JP2021083176A - Power supply device and image forming apparatus provided with the same - Google Patents

Abstract

To automatically reduce an electric charge in a smooth capacitor connected to an output of a rectification circuit when a power cable is pulled out such that electric shock during a maintenance time is prevented.SOLUTION: One end of a smooth capacitor of a power supply device is connected to an output terminal of a rectification circuit. A first power supply unit generates a first DC voltage when a voltage smoothed by the smooth capacitor is applied thereto. A second power supply unit generates a second DC voltage while receiving power supply from an AC power source. A control circuit is operated when the second DC voltage is applied thereto. A first switch that is in an ON state supplies an electric charge in the smooth capacitor to a first switching control circuit. A second switch that is in an ON state brings the first switch into an OFF state. The second switch that is in an OFF state brings the first switch into an ON state. When the control circuit is stopped due to a cessation of the AC power supply, the second switch enters an OFF state.SELECTED DRAWING: Figure 7

Description

The present invention relates to a power supply device that performs switching. The present invention also relates to an image forming apparatus including this power supply apparatus.

There are image forming devices such as multifunction devices, printers, copiers, and facsimile machines. AC power is input to the image forming apparatus from the AC power supply. The image forming apparatus operates by utilizing (rectifying) the input AC power. Then, some image forming devices detect the zero cross of the input AC voltage. Patent Document 1 describes an example of a power source for an image forming apparatus that detects zero cross of an AC voltage.

Specifically, in Patent Document 1, the first capacitor provided between the lines where the AC voltage is input from the AC power supply and the charge charged in the first capacitor are discharged and input from the AC power supply. A zero-cross detection resistor for detecting the zero-cross of the AC voltage, a first converter that converts the voltage after full-wave rectification of the AC voltage input from the AC power supply, and between the output line of the first converter and the frame ground of the device. The second condenser provided in, the discharge resistance that discharges the charge charged in the second condenser with a resistance value smaller than the zero cross detection resistance, the first state that cuts off the current to the discharge resistance, and the discharge resistance. A power supply that includes a first switch for switching a second state in which a current flows and a power supply that detects the zero-cross timing of the AC voltage input from the AC power supply based on a detection signal from the zero-cross detection resistor is described. An attempt is made to switch between a state in which zero cross detection is possible and a state in which power consumption is reduced (Patent Document 1: Claim 1, paragraph [0009]).

Japanese Unexamined Patent Publication No. 2013-123348

There is a power supply circuit that converts alternating current to direct current and outputs it. A device including such a power supply circuit includes, for example, an image forming device. A rectifier circuit is provided in the power supply circuit for AC / DC conversion, for example. Then, in order to smooth the output voltage of the rectifier circuit, a smoothing capacitor may be connected to the output terminal of the rectifier circuit.

For example, using a power cord (AC cord), the image forming apparatus is connected to an AC power supply (power distribution outlet). For example, the power cord may come out of the outlet due to a momentum caught in the foot. In addition, when not used for a long period of time, the power cord of the image forming apparatus is unplugged from the outlet. In this way, the power supply from the AC power supply to the image forming apparatus may be stopped (cut off). When the power supply from the AC power supply is stopped, a large amount of electric charge may remain in the smoothing capacitor connected to the output terminal of the rectifier circuit.

Then, the maintenance person (serviceman) may touch the power supply circuit for replacement or inspection. There is a risk of electric shock when the serviceman touches the capacitor connected to the output terminal of the rectifier circuit. In addition, a serviceman may drop the power supply circuit at hand due to the shock of electric shock. If dropped, part of the power supply circuit may be damaged. In addition, the possibility that a circuit abnormality will occur due to discharge at the time of electric shock is not zero. Therefore, there is a problem that electric shock should be prevented when the power supply from the AC power supply is stopped.

In the power supply described in Patent Document 1, the first capacitor (a capacitor between the input lines of AC voltage) and the second capacitor (a capacitor provided between the output line of the first converter and the frame ground of the apparatus). Discharge resistance is provided. However, there is no description about the discharge of the capacitor (the capacitor that smoothes the output voltage of the rectifier circuit) connected to the output terminal of the rectifier circuit. Therefore, the technique described in Patent Document 1 cannot solve the above problem.

The present invention has been made in view of the above problems of the prior art, and automatically charges the smoothing capacitor connected to the output of the rectifier circuit when the power cord is unplugged so as to eliminate electric shock during maintenance. Reduce to.

In order to achieve the above object, the power supply device according to the present invention includes a power supply cord, a rectifier circuit, a smoothing capacitor, a first power supply unit, a second power supply unit, a control circuit, and a supply switch unit. The power cord is connected to the AC power supply. The rectifier circuit rectifies an AC voltage supplied from the AC power supply via the power strip. One end of the smoothing capacitor is connected to the output terminal of the rectifier circuit. The smoothing capacitor smoothes the voltage output by the rectifier circuit. The other end of the smoothing capacitor is connected to the negative electrode terminal of the rectifier circuit. A voltage smoothed by the smoothing capacitor is applied to the first power supply unit to generate and output a first DC voltage. The second power supply unit generates and outputs a second DC voltage while power is being supplied from the AC power supply. The control circuit operates by applying the second DC voltage. The first power supply unit includes a first transformer, a first switching element, and a first switching control circuit. The first transformer includes a primary winding whose one end is connected to one end of the smoothing capacitor. The first switching element is connected to the other end of the primary winding of the first transformer. The first switching control circuit controls ON / OFF of the first switching element. The first switching control circuit operates by applying a voltage smoothed by the smoothing capacitor. The supply switch unit includes a first switch and a second switch. The first switch is connected to one end of the smoothing capacitor. The first switch supplies the electric charge stored in the smoothing capacitor to the first switching control circuit in the ON state. When the first switch is in the OFF state, the power supply to the first switching control circuit is stopped. The second switch is connected to one end of the smoothing capacitor. When in the ON state, the second switch turns the first switch into an OFF state. When in the OFF state, the second switch turns the first switch into an ON state. When the first power supply unit is operated, the control circuit turns off the second switch. When the first power supply unit is stopped, the control circuit turns on the second switch. The second switch is turned off when the control circuit is stopped because the power cord is no longer connected to the AC power supply.

