JP6981189B2 - Power supply and image forming equipment - Google Patents

Description

The present invention relates to a power supply device and an image forming apparatus including the power supply device.

In an image forming apparatus such as an MFP (Multi Function Peripheral) which is a multi-function digital composite machine, a charge holding means for holding a charge supplied from an external AC power source and a charge holding means for holding the charge are supplied from the AC power supply via the charge holding means. In many cases, a power supply device having a configuration including a switching element for converting the electric power on the primary side into a low voltage and supplying it to the secondary side by switching the current is used.

Further, in general, when the AC power supply is turned off for some reason, a discharge circuit for discharging the charge held by the charge holding means is provided, and the charge holding means is provided by this discharge circuit. Discharging the residual charge is performed.

As a power supply device provided with such a discharge circuit, the one shown in FIG. 8 has been conventionally known. The power supply device 700 rectifies the input from the external AC power supply 800 such as a commercial power supply by the rectifier circuit 701, and then holds the electric charge in the smoothing capacitor 702. A switching element 704 composed of a primary winding 703a of the transformer 703 and, for example, a field effect transistor (hereinafter, also referred to as FET) is connected in series to both ends of the smoothing capacitor 702. Specifically, one end of the primary winding 703a of the transformer 703 is connected to the positive terminal of the smoothing capacitor 702, the drain of the switching FET 704 is connected to the other end of the primary winding 703a, and the source of the switching FET 704 is connected. Is connected to the negative terminal of the smoothing capacitor 702. Reference numeral 703b is a secondary winding of the transformer 703. These transformers 703 and the switching FET 704 form a main converter that converts the voltage of the AC power supply 800 into a DC low voltage and supplies it to the secondary side of the transformer 703.

Further, a discharge FET 712 is connected to both ends of the smoothing capacitor 702 via a discharge resistor 711. These discharge resistors 711 and discharge FETs 712 form a discharge circuit 710 for discharging the residual charge of the smoothing capacitor 712 when it is detected that the AC power supply 800 is turned off.

In the power supply device 700 shown in FIG. 8, the discharge FET 712 in the discharge circuit 710 is always off, and the discharge circuit 710 does not operate. On the other hand, the switching FET 704, which is a switching element, receives a switching signal from the main converter control unit 705 and performs a switching operation. This switching operation generates an electromotive force in the secondary winding 703b of the transformer 703, and this electromotive force is used as the electric power on the secondary side. The ratio of the primary winding 703a and the secondary winding 703b of the transformer 703, the bals width of the switching signal from the main converter control unit 705, etc. are set so that a predetermined voltage such as 24V or 5V can be obtained on the secondary side. It is set.

On the other hand, when it is detected by the AC power off detection circuit (not shown) that the AC power supply 800 is turned off, the output of the switching signal from the main converter control unit 705 is stopped, and the drive signal is sent to the gate of the discharge FET 712 in the discharge circuit 710. # Is input. This drive signal turns on the discharge FET 112, and the residual charge of the smoothing capacitor 702 is discharged via the discharge resistor 711 and the discharge FET 712, as shown by the broken line arrow in the figure.

Patent Document 1 discloses a power supply device that prevents the coil of the discharge circuit and the switching element from being burnt out due to an excessive discharge current. Specifically, the power supply circuit 8 includes a PFC (power factor improvement) circuit 3, a capacitor C that smoothes the output voltage of the PFC circuit 3, and a discharge control circuit 4 that controls the discharge of the capacitor C. The discharge control circuit 4 turns on the coil L1 (primary winding of the transformer 13), the switching element Q2, and the switching element Q2 connected in series between the output lines 16a and 16b of the PFC circuit 3 by a pulse signal. It has a switching control unit 15 for turning off, and the switching control unit 15 gradually discharges the charge of the capacitor C through the coil L1 and the switching element Q2 while changing the duty of the pulse signal.

Further, Patent Document 2 describes a transmission means for transmitting the state of the primary circuit to the secondary circuit and a primary smoothing capacitor in order to prevent malfunction without complicating the system and to promptly reduce the voltage of the primary smoothing capacitor. It is provided with C1, at least one constant voltage element D1, and at least one switching elements Q1 and Q2. When the voltage of the primary smoothing capacitor becomes a certain value or less, the switching element operates, and the transmission means PC1 performs primary smoothing to the secondary circuit. A power supply device for notifying that the voltage of a capacitor is below a certain value is disclosed.

