JP6132439B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a detection device including a power supply, a sensor that outputs an analog voltage as a detection result, and a control circuit including an A / D conversion circuit that digitizes the analog output voltage of the sensor, and image formation including the detection device Relates to the device.

  In general, an image forming apparatus such as a multifunction machine, a copier, a printer, or a facsimile includes a large number of circuits and elements. In order to apply an appropriate voltage to each of these circuits and elements, a plurality of types of power supplies having different voltages may be provided in the image forming apparatus. An example of a power supply circuit that provides a plurality of types of voltages by providing a plurality of power conversion circuits is described in Patent Document 1.

Specifically, Patent Document 1 is a power supply circuit that steps down a power supply voltage from a DC power supply to a predetermined voltage and supplies power, and steps down the power supply voltage from the DC power supply to a predetermined voltage Va and outputs it. A power supply circuit including a DCDC converter and a regulator that steps down an output voltage from the DCDC converter to at least one predetermined voltage Vb and supplies power is described. When a predetermined signal is input in the low power consumption operation mode, the DCDC converter of this power supply circuit is deactivated and stops operating, and outputs a power supply voltage from a DC power supply. With this configuration, in the case of normal power consumption, the DCDC converter is operated, while in the sleep state, when the power consumption is small, the DCDC converter is deactivated to reduce power consumption and pass through the DCDC converter. A power source having a desired voltage value is supplied to a power supply destination device only by a regulator to reduce power consumption in a sleep state (see Patent Document 1: Claim 1, Claim 2, paragraph [0008]).
JP2002-320380

  When the main power supply of the image forming apparatus is turned on, the image forming apparatus is activated and can execute jobs such as copying and scanning (starts up in a normal mode). Keeping the image forming apparatus in a state where the job can be started immediately (normal mode) requires a certain amount of power consumption such as holding the toner image fixing roller at a high temperature. Therefore, the image forming apparatus has a power saving mode (sometimes referred to as “sleep mode”) for reducing power consumption. In the power saving mode, the power supply portion is reduced as compared with the normal mode. As a result, the state of the image forming apparatus can be held with reduced power consumption. For example, in the power saving mode, power supply to a predetermined portion such as an unnecessary sensor or a printing-related portion such as a fixing unit is stopped.

  On the other hand, there are processes to be performed even in the power saving mode. Therefore, there is a case where power supply is continued to a control circuit such as a CPU even in the power saving mode. For example, the control circuit performs a predetermined process when it is performed during the power saving mode, such as a process defined by the OS or a process related to network communication.

  Thus, in the power saving mode, there is a portion that stops power supply while there is a portion that continues power supply. Therefore, in some cases, a switch is connected in parallel to the power supply line that connects the power supply and the control circuit that continues to supply power even in the power saving mode, and multiple sensors and loads that stop the power supply in the power saving mode are connected via the switch. is there.

  An example of such a conventional power supply circuit configuration will be described with reference to FIG. FIG. 10 is a diagram illustrating an example of a circuit configuration of a conventional power supply. In FIG. 10, power is supplied to the control circuit 901 from the DC power supply Va. Further, the magnitude of the voltage of the power supply Va is a voltage within an appropriate applied voltage range in the specification of the control circuit 901. In the circuit shown in FIG. 10, a switch 902 is connected on the power supply line from the power source Va to the control circuit 901. A plurality of loads 904 such as sensors 903 (for example, temperature sensors) are connected in parallel to the downstream side of the switch 902. If wiring is performed in this way and the switch 902 is turned OFF in the power saving mode, power is supplied to the control circuit 901 and power is supplied to the sensor 903 and the load 904 connected downstream from the switch 902. Can be stopped.

  In the circuit configuration illustrated in FIG. 10, a sensor 903 that outputs an analog voltage having a magnitude corresponding to a detection target state may be connected to the downstream side of the switch 902. In some cases, the analog output of the sensor 903 is input to the A / D input port of the control circuit 901. In this case, the analog voltage input by the A / D conversion circuit 905 incorporated in the control circuit 901 is converted into a digital value. The control circuit 901 recognizes the current state (for example, temperature) of the detection target based on the converted digital value.

  The A / D conversion circuit 905 in the control circuit 901 may use the power supply voltage Va as a reference voltage for A / D conversion. In this case, if the voltage (reference voltage) input from the power source Va to the control circuit 901 is the same as the voltage applied to the sensor 903, it may be converted into a digital value with high accuracy. However, the switch 902 may cause a voltage drop. Therefore, there is a difference between the applied voltage of the sensor 903 and the voltage input to the control circuit 901 from the power supply Va. In other words, when a circuit as shown in FIG. 10 is configured and power is supplied to the control circuit 901 and the sensor 903, a digital value obtained by A / D conversion in the control circuit 901 or a detection result based on the digital value is displayed. Accuracy and accuracy may be impaired.

  Further, the magnitude of the current flowing through the switch 902 is influenced by the processing state of the image forming apparatus and is not constant. For example, the output current of the switch 902 varies depending on whether or not a job is being executed. Further, even during job execution, it may vary depending on the type of job to be executed. The magnitude of the voltage drop at the switch 902 is affected by temperature. The magnitude of the voltage drop at the switch 902 varies depending on the magnitude of the current flowing through the switch 902. Therefore, when power is supplied with a circuit configuration as shown in FIG. 10, the difference between the voltage of the power supply Va supplied to the control circuit 901 and the voltage applied to the sensor 903 varies. Therefore, even if the state of the detection target is the same, the digital value obtained by A / D conversion varies from time to time. Accordingly, there is a problem in that fluctuations in the magnitude of the voltage dropped by the switch 902 may deteriorate the accuracy and accuracy of the obtained digital value and the detection result based on the digital value.

  In the invention described in Patent Document 1, in consideration of the power consumed by the DCDC converter itself, in the sleep mode, the DCDC converter is stopped to reduce the consumed power. However, there is no description about the digital value obtained by A / D conversion of the sensor that outputs the analog voltage by the control circuit, and the problem of the accuracy and accuracy of the detection result based on the digital value. Can not.

  In view of the above-described problems of the prior art, the present invention stops power supply to the sensor unit while continuing power supply to the control circuit in the power saving mode, and applies the control circuit and the sensor simply and inexpensively. The same voltage is used to improve the accuracy and accuracy of the digital value obtained based on the analog output voltage of the sensor and the detection result based on the digital value.