According to the present invention, when the control circuit is stopped due to the stop of the power supply from the AC power supply, the electric charge of the smoothing capacitor connected to the output of the rectifier circuit can be automatically reduced. It is possible to eliminate the electric shock during maintenance of the service person.

It is a figure which shows an example of the printer which concerns on embodiment. It is a figure which shows an example of the power supply device which concerns on embodiment. It is a figure which shows an example of the power supply device which concerns on embodiment. It is a figure which shows an example of the power supply device which concerns on embodiment. It is a figure which shows an example of the state of the power supply device which concerns on embodiment in an active mode. It is a figure which shows an example of the state of the power supply device which concerns on embodiment in a sleep mode. It is a figure which shows an example of the state of the power supply apparatus which concerns on embodiment when the power cord is unplugged. It is a figure which shows an example of the operation of the power supply device which concerns on embodiment when the charge of a smoothing capacitor is consumed.

Hereinafter, an image forming apparatus including a power supply device 5 (switching power supply board) according to the present invention will be described with reference to FIGS. 1 to 8. The printer 100 will be described as an example of the image forming apparatus. However, each element such as the configuration and the arrangement described in the present embodiment does not limit the scope of the invention and is merely an explanatory example.

(Printer 100)
The printer 100 according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an example of a printer 100 according to an embodiment.

As shown in FIG. 1, the printer 100 includes a control unit 1, a storage unit 2, an operation panel 3, a printing unit 4, and a power supply device 5. First, the control unit 1 is a board (main control board). The control unit 1 controls the operation of the printer 100. The control unit 1 controls operations in jobs such as copying and transmission. The control unit 1 includes a CPU 10, an image processing circuit 11, and a communication unit 12. The CPU 10 performs processing and calculation related to the job.

For example, the image processing circuit 11 is an ASIC. The image processing circuit 11 generates image data based on the print data received by the communication unit 12. The image processing circuit 11 performs image processing of the generated image data to generate output image data. The output image data is used for the print job.

The communication unit 12 includes communication hardware (communication circuit) and communication memory. The communication memory stores communication software. The communication unit 12 communicates with the computer 200. For example, the computer 200 is a PC or a server. The communication unit 12 receives print data from the computer 200. The print data includes, for example, data described in a page description language. The control unit 1 (image processing circuit 11) analyzes the data described in the page description language and generates image data. Based on the generated image data, the control unit 1 causes the printing unit 4 to print.

The storage unit 2 includes a RAM, a ROM, and a storage. The storage is, for example, an HDD or SSD. The control unit 1 controls each unit based on the program and data of the storage unit 2.

The operation panel 3 accepts the user's settings. The operation panel 3 includes a display panel 31, a touch panel 32, and a hard key 33. The control unit 1 displays a message or a setting screen on the display panel 31. The control unit 1 displays the operation image on the display panel 31. For example, operating images are buttons, keys, and tabs. Based on the output of the touch panel 32, the control unit 1 recognizes the operated operation image. The hard key 33 includes a start key and a numeric keypad. The touch panel 32 and the hard key 33 accept the user's setting operation (operation related to the job). For example, the operation panel 3 accepts settings related to reading a document. For example, the operation panel 3 accepts the setting of the document size to be read. The control unit 1 recognizes the setting contents based on the output of the operation panel 3.

The printing unit 4 includes an engine control unit 40, a paper feeding unit 41, a paper conveying unit 42, an image forming unit 43, and a fixing unit 44. The engine control unit 40 controls the operations of the paper feed unit 41, the paper transport unit 42, the image forming unit 43, and the fixing unit 44. At the time of a print job, the control unit 1 instructs the engine control unit 40 to start feeding. Based on this instruction, the engine control unit 40 supplies the paper to the paper feed unit 41. The paper transport unit 42 includes a transport roller pair for paper transport and a transport motor. The transport roller pair transports the paper. The transfer motor rotates a pair of transfer rollers. The control unit 1 instructs the engine control unit 40 to transfer the paper. Based on this instruction, the engine control unit 40 rotates the transfer roller pair and the transfer motor.

The image forming unit 43 includes, for example, a photoconductor drum, a charging device, an exposure device, a developing device, and a transfer roller. The control unit 1 instructs the engine control unit 40 to form an image. Based on this instruction and the output image data supplied from the control unit 1, the engine control unit 40 causes the image forming unit 43 to form a toner image. The engine control unit 40 causes the image forming unit 43 to transfer the toner image to the transport paper. The fixing unit 44 includes a heater, a fixing rotating body, and a fixing motor. The heater heats the fixing rotating body. The paper comes into contact with the fixing rotating body. As a result, the toner image is fixed on the paper. The control unit 1 instructs the engine control unit 40 to fix the toner image. Based on this instruction, the engine control unit 40 causes the fixing unit 44 to fix the transferred toner image on the paper. The paper transport unit 42 discharges the printed paper to the outside of the machine.

(Power supply by power supply device 5)
Next, an example of the power supply device 5 according to the embodiment will be described with reference to FIGS. 2 and 3. 2 and 3 are diagrams showing an example of the power supply device 5 according to the embodiment.

The power supply device 5 (switching power supply board) is connected to the power supply cord 50. The power supply device 5 is connected to the AC power supply AC via the power cord 50. The AC power supply AC is, for example, a commercial power supply. The power cord 50 is connected to an AC power AC outlet (power distribution outlet). The power supply device 5 receives power from the AC power supply AC.