Japanese Unexamined Patent Publication No. 2014-107933 Japanese Unexamined Patent Publication No. 2016-5340

However, in the conventional power supply device shown in FIG. 8, not only the discharge resistor 711 and the discharge FET 712 for forming the discharge circuit 710 are required, but also the power on the primary side is large, so that the discharge resistor 711 is used. As a result, it is necessary to use a metal oxide film resistor and a component for high power such as a power FET as a discharge FET 712, which has a drawback of high cost.

For this reason, it is conceivable to simplify the circuit by simply configuring the discharge circuit 710 with only resistors, but in this case, there is a problem that power consumption increases because current always flows through the resistors. ..

Further, the power supply device described in Patent Document 1 also has a dedicated smoothing circuit, and has a problem that it is expensive. Further, the technique described in Patent Document 2 is a technique for controlling the discharge start timing, and is different from the technique for simplifying the configuration of the discharge circuit.

The present invention has been made in view of such a technical background, and is a discharge circuit that discharges the residual charge of the charge holding means for holding the charge supplied from the AC power supply when the AC power supply is turned off. It is an object of the present invention to provide a power supply device having a simplified configuration of the above, and further to provide an image forming device equipped with this power supply device.

The above problem is solved by the following means.
(1) By switching between the charge holding means for holding the charge supplied from the AC power supply and the current supplied from the AC power supply via the charge holding means, the power on the primary side is converted into a low voltage. The switching element for supplying to the secondary side, the AC power off detecting means capable of detecting that the AC power has been turned off, and the AC power off detecting means detecting that the AC power has been turned off. If so, the driving means comprises a driving means for driving the switching element so that the current is limited and discharging the residual charge held in the charge holding means via the switching element . A power supply device characterized in that the switching element is completely conductive at a predetermined timing after the discharge of the residual charge held by the charge holding means is started.
(2) The power supply device according to item 1 above, wherein when the AC power off detecting means detects that the AC power supply has been turned off, the driving means operates the switching element in a linear region.
(3) The power supply device according to item 1 or 2 above, wherein the driving means drives the switching element so that the current limitation due to the switching element is gradually released.
(4) The switching element is a field-effect transistor, and the driving means drives the field-effect transistor so that the current is limited by adjusting the gate-source voltage of the field-effect transistor. The power supply device according to any one of 3.
(5) By switching between the charge holding means for holding the charge supplied from the AC power supply and the current supplied from the AC power supply via the charge holding means, the power on the primary side is converted into a low voltage. The switching element for supplying to the secondary side, the AC power off detecting means capable of detecting that the AC power has been turned off, and the AC power off detecting means detecting that the AC power has been turned off. When this is done, a power supply device including a driving means for driving the switching element so that the current is limited and discharging the residual charge held in the charge holding means via the switching element, and the above-mentioned The off-time measuring means for measuring the off-state time of the AC power supply detected by the AC power-off detecting means, the off-state time of the AC power supply measured by the off-time measuring means, and the operation mode and / or the load state. An image forming apparatus comprising: a control means for controlling whether or not residual charge is discharged via a switching element according to the above.
(6) The image forming apparatus according to item 5 above, wherein when the AC power supply off detection means of the power supply device detects that the AC power supply is turned off, the drive means operates the switching element in a linear region. ..
(7) The image forming apparatus according to item 5 or 6 above, wherein the driving means of the power supply device drives the switching element so that the current limitation by the switching element is gradually released.
(8) The image according to any one of claims 5 to 7, wherein the driving means of the power supply device completely conducts the switching element at a predetermined timing after the discharge of the residual charge held in the charge holding means is started. Forming device.
(9) The switching element of the power supply device is a field-effect transistor, and the driving means drives the field-effect transistor so that the current is limited by adjusting the gate-source voltage of the field-effect transistor. The image forming apparatus according to any one of the above items 5 to 8.
(10) The above item 5 includes an AC off monitor circuit for saving necessary data to a memory when the AC power is turned off, and the AC off monitor circuit is used as the AC power off detecting means of the power supply device. 9. The image forming apparatus according to any one of 9.

