second series circuit 13B to the gate of the switching element Q11, not the first series circuit 13A, and the gate capacitance is charged. On the other hand, when the switching element Q11 is turned off, the charge accumulated in the gate capacitor is extracted from the first series circuit 13A.

  When the switching element Tr11 is turned on, the resistor R11 is bypassed, so that the resistance connected to the gate of the switching element Q11 (hereinafter referred to as “gate resistance”) is two resistors R13 and R12. On the other hand, when the switching element Tr11 is turned off, the resistor R11 is incorporated into the second series circuit 13B, so that the gate resistance of the switching element Q11 becomes three resistors R13, R12, and R11. Therefore, when the switching element Tr11 is turned on, the gate resistance is smaller than when the switching element Tr11 is turned off, so that the switching speed is increased. On the other hand, when the switching element Tr11 is turned off, the gate resistance is larger than when the switching element Tr11 is turned on, so that an inrush current generated when the switching element Q11 is turned on is suppressed.

  Note that the ratio of the resistance values of the resistors R11, R12, and R13 may be 2: 3: 1, for example, but this is an example. Further, the resistor R12 may be omitted.

  The current detection unit 14 detects a current flowing through the source of the switching element Q11. Specifically, the current detection unit 14 includes a Zener diode ZD, resistors R21 and R22, and a capacitor C2.

  The Zener diode ZD has a cathode connected to the source of the switching element Q11 and an anode connected to the second potential line Ln2. The resistor R21 (an example of a fourth resistor) is connected between the cathode of the Zener diode ZD and the first control unit 71. One end of the capacitor C2 (an example of the second capacitor) is connected to the first control unit 71, and the other end is connected to the anode of the Zener diode ZD. The resistor R22 (an example of a fifth resistor) is connected in parallel with the Zener diode ZD.

  When the switching element Q11 is turned on, a part of the current flowing between the drain and the source (hereinafter referred to as “drain current I”) is supplied to the capacitor C2 via the resistor R21, and the capacitor C2 is charged. The charging voltage of the capacitor C2 is supplied to the first control unit 71 as a measured value of the drain current I.

  On the other hand, when the voltage between the resistors R22 exceeds the breakdown voltage of the Zener diode ZD connected in parallel to the resistor R22 due to the increase in the drain current I, the Zener diode ZD is turned on, and the voltage rise between the resistors R22 is suppressed. This prevents the charging voltage of the capacitor C <b> 2 from exceeding the breakdown voltage of the Zener diode ZD and prevents an excessive voltage from being supplied to the first control unit 71.

  The detection unit 72 has one end connected to the terminal T7 and the other end connected to the first control unit 71, detects the voltage Vout output from the secondary side circuit 7B, and the voltage Vout is smaller than a predetermined reference voltage. Then, a duty increase command for increasing the duty ratio of the PWM signal supplied to the gate of the switching element Q11 is output to the first control unit 71. Further, when the voltage Vout is higher than the reference voltage, the detection unit 72 outputs a duty reduction command for reducing the duty ratio to the first control unit 71. In addition, when the voltage Vout is the same as the reference voltage, the detection unit 72 outputs a duty maintenance command for maintaining the duty ratio to the first control unit 71.

  Here, when the load Z connected to the secondary side circuit 7B is driven and the power demand of the load Z is high, the voltage Vout decreases, so the detection unit 72 issues a duty increase command to the first control unit 71. Output to. On the other hand, when the load Z is not driven and the power demand of the load Z is low, the voltage Vout increases or maintains a constant voltage, so that the detection unit 72 issues a duty reduction command or duty maintenance command to the first control unit 71. Output to.

  The first control unit 71 is configured by a hardware circuit such as an ASIC or FPGA, for example. Then, when the duty increase command is output from the detection unit 72, the first control unit 71 increases the duty ratio of the PWM signal supplied to the gate of the switching element Q11 by a predetermined step. In addition, when the duty reduction command is output from the detection unit 72, the first control unit 71 reduces the duty ratio of the PWM signal supplied to the gate of the switching element Q11 by a predetermined step. Moreover, the 1st control part 71 maintains the duty ratio of the PWM signal supplied to the gate of the switching element Q11, when the duty maintenance instruction | command is output from the detection part 72. FIG. As a result, while the duty increase command is output from the detection unit 72, the duty ratio of the PWM signal of the switching element Q11 is increased by a predetermined step, and the voltage Vout approaches the reference voltage. In addition, while the duty reduction command is output from the detection unit 72, the duty ratio of the PWM signal is decreased by predetermined steps, and the voltage Vout approaches the reference voltage. Further, while the duty maintaining command is output from the detection unit 72, the duty ratio of the PWM signal is maintained. With the above operation, the voltage Vout is maintained at the reference voltage, and a constant voltage is supplied to the load Z.