As shown in FIG. 2, the power supply device 5 includes a first power supply unit 6, a second power supply unit 7, and a control circuit 8. The first power supply unit 6 is a power supply circuit that operates in the active mode. The active mode is sometimes called the normal mode. The second power supply unit 7 is a power supply circuit that operates in both an active mode (normal mode) and a sleep mode (power saving mode). That is, while the power supply device 5 is supplied with power from the AC power supply AC (when the power cord 50 is connected to the AC outlet), the second power supply unit 7 operates. The control circuit 8 operates by applying a second DC voltage V2 generated by the second power supply unit 7 (see FIG. 4). The control circuit 8 controls the first power supply unit 6.

The active mode is a mode in which power is supplied to all parts of the printer 100. In active mode, printing can be started immediately. The sleep mode is a mode in which power supply to a predetermined portion (sleep stop portion) of the printer 100 is stopped. The sleep mode is a mode in which the power consumption of the printer 100 is kept low. Even in the sleep mode, the power supply to the predetermined portion (supply continuation unit 101) can be continued.

The sleep stop portion includes, for example, a part of the control unit 1 (a part other than the CPU 10, the image processing circuit 11, and the communication unit 12), a storage unit 2, a part of the operation panel 3 (for example, the display panel 31), and a printing unit 4. Is. The supply continuation unit 101 is, for example, a communication unit 12, a part of the sensors provided in the printer 100, a touch panel 32, and a part of the hard keys 33. The active mode can be said to be a mode in which the first power supply unit 6 and the second power supply unit 7 supply electric power to both the sleep stop portion and the supply continuation portion 101. The sleep mode can be said to be a mode in which the second power supply unit 7 supplies power only to the supply continuation unit 101.

The efficiency of the second power supply unit 7 in the sleep mode is higher than that of the first power supply unit 6. In other words, the second power supply unit 7 has higher efficiency when the power consumption is smaller than that of the first power supply unit 6. For example, the first power supply unit 6 and the second power supply unit 7 have different capacities. Sleep mode consumes less power than active mode. Therefore, the capacity of the second power supply unit 7 is smaller than that of the first power supply unit 6. For example, the second power supply unit 7 uses a transformer smaller than the first power supply unit 6.

Further, the first power supply unit 6 and the second power supply unit 7 may have different magnitudes of generated voltage. For example, the first power supply unit 6 generates a voltage (motor operating voltage) larger than that of the second power supply unit 7 (see FIG. 3). The motor 4a rotates, for example, the rollers included in the paper feeding unit 41, the paper conveying unit 42, the image forming unit 43, and the fixing unit 44. On the other hand, in the sleep mode, the motor 4a is not rotated. Therefore, the second power supply unit 7 may generate a voltage smaller than that of the first power supply unit 6. The second power supply unit 7 generates a voltage sufficient to operate the supply continuation unit 101.

In the sleep mode, the control unit 1 stops the first power supply unit 6. The control unit 1 inputs a signal (sleep control signal S1) notifying whether the mode is the active mode or the sleep mode to the control circuit 8 of the power supply device 5. Based on the level of the sleep control signal S1, the control circuit 8 switches between the operation and the stop of the operation of the first power supply unit 6.

The printer 100 includes a main power switch 102. When the main power of the printer 100 is turned on by the main power switch 102, the control circuit 8 of the power supply device 5 operates the first power supply unit 6. All parts of the printer 100 are activated by the power supply from the first power supply unit 6. When the main power is turned on, the printer 100 starts in the active mode. When the main power is turned on, the control circuit 8 activates the printer 100 in the active mode.

The conditions for transition from the active mode to the sleep mode are predetermined. For example, the transition condition is that after the printer 100 is started or the print job is completed, the sleep transition time has elapsed without receiving print data or operating the operation panel 3. Further, the operation panel 3 may be provided with a button for transition. In this case, one of the transition conditions includes the operation of the transition button.

The control unit 1 (CPU 10 or communication unit 12) confirms whether or not the transition condition is satisfied. When the transition condition is satisfied, the control unit 1 (CPU 10 or communication unit 12) changes the level of the sleep control signal S1 to a level indicating the sleep mode. As a result, the control circuit 8 stops the first power supply unit 6. As a result, the printer 100 goes into sleep mode.

The conditions for returning from the sleep mode to the active mode are also predetermined. For example, the return condition is that the communication unit 12 has received the print data. Further, a return button may be provided on the operation panel 3. In this case, one of the return conditions includes the operation of the return button. The communication unit 12 confirms whether or not the return condition is satisfied. When the return condition is satisfied, the control unit 1 (CPU 10 or communication unit 12) changes the level of the sleep control signal S1 to a level indicating that the sleep control signal S1 is in the active mode. As a result, the control circuit 8 starts the operation of the first power supply unit 6. As a result, the printer 100 is in the active mode.

Next, an example of the power supply system in the printer 100 will be described with reference to FIG. The printer 100 includes a power supply device 5 (primary power supply) and a secondary power supply unit 5a. The power supply device 5 includes a first power supply unit 6 and a second power supply unit 7. The first power supply unit 6 and the second power supply unit 7 are switching power supplies.

The secondary power supply unit 5a includes a plurality of power conversion circuits. The power conversion circuit is, for example, a regulator or a DCDC converter. Each power conversion circuit converts the power supplied from the power supply device 5. Each power conversion circuit generates and outputs a voltage (set voltage) of a predetermined magnitude.

To operate the main control board (CPU 10, image processing circuit 11, communication unit 12), storage unit 2, operation panel 3 (display panel 31, touch panel 32, hard key 33), and engine board (engine control unit 40), Multiple types of voltage are required. The secondary power supply unit 5a is applied with the generated voltage of the power supply device 5 to generate a plurality of types of DC voltage. In other words, the secondary power supply unit 5a generates a voltage required for the operation of the printer 100. The voltage generated by the secondary power supply unit 5a is supplied to each unit (each device). The printer 100 includes a power supply sequence circuit 5b. The power supply sequence circuit 5b controls the order of starting and stopping each power conversion circuit so that an abnormal operation does not occur.