According to the invention described in the preceding paragraph (1), the power supply device switches between a charge holding means for holding the charge supplied from the AC power supply and a current supplied from the AC power supply via the charge holding means. It is equipped with a switching element that converts the electric charge on the primary side to a low voltage and supplies it to the secondary side, but when it is detected that the AC power supply is turned off, the current of the switching element is limited. In other words, the switching element is driven into a state of operating as a resistor, and the residual charge held in the charge holding means is discharged via the switching element. That is, since the switching element for converting the power on the primary side and supplying it to the secondary side is also used as a component of the discharge circuit, the conventional dedicated discharge resistor and discharge FET are not required. The circuit configuration can be simplified accordingly, and the cost can be reduced.
Further, after the discharge of the residual charge held in the charge holding means is started, the switching element is completely conductive at a predetermined timing. That is, since the switching element is completely conductive with the residual charge amount of the charge holding means reduced, it is possible to shorten the time required for discharging while preventing damage to the switching element due to an excessive discharge current.

According to the invention described in the previous section (2), when it is detected that the AC power supply is turned off, the switching element is operated in the linear region, so that the switching element can be put into an operating state in which the current is limited. The residual charge held in the charge holding means can be gradually discharged via the switching element.

According to the invention described in the preceding paragraph (3), since the switching element is driven so that the current limitation by the switching element is gradually released, the discharge current also decreases as the residual charge amount of the charge holding means decreases. This can be prevented and the time required for discharge can be shortened.

According to the invention described in the previous section ( 4 ), the field-effect transistor is driven so that the current is limited by adjusting the gate-source voltage of the field-effect transistor, so that the residue held by the charge holding means is retained. The charge can be gradually discharged via the field effect transistor.

According to the invention described in the previous section ( 5 ), whether or not to discharge the residual charge via the switching element according to the time of the AC power supply off state and the operation mode and / or load state of the image forming apparatus. Is controlled, for example, when the AC power supply is off for a short time and is temporarily off, the discharge operation via the switching element is forcibly performed and the operation of the image forming apparatus is stopped. It is possible to prevent the convenience from being impaired.

According to the invention described in the preceding paragraph ( 10 ), when the image forming apparatus includes an AC off monitor circuit for saving necessary data to a memory when the AC power is turned off, the AC off detecting means is provided. By using the AC off monitor circuit as an AC off monitor circuit, it is possible to avoid the waste of separately creating the AC off detecting means.

It is a schematic block diagram of the image forming apparatus which used the power supply apparatus which concerns on one Embodiment of this invention. It is a circuit diagram which shows an example of a power supply circuit. It is a figure which shows the relationship between the drain current of an N channel field effect transistor, and the voltage between a drain source. It is a figure which shows the state which replaced the discharge circuit drive part in the power supply device of FIG. 2 with a concrete circuit configuration as an example. It is a figure for demonstrating the state of measuring the time (time in the off state) that the off is sustained from the timing T1 when the off of an AC power source is detected. It is a table which shows the relationship between the operation mode and / or the load state of an image forming apparatus, and the permissible time of the off state of an AC power supply. It is a flowchart which shows the operation of the main body control part. It is a circuit diagram which shows an example of the conventional power supply device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 in which the power supply apparatus 10 according to the embodiment of the present invention is used.

The image forming apparatus 1 is configured by arranging a paper feeding unit 200 at the lower part of the apparatus main body 1A, a color image forming unit 100 at the center portion, and a paper ejection unit 600 at the upper portion. A sheet transport path 206 for transporting the sheet (paper) S unwound from the paper feed unit 200 upward is provided from the paper feed unit 200 to the paper discharge unit 600.

The color image forming unit 100 is horizontally hung between the drive roller 51 and the driven roller 50 arranged substantially in the center of the apparatus main body 1A in the vertical direction and the driven and driven rollers 51 and 50, and travels in the direction of the arrow. It is equipped with an intermediate transfer belt 60 and image forming units 62Y, 62M, 62C, 62K of each color of yellow (Y), magenta (M), cyan (C), and black (K) arranged along the traveling direction. ing.