  Further, when the drain current I detected by the current detection unit 14 is larger than a predetermined threshold, the first control unit 71 drives the switching element Q11 in the normal operation mode in which the switching operation is continuously performed. On the other hand, when the drain current I detected by the current detector 14 is equal to or less than the threshold, the first controller 71 is in an intermittent operation mode in which a continuous period in which the switching operation is continuously performed and a pause period in which the switching operation is paused are repeated. The switching element Q11 is driven.

  When the load Z is driven, the drain current I increases because the duty ratio of the PWM signal of the switching element Q11 increases as the voltage Vout decreases. On the other hand, when the load Z connected to the secondary side circuit 7B is not driven, the duty ratio of the PWM signal of the switching element Q11 is reduced or maintained, so that the drain current I does not increase.

  Therefore, if the drain current I is larger than the threshold value, the first control unit 71 determines that the load Z is driven and drives the switching element Q11 in the normal operation mode. On the other hand, if the drain current I is equal to or smaller than the threshold value, the first control unit 71 determines that the load Z is not driven, and drives the switching element Q11 in the intermittent operation mode. Thereby, when the load Z is not driven, the switching element Q11 is driven intermittently, so that power consumption can be reduced. As the threshold value, a predetermined value that can be regarded as the load Z being driven is employed.

  When the switching element Q11 is operated in the intermittent operation mode, the second control unit 15 lowers the charging voltage of the capacitor C1 from the ON voltage of the switching element Tr11 and turns off the switching element Tr11 during the idle period.

  Specifically, the second control unit 15 includes a diode D1, a base resistor Rb, and a capacitor C1. The anode of the diode D1 (an example of the first diode) is connected to the source of the switching element Q11. One end of the base resistor Rb is connected to the cathode of the diode D1 and the base of the switching element Tr11, and the other end is connected to the anode of the Zener diode ZD. The capacitor C1 is connected in parallel with the base resistor Rb.

  When the switching element Q11 is turned on, a part of the drain current I charges the capacitor C1 through the diode D1. When the charging voltage of the capacitor C1 becomes larger than the ON voltage of the switching element Tr11, the switching element Tr11 is turned on. As a result, the resistor R11 is bypassed, and the gate resistance of the switching element Q11 becomes two resistors R13 and R12, which is lower than when the switching element Tr11 is off.

  Further, when the idle period is started in the intermittent operation mode, the switching element Q11 does not perform the switching operation, so that the supply of the drain current I to the capacitor C1 is stopped, and the charging voltage of the capacitor C1 gradually decreases. When the charging voltage of the capacitor C1 becomes equal to or lower than the ON voltage of the switching element Tr11, the switching element Tr11 is turned off. Thereby, the resistor R11 is incorporated in the second series circuit 13B, and the gate resistance of the switching element Q11 becomes three resistors R13, R12, and R11 in the idle period.

  When the pause period ends and the continuous period starts, the switching operation of the switching element is resumed, and the capacitor C1 is charged by the drain current I. When the charging voltage of the capacitor C1 becomes larger than the ON voltage of the switching element Tr11, the switching element Tr11 is turned on. Here, even if the continuous period is started, the charging voltage of the capacitor C1 gradually increases, and thus cannot immediately exceed the ON voltage of the switching element Tr11. Therefore, at the start of the continuous period, the switching element Tr11 is turned off, and the gate resistance of the switching element Q11 is composed of three resistors R13, R12, and R11. As a result, the occurrence of an excessive inrush current at the start of the continuous period is suppressed.

  The tertiary winding L3 is magnetically connected to the secondary winding L2. The tertiary winding L3 has a terminal T3 connected to the first controller 71 and a terminal T4 connected to the second potential line Ln2. The capacitor CB is connected in parallel with the tertiary winding L3.