(Power supply device 5)
Next, the power supply device 5 according to the embodiment will be described with reference to FIG. FIG. 4 is a diagram showing an example of the power supply device 5 according to the embodiment.

The power supply device 5 includes a rectifier circuit 51, a smoothing capacitor C0, a first power supply unit 6, a second power supply unit 7, a control circuit 8, and a supply switch unit 9.

The rectifier circuit 51 is connected to an AC power supply AC (live and neutral). The power cord 50 connects the AC power supply AC and the rectifier circuit 51. The rectifier circuit 51 is a full-wave rectifier. The rectifier circuit 51 is, for example, a diode bridge. The rectifier circuit 51 outputs a DC voltage.

One end of the smoothing capacitor C0 is connected to the output terminal 51a of the rectifier circuit 51. The other end of the smoothing capacitor C0 is connected to the negative electrode terminal 51b of the rectifier circuit 51. The smoothing capacitor C0 stores the electric charge output by the rectifier circuit 51. Then, the smoothing capacitor C0 smoothes the voltage output by the rectifier circuit 51.

The first power supply unit 6 includes a first transformer 61, a first switching element Q1, a first switching control circuit 62, a first rectifier diode D1, a first capacitor C1, a first error amplifier 63, and a first photocoupler. The first photocoupler includes a first light emitting diode LED1 and a first phototransistor PT1.

The first power supply unit 6 is a switching power supply including the first transformer 61. The first transformer 61 includes a primary winding Lp1 and a secondary winding Ls1. One end (input terminal) of the first transformer 61 is connected to one end of the smoothing capacitor C0. That is, the voltage smoothed by the smoothing capacitor C0 is applied to the primary winding Lp1 of the first transformer 61. The first transformer 61 includes an auxiliary winding Lt1 (tertiary winding). The auxiliary winding Lt1 lowers the voltage smoothed by the smoothing capacitor C0. The auxiliary winding Lt1 supplies a stepped-down voltage to the first switching control circuit 62.

The first switching element Q1 is, for example, an N-channel type FET. One end (drain) of the first switching element Q1 is connected to the other end of the primary winding Lp1 of the first transformer 61. The other end (source) of the first switching element Q1 is connected to the negative electrode terminal 51b (the other end of the smoothing capacitor C0) of the rectifier circuit 51. The current flowing through the primary winding Lp1 of the first transformer 61 and the first switching element Q1 returns to the rectifier circuit 51. The gate of the first switching element Q1 is connected to the first switching control circuit 62. The first switching control circuit 62 controls ON / OFF of the first switching element Q1. When the first switching control circuit 62 switches the first switching element Q1, the first power supply unit 6 generates and outputs a first DC voltage V1 having a preset size.

The voltage between the terminals of the secondary winding Ls1 of the first transformer 61 becomes the output voltage of the first power supply unit 6 (first DC voltage V1). In the active mode, the first DC voltage V1 is applied to the sleep stop portion.

A first rectifying diode D1 is provided in the secondary winding Ls1. The first rectifying diode D1 prevents backflow of current. The first capacitor C1 and the first error amplifier 63 are connected between the positive terminal and the negative terminal (both ends of the secondary winding Ls1) of the secondary winding Ls1. The first capacitor C1 smoothes the first DC voltage V1. The first error amplifier 63 detects, for example, an error between the first DC voltage V1 and the output voltage target value.

The first light emitting diode LED1 of the first photocoupler is provided between the first error amplifier 63 and the positive terminal of the secondary winding Ls1. Further, the collector of the first phototransistor PT1 of the first photocoupler is connected to the first switching control circuit 62. The emitter of the first phototransistor PT1 is connected to the negative electrode terminal 51b of the rectifier circuit 51.

The first switching control circuit 62 is a power supply control IC. The first switching control circuit 62 inputs a PWM signal to the first switching element Q1. The PWM signal is input to the gate of the first switching element Q1. The first switching control circuit 62 controls the output of the first power supply unit 6 based on the ON / OFF of the first phototransistor PT1.

When the PWM signal is at the High level, the first switching element Q1 is turned on. When the first switching element Q1 is in the ON state, a current flows through the first transformer 61 and the first switching element Q1. When the PWM signal is at the Low level, the first switching element Q1 is turned off. When the first switching element Q1 is in the OFF state, no current flows through the first transformer 61 and the first switching element Q1.

The first light emitting diode LED1 lights up when the first DC voltage V1 (voltage between terminals of the secondary winding Ls1) exceeds a predetermined set voltage. For example, the set voltage is the maximum value within the permissible range of the first DC voltage V1. For example, while the first light emitting diode LED1 is turned off, the first phototransistor PT1 is turned off. When the first light emitting diode LED1 is lit, the first phototransistor PT1 is turned on.

The first switching control circuit 62 recognizes the ON / OFF state of the first phototransistor PT1. For example, when the first phototransistor PT1 is turned on while the first power supply unit 6 is operating (in the active mode), the first switching control circuit 62 reduces the duty ratio of the PWM signal. On the other hand, when the first phototransistor PT1 is in the OFF state, the first switching control circuit 62 increases the duty ratio of the PWM signal. As described above, the first photocoupler is used for feedback control of the magnitude of the first DC voltage V1.

The second power supply unit 7 includes a second transformer 71, a second switching element Q2, a second switching control circuit 72, a second rectifier diode D2, a second capacitor C2, a second error amplifier 73, a second photocoupler, and a control circuit 8. ,including. The second photocoupler includes a second light emitting diode LED2 and a second phototransistor PT2.

The second power supply unit 7 is a switching power supply including the second transformer 71. The second transformer 71 includes a primary winding Lp2 and a secondary winding Ls2. One end (input terminal) of the second transformer 71 is connected to one end (output terminal 51a of the rectifier circuit 51) of the smoothing capacitor C0. That is, a voltage smoothed by the smoothing capacitor C0 is applied to the primary winding Lp2. The second transformer 71 includes an auxiliary winding Lt2 (tertiary winding). The auxiliary winding Lt2 lowers the voltage smoothed by the smoothing capacitor C0. The auxiliary winding Lt2 supplies a stepped-down voltage to the second switching control circuit 72.