The toner images created by the image-forming units 62Y, 62M, 62C, and 62K are superimposed and transferred to the transfer belt 60, and the transfer end of the transfer belt 60 is transferred to the sheet S transferred through the sheet transfer path 206 (FIG. Secondary transfer is performed at the middle right end), and the sheet S is fed to the fixing unit 300 to fix the toner image. The fixing unit 300 is provided with a fixing heater 301 for heating the fixing roller to a predetermined temperature.

Each image forming unit 62Y, 62M, 62C, 62K images by an electrostatic copying method, and has a charger arranged around them, four laser diodes, a polygon mirror, a scanning lens, and the like. It includes an exposure unit 40 including a print head 21, four reflection mirrors 22 and the like, developers 61Y, 61M, 61C, 61K, a photoconductor drum, a transfer device and the like.

Further, as a replenishment mechanism for replenishing toner to the developing units 61Y, 61M, 61C, 61K of each image forming unit 62Y, 62M, 62C, 62K, the toner cartridge 70Y, 70M, 70C, 70K and the sub hopper 80Y, 80M, 80C, 80K Is located above the image processing units 62Y, 62M, 62C, 62K.

Reference numeral 400 is a means of communication with an external device, and reference numeral 500 is an operation panel unit including a key unit and a display unit.

Reference numeral 10 is a power supply circuit. In this embodiment, an AC input from an AC100V power supply, which is a commercial power supply, is converted into a DC having a constant voltage to supply electric power to each load of the image forming apparatus 1.

As shown in FIG. 2, the power supply circuit 10 includes a rectifying circuit 111 that converts an AC input from an AC100V power supply (AC power supply) 800 into DC, and a charge holding means that smoothes the output of the rectifying circuit 111 and holds a charge. 112, the primary winding 113a of the transformer 113 connected to the positive terminal of the smoothing capacitor 112, the other end of the primary winding 113a, and the switching element 114 connected to the negative terminal of the smoothing capacitor 112. It also includes a main converter control unit 115, an AC off-monitor circuit 118, a discharge circuit drive unit 120, and the like.

The switching element 114 receives a pulse signal from the main converter control unit 115 and performs a switching operation, and turns on and off the current flowing from the smoothing capacitor 112 to the primary winding 113a of the transformer 113 to turn on and off the secondary winding of the transformer 113. A low voltage electromotive force is induced in 113b. Using the electromotive force induced in the secondary winding 113b of the transformer 113, a constant voltage power supply such as 5V or 24V is created and used as a power source for the main body control unit 20 of the image forming apparatus 1 and various loads. That is, the switching element 114 plays a role of converting the electric power on the primary side into a low voltage and supplying it to the secondary side by switching the current supplied from the AC power supply 800 via the smoothing capacitor 112. Then, these transformer 113 and the switching element 114 form a main converter that converts the voltage of the AC power supply 800 into a DC low voltage and supplies it to the secondary side of the transformer 113. The ratio of the primary winding 113a to the secondary winding 113b of the transformer 113, the bals width of the switching signal from the main converter control unit 115, etc. are set so that the voltage on the secondary side becomes a predetermined voltage such as 24V or 5V. Is set to.

In this embodiment, an N-channel field effect transistor (FET) is used as the switching element 114, and the pulse signal output from the main converter control unit 115 is input to the gate of the field effect transistor. .. In the following description, the switching element 114 is also referred to as an FET 114.

The AC off monitor circuit 118 is a known circuit that detects that the AC power supply 800 has been turned off. In this embodiment, the AC off-monitor circuit 118 includes a pair of forward and reverse photocouplers, the photodiodes of each photocoupler operate with a forward current and a reverse current, and the signal at this time is received by the phototransistor of each photocap. The capacitor is charged according to the received signal, and the charging voltage of the capacitor is monitored to detect that the AC power supply 800 is turned off, for example, when the capacitor voltage drops below the threshold value. In the AC off monitor circuit 118, when it is detected that the AC power supply 800 is turned off, the main body control unit 20 that receives the off detection signal stores necessary data related to the setting, operation mode, etc. of the image forming apparatus 1 in memory (FIG. Although it is used for retracting to (not shown), in this embodiment, it is also used as an AC off detection means for discharge control. Therefore, it is not necessary to separately provide a dedicated circuit for detecting that the AC power supply 800 is turned off in order to start discharging the electric charge of the smoothing capacitor 112.