  The voltage generated in the secondary winding L2 is transmitted to the tertiary winding L3, smoothed by the capacitor CB, and supplied to the first control unit 71. Thereby, electric power is supplementarily supplied to the 1st control part 71 by the tertiary winding L3 and the capacitor | condenser CB.

  The secondary side circuit 7B includes a secondary winding L2, a diode D4, and a capacitor CC. The secondary winding L2 has one end connected to the terminal T7 via the diode D4 and the other end connected to the terminal T8. The diode D4 has an anode connected to one end of the secondary winding L2, and a cathode connected to the terminal T7. The load Z is connected to terminals T7 and T8.

  The voltage generated in the secondary winding L2 is rectified by the diode D4, smoothed by the capacitor CC, and supplied to the load Z as the voltage Vout.

  As the load Z, an electric device constituting the image forming apparatus 1 is adopted, and the fixing unit 105, the image forming unit 103, the overall control unit 500, the document reading unit 200, the document feeding unit 300, and the operation key unit shown in FIG. 401 and the display unit 403 can be employed.

  The terminal T2 is connected to a noise removing snubber circuit 18 composed of a parallel circuit of a capacitor and a resistor. Further, a diode D3 having an anode connected to the terminal T1 and a cathode connected to the snubber circuit 18 is connected between the snubber circuit 18 and the terminal T1. The diode D3 prevents current from flowing from the snubber circuit 18 toward the terminal T1.

  Between the drain and source of the switching element Q11, a noise removing snubber circuit 17 comprising a series circuit of a capacitor and a resistor is connected.

  FIG. 4 is a diagram illustrating an example of a waveform of the power supply device 700 in the normal operation mode. In FIG. 4, the first row shows a waveform diagram of the drain current I of the switching element Q11, the second row shows a waveform diagram of the PWM signal supplied to the gate of the switching device Q11, and the third row shows the base of the switching device Tr11. The waveform diagram of the base voltage supplied to is shown.

  In the normal operation mode, the first controller 71 continuously switches the switching element Q11. Therefore, the PWM signal is supplied to the gate of the switching element Q11 without providing a pause period. When the PWM signal rises and the switching element Q11 is turned on, the charges accumulated in the parasitic capacitance during the period when the switching element Q11 is turned off are discharged at once. As a result, an inrush current Ip is generated in the drain current I when the PWM signal rises. Thereafter, the drain current I gradually increases until the PWM signal falls.

  Since the drain current I is not supplied to the capacitor C1 during the period in which the PWM signal is at a low level, the base voltage gradually decreases as the charging voltage of the capacitor C1 decreases. In the normal operation mode, the period during which the PWM signal is at a low level is significantly shorter than the suspension period in the intermittent operation mode. In addition, the charging voltage of the capacitor C1 cannot be instantaneously reduced when the PWM signal falls, but gradually decreases. Therefore, before the charging voltage of the capacitor C1 falls below the ON voltage of the switching element Tr11, the PWM signal is raised and the supply of the drain current I to the capacitor C1 is started. As a result, in the normal operation mode, the base voltage does not fall below the ON voltage of the switching element Tr11, and the switching element Q11 maintains the ON state. Thereby, in the normal operation mode, the gate resistance of the switching element Q11 at the time of turn-on becomes two resistors R13 and R12, and the switching loss is reduced.

  FIG. 5 is a diagram illustrating an example of a waveform of the power supply device 700 in the intermittent operation mode. In FIG. 5, the first row shows the waveform diagram of the drain current I of the switching element Q11, the second row shows the waveform diagram of the PWM signal supplied to the gate of the switching device Q11, and the third row shows the base of the switching device Tr11. The waveform diagram of the base voltage supplied to is shown.

  In the intermittent operation mode, a continuous period TA in which the switching operation of the switching element Q11 is continuously executed and a pause period TB in which the switching operation is paused are repeated. Here, a predetermined value is adopted as the time between the continuous period TA and the pause period TB. In the following description, when distinguishing between the continuous period TA and the idle period TB, the symbols “_1”, “_2”... Are appended after the continuous period TA and the idle period TB.

  In the continuous period TA_1, the PWM signal is supplied to the switching element Q11 as in the normal operation mode. At the start of the continuous period TA_1, the charge accumulated in the parasitic capacitance is discharged all at once and an inrush current Ip is generated. Therefore, the base voltage increases instantaneously, and then the capacitor C1 is charged by the drain current I, and the capacitor C1 The charging current gradually increases. At time t1, the base voltage exceeds the ON voltage of the switching element Tr11, and the switching element Tr11 is turned on.