The second switching element Q2 is, for example, an N-channel type FET. One end (drain) of the second switching element Q2 is connected to the other end of the primary winding Lp2 of the second transformer 71. The other end (source) of the second switching element Q2 is connected to the negative electrode terminal 51b (the other end of the smoothing capacitor C0) of the rectifier circuit 51. The current flowing through the primary winding Lp2 of the second transformer 71 and the second switching element Q2 returns to the rectifier circuit 51. The gate of the second switching element Q2 is connected to the second switching control circuit 72. The second switching control circuit 72 controls ON / OFF of the second switching element Q2. When the second switching control circuit 72 switches the second switching element Q2, the second power supply unit 7 generates and outputs a second DC voltage V2 having a preset size.

The second power supply unit 7 operates while the power supply device 5 is supplied with power from the AC power supply AC (while the power cord 50 is connected to the AC outlet). That is, the second power supply unit 7 operates in both the active mode and the sleep mode. One diode for operating the second switching control circuit 72 is connected to each of the AC power input terminals (third diode D3 and fourth diode D4). The outputs of these diodes are input to the second switching control circuit 72. As a result, the second switching control circuit 72 can be operated at all times (in any mode) while the power cord 50 and the AC power supply AC are connected. While the power cord 50 and the AC power AC are connected, the second DC voltage V2 can always be generated and the control circuit 8 can be operated. The voltage between the terminals of the secondary winding Ls2 of the second transformer 71 becomes the output voltage of the second power supply unit 7 (second DC voltage V2). The second DC voltage V2 is applied to the control circuit 8 and the supply continuation unit 101.

A second rectifying diode D2 is provided on the secondary winding Ls2. The second rectifying diode D2 prevents backflow of current. The second capacitor C2 and the second error amplifier 73 are connected between the positive terminal and the negative terminal of the secondary winding Ls2 (both ends of the secondary winding Ls2 of the second transformer 71). The second capacitor C2 smoothes the second DC voltage V2. The second error amplifier 73 detects, for example, an error between the second DC voltage V2 and the output voltage target value.

The second light emitting diode LED2 of the second photocoupler is provided between the second error amplifier 73 and the positive terminal of the secondary winding Ls2. Further, the collector of the second phototransistor PT2 of the second photocoupler is connected to the second switching control circuit 72. The emitter of the second phototransistor PT2 is connected to the negative electrode terminal 51b of the rectifier circuit 51.

The second switching control circuit 72 is a power supply control IC. The second switching control circuit 72 inputs a PWM signal to the second switching element Q2. The PWM signal is input to the gate of the second switching element Q2. The second switching control circuit 72 controls the output of the second power supply unit 7 based on the ON / OFF of the second phototransistor PT2.

When the PWM signal is at the high level, the second switching element Q2 is turned on. When the second switching element Q2 is in the ON state, a current flows through the second transformer 71 and the second switching element Q2. When the PWM signal is at the Low level, the second switching element Q2 is turned off. When the second switching element Q2 is in the OFF state, no current flows through the second transformer 71 and the second switching element Q2.

The second light emitting diode LED2 lights up when the second DC voltage V2 (voltage between terminals of the secondary winding of the second power supply unit 7) exceeds a predetermined set voltage. For example, the set voltage is, for example, the maximum value in the allowable range of the second DC voltage V2. For example, while the second light emitting diode LED2 is off, the second phototransistor PT2 is in the OFF state. When the second light emitting diode LED2 is lit, the second phototransistor PT2 is turned on.

The second switching control circuit 72 recognizes the ON / OFF state of the second phototransistor PT2. For example, when the second phototransistor PT2 is turned on during the operation of the second power supply unit 7, the second switching control circuit 72 reduces the duty ratio of the PWM signal. On the other hand, when the second phototransistor PT2 is in the OFF state, the second switching control circuit 72 increases the duty ratio of the PWM signal. As described above, the second photocoupler is used for feedback control of the magnitude of the second DC voltage V2.

The control circuit 8 of the power supply device 5 is a circuit that controls ON / OFF of the operation of the first switching control circuit 62 (first power supply unit 6). The power supply device 5 includes a supply switch unit 9 in order to switch ON / OFF of the operation of the first switching control circuit 62 (first power supply unit 6). The supply switch unit 9 includes a first switch TR0, a second switch PT0, a first resistor R1, a second resistor R2, and a constant voltage diode ZD. For example, the first switch TR0 is a PNP type transistor. The second switch PT0 is a phototransistor.

One end of the smoothing capacitor C0, the emitter of the first switch TR0 (transistor), one end of the second switch PT0 (collector of the phototransistor), and one end of the first resistor R1 are connected. That is, the output of the rectifier circuit 51 (voltage between terminals of the smoothing capacitor C0) is applied to the first switch TR0, the second switch PT0, and the first resistor R1. The base of the first switch TR0 (transistor), the other end of the second switch PT0 (emitter of the phototransistor), the other end of the first resistor R1, and one end of the second resistor R2 are connected. The other end of the second resistor R2 is connected to the other end of the smoothing capacitor C0.

When the second switch PT0 is in the ON state, the emitter and the base of the first switch TR0 (transistor) have the same potential. Since the emitter and the base have the same potential, the first switch TR0 is in the OFF state. When the second switch PT0 is in the OFF state, the voltage at the base of the first switch TR0 (transistor) becomes smaller than the voltage of the emitter due to the voltage division of the first resistor R1 and the second resistor R2. As a result, the first switch TR0 is turned on. By controlling the ON / OFF of the second switch PT0, the ON / OFF of the first switch TR0 can be switched.