  In order to solve the above-mentioned problem, the detection device according to claim 1 has a normal mode and a power saving mode, and shifts to the power saving mode when a predetermined transition condition is satisfied, and a predetermined return condition is satisfied. When satisfied, returns to the normal mode and is connected to the first power source for supplying power in both the normal mode and the power saving mode, and is based on the first power source in the normal mode. A second power source including a power generation switch unit that stops power supply in the power saving mode, a sensor unit that receives power from the second power source and outputs an analog voltage as a detection result, An analog-to-digital conversion circuit that converts an analog voltage output from the sensor unit into a digital value using a voltage based on power supplied from two power sources as a reference voltage; A control circuit connected in parallel with a server unit, and in the normal mode, power from the second power source is supplied to the control circuit, and in the power saving mode, power from the first power source is supplied to the control circuit. A supply source switching unit that performs switching to supply is provided.

  According to the present invention, while continuing power supply to the control circuit even in the power saving mode, the applied voltage of the control circuit and the sensor is made the same magnitude easily and inexpensively, and the accuracy of the digital value obtained based on the sensor, Improve the accuracy of detection results based on digital values.

1 is a diagram illustrating an example of a structure of a multifunction machine. 2 is a diagram illustrating an example of a hardware configuration of a multifunction peripheral. FIG. It is a figure which shows an example of an example of the electric power supply system of a multifunctional machine. It is a figure which shows an example of the operation detection part which detects generation | occurrence | production of the return factor to normal mode. It is a figure which shows an example of a detection apparatus. It is a figure which shows an example of the production | generation of the 2nd power supply based on a 1st power supply. It is a figure which shows an example of the A / D conversion circuit contained in a control circuit (CPU). It is a figure which shows an example of the electric power supply state to the detection apparatus in normal mode. It is a figure which shows an example of the electric power supply state to the detection apparatus in power saving mode. It is a figure which shows an example of the circuit structure of the conventional electric power supply.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the following description, an MFP 100 will be described as an example of an image forming apparatus including the detection apparatus 1 according to the embodiment. However, each element such as configuration and arrangement described in each embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of MFP 100)
First, an outline of the multifunction peripheral 100 according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of the structure of the multifunction peripheral 100.

  As shown in FIG. 1, the multifunction peripheral 100 of the present embodiment has an operation panel 2 attached to the side. The multi-function device 100 includes a document transport unit 3a and an image reading unit 3b at the top. In addition, the multifunction peripheral 100 includes, as the printing unit 4, a paper feeding unit 4a, a first conveyance unit 4b, an image forming unit 4c, a fixing unit 4d, and a second conveyance unit 4e.

  The operation panel 2 displays various messages and setting screens. The document transport unit 3a transports the documents set on the document tray 31 one by one toward the reading position. The image reading unit 3b reads the document transported by the document transport unit 3a and the document placed on the placement reading contact glass, and generates image data of the document.

  The paper feed unit 4a accommodates a plurality of sheets and sends out the sheets during printing. The first transport unit 4b transports the paper supplied from the paper feed unit 4a to the image forming unit 4c. The image forming unit 4c includes a photosensitive drum 41, a developing device 42, and the like. An electrostatic latent image is formed on the peripheral surface of the photosensitive drum 41, and the developing device 42 develops the electrostatic latent image with toner. The toner image is transferred to a sheet. The fixing unit 4d includes a heating roller 43 incorporating a heater and a pressure roller 44 that is in pressure contact with the heating roller 43. The fixing unit 4d fixes the toner image on the paper. The second transport unit 4 e transports the paper that has passed through the fixing unit 4 d toward the discharge tray 45.

(Hardware configuration of MFP 100)
Next, a hardware configuration of the multifunction peripheral 100 according to the embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of a hardware configuration of the multifunction peripheral 100.

  As illustrated in FIG. 2, the multifunction peripheral 100 according to the present embodiment includes a control unit 5. The control unit 5 controls each unit by performing control related to the operation of the image forming apparatus (multifunction device 100). In addition, the control unit 5 performs processing related to communication for performing network communication by the communication unit 51. The control unit 5 includes a CPU 6 (corresponding to a control circuit), an image processing unit 52 that generates image data used for printing and transmission, and other electronic circuits and elements.

  The CPU 6 is a central processing unit, and controls and performs each part of the multifunction peripheral 100 based on a control program and control data stored in the storage unit 53. Further, the state of the detection target of the sensor unit 7 is recognized based on the output value of the sensor unit 7 installed in the multifunction peripheral 100. For example, the CPU 6 recognizes the temperature to be detected by the temperature sensor 71 based on the analog output of the temperature sensor 71. The storage unit 53 is configured by a combination of nonvolatile and volatile storage devices such as ROM, RAM, flash ROM, and HDD.

  Then, the control unit 5 performs printing by paper conveyance, toner image formation, transfer, and fixing (a paper feeding unit 4a, a first conveyance unit 4b, an image forming unit 4c, a fixing unit 4d, a second conveyance). Part 4e). An engine control unit may be provided separately, and the control unit 5 may give an instruction to the engine control unit to cause the engine control unit to control the printing operation of the printing unit 4.

  A communication unit 51 is connected to the control unit 5. The communication unit 51 is an interface for communicating with the computer 200 such as a personal computer via the network 300. The communication unit 51 receives print data including image data and print settings from the computer 200. Then, the control unit 5 causes the printing unit 4 to perform printing based on the printing data (printer function). The communication unit 51 can transmit image data based on reading a document to the computer 200 (transmission function).

  The control unit 5 controls the operations of the image reading unit 3b and the document conveying unit 3a. The control unit 5 controls operations such as display on the operation panel 2. Further, the control unit 5 recognizes the setting contents made on the operation panel 2 and recognizes the job contents, settings, and execution instructions.

(Power supply system)
Next, a power supply system of the multifunction peripheral 100 according to the embodiment will be described with reference to FIG. FIG. 3 is a diagram illustrating an example of the power supply system of the multifunction peripheral 100.

  First, a power supply device 54 is provided in the multifunction peripheral 100. The power supply 54 is connected to the commercial power supply 55 by a power cord, an outlet, or the like. The power supply device 54 rectifies and transforms the commercial power supply 55. The power supply device 54 generates a plurality of types of voltages having different sizes to be supplied to each part of the multifunction device 100 in the multifunction device 100. The power supply device 54 supplies power by applying the generated voltage to each part.

  The multifunction device 100 is provided with a main power switch 56. The main power switch 56 is provided at a predetermined location such as the operation panel 2 or the side surface of the multifunction peripheral 100. The user can turn on / off the main power supply of the multifunction peripheral 100 by operating the main power switch 56. When the main power is turned on, the power supply device 54 starts a predetermined operation. On the other hand, when the main power supply is turned off, all or a part of the power supply device 54 stops operating (main power supply OFF).