  In the continuous period TA_1 after time t1, since the low level period of the PWM signal is short, the base voltage slightly rises and falls as in the normal operation mode, but does not fall below the ON voltage of the switching element Tr11. Therefore, the switching element Tr11 is kept on in the continuous period TA_1 after the time t1. Therefore, the gate resistance becomes two resistors R13 and R12, and the switching loss is reduced.

  When the continuous period TA_1 ends and the rest period TB_1 starts, the drain current I is no longer supplied to the capacitor C1, so that the capacitor C1 starts discharging, and the charging voltage of the capacitor C1 gradually decreases. Along with this, the base voltage of the switching element Tr11 gradually decreases.

  At time t2, the charging voltage of the capacitor C1 falls below the ON voltage of the switching element Tr11, and the switching element Tr11 is turned off. Thereafter, in the idle period TB_1, since the base voltage does not increase, the switching element Tr11 maintains the off state.

  When the pause period TB_1 ends and the continuous period TA_2 starts, supply of the drain current I to the capacitor C1 starts, and the base voltage of the switching element Tr11 increases. At time t3, as with time t1, the switching element Tr11 is turned on. As described above, in the intermittent operation mode, the continuous period TA and the pause period TB are repeated, and the power supply apparatus 700 repeats the above operation.

  At the start of the continuous period TA, the PWM signal is raised to a high level. However, since the base voltage cannot instantaneously exceed the ON voltage of the switching element Tr11, the switching element Tr11 is in the OFF state following the idle period TB. To maintain. Accordingly, at the start of the continuous period TA, the gate resistance is three resistors R13, R12, and R11. Thereby, the inrush current Ip_1 of the first pulse of the PWM signal in the continuous period TA is smaller than the inrush current Ip_X after the second pulse. On the other hand, since the switching element Tr11 is turned on after the second pulse in the continuous period TA, the gate resistance becomes two of the resistors R13 and R12, and the inrush current Ip_X is larger than the inrush current Ip_1.

  FIG. 6 is a diagram illustrating an example of a circuit configuration of the power supply device 700X in the comparative example of the present disclosure. In the power supply device 700X, the same members as those in the power supply device 700 are denoted by the same reference numerals, and description thereof is omitted.

  The power supply device 700 </ b> X does not include the second control unit 15. Further, the power supply device 700X is provided with a resistor R23X and a diode D2 between the gate of the switching element Q21 and the control unit 71X instead of the resistance value switching unit 13. Specifically, the resistor R23X has one end connected to the gate of the switching element Q21 and the other end connected to the anode of the diode D2. The cathode of the diode D2 is connected to the control unit 71X. The resistor R21X is connected in parallel with the diode D2.

  Similarly to the first control unit 71, the control unit 71X switches between the intermittent operation mode and the normal operation mode using the current detected by the current detection unit 14.

  When the switching element Q21 is turned on, since there is the diode D2, charges are injected from the control unit 71X into the gate capacitance through the paths of the resistors R21X and R23X, not the path of the diode D2 and the resistor R23X. On the other hand, when the switching element Q21 is turned off, the electric charge accumulated in the gate capacitance is extracted through the resistor R23X and the diode D2. Therefore, as with power supply device 700, the gate resistance is lower when switching element Q21 is turned off than when it is turned on.

  FIG. 7 is a diagram illustrating an example of a waveform of the power supply device 700X in the normal operation mode. In section (a) of FIG. 7, the first row shows a waveform diagram of the drain current I of the switching element Q21, and the second row shows a waveform diagram of a PWM signal supplied to the gate of the switching device Q21.

  In section (b) of FIG. 7, the first row is an enlarged view of the waveform of one pulse of the PWM signal of section (a), and the second row is an enlarged view of the waveform of one pulse of drain current I of section (a). It is.

  In the normal operation mode, similarly to the power supply device 700, the power supply device 700X has two gate resistances R23X and R21X between the switching element Q21 and the control unit 71X. Therefore, the waveform diagram of the power supply device 700X in the first and second rows in the section (a) of FIG. 7 shows the same waveform as the waveform diagram of the power supply device 700 in the first and second rows in FIG. .