The collector of the first switch TR0 (transistor) is connected to one end of the constant voltage diode ZD. The other end of the constant voltage diode ZD is connected to the first switching control circuit 62. When the first switch TR0 is turned on, the voltage smoothed by the smoothing capacitor C0 (the output voltage of the rectifier circuit 51) is applied to the constant voltage diode ZD. Then, a constant voltage by the constant voltage diode ZD is applied to the first switching control circuit 62. By applying this constant voltage, the first switching control circuit 62 operates.

The power supply device 5 includes a control photocoupler for controlling the operation of the first power supply unit 6. The control photocoupler includes a control LED 81 and a second switch PT0. The control circuit 8 controls the lighting of the control LED 81 to control the ON / OFF of the second switch PT0. One end of the control LED 81 is connected to the control circuit 8. The other end of the control LED 81 is connected to the negative terminal of the secondary winding Ls2 of the second transformer 71. The control LED 81 irradiates the second switch PT0 with light. When the first power supply unit 6 (first switching control circuit 62) is operated, the control circuit 8 turns off the control LED 81. When the first power supply unit 6 is not operated (in the sleep mode), the control circuit 8 lights the control LED 81.

Further, the power supply device 5 includes an application control element 91. The application control element 91 is connected to the first rectifying diode D1. The application control element 91 controls the application of the first DC voltage V1 to the device connected to the first power supply unit 6. In other words, the application control element 91 controls the supply of electric power to the predetermined sleep stop portion and the stop of supply of electric power to the sleep stop portion. The application control element 91 is, for example, a relay. The application control element 91 is normally open.

(State of power supply device 5 in each mode)
Next, an example of the state of the power supply device 5 according to the embodiment in each mode will be described with reference to FIGS. 5 to 8. FIG. 5 is a diagram showing an example of the state of the power supply device 5 according to the embodiment in the active mode. FIG. 6 is a diagram showing an example of the state of the power supply device 5 according to the embodiment in the sleep mode. FIG. 7 is a diagram showing an example of the state of the power supply device 5 according to the embodiment when the power supply cord 50 is disconnected. FIG. 8 is a diagram showing an example of the operation of the power supply device 5 according to the embodiment when the electric charge of the smoothing capacitor C0 is consumed.

1. 1. Active Mode First, an example of the state of the power supply device 5 in the active mode will be described with reference to FIG. As a premise, when the multifunction device is in the active mode, the power cord 50 is connected to the AC power supply AC, and AC power is supplied to the rectifier circuit 51.

(1-1) The second switching control circuit 72 is operated by the power supply from the AC power supply AC.
(1-2) The second switching control circuit 72 operates, and the second DC voltage V2 is generated.
(1-3) Since the second DC voltage V2 is generated, the control circuit 8 operates.
(1-4) The control circuit 8 turns off the control LED 81 for the operation of the first power supply unit 6.
(1-5) When the control LED 81 is turned off, the second switch PT0 is turned off.
(1-6) When the second switch PT0 is turned off, the first switch TR0 is turned on (conducting state).
(1-7) Since the first switch TR0 is in the ON state, power is supplied from the rectifier circuit 51 to the first switching control circuit 62.
(1-8) The first switching control circuit 62 operates by the supplied electric power.
(1-9) The first switching control circuit 62 operates, and the first DC voltage V1 is generated.
(1-10) In order to supply power from the first power supply unit 6, the control circuit 8 turns the applied control element 91 into an ON state (closed state).

2. Sleep Mode Next, an example of the state of the power supply device 5 in the sleep mode will be described with reference to FIG. As a premise, when the multifunction device is in the sleep mode, the power cord 50 is connected to the AC power supply AC, and AC power is supplied to the rectifier circuit 51.

(2-1) The second switching control circuit 72 is operated by the power supply from the AC power supply AC.
(2-2) The second switching control circuit 72 operates, and the second DC voltage V2 is generated.
(2-3) Since the second DC voltage V2 is generated, the control circuit 8 operates.
(2-4) In order to stop the first power supply unit 6, the control circuit 8 lights the control LED 81.
(2-5) The second switch PT0 is turned on by lighting the control LED 81.
(2-6) When the second switch PT0 is turned on, the first switch TR0 is turned off (non-conducting state).
(2-7) When the first switch TR0 is turned off, power is not supplied from the rectifier circuit 51 to the first switching control circuit 62.
(2-8) Since power is not supplied, the first switching control circuit 62 does not operate.
(2-9) Since the first switching control circuit 62 is stopped, the first power supply unit 6 does not generate the first DC voltage V1.
(2-10) Since it is not necessary to supply power from the first power supply unit 6, the control circuit 8 sets the applied control element 91 in the OFF state (open state).

3. 3. When the power cord 50 is disconnected Next, an example of the state of the power supply device 5 when the power cord 50 is disconnected (when the power supply from the AC power supply AC is stopped) will be described with reference to FIG. Since it was in the active mode or the sleep mode until the power cord 50 was pulled out, electric charges were accumulated in the smoothing capacitor C0.

(3-1) The operation of the second switching control circuit 72 is stopped by stopping the power supply from the AC power supply AC.
(3-2) The second DC voltage V2 is not generated due to the stoppage of the second switching control circuit 72.
(3-3) Since the second DC voltage V2 is no longer generated, the control circuit 8 is stopped.
(3-4) The control LED 81 is maintained in the extinguished state by stopping the generation of the second DC voltage V2 and stopping the control circuit 8.
(3-5) The second switch PT0 maintains the OFF state when the control LED 81 is turned off.
(3-6) Since the second switch PT0 is turned off and the electric charge is stored in the smoothing capacitor C0, a bias voltage is applied and the first switch TR0 is turned on.
(3-7) When the first switch TR0 is turned on, the electric charge (current) stored in the smoothing capacitor C0 is supplied to the first switching control circuit 62.
(3-8) The first switching control circuit 62 operates by supplying the electric charge.
(3-9) Since the first switching control circuit 62 operates, the first power supply unit 6 generates the first DC voltage V1.
(3-10) The electric charge of the smoothing capacitor C0 is consumed by the operation of the first switching control circuit 62 and the generation of the first DC voltage V1 of the first power supply unit 6.
(3-12) Since the application control element 91 is a normally open type element, the first DC voltage V1 generated for charge consumption is not applied to the device connected to the first power supply unit 6.