  The power supply device 54 includes a primary power supply unit 57. The primary power supply unit 57 is a switching power supply circuit that generates a DC voltage from the commercial power supply 55. The primary power supply unit 57 includes a coil, a capacitor, a semiconductor switch, and a backflow prevention diode. The primary power supply unit 57 generates a DC voltage (for example, DC 24V) for driving the motor.

  Further, the power supply device 54 is provided with a secondary power supply unit 58 that steps down the voltage generated by the primary power supply unit 57. The secondary power supply unit 58 includes a plurality of power conversion circuits 59 such as a DCDC converter and a regulator according to the type of voltage to be generated. The secondary power supply unit 58 is arranged on the substrate provided in the control unit 5, the storage unit 53, the printing unit 4, the communication unit 51, the document conveying unit 3a, the image reading unit 3b, the operation panel 2, and the like. In order to operate circuits such as processors, microcomputers, and memories, multiple types of DC voltages of different sizes are generated. For example, the secondary power supply unit 58 generates a voltage such as DC5V, 3.3V, 2.5V, 1.8V, and 1.2V, and applies the generated voltage to each circuit.

  In addition, the power control unit 50 is provided in the multifunction device 100. The power supply control unit 50 is arranged in the multifunction peripheral 100 and voltage for circuits to the document conveying unit 3a, the image reading unit 3b, the operation panel 2, the storage unit 53, the control unit 5, the printing unit 4, and the communication unit 51. Controls the supply and stop of driving power to the motor. The power supply control unit 50 supplies and supplies power in units constituting the multi-function peripheral 100 such as the document conveyance unit 3a, the image reading unit 3b, the operation panel 2, the storage unit 53, the control unit 5, the printing unit 4, and the communication unit 51. You can stop. Further, a switch may be provided for each electronic circuit such as a processor or a microcomputer so that power can be supplied and stopped for each electronic circuit.

(Normal mode and power saving mode)
Next, a normal mode and a power saving mode in the multifunction peripheral 100 according to the embodiment will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of an operation detection unit that detects the occurrence of a return factor to the normal mode.

  First, when the main power is turned on by the main power switch 56, the start-up process (warm-up process) of the multifunction peripheral 100 is started. When the main power is turned on, the power control unit 50 operates the primary power supply unit 57 and the secondary power supply unit 58 (the primary power supply unit 57 may be operated even when the main power supply is OFF). As a result, all types of voltages to be supplied to circuits, elements, and chips are generated by the secondary power supply unit 58. Then, the power supply control unit 50 generates a voltage generated in each unit of the multifunction device 100 (the document conveyance unit 3a, the image reading unit 3b, the operation panel 2, the storage unit 53, the control unit 5, the printing unit 4, the communication unit 51, and the like). (Power) supply is started. As a result, various circuits such as a processor, a microcomputer, a memory, an element, and a chip included in the multi-function device 100 are activated. For example, after the main power supply is turned on, the main program and the OS 5a are read from the storage unit 53, and the control unit 5 is activated.

  In addition, a process for making the MFP 100 ready to execute a job is started. For example, a process of warming the fixing unit 4d is performed. Then, the multifunction device 100 is activated in the normal mode. In other words, when the main power switch 56 is turned on, the multifunction device 100 first enters the normal mode.

  The normal mode is a mode in which jobs are being executed and all types of jobs can be immediately executed. In other words, the normal mode is a mode in which all functions can be used. The normal mode can also be said to be a mode in which power is supplied to a portion (supply stop portion) where power is not supplied in the power saving mode. Therefore, in the normal mode, the power supply control unit 50 controls the multifunction peripheral 100 such as the document conveyance unit 3a, the image reading unit 3b, the operation panel 2, the storage unit 53, the control unit 5, the printing unit 4, the communication unit 51, and various sensors. Power is supplied to all the constituent parts.

  For example, in the normal mode, the power supply control unit 50 operates by supplying power to the control unit 5 and the storage unit 53. Further, the power supply control unit 50 energizes the heater so that the temperature of the fixing unit 4d is maintained at a temperature suitable for fixing. Therefore, even when the job is not executed, the multifunction peripheral 100 consumes relatively large power.

  Therefore, in order to reduce power consumption when the multifunction device 100 is not used (standby state), the multifunction device 100 has a power saving mode. The power saving mode is a mode in which power supply to a predetermined supply stop portion is stopped and power consumption is reduced as compared with the normal mode.

  In the power saving mode, the power control unit 50 supplies power to all or a part of the multifunction peripheral 100 such as the document conveyance unit 3a, the image reading unit 3b, the operation panel 2, the storage unit 53, and the printing unit 4. Stop and stop power supply to unnecessary parts. On the other hand, predetermined processing (processing by one or a plurality of functional modules of the OS 5 a, the OS 5 a is stored in the storage unit 53 and has real-time characteristics) or printing from the computer 200 is performed in the power saving mode. In order to be able to receive real-time data reception and communication requests from the network 300 to the multifunction peripheral 100, the power supply control unit 50 is used for the voltages for the primary power supply unit 57, the CPU 6, and the communication unit 51 even in the power saving mode. The secondary power supply unit 58 that generates the power is operated, and the power supply to the CPU 6 and the communication unit 51 is continued.

  Next, transition between the normal mode and the power saving mode will be described.

  First, as described above, when the main power of the multi-function device 100 is turned on, the normal mode starts. And the control part 5 confirms whether the conditions for transfer to power saving mode were satisfied. The transition condition can be determined in advance as appropriate. In the MFP 100 according to the present embodiment, the operation of the mode switching key 21 for instructing switching between the normal mode and the power saving mode, such as the power saving key provided on the operation panel 2, is the transition condition to the power saving mode. Is done. In addition, after entering the normal mode or after the job is completed, the operation detection unit cannot detect that the operation or input has been performed on the multifunction device 100 (no operation and remains in a standby state), and the predetermined power saving The passage of the mode transition time (for example, several minutes) is also a condition for shifting to the power saving mode. For example, the CPU 6 provided in the control unit 5 measures the power saving mode transition time.

  As illustrated in FIG. 4, an operation detection unit that detects operations and inputs to the multifunction device 100 is provided in the multifunction device 100. The operation detection unit includes the communication unit 51, the touch panel unit 22 of the operation panel 2, the insertion / removal detection sensor S1, the cover open / close detection sensor S2, the document set sensor S3, and the open / close detection sensor S4. The power supply control unit 50 supplies power to each operation detection unit even in the power saving mode.