  The left side of the first row of section (b) of FIG. 7 shows the waveform of one pulse of the PWM signal when the resistance R21X is small, and the right side of the second row shows the PWM signal when the resistance value of the resistor R21X is increased. A waveform for one pulse is shown.

  As shown on the right side of the first row in section (b) of FIG. 7, the PWM signal applied to the gate of the switching element Q21 has a resistance value of the gate resistance of the switching element Q21 as the value of the resistance R21X increases. Since it increases, the slope at the time of rising is gentle.

  Accordingly, as shown in the second row of section (b) of FIG. 7, the inrush current Ip generated at the rise of the drain current I decreases as the resistance value of the resistor R21X increases. From the above, the inrush current Ip can be reduced by increasing the gate resistance of the switching element Q21.

  FIG. 8 is a diagram illustrating an example of a waveform of the power supply device 700X in the intermittent operation mode. In FIG. 8, the first row shows a waveform diagram of the drain current I of the switching element Q21, and the second row shows a waveform diagram of the PWM signal supplied to the gate of the switching device Q21.

  As shown in FIG. 8, in the intermittent operation mode, the power supply device 700 repeats the continuous period TA and the pause period TB, similarly to the power supply device 700X.

  The inrush current Ip_1 generated at the first pulse in the continuous period TA is larger than the inrush current Ip_X generated after the second pulse. This is because at the end of the idle period TB, a large charge is accumulated in the parasitic capacitance of the switching element Q11, and this large charge is discharged at once in the first pulse of the continuous period TA.

  As described above, in the power supply device 700X, when the switching element Q21 is turned on, the gate resistance is always composed of two resistors R23X and R21X, so that an excessive inrush current Ip is generated in the first pulse of the continuous period TA. There's a problem.

  On the other hand, in the power supply device 700, as shown in FIG. 5, since the switching element Tr11 is turned off at the start of the continuous period TA, the gate resistance of the switching element Q11 is the resistance R13, R12, R11. It consists of three. As a result, in the first pulse of the continuous period TA, the switching speed when the switching element Q11 is turned on becomes slow, and the charge accumulated in the parasitic capacitance is slowly discharged. Therefore, the inrush current Ip_1 shown in FIG. 5 is significantly lower than the inrush current Ip_1 shown in FIG. As a result, the power supply apparatus 700 can prevent an excessive inrush current Ip_1 from being generated at the first pulse of the continuous period TA.

(Effect of Embodiment 1)
(1) As shown in the right diagram of section (b) of FIG. 7, in order to suppress the inrush current Ip, it is conceivable to increase the value of the resistor R21X to delay the switching speed of the switching element Q11. . However, this slows down the switching speed of the switching element Q11 even in the normal operation mode, resulting in an increase in switching loss, leading to heat generation of the switching element Q11 and deterioration of efficiency.

  Therefore, in the power supply device 700 of the first embodiment, the switching element Tr11 and the second control unit 15 that bypass the resistor R11 that is a part of the gate resistance of the switching element Q11 are provided. As a result, in the intermittent operation mode, the base voltage of the switching element Tr11 falls below the ON voltage in the idle period TB, and the switching element Tr11 is turned off. As a result, the base resistance of the switching element Q11 becomes three resistors R11, R12, and R13, and the switching speed when the switching element Q11 is turned on at the start of the continuous period TA after the end of the idle period TB can be slowed. As a result, it is possible to suppress the occurrence of an excessive inrush current Ip at the start time of the continuous period TA.

  On the other hand, in the normal operation mode, since the switching element Tr11 is turned on by the second control unit 15, the resistor R11 is bypassed, and the gate resistance of the switching element Q11 is composed of two resistors R13 and R12. As a result, since the switching speed of the switching element Q11 is increased, the switching loss is improved, the heat generation of the switching element Q11 and the deterioration of efficiency are prevented, and the generation of vibration noise in the transformer T can be prevented.

  (2) The resistance value switching unit 13 includes a resistor R13 connected to the gate of the switching element Q11 and a diode D2 having an anode connected to the resistor R13 and a cathode connected to the first control unit 71. 13A and a resistor R12 connected to the anode of the diode D2 and a second series circuit 13B having one end connected to the resistor R12 and the other end connected to the first control unit 71.