4. When the electric charge of the smoothing capacitor C0 is consumed Next, an example of the flow until the electric charge of the smoothing capacitor C0 is consumed and the first power supply unit 6 is stopped will be described with reference to FIG.

(4-1) The voltage between the terminals of the smoothing capacitor C0 decreases due to the consumption of the electric charge of the smoothing capacitor C0.
(4-2) Due to the decrease in the voltage between the terminals of the smoothing capacitor C0, the supply of the current (voltage) to the first switching control circuit 62 is stopped, and the first switching control circuit 62 is stopped.
(4-3) The first switching control circuit 62 is stopped, and the generation of the first DC voltage V1 is stopped.
(4-4) The electric charge of the smoothing capacitor C0 is consumed by the time the generation of the first DC voltage V1 is stopped, and the electric charge stored in the smoothing capacitor C0 is reduced to the extent that electric shock does not occur.

In this way, the power supply device 5 according to the embodiment includes a power supply cord 50, a rectifier circuit 51, a smoothing capacitor C0, a first power supply unit 6, a second power supply unit 7, a control circuit 8, and a supply switch unit 9. The power cord 50 is connected to the AC power supply AC. The rectifier circuit 51 rectifies the AC voltage supplied from the AC power supply AC via the power supply cord 50. One end of the smoothing capacitor C0 is connected to the output terminal 51a of the rectifier circuit 51. The smoothing capacitor C0 smoothes the voltage output by the rectifier circuit 51. The other end of the smoothing capacitor C0 is connected to the negative electrode terminal 51b of the rectifier circuit 51. The first power supply unit 6 generates and outputs a first DC voltage V1 by applying a voltage smoothed by the smoothing capacitor C0. The second power supply unit 7 generates and outputs a second DC voltage V2 while power is being supplied from the AC power supply AC. The control circuit 8 operates by applying a second DC voltage V2. The first power supply unit 6 includes a first transformer 61, a first switching element Q1, and a first switching control circuit 62. The first transformer 61 includes a primary winding whose one end is connected to one end of the smoothing capacitor C0. The first switching element Q1 is connected to the other end of the primary winding of the first transformer 61. The first switching control circuit 62 controls ON / OFF of the first switching element Q1. The first switching control circuit 62 operates by applying a voltage smoothed by the smoothing capacitor C0. The supply switch unit 9 includes a first switch TR0 and a second switch PT0. The first switch TR0 is connected to one end of the smoothing capacitor C0. The first switch TR0 supplies the electric charge stored in the smoothing capacitor C0 to the first switching control circuit 62 when it is in the ON state. When the first switch TR0 is in the OFF state, the power supply to the first switching control circuit 62 is stopped. The second switch PT0 is connected to one end of the smoothing capacitor C0. When in the ON state, the second switch PT0 sets the first switch TR0 in the OFF state. When in the OFF state, the second switch PT0 turns the first switch TR0 into the ON state. When the first power supply unit 6 is operated, the control circuit 8 turns off the second switch PT0. When the first power supply unit 6 is stopped, the control circuit 8 turns on the second switch PT0. The second switch PT0 is turned off regardless of the control of the control circuit 8 when the control circuit 8 is stopped because the power cord 50 is no longer connected to the AC power supply AC.

When the power cord 50 is disconnected from the AC power supply AC (outlet), power is not supplied. As a result, the control circuit 8 stops. By stopping (stopping control) the control circuit 8, the second switch PT0 is turned off even when the printer 100 is in the sleep mode. When the smoothing capacitor C0 has a large charge (when the voltage between the terminals of the smoothing capacitor C0 is large), the first switch TR0 connected to one end of the smoothing capacitor C0 is automatically turned on according to the OFF of the second switch PT0. It becomes. As a result, the electric charge stored in the smoothing capacitor C0 flows into the first switching control circuit 62. When the control circuit 8 is stopped due to the stop of the power supply from the AC power supply AC, the first power supply unit 6 automatically starts the operation by using the electric charge of the smoothing capacitor C0.

When the control circuit 8 is stopped, the first power supply unit 6 can be operated only by the energy stored in the power supply device 5 (smoothing capacitor C0). By the operation of the first power supply unit 6, the electric charge stored in the smoothing capacitor C0 can be consumed. As the charge of the smoothing capacitor C0 decreases, the operation of the first switching control circuit 62 automatically stops. As described above, when the power supply from the AC power supply AC (commercial power supply) is stopped, the charge consumption of the smoothing capacitor C0 is automatically started immediately. There is no need to detect zero cross. As a result, it is possible to eliminate electric shock during maintenance. Damage to the power supply device 5 due to electric shock can be eliminated.

The power supply device 5 includes an application control element 91. The application control element 91 is provided in the secondary winding of the first transformer 61. The application control element 91 controls ON / OFF of application of the first DC voltage V1 to the device connected to the first power supply unit 6. When the power cord 50 is connected to the AC power supply AC and the first power supply unit 6 is operated, the control circuit 8 turns on the applied control element 91. The application control element 91 is normally open. Therefore, when the first switching control circuit 62 automatically operates due to the consumption of electric charge, the first DC voltage V1 is a device connected to the first power supply unit 6 even if the control circuit 8 is not operating. Is not applied to. Even if the first power supply unit 6 temporarily operates after the power cord 50 is disconnected, the device connected to the first power supply unit 6 does not start and does not operate. Unnecessary operation can be prevented.