  The communication unit 51 receives input of printing data from the computer 200. When the printing data is received, the communication unit 51 transfers the printing data to the control unit 5 and the storage unit 53. The touch panel unit 22 detects an operation on the operation panel 2 by the user, and notifies the control unit 5 when there is an operation.

  The insertion / removal detection sensor S1 detects insertion / removal of the paper feed cassette 46 (see FIG. 1) of the paper feed unit 4a, and the output differs depending on whether the paper feed cassette 46 is attached or removed. The cover open / close detection sensor S2 detects the opening / closing of a cover (for example, the right side cover 47, see FIG. 1) of the multi-function device 100 provided for jam processing, maintenance, etc., and is closed when the cover is open. The output is different when The document set sensor S3 is a sensor for detecting the presence or absence of a document on the document tray 31 on which the document of the document transport unit 3a is placed (see FIG. 1). The output of the document set sensor S3 differs depending on whether the document is placed or not. The open / close detection sensor S4 is a sensor for detecting whether or not the document transport unit 3a is lifted for copying or the like. The output of the open / close detection sensor S4 differs depending on whether the document transport unit 3a is lifted or lowered.

  Outputs of these operation detection units are input to the control unit 5. Accordingly, the control unit 5 and the power supply control unit 501 can recognize the presence / absence of an operation on the multifunction peripheral 100. Then, it is possible to recognize whether or not the power saving mode transition time has elapsed while detecting that there is no operation or input to the multifunction device 100. Then, when recognizing that the power saving mode transition condition is satisfied, the control unit 5 gives the power control unit 50 an instruction to shift to the power saving mode. In response to this instruction, the power supply control unit 50 stops power supply to a predetermined supply stop portion. The outputs of these operation detection units are input to the power supply control unit 50, and when the power supply control unit 50 recognizes that the condition for shifting to the power saving mode is satisfied, without waiting for an instruction from the control unit 5, The power supply control unit 50 may stop power supply to the supply stop portion.

  On the other hand, during the power saving mode, the control unit 5 confirms whether a predetermined condition for returning to the normal mode is satisfied. In other words, the control unit 5 confirms whether or not the power saving mode should be canceled. This confirmation may be performed by the power supply control unit 50.

  Based on the output of the operation detection unit, when it can be recognized that an operation or input has been made on the multifunction peripheral 100, the control unit 5 determines that the return condition is satisfied. For example, the control unit 5 determines that the return condition is satisfied when the communication unit 51 receives print data.

  When the control unit 5 recognizes that the return condition is satisfied, the control unit 5 instructs the power supply control unit 50 to return to the normal mode. Upon receiving this instruction, the power supply control unit 50 resumes power supply to the power supply stop portion in the power saving mode. When it is recognized that the condition for returning to the normal mode is satisfied based on the output of each operation detection unit, the power supply control unit 50 resumes power supply to the supply stop portion without waiting for an instruction from the control unit 5. You may do it.

(Detecting device 1)
Next, the detection apparatus 1 according to the embodiment will be described with reference to FIGS. The detection device 1 according to the embodiment is included in the multifunction peripheral 100. FIG. 5 is a diagram illustrating an example of the detection device 1. FIG. 6 is a diagram illustrating an example of generation of the second power supply V2 based on the first power supply V1. FIG. 7 is a diagram illustrating an example of the A / D conversion circuit 9 included in the control circuit (CPU 6).

  As illustrated in FIG. 5, the detection device 1 according to the embodiment includes a first power supply V1, a second power supply V2, a CPU 6 (control circuit), a sensor unit 7, and a supply source switching unit 8.

  The first power supply V <b> 1 is generated by the secondary power supply unit 58 in the power supply device 54. The output of one or a plurality of secondary power supply units 58 is used as the first power supply V1. The magnitude of the voltage of the first power supply V1 in the present embodiment is, for example, about 3.3V (may be other than 3.3V). The magnitude of the voltage of the first power supply V1 is constant in both the normal mode and the power saving mode, and power is supplied in both the normal mode and the power saving mode. In other words, the power conversion circuit 59 corresponding to the first power supply V1 operates in both the normal mode and the power saving mode, and outputs a voltage.

  The second power supply V2 is generated from the first power supply V1. This point will be described with reference to FIG.

  As shown in FIG. 6, the second transistor Tr2 is connected to the first power supply V1. The second transistor Tr2 is a power supply generation switch unit 80 that generates the second power supply V2. Specifically, the second transistor Tr2 is a pnp type transistor. The first power supply V1 is connected to the emitter of the second transistor Tr2. The second power supply V2 is output from the collector of the second transistor Tr2. In other words, the collector of the second transistor Tr2 outputs a voltage as the second power supply V2.

  The sleep signal sg1 is input to the pace of the second transistor Tr2. The sleep signal sg1 is input by either the power control unit 50 or the control unit 5 (both may be performed). The sleep signal sg1 is in a low state when in the normal mode, and is in a high state when in the power saving mode. Thereby, the second transistor Tr2 is turned on in the normal mode and turned off in the power saving mode. The second transistor Tr2 (power generation switch unit 80) is connected to the first power supply V1 and receives power supply. The second transistor Tr2 is turned on in the normal mode and outputs a voltage as the second power supply V2 (power is supplied). On the other hand, the second transistor Tr2 is turned off in the power saving mode, and stops the voltage output as the second power supply V2 (stops the power supply). As described above, the second power supply V2 includes the power generation switch unit 80 that supplies power based on the first power supply V1 in the normal mode and stops power supply in the power saving mode.

  When an npn transistor is used as the second transistor Tr2, the power supply control unit 50 or the control unit 5 inputs a sleep signal sg1 that is in a high state in the normal mode and in a low state in the power saving mode ( The connection between the collector and the emitter is reversed from that of pnp). As a result, even if an npn transistor is used as the second transistor Tr2, the second transistor Tr2 can be turned on in the normal mode, and the second transistor Tr2 can be turned off in the power saving mode.

  As shown in FIG. 5, the sensor unit 7, the load 70, the CPU 6 (control circuit), and the like are connected in parallel to the second power source V2 (the collector of the power generation switch unit 80).

  The sensor unit 7 is supplied with electric power from the second power supply V2. And an analog voltage is output as a detection result as a detection result. As shown in FIG. 5, in the multi-function device 100 of this embodiment, one of the sensor units 7 is a temperature sensor 71 including a series circuit of a thermistor 72 and a resistor 73. In other words, the sensor unit 7 includes at least one temperature sensor 71.

