JP6606362B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to overvoltage protection of a power supply device.

  Patent Document 1 discloses an overvoltage protection circuit that protects a power supply device by providing a current fuse in an input unit and configuring the current fuse to blow when a voltage exceeding the rated voltage is supplied to the power supply device. is doing.

Japanese Patent Laid-Open No. 2003-143838

  However, in the configuration described in the cited document 1, even when the input voltage from the external power source is in an overvoltage state for a relatively short period of time, even if the current fuse is blown and the input voltage returns to the normal state, the power supply device Will not work.

  The present invention provides a power supply device operable even after an input from an external power supply is in an overvoltage state, and an image forming apparatus including the power supply device.

According to one aspect of the present invention, the power supply, a second converting first converting means for converting an AC voltage from an external power source to the first direct voltage, the AC voltage from the external power supply to the second DC voltage A switching means set to any one of a conversion means, a first state in which the AC voltage is supplied to the second conversion means, and a second state in which the supply of the AC voltage to the second conversion means is interrupted; The detection means for detecting the AC voltage, a detection state in which the detection means detects the AC voltage, and a non-detection state in which the detection means does not detect the AC voltage. Control means for controlling, and when the AC voltage exceeds a threshold value in the detection state, the detection means sets the switching means to the second state and detects from the non-detection state. After transition to the state During constant is characterized by being configured so as to set regardless the switching means to the value of the AC voltage to the second state.

  According to the present invention, even if the input from the external power supply is in an overvoltage state, the power supply device can operate after returning to the normal state.

The block diagram of the power supply device by one Embodiment. 1 is a configuration diagram of an image forming apparatus according to an embodiment. 6 is a flowchart illustrating an operation of the image forming apparatus according to the embodiment. The block diagram of the power supply device by one Embodiment. The figure which shows the voltage waveform in each point of FIG. The figure which shows the voltage waveform in each point of FIG.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
FIG. 2 is a configuration diagram of the image forming apparatus 6 including the power supply device 7 according to the present embodiment. The commercial power supply 2 is an external power supply for the power supply device 7 and is connected to the converter 3 of the power supply device 7. Commercial power supply 2 is connected to converter 4 via relay RL1. Converter 3 converts the AC voltage of commercial power supply 2 into a DC voltage. In this example, it is assumed that the converter 3 outputs a DC voltage of 3.3V. For example, the 3.3 V DC voltage output from the converter 3 is supplied to the sensor 8 and the CPU 24 in the controller 5 that controls various operations of the image forming apparatus 6. The relay RL1 is an energy saving switch, and the CPU 24 suppresses power consumption by turning off the relay RL1 in a standby state or a sleep state. When the user instructs the image forming apparatus 6 to form an image, the CPU 24 turns on the relay RL1 and supplies the converter 4 with an AC voltage from the commercial power supply 2. Converter 4 converts the AC voltage of commercial power supply 2 into a DC voltage. In this example, it is assumed that the converter 4 outputs a DC voltage of 24V. The DC voltage output from the converter 4 is supplied to the motor 9, the high-voltage power supply 10, the fan 11, the scanner 12, and the solenoid 13 through the controller 5. Thereafter, the CPU 24 controls the motor 9, the high-voltage power supply 10, the fan 11, the scanner 12, the solenoid 13 and the like in accordance with the detection timing of the output of the sensor 8 to perform an image forming operation.

  The fan 11 prevents the temperature inside the image forming apparatus 6 from increasing due to the image forming operation. The motor 9 drives each roller of the conveyance unit 16 that conveys the photosensitive member D and the recording material. The high voltage power supply 10 supplies a necessary bias to the charging unit 17, the transfer unit 18, and the developing unit 19. The charging unit 17 charges the surface of the photoconductor D to a uniform potential, and the scanner 12 exposes the charged photoconductor D to form an electrostatic latent image. The developing unit 19 develops the electrostatic latent image on the photoreceptor D with the toner 20 to form a toner image. The transfer unit 18 transfers the toner image formed on the photoreceptor D to the recording material P. The solenoid 13 is for picking up the recording material P of the paper feed cassette 14 and feeding it to the transport unit 16. The fixing device 15 heats and pressurizes the recording material P to fix the toner image on the recording material P.

  When the image forming operation is completed, the CPU 24 turns off the relay RL1 to stop the power supply to the converter 4 and shift to the energy saving state. As described above, the power supply device 7 of the image forming apparatus 6 includes two converters, the converter 3 is always in an operating state, and the converter 4 is configured to be able to be switched between operation / stop, so as to save energy. ing.