The discharge circuit drive unit 120 is a circuit for forming a discharge circuit that drives the FET 114 to discharge the residual charge of the smoothing capacitor 112 when the AC power supply 800 is detected by the AC off monitor circuit 118. In this embodiment, a switch unit 116 and a discharge control unit 117 are provided. The discharge circuit drive unit 120 uses the FET 114 to form a discharge circuit. Specifically, when it is detected that the AC power supply 800 is turned off, the main body control unit 20 that receives the off detection signal stops the driving of the FET 114 by the main converter 115 and sends a signal to the discharge control unit 117. .. Upon receiving this signal, the discharge control unit 117 turns on the switch unit 116 and outputs a drive signal to the gate of the FET 114 to drive the FET.

The drive signal output from the discharge control unit 117 to the gate of the FET 114 is a signal for operating the FET 114 in the linear region.

FIG. 3 is a diagram showing the relationship between the drain current (hereinafter referred to as Id) of the N-channel FET 114 and the voltage between the drain and source (hereinafter referred to as Vds). As shown in FIG. 3, when Vds increases to a certain value or more, the value of Id becomes almost unchanged and constant. In the "saturation region" where this graph is flat, it operates as a current source in which the current value does not change even if Vds changes, and it is used in this saturation region when normal switching operation is performed. On the contrary, in the "linear region" where Id changes according to the change of Vds, the FET 114 can be regarded as a variable resistance element that can be controlled by the gate-source voltage (hereinafter referred to as Vgs).

Therefore, in this embodiment, when it is detected that the AC power supply 800 is turned off by utilizing this characteristic, the Vgs of the FET 114 which is the switching element on the primary side is controlled to operate the FET 114 in the linear region. It functions as a variable resistance element and realizes a discharge circuit of a smoothing capacitor 112. As a result, the residual charge charged in the smoothing capacitor 112 is gradually discharged by the route indicated by the broken line arrow D in FIG.

FIG. 4 is a diagram showing a power supply device 10 in a state where the discharge circuit drive unit 120 in the power supply device of FIG. 2 is replaced with a specific circuit configuration as an example. In the power supply device 10 of FIG. 4, the same components as those of the power supply device 10 of FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

The discharge circuit drive unit 120 includes a resistor 121, a transistor 122, and a capacitor 123 as an example of the switch unit 116 in FIG. 2, and both ends of the resistor 121 are connected to the gate of the FET 114 and the emitter of the transistor 122, respectively. The collector of the transistor 122 is connected to the power supply Vcc, the emitter is connected to one end of the resistor 121 and the capacitor 123, and the other end of the capacitor is grounded. Further, a resistor 130 is interposed between the main converter 115 and the gate of the FET 114.

In the power supply circuit 10 shown in FIG. 4, when it is detected by the AC off monitor circuit 118 that the AC power supply 800 is turned off, the main body control unit 20 that receives the off detection signal stops the driving of the FET 114 by the main converter 115. , Sends a discharge start command to the discharge control unit 117. The discharge control unit 117 that has received this discharge start command drives the transistor 122. As a result, electric charges are gradually charged from the power supply Vcc to the capacitor 123, the voltage of the emitter of the transistor 122 rises, and the gate voltage of the FET 114 rises. The voltage of the emitter of the transistor 122, that is, the gate voltage of the FET 114, is set to rise until the voltage of the FET 114 is such that it operates in the linear region. As a result, the FET 114 operates as a resistor that limits the current, so that the residual charge charged in the smoothing capacitor 112 is gradually discharged by the route indicated by the broken line arrow D in FIG.