  The temperature sensor 71 is a series circuit of a thermistor 72 and a resistor 73. The temperature sensor 71 uses the change in the resistance value of the thermistor 72 corresponding to the temperature to output an analog voltage corresponding to the temperature of the detection target. In the series circuit, one end on the thermistor 72 side is connected to the second power supply V2. The other end on the resistor 73 side is connected to the ground. Then, the voltage between the thermistor 72 and the resistor 73 is input to the CPU 6 as the analog output voltage Vout of the temperature sensor 71.

  The temperature sensor 71 is not limited to one, and a plurality of temperature sensors 71 may be provided. A temperature sensor 71 for detecting the outside air temperature is provided in the vicinity of the intake and exhaust (not shown) of the multifunction device 100. A temperature sensor 71 for detecting the temperature of the rotating body of the fixing unit 4d is provided in the fixing unit 4d (see FIG. 1). Further, a temperature sensor 71 for detecting the temperature of the photosensitive drum 41 is provided in the image forming unit 4c (see FIG. 1). Also, a temperature sensor 71 for detecting the temperature of the developing device 42 may be provided in the image forming unit 4c.

  Furthermore, the sensor unit 7 may be any sensor that outputs an analog voltage as a detection result, and is not limited to the temperature sensor 71. For example, a distance measuring sensor in which the magnitude of the analog output voltage Vout differs from the distance to the detection target, or a sensor for detecting the approach or presence of a person by receiving infrared rays emitted by a person, and the amount of incident infrared rays In some cases, a pyroelectric sensor that outputs an analog voltage of a magnitude corresponding to the sensor unit 7 is connected in parallel to the second power supply V2.

  Various circuits (memory, microcomputer, chip, substrate, etc.) using the voltage generated by the second power supply V2 as a drive voltage are connected in parallel to the second power supply V2 as a load 70. For example, when the second power supply V2 outputs about 3.3V DC, a circuit having 3.3V as the driving voltage is connected as the load 70. Moreover, the load 70 connected in parallel with the sensor unit 7 and the CPU 6 is not limited to one for the second power supply V2, and a plurality of loads 70 can be connected in parallel to the second power supply V2. For convenience, only one load 70 is shown in FIG.

  The sensor unit 7 and the load 70 connected in parallel with the CPU 6 with respect to the second power supply V2 are portions that stop power supply in the power saving mode.

  The analog voltage output from the sensor unit 7 is input to the CPU 6. The CPU 6 has a plurality of analog input ports 61. The CPU 6 converts the analog voltage input from the sensor unit 7 into a digital value using a voltage (voltage input to the power supply port 62 of the CPU 6) based on the power supplied from the second power supply V2 as a reference voltage. / D conversion circuit 9 is included.

  Here, the A / D conversion circuit 9 (analog-digital conversion circuit) built in the CPU 6 will be described with reference to FIG.

  As shown in FIG. 7, the A / D conversion circuit 9 includes an input switching circuit 91, a sample hold circuit 92, a comparator 93, an A / D conversion control circuit 94, an A / D conversion result register 95, and a D / A conversion circuit. 96 (digital-to-analog converter). As illustrated in FIG. 7, the CPU 6 according to the embodiment includes a successive approximation type A / D conversion circuit 9. However, the CPU 6 may include another type of A / D conversion circuit 9. Further, the A / D conversion circuit 9 may be externally attached to the outside of the CPU 6.

  Each analog input port 61 of the CPU 6 is connected to the input switching circuit 91. The input switching circuit 91 is, for example, a multiplexer. Based on an instruction from the CPU 6, the input switching circuit 91 selects a port corresponding to the sensor unit 7 that performs detection from among a plurality of inputs. The input switching circuit 91 connects one of the analog voltages input to the port to the sample and hold circuit 92. As a result, the output of the sensor unit 7 used in the detection to be performed is input to the sample hold circuit 92. For example, when detecting the outside temperature, the multiplexer connects the sample hold circuit 92 to the analog input port 61 to which the output of the temperature sensor 71 for detecting the outside temperature is inputted.

  The sample hold circuit 92 includes an element such as a capacitor, and holds the voltage value of the input analog signal during A / D conversion. Then, the sample hold circuit 92 inputs the held voltage to the comparator 93.

  The D / A conversion circuit 96 is supplied from the second power supply V2 and is a voltage at a stage (magnitude) based on an instruction from the A / D conversion control circuit 94 with reference to the magnitude of the voltage input to the power supply port 62. Is output. In the A / D conversion circuit 9 of the present embodiment, first, the A / D conversion control circuit 94 temporarily sets the most significant bit to “1”. The D / A conversion circuit 96 outputs a voltage value corresponding to the set value (the most significant bit is “1” and the other bits are “0”). The comparator 93 compares the voltage value held by the sample hold circuit 92 (the output voltage of the sensor unit 7) with the voltage value output by the D / A conversion circuit 96. When the output voltage of the sensor unit 7 is larger, the A / D conversion control circuit 94 sets “1” as the value of the most significant bit. On the other hand, when the output voltage of the sensor unit 7 is smaller, the A / D conversion control circuit 94 sets “0” as the value of the most significant bit. The current set value is stored in the A / D conversion result register 95.

  Then, when the setting of the current bit based on the comparison is completed, the A / D conversion control circuit 94 temporarily sets the bit one bit lower than the completed setting to “1”. Then, the D / A conversion circuit 96 outputs a voltage value corresponding to the current set value, including the bit currently being set. The comparator 93 compares the voltage value held by the sample hold circuit 92 (the output voltage of the sensor unit 7) with the current voltage value output by the D / A conversion circuit 96. When the output voltage of the sensor unit 7 is larger, the A / D conversion control circuit 94 sets “1” as the value of the current bit. On the other hand, when the output voltage of the sensor unit 7 is smaller, the A / D conversion control circuit 94 is set to “0” as the current bit value. This comparison operation is repeated up to the least significant bit. The value of each bit is accumulated in the A / D conversion result register 95. The A / D conversion circuit 9 of the CPU 6 converts the input analog voltage into a digital value of 8 bits or more.