  Therefore, when the switching element Q11 is turned off, charges are extracted from the gate capacitance of the switching element Q11 not via the second series circuit 13B but via the first series circuit 13A, so that the switching speed when the switching element Q11 is turned off is increased. The switching speed can be faster than the turn-on switching speed, and the switching loss can be reduced.

  (3) When the switching element Q11 is turned on, the capacitor C2 is charged by the drain current I, and the charging voltage of the capacitor C2 is input to the first control unit 71. The first control unit 71 measures the drain current I by this charging voltage. can do. The cathode of the Zener diode ZD is connected to one end of the capacitor C2 via the resistor R21, and the anode of the Zener diode ZD is connected to the other end of the capacitor C2. Therefore, it is possible to prevent the charging voltage of the capacitor C2 from exceeding the breakdown voltage of the Zener diode ZD, and it is possible to prevent the first control unit 71 from being damaged due to an excessive voltage input.

  Furthermore, since the second control unit 15 is connected in parallel with the Zener diode ZD, an excessive voltage is applied to the circuit elements of the second control unit 15 and damage to the circuit elements constituting the second control unit 15 can be prevented. .

(Embodiment 2)
FIG. 9 is a diagram illustrating an example of a circuit configuration of the power supply device 700 according to the second embodiment of the present disclosure. The power supply device 700 according to the second embodiment is characterized in that the first control unit 701 controls on / off of the switching element Tr11 instead of the second control unit 15. In the present embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  Similar to the first control unit 71, the first control unit 701 has a function of controlling the switching operation of the switching element Q11 and a function of switching between the normal operation mode and the intermittent operation mode using the current detected by the current detection unit 14. In addition, a function of controlling on / off of the switching element Tr11 is provided. Therefore, in the first embodiment, the base of the switching element Tr11 is connected to the base resistance Rb of the second control unit 15, but in the second embodiment, the base of the switching element Tr11 is first connected via the base resistance R31. A control unit 701 is connected. Other than that, the power supply device 700 of the second embodiment is the same as the power supply device 700 of the first embodiment.

  The first controller 701 turns on the switching element Tr11 until the first on-period of the switching element Q11 ends after the continuous period TA is started, and turns off the switching element Tr11 during the other periods.

  FIG. 10 is a diagram illustrating an example of waveforms in the intermittent operation mode in the power supply device 700 according to the second embodiment of the present disclosure. In FIG. 10, the first row shows a waveform diagram of the drain current I of the switching element Q11, and the second row shows a waveform diagram of a PWM signal supplied to the gate of the switching device Q11.

  As shown in the second row of FIG. 10, the first control unit 701 turns off the switching element Tr11 in a period TM in which the first pulse of the PWM signal is at a high level from the start time of the continuous period TA. Thereby, the resistor R11 is incorporated in the second series circuit 13B, and the gate resistance when the switching element Q11 is turned on is composed of three resistors R13, R12, and R11. Therefore, the switching speed is reduced in the period TM, and the charge accumulated in the parasitic capacitance of the switching element Q11 is gradually discharged at the start of the continuous period TA. As a result, as shown in the first row of FIG. 10, the inrush current Ip_1 in the first pulse of the continuous period TA is significantly smaller than the inrush current Ip_1 shown in the first row of FIG.

  When the period TM ends, the first control unit 701 turns on the switching element Tr11. As a result, the resistor R11 is bypassed, and the gate resistance when the switching element Q11 is turned on is composed of two resistors R13 and R12, thereby reducing the switching loss. Further, after the second pulse of the continuous period TA, the period during which the PWM signal is at a low level is short, so the amount of charge accumulated in the parasitic capacitance of the switching element Q11 is not as great as at the start of the continuous period TA. The inrush current Ip_X is smaller than the inrush current Ip_1. Therefore, the inrush current Ip is suppressed even if the gate resistance of the switching element is composed of three resistors R13, R12, and R11.

  Thereafter, until the next continuous period TA is started, the switching element Tr11 is turned on to reduce the switching loss. When the continuous period TA is started again, the switching element Tr11 is turned off in the period TM, the gate resistance of the switching element Q11 is composed of three resistors R13, R12, and R11, and one pulse of the continuous period TA. Occurrence of an excessive inrush current Ip in the eyes is suppressed.