As described above, in this embodiment, when it is detected that the AC power supply 800 is turned off, the FET 114 is driven so that the current is limited, in other words, the FET 114 operates as a resistor, and a smoothing capacitor is used. The residual charge held in the 112 is discharged via the FET 114. That is, since the FET 114 for converting the electric power on the primary side and supplying it to the secondary side is also used as a component of the discharge circuit, a dedicated discharge resistor or a discharge FET as in the conventional case becomes unnecessary. The branch circuit configuration can be simplified and the cost can be reduced. In this embodiment, it is necessary to newly provide the discharge circuit drive unit 120, but since the discharge circuit drive unit 120 is a signal system circuit, it can be configured with inexpensive parts and is made of metal oxide like a conventional discharge circuit. It is not necessary to use parts for high power such as film resistors and power FETs, and the cost reduction effect is expected accordingly.

Further, during discharging, Vgs applied to the gate of the FET 114 is adjusted from the discharge control unit 117 so that the current limitation of the FET is gradually released, in other words, the resistance value of the FET 114 is gradually reduced. You may. In this way, by driving the FET 114 so that the current limitation by the FET 114 is gradually released, it is possible to prevent the discharge current from decreasing as the residual charge amount of the smoothing capacitor 112 decreases, and the time required for discharge is shortened. be able to.

Further, the FET 114 may be completely conductive in the saturation region at a predetermined timing after the start of discharge, for example, when a predetermined time has elapsed or when the voltage of the smoothing capacitor 112 becomes equal to or lower than a predetermined value. In this case, the FET 114 is completely conductive with the residual charge amount of the smoothing capacitor 112 reduced, and the time required for discharging can be shortened while preventing damage to the FET 114 due to an excessive discharge current.

Further, in the embodiment shown in FIG. 4, the main body control unit 20 includes an off-time measurement unit 21 configured by a part of its functions. As shown in FIG. 5, the off time measuring unit 21 measures the time during which the off is sustained (time in the off state) from the timing T1 when the off of the AC power supply 800 is detected by the AC off monitor circuit 118. Is.

When it is detected that the AC power supply 800 is turned off, the main body control unit 20 immediately stops the drive system output (for example, 24V) and holds the control system output (for example, 5V), which hinders the next return. Controls such as saving necessary data in the memory are performed so that there is no such thing. However, the AC power supply 800 may be temporarily interrupted for various reasons and recovered immediately. If the drive system output is stopped or necessary data is saved in the memory each time a momentary interruption occurs, the image forming apparatus 1 is unnecessarily brought down, which is not convenient.

Therefore, the off time measuring unit 21 measures the off state time of the AC power supply 800, and in the case of a short time off, the main body control unit 20 controls so as not to form a discharge circuit, and turns off until the timing T2 in FIG. When the state is maintained, a discharge start command is output to the discharge control unit 117 to control the discharge circuit to be formed.

However, the time (T2-T1) in which the AC power supply 800 is allowed to be turned off differs depending on the operation mode and / or the load state of the image forming apparatus 1. Therefore, in this embodiment, the time allowed for the AC power supply 800 to be turned off is allowed. Is preset according to the operation mode and / or the load state of the image forming apparatus 1 as shown in the table of FIG. In the example of FIG. 6, when the image forming apparatus 1 is in the sleep mode, the smoothing capacitor 112 starts discharging when the AC power supply 800 is kept off for 500 ms. Further, when the image forming apparatus 1 is in the standby mode, the discharge is started when the AC power supply 800 is kept off for 250 ms. Further, when the image forming apparatus 1 is in the operating state, the discharge is started when the AC power supply 800 is off for 100 ms when the load is light, 50 ms when the load is medium, and 22 ms when the load is maximum. It has become.

FIG. 7 is a flowchart showing the operation of the main body control unit 20.

In step S01, the main converter unit 115 is operated to drive the FET 114 by switching. As a result, the power on the primary side is converted to the secondary side.

Next, in step S02, it is checked whether or not it is detected that the AC power supply 800 is turned off. If it is not detected (NO in step S02), the process returns to step S01. If it is detected (YES in step S02), the off state time is measured in step S03, and it is determined in step S04 whether or not a certain time has elapsed while the off state remains. As described above, the fixed time varies depending on the operation mode and the load state of the image forming apparatus 1.

If a certain period of time has not elapsed (NO in step S04), it is checked in step S05 whether the AC power supply 800 has recovered from the off state to the on state. If it has not recovered (NO in step S05), the process returns to step S03. When the state is restored to the ON state (YES in step S05), the process returns to step S01.