  Here, the D / A conversion circuit 96 includes, for example, a ladder-shaped resistor network, a switch for selecting a resistor to be conducted, and the like. The D / A conversion circuit 96 uses the voltage supplied from the second power supply V2 and input to the power supply port 62 of the CPU 6 as a positive reference voltage. Further, the D / A conversion circuit 96 uses the ground (substantially 0 V) as a negative reference voltage (a voltage other than the ground may be used as a negative reference voltage). Then, by switching the magnitude of the resistor connected to the reference voltage, the D / A conversion circuit 96 outputs an analog voltage corresponding to the instructed digital value. Therefore, the digital value obtained by the A / D conversion circuit 9 is that the output of the sensor unit 7 (the output voltage of the temperature sensor 71) is the potential difference (the magnitude of the reference voltage) between the reference voltage and the negative reference voltage (ground). This is a value indicating the number of stages among the stages divided by the power of 2 bits. Therefore, A / D conversion is affected by the magnitude and accuracy of the voltage (reference voltage) of the second power supply V2.

  Specifically, when A / D conversion of an analog voltage of a certain magnitude is performed, the larger the voltage of the second power supply V2 (the voltage input to the power supply port of the CPU 6) is, the smaller the potential difference per minimum unit (one step) is. Since it increases, the resulting digital value tends to decrease. Conversely, the smaller the voltage of the second power supply V2 (the voltage input to the power supply port of the CPU 6) is, the larger the obtained digital value tends to be.

  Then, the CPU 6 recognizes the temperature based on the obtained digital value. For example, the storage unit 53 stores a table 53a in which temperatures for digital values are defined. Then, the CPU 6 compares the digital value obtained by the A / D conversion circuit 9 with the table 53a to recognize the temperature to be detected. For example, when detecting the outside air temperature (environment temperature around the MFP 100), the CPU 6 compares the digital value of the analog output of the temperature sensor 71 for detecting the outside air temperature with the table 53a of the storage unit 53 to obtain the current value. Recognize outside temperature. Similarly, the output voltage from the sensor unit 7 that is not the temperature sensor 71 can also be A / D converted by the A / D conversion circuit 9. Then, the CPU 6 determines and recognizes the detection target state based on the obtained digital value.

  Then, as shown in FIG. 5, a supply source switching unit 8 is provided for the CPU 6. Specifically, the supply source switching unit 8 supplies power from the second power supply V2 to the CPU 6 (control circuit) in the normal mode, and supplies power from the first power supply V1 to the control circuit in the power saving mode. Switching is performed as follows.

  In terms of circuit, the supply source switching unit 8 is a transistor (first transistor Tr1). As shown in FIG. 5, the supply source switching unit 8 (first transistor Tr1) is a pnp type transistor. The base of the first transistor Tr1 is connected to the second power supply V2. In other words, the second power supply V2 is input to the base of the first transistor Tr1. The emitter of the first transistor Tr1 is connected to the first power supply V1. The collector of the first transistor Tr1 is connected in the middle of the power supply line of the second power source V2 and the CPU 6 (control circuit). The second power source V2 is connected to the downstream side (the power port 62 side of the CPU 6) from the branch point 81 for connecting the CPU 6, the sensor unit 7, and the load 70.

(Power supply to the detection device 1 in the normal mode)
Next, power supply to the detection apparatus 1 in the normal mode will be described with reference to FIGS. FIG. 8 is a diagram illustrating an example of a power supply state to the detection device 1 in the normal mode. In addition, in FIG. 8, illustration of sensor parts 7 other than the temperature sensor 71 is omitted for the sake of convenience among those connected in parallel to the second power supply V2.

  As shown in FIG. 6, in the normal mode, the power generation switch unit 80 (second transistor Tr2) is in the ON state. Based on the power from the first power supply V1, the second transistor Tr2 supplies power, and the second power supply V2 supplies power to the connected CPU 6 (control circuit), temperature sensor 71 (sensor unit 7), and load 70. Supply. As indicated by a two-dot chain line arrow in FIG. 8, a current flows (a voltage is applied) to the CPU 6, the temperature sensor 71, and the load 70.

  On the other hand, the output of the second power supply V2 is input to the base of the first transistor Tr1 (supply source switching unit 8). In other words, the base potential of the first transistor Tr1 does not become smaller than the emitter potential (output voltage of the first power supply V1) as the first transistor Tr1 is turned on. Therefore, in the normal mode, the first transistor Tr1 is in an OFF state. As a result, as shown in FIG. 8, the power from the first power supply V1 (the voltage output from the first power supply V1) is not input to the power supply port 62 of the CPU 6.

  Further, the output (power supply line) of the second power supply V2 is branched to the detection device 1 of the present embodiment because of the parallel connection. A diode is provided between the branch point 81 and the power supply port 62 of the CPU 6. In the following description, the diode provided for the CPU 6 is referred to as “first diode D1”.

  Also, at least one diode is provided between the branch point 81 and the temperature sensor 71 (sensor unit 7). The diode provided between the branch point 81 and the sensor unit 7 is referred to as “second diode D2”.

  The first diode D1 and the second diode D2 have the same specifications. For example, the magnitude of the voltage dropping in the forward direction is the same. For example, the first diode D1 and the second diode D2 have similar temperature characteristics.

  Therefore, during the normal mode, regardless of the temperature, the magnitude of the voltage (reference voltage of the A / D conversion circuit 9) supplied from the second power supply V2 and input to the power supply port 62 of the CPU 6 and the temperature sensor 71 (sensor The voltages applied to part 7) are the same or substantially the same. Thus, since the reference voltage of the A / D conversion circuit 9 of the CPU 6 and the voltage applied to the temperature sensor 71 match or substantially match, the CPU 6 obtains a digital value obtained by the A / D conversion circuit 9 or a digital value. The temperature recognized based on the value is accurate and highly accurate.

  Further, the magnitude of the current supplied from the second power supply V2 may vary depending on the operating state (power consumed) of the connected load 70. As described above, the load 70 connected to the second power supply V2 is a circuit or element such as a memory or a microcomputer. The processing states of these circuits and elements change depending on the state of the multi-function device 100 such as whether a job is being executed or is waiting. Therefore, the magnitude of the current supplied from the second power supply V <b> 2 (the total value of the currents flowing through the sensor unit 7 and the load 70) varies depending on the state of the multifunction device 100.

  The magnitude of the voltage drop in the second transistor Tr2 changes according to the magnitude of the current flowing through the second transistor Tr2. However, in the normal mode, the CPU 6 and the temperature sensor 71 (sensor unit 7) are connected in parallel to the second power supply V2. Therefore, even if the current flowing through the second transistor Tr2 (load current) fluctuates and the magnitude of the voltage dropped at the second transistor Tr2 changes, the voltage is supplied from the second power supply V2 and input to the power supply port 62 of the CPU 6. The voltage (reference voltage of the A / D conversion circuit 9) to be applied and the voltage applied to the temperature sensor 71 (sensor unit 7) are the same or substantially the same.