  FIG. 1 is a configuration diagram of a power supply device 7 according to the present embodiment. The bridge diode D1 and the capacitor C2 of the converter 3 constitute a rectifier circuit, and the AC voltage applied from the commercial power supply 2 is rectified / smoothed by the rectifier circuit and supplied to the power supply controller 23 via the resistor R27. Is done. Thereby, the power supply control part 23 starts. The power supply control unit 23 turns on / off the FET Q2 by controlling the gate voltage of the FET Q2 via the signal line S3. As a result, the current flowing through the winding L1 of the transformer T1 changes, and electromotive force is generated in the winding L2 and the winding L3. The electromotive force generated in the winding L2 charges the capacitor C3 via the resistor R11 and the diode D2. Further, the electromotive force generated in the winding L3 charges the capacitor C4 through the diode D3. The power supply control unit 23 controls on / off of the FET Q2 so that the voltage of the capacitor C4 is stabilized at 3.3V, and uses the voltage of the capacitor C4 as a 3.3V power supply. The voltage of the capacitor C3 is applied to the power supply control unit 23 as the control power supply Vcc1.

  The voltage from the 3.3V power supply is supplied to the CPU 24 in the controller 5, thereby starting the CPU 24. When activated, the CPU 24 starts operation control of the image forming apparatus 6. At the time of activation, the CPU 24 sets the signal line S4 to a low level and turns off the transistor Q3. Therefore, no current flows through the photocoupler PC1, and the control power supply Vcc1 is not applied to the voltage detector 1. In a state where the control power supply Vcc1 is not applied to the voltage detection unit 1, the signal line S2 from the voltage detection unit 1 is at a low level, and thus the relay RL1 is turned off.

  When image formation is started by an instruction from the user, the CPU 24 sets the signal line S4 to high level. When the signal line S4 becomes high level, the transistor Q3 is turned on, and a current flows from the 3.3V power source to the photocoupler PC1 via the resistor R12, whereby the voltage of the control power source Vcc1 is applied to the gate of the FET Q1. When applied, FET Q1 is turned on. Further, the control power supply Vcc1 starts to supply power to the comparator 21, and thereby the comparator 21 is activated. When the FET Q1 is turned on, a voltage obtained by dividing the voltage of the capacitor C2 by the resistors R1 and R2 is input to the inverting input terminal of the comparator 21. Further, when a current flows from the control power supply Vcc1 to the Zener diode ZD1 via the resistor R5, a voltage generated in the Zener diode ZD1 is input to the non-inverting input terminal of the comparator 21. Hereinafter, the Zener voltage input to the non-inverting input terminal of the comparator 21 is referred to as a reference voltage. The comparator 21 outputs a high level or a low level to the signal line S1 by comparing a voltage obtained by dividing the output voltage of the rectifier circuit with a reference voltage. Specifically, a high level is output when the reference voltage is higher than a voltage obtained by dividing the output voltage of the rectifier circuit, and a low level is output otherwise. In the present embodiment, whether or not the voltage of the commercial power supply 2 is in an overvoltage state is determined by comparing the reference voltage with a voltage obtained by dividing the output voltage of the rectifier circuit. The comparator 21 sets the signal line S1 to a low level when the commercial power supply 2 is in an overvoltage state, and sets the signal line S1 to a high level otherwise. As described below, when the signal line S1 becomes high level, the relay RL1 is turned on and the converter 4 is activated, and when the signal line S1 becomes low level, the relay RL1 is turned off and the converter 4 stops.

  Hereinafter, the operation in the normal state, that is, the operation when the commercial power supply 2 is not in the overvoltage state will be described first. In this case, as described above, the comparator 21 outputs a high level to the signal line S1. When a high level is output to the signal line S1, power is supplied to the comparator 22 and the comparator 22 is activated. A voltage obtained by dividing the voltage of the signal line S1 by the resistors R7 and R8 is input to the inverting input terminal of the comparator 22. On the other hand, the voltage of the signal line S1 is input to the non-inverting input terminal of the comparator 22 via an RC filter including a resistor R6 and a capacitor C1. That is, the voltage input to the non-inverting input terminal of the comparator 22 rises gently according to the RC filter time constant. As is apparent from the circuit of FIG. 1, when the voltage input to the non-inverting input terminal of the comparator 22 becomes constant, the comparator 22 outputs a high level to the signal line S2. When the signal line S2 becomes high level, the relay RL1 is turned on, and the AC voltage from the commercial power source 2 is applied to the converter 4. The reason why the relay RL1 is not controlled by the output of the comparator 21 but is controlled via the comparator 22 will be described later.