After a certain period of time has elapsed in step S04 (YES in step S04), the operation of the main converter control unit 115 is stopped in step S06, necessary data is saved in the memory, and then the discharge control unit 117 is moved in step S07. Make it work. The FET 114 is driven in the linear region by the operation of the discharge control unit 117, and the residual charge of the smoothing capacitor 112 is discharged by the route indicated by the broken line arrow D in FIG. After the start of discharge, the resistance value of the FET 114 may be gradually reduced by adjusting the Vgs of the FET 114.

Next, in step S08, it is determined whether or not a predetermined timing (for example, a timing at which a predetermined fixed time has elapsed from the start of discharge) has arrived. If it has not arrived (NO in step S08), wait until it arrives. When it arrives (YES in step S08), in step S09, the discharge control unit 117 is instructed to completely conduct the FET 114.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

For example, the case where the power supply device 10 is used for the image forming apparatus 1 is shown, but when it is detected that the AC power supply 800 is turned off, it is necessary to discharge the residual charge of the smoothing capacitor 112, the image forming apparatus 20. The power supply device according to the present invention can be used in all the devices including.

1 Image forming device 1A Device main body 10 Power supply device 111 Rectifier circuit 112 Smoothing capacitor (charge holding means)
113 Transformer 113a Primary winding, 113b Secondary winding 114 FET (switching element)
115 Main converter control unit 116 Switch unit 117 Discharge control unit 118 AC off monitor circuit 120 Discharge circuit drive unit 800 AC power supply

Claims (10)

Charge holding means for holding the charge supplied from the AC power supply,
A switching element for converting the power on the primary side into a low voltage and supplying it to the secondary side by switching the current supplied from the AC power supply via the charge holding means.
An AC power off detecting means capable of detecting that the AC power has been turned off,
When it is detected by the AC power off detecting means that the AC power is turned off, the switching element is driven so that the current is limited, and the residual charge held in the charge holding means is transferred to the switching element. And the drive means to discharge through
Equipped with
The driving means is a power supply device characterized in that the switching element is completely conductive at a predetermined timing after the discharge of the residual charge held in the charge holding means is started. The power supply device according to claim 1, wherein when the AC power off detecting means detects that the AC power supply has been turned off, the driving means operates the switching element in a linear region. The power supply device according to claim 1 or 2, wherein the driving means drives the switching element so that the current limitation due to the switching element is gradually released. The switching element is a field effect transistor, said drive means, according to claim 1 to 3 for driving so that the current of the field effect transistor is limited by adjusting the gate-source voltage of the field effect transistor The power supply described in any. By switching between the charge holding means for holding the charge supplied from the AC power supply and the current supplied from the AC power supply via the charge holding means, the power on the primary side is converted into a low voltage and the secondary side is converted. When it is detected that the AC power is turned off by the switching element for supplying to the side, the AC power off detecting means capable of detecting that the AC power is turned off, and the AC power off detecting means. A power supply device including a driving means for driving the switching element so that the current is limited and discharging the residual charge held in the charge holding means via the switching element.
An off-time measuring means for measuring the time of the AC power-off state detected by the AC power-off detecting means, and an off-time measuring means.
A control means for controlling whether or not to discharge the residual charge via the switching element according to the time in the off state of the AC power supply measured by the off time measuring means and the operation mode and / or the load state.
An image forming apparatus characterized by being equipped with. The image forming apparatus according to claim 5, wherein when the AC power off detecting means detects that the AC power is turned off, the driving means operates the switching element in a linear region. The image forming apparatus according to claim 5 or 6, wherein the driving means drives the switching element so that the current limitation due to the switching element is gradually released. The image forming apparatus according to any one of claims 5 to 7, wherein the driving means completely conducts the switching element at a predetermined timing after the discharge of the residual charge held in the charge holding means is started. The switching element is a field-effect transistor, and the driving means drives the field-effect transistor so that the current is limited by adjusting the gate-source voltage of the field-effect transistor. The image forming apparatus according to any one. Equipped with an AC off monitor circuit to save the necessary data to the memory when the AC power is turned off.
The image forming apparatus according to any one of claims 5 to 9, wherein the AC off monitor circuit is used as the AC power off detecting means.

Images