  Furthermore, in a state where the voltage drop in the power generation switch unit 80 (second transistor Tr2) is large, the voltage applied to the temperature sensor 71 (sensor unit 7) is small. Therefore, even when the temperature to be detected by the temperature sensor 71 is the same, the voltage output from the temperature sensor 71 is smaller when the voltage drop of the second transistor Tr2 is larger than when the voltage drop of the second transistor Tr2 is small. .

  On the other hand, in a state where the voltage drop at the power generation switch unit 80 (second transistor Tr2) is large, the reference voltage of the A / D conversion circuit 9 of the CPU 6 is also small. Therefore, even if the analog voltage input from the sensor unit 7 (temperature sensor 71) to the A / D conversion circuit 9 is the same, the voltage of the second transistor Tr2 is smaller than when the voltage drop at the second transistor Tr2 is small. When the drop is large, the resulting digital value tends to increase.

  As described above, even if the voltage dropped in the second transistor Tr2 varies, the temperature sensor 71 and the A / D conversion circuit 9 cancel out changes in the output characteristics. Therefore, the temperature recognized by the CPU 6 based on the digital obtained by the A / D conversion circuit 9 is accurate and highly accurate.

(Power supply to the detection device 1 in the power saving mode)
Next, power supply to the detection device 1 in the power saving mode will be described with reference to FIGS. 6 and 9. FIG. 9 is a diagram illustrating an example of a power supply state to the detection device 1 in the power saving mode.

  As shown in FIG. 6, in the power saving mode, the power generation switch unit 80 (second transistor Tr2) is in an OFF state. Therefore, in the power saving mode, as shown in FIG. 9, the power supply from the second power source V2 to the CPU 6 (control circuit), the temperature sensor 71 (sensor unit 7), and the load 70 is stopped.

  The output of the second power supply V2 is input to the base of the first transistor Tr1 (supply source switching unit 8). Then, the output potential of the second power supply V2 (the collector potential of the second transistor Tr2) is zero (ground level). Therefore, the base potential of the first transistor Tr1 with respect to the potential of the emitter of the first transistor Tr1 (pnp transistor) (the output voltage of the first power supply V1) decreases as the first transistor Tr1 is turned on. Therefore, in the power saving mode, the first transistor Tr1 is turned on. As a result, as indicated by a two-dot chain line arrow in FIG. 9, the power from the first power supply V1 (the voltage output from the first power supply V1) is input to the power supply port 62 (reference voltage input port) of the CPU 6. .

  Specifically, when shifting from the normal mode to the power saving mode, the output of the second power supply V2 is stopped (the second power supply V2 is turned off). As the second power supply V2 is turned off, power supply from the first power supply V1 to the power supply port 62 of the CPU 6 is started. Here, when switching the power supply for supplying power to the CPU 6 (switching the supply source of the second power supply V2 and the first power supply V1), a voltage (minimum drive voltage) guaranteed as the lowest voltage driven by the CPU 6 is used. While not falling below, the first transistor Tr1 (source switching unit 8) is turned on.

  For example, a case where the minimum drive voltage of the CPU 6 is DC 2.5V will be described. When the power supply from the second power supply V2 is stopped due to the transition from the normal mode to the power saving mode, the voltage of the second power supply V2 gradually decreases. The first transistor Tr1 (supply source switching unit 8) is turned on while the voltage applied to the power supply port 62 of the CPU 6 does not fall below 2.5V while considering the voltage drop due to the first diode D1. When the voltage falls below the minimum drive voltage, the CPU 6 stops. However, in the detection device 1 of the present embodiment, before the CPU 6 stops (the voltage based on the second power supply V2 and the voltage applied to the CPU 6 is the minimum drive voltage). The voltage from the first power supply V1 is applied to the CPU 6 (below below). Therefore, the CPU 6 is not restarted when shifting from the normal mode to the power saving mode.

  In addition, since the portion for supplying power to the CPU 6 is switched at a time equal to or higher than the minimum driving voltage of the CPU 6, even when returning from the power saving mode to the normal mode, the power port 62 of the CPU 6 has the first power supply V1 or the second power supply V2 From either one, a voltage of at least the minimum driving voltage is applied to the CPU 6. Therefore, even when the normal mode is restored from the power saving mode, the CPU 6 is not restarted.

  A first diode D1 is provided between the branch point 81 of the output (power supply line) of the second power supply V2 and the CPU 6. The direction of the first diode D1 in the wiring is opposite to the second power supply V2. Therefore, the first diode D1 functions as an element that prevents current from flowing from the first power supply V1 toward the second power supply V2 (prevents the voltage of the first power supply V1 from being applied to the second power supply V2). In other words, the first diode D1 also functions as a backflow prevention diode.

  As described above, the detection device 1 according to the embodiment has the normal mode and the power saving mode, and shifts to the power saving mode when the predetermined transition condition is satisfied, and the predetermined return condition is satisfied. The first power supply V1 that returns to the normal mode, supplies power in both the normal mode and the power saving mode, and is connected to the first power supply V1, supplies power based on the first power supply V1 in the normal mode, and saves power. In the power mode, the second power source V2 including the power source generation switch unit 80 that stops power supply, the sensor unit 7 that receives power supply from the second power source V2 and outputs an analog voltage as a detection result, and the second power source V2 An A / D conversion circuit 9 that converts an analog voltage output from the sensor unit 7 into a digital value using a voltage based on the supplied power as a reference voltage is provided in parallel with the sensor unit 7 with respect to the second power supply V2. In the normal mode, the connected control circuit supplies power from the second power supply V2 to the control circuit, and in the power saving mode, the supply source performs switching so as to supply power from the first power supply V1 to the control circuit. A switching unit 8 is provided.

  As a result, power can be supplied to the control circuit in both the normal mode and the power saving mode. In the normal mode, a voltage based on the second power supply V2 and having the same magnitude is applied to both the sensor unit 7 and the control circuit by switching of the supply source switching unit 8. Furthermore, even if the output voltage of the second power source V2 varies (the voltage drops at the power generation switch unit 80) or changes in temperature, the second power source V2 is connected to both the sensor unit 7 and the control circuit. The same voltage from is applied. Therefore, the voltage supplied from the second power source V2 to the A / D conversion circuit 9 provided in the control circuit and used as the reference voltage in the A / D conversion and the voltage applied to the sensor unit 7 should have the same magnitude. it can. For example, the voltage range handled by the A / D conversion circuit 9 that performs quantization for the range of the power supply voltage (reference voltage) of the second power supply V2 from the ground (0V) and the voltage range that can be used as an analog output of the sensor. Can be almost matched. Therefore, the accuracy and accuracy of the obtained digital value and the detection result based on the digital value can be improved.