  The bridge diode D5 and the capacitor C5 of the converter 4 constitute a rectifier circuit, and the AC voltage applied from the commercial power supply 2 is rectified / smoothed by the rectifier circuit and supplied to the power supply control unit 25 via the resistor R28. The Thereby, the power supply control part 25 starts. The power supply control unit 25 controls the gate voltage of the FET Q4 via the signal line S5, thereby turning on / off the FET Q4. As a result, the current flowing through the winding L4 of the transformer T2 changes, and an electromotive force is generated in the winding L5 and the winding L6. The electromotive force generated in the winding L5 charges the capacitor C6 via the resistor R17 and the diode D6. The electromotive force generated in the winding L6 charges the capacitor C7 via the diode D7. The power supply control unit 25 performs on / off control of the FET Q4 so that the voltage of the capacitor C7 is stabilized at 24V, and uses the voltage of the capacitor C7 as a 24V power supply. The voltage of the capacitor C6 is applied to the power supply control unit 25 as the control power supply Vcc2.

  Next, the case where the commercial power supply 2 is in an overvoltage state will be described. In this case, as described above, the comparator 21 outputs a low level to the signal line S1. When the signal line S1 is at a low level, power is not supplied to the comparator 22, and the comparator 22 outputs a low level, so that the relay RL1 is turned off. Therefore, the AC voltage from the commercial power source 2 is not applied to the converter 4 and the converter 4 does not operate.

  Next, the reason for providing the comparator 22 will be described. The comparator 22 is provided for preventing malfunction in a transient state. Specifically, consider a case where the comparator 21 is activated earlier than the FET Q1 is turned on when the CPU 24 changes the signal line S4 to the high level. In this case, the voltage based on the capacitor C2 is not input to the inverting input terminal of the comparator 21, and the comparator 21 sets the signal line S1 to the high level regardless of the state of the commercial power supply 2. Thereby, relay RL1 is turned on, and converter 4 is activated even if commercial power supply 2 is in an overvoltage state. In the present embodiment, in order to prevent such malfunction during the transition period, the voltage input to the non-inverting input terminal of the comparator 22 is gradually increased by the RC filter.

  Next, the circuit of FIG. 1 will be described with specific numerical examples. Hereinafter, the reference voltage of the comparator 21, that is, the Zener voltage of the Zener diode ZD1 is set to 5.2V. Then, in order to detect that the commercial power source 2 becomes 170 VAC or higher, the resistance values of the resistors R1 and R2 are set to 10 MΩ and 220 kΩ, respectively. When the voltage value of the commercial power supply 2 is 115 VAC, the voltage of the capacitor C2 is 115 × √2 = 162V. Therefore, the voltage input to the inverting input terminal of the comparator 21 is 162 × 0.22 / 10.22 = 3.5V, which is smaller than the reference voltage of 5.2V. Therefore, the comparator 21 sets the signal line S1 to the high level, and the converter 4 outputs a DC voltage of 24V. On the other hand, when the voltage value of the commercial power supply 2 is 230 VAC, the voltage of the capacitor C2 is 230 × √2 = 325V. Therefore, the voltage value input to the inverting input terminal of the comparator 21 is 325 × 0.22 / 0.22 = 7.0 V, which is higher than the reference voltage. Therefore, the comparator 21 sets the signal line S1 to the low level, and the converter 4 stops the output of the DC voltage.

  The comparator 21 is driven by a voltage output from the control power supply Vcc1. Here, it is assumed that the control power supply Vcc1 is 15V. Normally, the high level voltage output from the comparator 21 is lower than the control power supply Vcc1 by several volts. In this example, it is assumed that the voltage drops by 2V. In this case, the comparator 21 outputs 13V as a high level. Here, for example, when the resistance values of the resistor R7 and the resistor R8 are 57.6 kΩ and 100 kΩ, respectively, 8.2 V is input to the inverting input terminal of the comparator 22. When the resistance value of the resistor R6 is 10 kΩ and the capacitance of the capacitor C1 is 1 uF, the time constant τ = 0.01 seconds. Therefore, when the comparator 21 outputs 13 V as a high level, the voltage applied to the non-inverting input terminal of the comparator 22 becomes 63% of 13 V, that is, 8.2 V after 0.01 second. Therefore, for a period of 0.01 seconds after the CPU 24 sets the signal line S1 to the high level, the relay RL1 remains off regardless of the voltage of the commercial power supply 2.