The supply switch unit 9 includes a first switch TR0, a second switch PT0, a first resistor R1, and a second resistor R2. The first switch TR0 is a transistor. The emitter of the first switch TR0 (transistor), one end of the smoothing capacitor C0, one end of the second switch PT0, and one end of the first resistor R1 are connected. The base of the first switch TR0 (transistor), the other end of the second switch PT0, the other end of the first resistor R1, and one end of the second resistor R2 are connected. When the second switch PT0 is in the ON state, the emitter and the base of the first switch TR0 (transistor) have the same potential, so that the first switch TR0 is in the OFF state. When the second switch PT0 is in the OFF state, the first switch TR0 is in the ON state due to the potential difference between the emitter and the base of the first switch TR0 (transistor). When the power supply from the AC power supply AC (commercial power supply) is stopped, the control circuit 8 is stopped and the second switch PT0 is no longer controlled. When the second switch PT0 is turned off by stopping the control circuit 8, the first switch TR0 (transistor) is automatically turned on. An expensive control circuit 8 or detection circuit is not required for the automatic state change of the first switch TR0. When the supply of AC power is stopped, the charge consumption of the smoothing capacitor C0 by the first power supply unit 6 is automatically started.

The supply switch unit 9 includes a constant voltage diode ZD. One end of the constant voltage diode ZD is connected to the collector of the first switch TR0 (transistor). The other end of the constant voltage diode ZD is connected to the first switching control circuit 62. A voltage above a certain level can be supplied to the first switching control circuit 62. Further, it is possible to prevent the voltage between the terminals of the smoothing capacitor C0 from becoming too small.

The second power supply unit 7 includes a second transformer 71, a second switching element Q2, and a second switching control circuit 72. The second transformer 71 includes a primary winding whose one end is connected to one end of the smoothing capacitor C0. The second switching element Q2 is connected to the other end of the primary winding of the second transformer 71. The second switching control circuit 72 controls ON / OFF of the second switching element Q2. The second power supply unit 7 and the control circuit 8 can be operated while power is being supplied from the AC power supply AC (commercial power supply).

The image forming apparatus (printer 100) according to the embodiment includes the power supply device 5 described above. It is possible to provide an image forming apparatus including a power supply device 5 that does not cause an electric shock during maintenance. An image forming apparatus that is easy to maintain can be provided.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to this, and various modifications can be made without departing from the gist of the invention.

The present invention can be used in a power supply device and an image forming device including the power supply device.

100 Printer (image forming device) 5 Power supply device 50 Power supply cord 51 Rectifier circuit 51a Output terminal 51b Negative voltage terminal 6 First power supply unit 61 First transformer Lp1 Primary winding Ls1 Secondary winding 62 First switching control circuit Q1 First Switching element 7 2nd power supply unit 71 2nd transformer Lp2 1st winding Ls2 2nd winding 72 2nd switching control circuit Q2 2nd switching element 8 control circuit 9 Supply switch unit TR0 1st switch PT0 2nd switch R1 1st Resistance R2 2nd resistance ZD constant voltage diode 91 Applied control element AC AC power supply C0 Smoothing condenser V1 1st DC voltage V2 2nd DC voltage

Claims (6)

The power cord connected to the AC power supply and
A rectifier circuit that rectifies the AC voltage supplied from the AC power supply via the power strip, and
A smoothing capacitor whose one end is connected to the output terminal of the rectifier circuit, smoothes the voltage output by the rectifier circuit, and the other end is connected to the negative electrode terminal of the rectifier circuit.
A first power supply unit to which a voltage smoothed by the smoothing capacitor is applied to generate and output a first DC voltage, and
A second power supply unit that generates and outputs a second DC voltage while power is being supplied from the AC power supply.
A control circuit that operates by applying the second DC voltage,
Including the supply switch section
The first power supply unit
A first transformer containing a primary winding, one end of which is connected to one end of the smoothing capacitor,
A first switching element connected to the other end of the primary winding of the first transformer,
A first switching control circuit that controls ON / OFF of the first switching element and operates by applying a voltage smoothed by the smoothing capacitor is included.
The supply switch unit includes a first switch and a second switch.
The first switch is
Connected to one end of the smoothing capacitor
When in the ON state, the electric charge stored in the smoothing capacitor is supplied to the first switching control circuit.
When in the OFF state, the power supply to the first switching control circuit is stopped, and the power supply is stopped.
The second switch is
Connected to one end of the smoothing capacitor
When in the ON state, the first switch is set to the OFF state.
When in the OFF state, the first switch is set to the ON state.
The control circuit
When operating the first power supply unit, the second switch is turned off and the second switch is turned off.
When the first power supply unit is stopped, the second switch is turned on.
The second switch is a power supply device that is turned off when the control circuit is stopped because the power cord is no longer connected to the AC power supply. An application control element provided in the secondary winding of the first transformer and controlling ON / OFF of application of the first DC voltage to the device connected to the first power supply unit is included.
The applied control element is normally open and has
The control circuit
The power supply device according to claim 1, wherein the power supply cord is connected to the AC power supply, and the applied control element is turned on when the first power supply unit is operated. The supply switch unit includes the first switch, the second switch, the first resistor, and the second resistor.
The first switch is a transistor and
The emitter of the transistor, one end of the smoothing capacitor, one end of the second switch, and one end of the first resistor are connected to each other, and the base of the transistor, the other end of the second switch, and the first one are connected. When the other end of the resistor and one end of the second resistor are connected and the second switch is in the ON state, the emitter and the base are set to the same potential to turn the first switch into the OFF state.
The power supply device according to claim 1 or 2, wherein when the second switch is in the OFF state, the first switch is turned on due to a potential difference between the emitter and the base. The supply switch section includes a constant voltage diode.
The constant voltage diode is
One end is connected to the collector of the transistor,
The power supply device according to claim 3, wherein the other end is connected to the first switching control circuit. The second power supply unit
A second transformer containing a primary winding, one end of which is connected to one end of the smoothing capacitor,
A second switching element connected to the other end of the primary winding of the second transformer, and
The power supply device according to any one of claims 1 to 4, further comprising a second switching control circuit that controls ON / OFF of the second switching element. An image forming apparatus including the power supply device according to any one of claims 1 to 5.

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