  When the voltage drop at the power generation switch unit 80 is large, the voltage applied to the sensor unit 7 is small. Therefore, if the detection target state is the same, the analog output voltage Vout from the sensor unit 7 tends to decrease as the voltage drop increases. On the other hand, the A / D conversion circuit 9 in the control circuit quantizes the ground (0 V) to the reference voltage with a predetermined number of steps. When the voltage drop in the power generation switch unit 80 is large and the voltage (reference voltage) supplied from the second power source V2 to the control circuit is small, the voltage per step (minimum unit) is small. For this reason, when the analog sensor output voltage is the same, the smaller the reference voltage, the larger the digital value obtained. Conversely, when the voltage drop is small, the analog output voltage Vout of the sensor is larger than when the voltage drop is large, but the digital value required by the A / D conversion circuit 9 is smaller than when the voltage drop is large. Is done. As described above, in the present detection device 1, when the magnitude of the drop voltage in the power generation switch unit 80 fluctuates, one output change acts so as to cancel the other output change, and the obtained digital value is converted. Impact is reduced. Therefore, the obtained digital value and the detection result based on the digital value are not easily affected by the change in the magnitude of the voltage drop in the power generation switch section 80, and the accuracy of the obtained digital value and the detection result based on the digital value is not affected. , Accuracy can be improved.

  In addition, the detection device 1 according to the embodiment is provided in a power supply line from the second power supply V2, and includes a branch point 81 for parallel connection, and a first diode D1 provided between the branch point 81 and the control circuit. And a second diode D2 having the same specifications as the first diode D1 and provided between the branch point 81 and the sensor unit 7.

  In the power saving mode, the first power supply V1 supplies power to the control circuit, and the second power supply V2 stops supplying power. Thereby, the first diode D1 provided between the second power supply V2 and the control circuit can prevent the current from flowing from the first power supply V1 to the second power supply V2 in the power saving mode. Also, by providing a second diode D2 equivalent to the first diode D1 between the second power supply V2 and the sensor unit 7, in the normal mode, between the branch point 81 and the control circuit, and between the branch point 81 and the sensor unit. An equivalent voltage drop can be generated between 7. Therefore, the voltage applied to the control circuit and the sensor unit 7 can be made equal.

  The supply source switching unit 8 is a pnp-type first transistor Tr1. The base of the first transistor Tr1 is connected to the second power source V2, the emitter of the first transistor Tr1 is connected to the first power source V1, and the collector of the first transistor Tr1 receives power from the second power source V2. It is connected to a power supply line that inputs to the control circuit. As a result, the shift to the power saving mode causes the base potential of the first transistor Tr1 to drop as the power supply of the second power supply V2 stops, and the first transistor Tr1 is automatically turned on. The power from the first power supply V1 is supplied to the control circuit. Therefore, it is not necessary to control ON / OFF of the first transistor Tr1 from a control circuit or the like.

  In addition, the power generation switch unit 80 is connected to the first power supply V1, is turned on in the normal mode, outputs a voltage as the second power supply V2, is turned off in the power saving mode, and outputs a voltage output as the second power supply V2. The second transistor Tr2 to be stopped is included. Accordingly, it is possible to stop the power supply to the plurality of loads 70 in the power saving mode easily and inexpensively while applying the same voltage to the sensor unit 7 and the control circuit.

  The sensor unit 7 includes at least one temperature sensor 71 including the thermistor 72. Thereby, temperature can be detected accurately.

  In addition, the image forming apparatus (multifunction peripheral 100) includes the above-described detection device 1. Accordingly, it is possible to provide an image forming apparatus (multifunction peripheral 100) that is simple and inexpensive, and has high accuracy of a digital value obtained based on a sensor and high accuracy of a detection result based on the digital value.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention has a power saving mode and a normal mode, and includes a power source, a sensor that outputs an analog voltage as a detection result, and a control circuit including an A / D conversion circuit 9 that digitizes the analog output voltage Vout of the sensor. It can be used for the detection device 1 and the image forming apparatus.

DESCRIPTION OF SYMBOLS 100 MFP (image forming apparatus) 1 Detection apparatus 6 CPU (control circuit) 7 Sensor part 71 Temperature sensor 72 Thermistor 8 Supply source switching part 80 Power generation switch part 81 Branch point 9 A / D conversion circuit D1 1st diode D2 Second diode Tr1 First transistor Tr2 Second transistor V1 First power source V2 Second power source

Claims (6)

It has a normal mode and a power saving mode, transitions to the power saving mode when a predetermined transition condition is satisfied, returns to the normal mode when a predetermined return condition is satisfied,
A first power supply for supplying power in both the normal mode and the power saving mode;
A second power source including a power generation switch unit connected to the first power source, supplying power based on the first power source in the normal mode, and stopping power supply in the power saving mode;
A sensor unit that receives power supply from the second power source and outputs an analog voltage as a detection result;
An A / D conversion circuit that converts an analog voltage output from the sensor unit into a digital value using a voltage based on the power supplied from the second power source as a reference voltage; and parallel to the sensor unit with respect to the second power source A control circuit connected to the
In the normal mode, a power source switching unit that performs switching so that power from the second power source is supplied to the control circuit, and in the power saving mode, power from the first power source is supplied to the control circuit. A detection device comprising: A branch point for parallel connection, provided in a power supply line from the second power source;
A first diode provided between the branch point and the control circuit;
2. The detection device according to claim 1, comprising a diode having the same specifications as the first diode, and a second diode provided between the branch point and the sensor unit. The supply source switching unit is a pnp-type first transistor,
A base of the first transistor is connected to the second power source;
An emitter of the first transistor is connected to the first power source;
3. The detection device according to claim 1, wherein the collector of the first transistor is connected to a power supply line that inputs power from the second power supply to the control circuit.   The power supply generation switch unit is connected to the first power supply, is turned on in the normal mode, outputs a voltage as the second power supply, is turned off in the power saving mode, and outputs a voltage output as the second power supply. 4. The detection device according to claim 1, further comprising a second transistor that stops. 5.   5. The detection device according to claim 1, wherein the sensor unit includes at least one temperature sensor including a thermistor.   An image forming apparatus comprising the detection device according to claim 1.

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