(Effect of Embodiment 2)
In addition to the effects (2) and (3) of the first embodiment, the following effects can be obtained. In the power supply device 700 of the second embodiment, a switching element Tr11 that bypasses the resistor R11 that is a part of the gate resistance of the switching element Q11 is provided. In the intermittent operation mode, the first control unit 71 turns off the switching element Tr11 from the start of the continuous period TA to the end of the first on-period of the switching element Q11. As a result, the gate resistance of the switching element Q11 becomes three resistors R11, R12, and R13, and the switching speed when the switching element Q11 is turned on at the start of the continuous period TA can be reduced. As a result, it is possible to suppress the occurrence of an excessive inrush current Ip at the start time of the continuous period TA.

  On the other hand, in the normal operation mode, the switching element Tr11 is turned on by the first control unit 701, so that the resistor R11 is bypassed, and the gate resistance of the switching element Q11 is composed of two resistors R13 and R12. As a result, since the switching speed of the switching element Q11 is increased, the switching loss is improved, the heat generation of the switching element Q11 and the deterioration of efficiency are prevented, and the generation of vibration noise in the transformer T can be prevented.

C1, C2 Capacitor D1, D2, D3 Diode I Drain current T Transformer L1 Primary winding L2 Secondary winding Q11, Tr11 Switching element R11, R12, R13, R21, R22 Resistor Rb, R31 Base resistance TB Rest period TM period ZD Zener diode 7A Primary side circuit 7B Secondary side circuit 13 Resistance value switching unit 13A First series circuit 13B Second series circuit 14 Current detection unit 15 Second control unit 71 First control unit 72 Detection unit

Claims (5)

A transformer comprising a primary winding and a secondary winding, and transmitting power on the primary side to the secondary side;
A first switching element having a first conduction terminal connected to the primary winding;
A current detector connected to the second conduction terminal of the first switching element and detecting a current flowing through the second conduction terminal;
When the current detected by the current detection unit is greater than a predetermined threshold, the first switching element is driven in a normal operation mode in which a switching operation is continuously performed, and when the detected current is less than the threshold, A first controller that drives the first switching element in an intermittent operation mode that repeats a continuous period in which the switching operation is continuously performed and a pause period in which the switching operation is suspended;
A resistance switching unit including first and second resistors connected in series between the control terminal of the first switching element and the first control unit; and a second switching element connected in parallel to the second resistor;
A first diode having an anode connected to the second conduction terminal, a base resistor having one end connected to the cathode of the first diode and connected to a control terminal of the second switching element, and in parallel with the base resistance And a second control unit that lowers the charging voltage of the first capacitor below the on-voltage of the second switching element and turns off the second switching element during the idle period. Power supply. A transformer comprising a primary winding and a secondary winding, and transmitting power on the primary side to the secondary side;
A first switching element having a first conduction terminal connected to the primary winding;
A current detector connected to the second conduction terminal of the first switching element and detecting a current flowing through the second conduction terminal;
When the current detected by the current detection unit is greater than a predetermined threshold, the first switching element is driven in a normal operation mode in which a switching operation is continuously performed, and when the detected current is less than the threshold, A first controller that drives the first switching element in an intermittent operation mode that repeats a continuous period in which the switching operation is continuously performed and a pause period in which the switching operation is suspended;
A resistance switching unit including first and second resistors connected in series between the control terminal of the first switching element and the first control unit; and a second switching element connected in parallel to the second resistor. Prepared,
The first control unit is a power supply device that turns off the second switching element until the first on-period of the first switching element ends after the continuous period starts. The resistance value switching unit is
A first series circuit including the first resistor connected to the control terminal of the first switching element, and a second diode having an anode connected to the first resistor and a cathode connected to the first control unit. When,
A second series circuit including a third resistor connected to the anode of the second diode, and the second resistor having one end connected to the third resistor and the other end connected to the first controller. The power supply device according to claim 1 or 2 including. The current detection unit includes a Zener diode having a cathode connected to the second conduction terminal of the first switching element, a fourth resistor connected between the cathode of the Zener diode and the first control unit, A fifth resistor connected in parallel to the Zener diode; a second capacitor having one end connected to the first control unit and the other end connected to the anode of the Zener diode;
The second control unit has an anode of the first diode connected to a cathode of the Zener diode, and a terminal of the first capacitor opposite to the first diode connected to an anode of the Zener diode. Item 1. The power supply device according to Item 1.   An image forming apparatus comprising the power supply device according to claim 1.

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