  FIG. 3 is a flowchart for explaining the operation of the image forming apparatus 6 according to the present embodiment. When AC power is applied from the commercial power source 2 to the image forming apparatus 6, as described with reference to FIG. 1, the converter 3 outputs a DC voltage in S10, and the CPU 24 starts operation by this DC voltage. . When image formation is started in S11, in S12, the CPU 24 sets the signal line S4 to a high level. As a result, as described with reference to FIG. 1, if power is supplied to the voltage detection unit 1 and the commercial power source 2 is not in an overvoltage state, that is, a state equal to or higher than the threshold voltage, the converter 4 is activated and the DC voltage is Start output. In S13, the CPU 24 monitors whether the converter 4 has been activated. If not activated, the CPU 24 determines in S14 whether or not a predetermined time has elapsed since the signal line S4 was set to the high level. If the predetermined time has not elapsed, the processing from S13 is repeated. On the other hand, if the predetermined time has elapsed, the CPU 24 sets the signal line S4 to the low level in S18, and performs error processing in S19. The error processing includes displaying to the user that the commercial power source 2 is in an overvoltage state.

  On the other hand, when the converter 4 is activated and supplies a DC voltage in S13, the CPU 24 forms an image. In S15 and S16, the CPU 24 monitors that the converter 4 is operating until image formation is completed. When the image formation is completed, the CPU 24 sets the signal line S4 to the low level in S17. As a result, the supply of AC voltage from the commercial power source 2 to the converter 4 is interrupted, and the power supply to the voltage detection unit 1 is interrupted. Thereafter, the CPU 24 stands by until the next image formation is started. On the other hand, if the converter 4 stops outputting DC voltage before the end of image formation, the CPU 24 sets the signal line S4 to low level in S18 and performs error processing in S19.

  As described above, in this embodiment, the converter 3 converts the AC voltage from the external power source into the first DC voltage having the first voltage value, and the converter 4 converts the AC voltage from the external power source to the second DC voltage having the second voltage value. Convert to The converter 4 is supplied with an AC voltage via the relay RL1. That is, when the relay RL1 is turned on, an AC voltage is supplied to the converter 4, and when the relay RL1 is turned off, the supply of the AC voltage to the converter 4 is interrupted. The voltage detector 1 detects whether or not the AC voltage is greater than or equal to a threshold value. In the present embodiment, the voltage detection unit 1 detects whether or not the AC voltage is equal to or higher than a threshold by using a voltage obtained by rectifying the AC voltage. The controller 5 that is a control unit controls the voltage detection unit 1 to either a detection state in which the voltage detection unit 1 detects the AC voltage or a non-detection state in which the AC voltage is not detected. Specifically, the control unit finally turns on / off the FET Q1 through the signal line S4. Thereby, the control unit is in the state of the voltage detection unit 1 in either a detection state in which a voltage based on the AC voltage is supplied to the voltage detection unit 1 or a non-detection state in which a voltage based on the AC voltage is not supplied to the voltage detection unit 1 To control. In addition, a control part sets the voltage detection part 1 to a detection state, when using the voltage which the converter 4 outputs. In other cases, the voltage detection unit 1 is set to a non-detection state. Further, the control unit operates by the voltage output from the converter 3.

  Voltage detection unit 1 sets relay RL1 to the off state when the AC voltage is equal to or higher than the threshold value in the detection state. Voltage detector 1 sets relay RL1 to the off state in the non-detection state. Further, the voltage detection 1 sets the relay RL1 to the ON state while the AC voltage is less than the threshold value in the detection state.

  With this configuration, when the AC voltage from the external power source exceeds the input range of the converter 4, the AC voltage can be prevented from being supplied to the converter 4. Thereafter, when the AC voltage from the external power supply returns to normal, the power supply device can perform normal operation. In the present embodiment, the input range of the converter 3 is wider than the input range of the converter 4. For example, the input range of the converter 3 is 100 VAC to 240 VAC, and the input range of the converter 4 is 100 VAC to 127 VAC.

  Note that, when the voltage detection unit 1 transitions from the non-detection state to the detection state, the voltage detection unit 1 turns off the relay RL1 for a predetermined period regardless of the value of the AC voltage. In the present embodiment, the comparator 21 that is a comparator compares the voltage generated from the AC voltage with the voltage corresponding to the threshold value, and outputs a comparison result. Specifically, the comparator 21 outputs a predetermined voltage when the voltage generated from the AC voltage is lower than a threshold value. The rise of the output of the comparator 21 is moderated by the filter constituted by the resistor R6 and the capacitor C1, and thereby the time until the comparator 22 outputs a high level signal is delayed. With this configuration, it is possible to prevent malfunction when the voltage detection unit 1 is shifted from the non-detection state to the detection state.

<Second embodiment>
Hereinafter, the present embodiment will be described focusing on differences from the first embodiment. FIG. 4 is a configuration diagram of the power supply device 7 in the present embodiment. The same components as those in the first embodiment shown in FIG. In the present embodiment, the configuration of the voltage detection unit 1 and the drive circuit of the relay R1 are different from those in the first embodiment. First, regarding the voltage detection unit 1, in the first embodiment, an overvoltage is detected by a voltage after rectification by the converter 3. In the present embodiment, the voltage detection unit 1 detects whether or not it is an overvoltage state directly from the AC voltage of the commercial power supply 2.

  Also in this embodiment, when an AC voltage is supplied from the commercial power source 2, the converter 3 outputs a DC voltage of 3.3V, thereby starting the CPU 24. At this time, the CPU 24 sets the signal line S4 to a low level. Further, when starting the converter 4, the CPU 24 sets the signal line S4 to a high level. When the signal line S4 is set to the high level, the transistor Q3 is turned on, a current flows from the 3.3V power supply to the photodiode of the phototriac coupler SSR1 through the resistor R20, and the phototriac is turned on. When the phototriac of the phototriac coupler SSR1 is turned on, the triac Q5 is turned on, and the AC voltage from the commercial power supply 2 is supplied to the voltage detection unit 1. That is, the voltage detection unit 1 is activated. Thereby, the commercial power source 2 starts charging the capacitor C9 via the diode D8 and the resistor R26. At the same time, the AC voltage divided by the resistors R23 and R24 is applied to the Zener diode ZD2. In the present embodiment, whether or not the voltage of the commercial power supply 2 is equal to or higher than a predetermined value is detected based on whether or not the Zener diode ZD2 is conductive.

  For example, the commercial power supply 2 sets 170 VAC or more to an overvoltage state, and in order to detect this overvoltage state, the resistance values of the resistors R23 and R24 are set to 1 MΩ and 22 kΩ, respectively, and the zener voltage of the zener diode ZD2 is set to 5.2V. . In this case, if the voltage value of the commercial power supply 2 is 115 VAC, the voltage waveform at the point A in FIG. 4 is a sine waveform with a peak of 115 × √2 = 162 V as shown in FIG. Further, when the triac Q5 is in the ON state, a voltage obtained by half-wave rectifying the AC voltage from the commercial power source 2 with the diode D8 is applied at the point B. FIG. 6B shows a voltage waveform at point B. Since the voltage at the point C in FIG. 4 is obtained by dividing the voltage at the point B by the resistors R23 and R24, the peak is a half of 162 × 22/1022 = 3.5V as shown in FIG. Wave rectified waveform. The voltage at point C in FIG. 4 does not exceed 5.2 V, and therefore the capacitor C8 is not charged via the Zener diode ZD2. Therefore, the voltage waveform at the point D in FIG. 4 becomes substantially zero as shown in FIG. Therefore, transistor Q7 maintains an off state.

  Further, when the triac Q5 is in the on state, the AC voltage from the commercial power source 2 charges the capacitor C9 via the resistor R26. For example, when the resistance R26 is 100 kΩ and the capacitance of the capacitor C9 is 10 uF, the voltage waveform at the point E in FIG. 4 has a maximum value of about 1.15 V as shown in FIG. . The voltage at point E in FIG. 4 is set so as to maintain a voltage sufficient to pass a current through the photodiode of the photocoupler PC2. Therefore, the photocoupler PC2 is maintained in the on state, whereby a current flows through the winding of the relay RL1 due to the voltage from the 3.3V power source, and the relay RL1 is turned on. As a result, the converter 4 is activated. The time constant of the RC filter composed of the resistor R26 and the capacitor C9 is set sufficiently larger than the time constant of the RC filter composed of the resistor R23 and the capacitor C8. Thereby, malfunction at the time of starting of the voltage detection part 1 is prevented.

  On the other hand, it is assumed that the voltage of the commercial power source 2 is 230 VAC. In this case, the voltage waveform at the point A in FIG. 4 is a sine waveform having a peak of 230 × √2 = 325 V as shown in FIG. 5A. When the triac Q5 is in the ON state, the voltage waveform at the point B Is as shown in FIG. Therefore, the voltage waveform at the point C is a half-wave rectified waveform whose peak is 325 × 22/1022 = 7V. Accordingly, the capacitor C8 is charged through the Zener diode ZD2 from the time t1 when the voltage at the point C in FIG. 4 becomes 5.2V to the time t3 when the voltage reaches the peak 7V. For example, when the capacitance of the capacitor C8 is 0.1 uF, the voltage waveform at the point D in FIG. 4 changes as shown in FIG. Here, at time t2, the transistor Q7 is turned on by the voltage of the capacitor C8. On the other hand, when the TRIAC Q5 is in the ON state, the commercial power source 2 charges the capacitor C9, whereby the voltage at the point E in FIG. 4 at time t2 is about 0. 0 as shown in FIG. 24V. However, since the transistor Q7 changes to the on state at time t2, the charge of the capacitor C9 is discharged through the resistor R29, and the voltage at the point E in FIG. 4 after time t2 is as shown in FIG. It becomes approximately 0V. Therefore, the photocoupler PC2 is not turned on, so that no current flows through the relay RL1 and is turned off.

  In the present embodiment, as in the first embodiment, the voltage after rectification by the rectifier circuit of the converter 3 is not received by the voltage detection unit 1 and the overvoltage is detected, but the AC voltage from the commercial power supply 2 is used as the voltage. The detection unit 1 directly receives power and detects overvoltage. Therefore, the converter 3 and the voltage detector 1 can be configured independently, and the versatility of the converter 3 can be increased.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  3, 4: Converter, RL1: Relay, 1: Voltage detector, 5: Controller

Claims (11)

First conversion means for converting an AC voltage from an external power source into a first DC voltage;
Second conversion means for converting the AC voltage from the external power source into a second DC voltage;
A switching means set to one of a first state in which the AC voltage is supplied to the second conversion means and a second state in which the supply of the AC voltage to the second conversion means is cut off;
Detecting means for detecting the AC voltage;
Control means for controlling the detection means to any one of a detection state in which the detection means detects the AC voltage and a non-detection state in which the detection means does not detect the AC voltage;
With
The detection means sets the switching means to the second state when the AC voltage is equal to or higher than a threshold value in the detection state, and after the transition from the non-detection state to the detection state, the detection means A power supply apparatus configured to set the switching means to the second state regardless of an AC voltage value .   2. The power supply device according to claim 1, wherein the detection unit sets the switching unit to the second state in the non-detection state.   3. The power supply device according to claim 1, wherein the detection unit sets the switching unit to the first state while the AC voltage is less than the threshold in the detection state.   The control means controls the detection means to the detection state or the non-detection state by controlling supply of the AC voltage or a voltage generated from the AC voltage to the detection means. Item 4. The power supply device according to any one of Items 1 to 3.   5. The power supply device according to claim 4, wherein the control unit controls the supply of the AC voltage or a voltage generated from the AC voltage to the detection unit by a triac or a transistor.   The control means sets the detection means to the detection state when the second DC voltage is used, and sets the detection means to the non-detection state when the second DC voltage is not used. Item 6. The power supply device according to any one of Items 1 to 5.   The power supply device according to claim 1, wherein the control unit operates with the first DC voltage. The detection means includes
A comparison means for comparing a voltage generated from the AC voltage with a voltage corresponding to the threshold;
Delay means for delaying a signal indicating the comparison result output from the comparison means;
Equipped with a,
The power supply device according to any one of claims 1 to 7, characterized in that for controlling the switching means a signal indicating the comparison result delayed by the delay means. The switching unit power supply device according to any one of claims 1 8, characterized in that a relay. An image forming apparatus characterized in that it comprises a power supply device according to any one of claims 1 9. The image forming apparatus according to claim 10 , wherein the control unit sets the detection unit to the detection state when starting image formation.

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