Patent Publication Number: US-2021194251-A1

Title: Power source apparatus and a system

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a power source apparatus having a plurality of power sources. 
     Description of the Related Art 
     An electric device is connected to, for supplying power to its load, a power source apparatus or is provided with a built-in type power source. There is known a power source apparatus having a plurality of DC power sources, for example, an AC/DC power source which converts an AC voltage into a DC voltage. The AC/DC power source rectifies an AC voltage from a commercial power source through a diode bridge, and further performs smoothing through a smoothing capacitor. After that, the smoothed voltage is charged to a capacitor provided on a secondary side through a transformer to generate a DC voltage. The secondary side is equipped with a circuit which detects an output voltage of the AC/DC power source. The circuit controls a current flowing through the transformer by driving a switching element connected to a primary side of the transformer so that the output voltage becomes a predetermined value. 
     Further, in some electric devices, a DC/DC power source, which converts a DC voltage generated by an AC/DC power source into a DC voltage having another voltage value, is provided. Hereinafter, the AC/DC power source and the like will be simply referred to as a power source. 
     Generally, a power (i.e., rated power) which is allowed to be output by a power source is determined when it is designed. Therefore, a single power source may be insufficient to supply the power required for electric equipment to operate. In this case, the electric equipment is provided with a plurality of power sources. 
     In electric equipment provided with a plurality of power sources, in a case where outputs of the power sources are connected in parallel, the output current of the power source which has the largest output voltage may become the largest due to variations in the output voltages of the power sources. As a result, even though a plurality of power sources are provided, an output power of one power source becomes large, and the output power may exceed the rated power. 
     In order to prevent such a situation, there is known a configuration in which a load of the electric equipment is individually divided according to the rated power of the power source so that only one power source is connected to each load. However, the power source may fail due to an external electrical surge or a component failure. In a configuration in which a single power source is connected to a respective single load, when a particular power source fails, the load connected to the power source becomes inoperable. As a result, in the electric equipment having a plurality of power sources, as the number of power sources increases, the electric equipment connected to the power source tends to operate abnormally. 
     Japanese Patent No. 5088049 discloses electric equipment which is provided with, as a power source, a plurality of AC/DC power source and a single sub power source. In this electric equipment, an output voltage of each of the AC/DC power source is detected. In a case where the output voltage of the AC/DC power source drops due to a failure or the like, the sub power source is operated, and the sub power source and a load are connected with a switch. With this configuration, even if the AC/DC power source fails, instead of the failed AC/DC power source, the sub power source can supply power to the load. 
     However, in the configuration disclosed in Japanese Patent No. 5088049, since the sub power source and the load are connected with a switch, such as a semiconductor switch, the size and the cost of the substrate is increased due to the increased number of parts. Further, in the method disclosed in Japanese Patent No. 5088049, an operation of the sub power source is started in response to a detection of a decrease in the output voltage of the AC/DC power source. Therefore, the operation of the load may be stopped due to the occurrence of a period during which power is not supplied to the load. 
     SUMMARY OF THE INVENTION 
     A power source apparatus according to the present disclosure includes a plurality of first power sources, each connected to a load through a power supply line, and at least one second power source, which is a sub power source to be used in a case where the first power source is unable to output a predetermined voltage, wherein: the second power source is connected in parallel to the power supply line of at least one of the first power source through a diode, the second power source is provided on an anode side of the diode; the load is configured to operate at a voltage equal to or more than a first voltage; and the first power source outputs a second voltage higher than the first voltage; the second power source outputs a third voltage, which is higher than the first voltage, the voltage output through the diode from the second power source being lower than the second voltage, thereby, when the voltage output from the first power source becomes lower than the voltage output through the diode from the second power source, the diode conducts and power is supplied from the second power source to the load. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a power source apparatus and electric equipment according to at least one embodiment of the present disclosure. 
         FIG. 2  is a schematic circuit diagram illustrating an exemplary AC/DC power source. 
         FIG. 3A ,  FIG. 3B , and  FIG. 3C  are graphs each representing voltage change in an output voltage with respect to time. 
         FIG. 4  is a schematic diagram of a power source apparatus and electric equipment according to a second embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure is explained in detail with reference to drawings. 
     First Embodiment 
       FIG. 1  is a schematic diagram of an exemplary system configuration having a power source apparatus  1000  and electric equipment  2000  according to the present disclosure. The power source apparatus  1000  shown in  FIG. 1  includes at least one of main power sources  200  ( 200 - 1  to  200 -N) and one sub power source  300 . The sub power source  300  is a power source used in a case where the main power source  200  cannot output a predetermined voltage. Further, the power source apparatus  1000  and the electric equipment  2000  form an image forming apparatus which forms an image on a sheet, for example. 
     The electric equipment  2000  includes two or more loads  500  ( 500 - 1  to  500 -N), which are respectively separate load, and includes a controller  700  which controls these loads  500 . The load  500  includes at least one of a motor in the image forming apparatus and a high voltage generating circuit. Each of the main power source  200  and the sub power source  300  is an AC/DC power source which converts AC voltage to DC voltage, and functions as a direct-current power source which outputs direct-current voltage. Moreover, a voltage detector  701  and a display  702  are provided in the electric equipment  2000 . The configuration of the power source apparatus  1000  and the electric equipment  2000  may be defined arbitrarily. For example, the power source apparatus  1000  and the electric equipment  2000  may be separately provided. Alternatively, the power source apparatus  1000  may be built in the electric equipment  2000 . 
     The main power sources  200 - 1 ,  200 - 2 , . . .  200 -N are connected to corresponding load  500 - 1 ,  500 - 2 , . . .  500 -N through the electric power supply line, respectively. Thus, the outputs of the main power source  200 - 1  to  200 -N are not connected to each other. Although each of the rated power of the main power source  200 - 1  to  200 -N does not need to be the same, a target output voltage of each output voltage Vout 1  is set to an identical voltage value. 
     The sub power source  300  is connected, through a diode  301 - 1 , in parallel to a power supply line which connects the main power source  200 - 1  and the load  500 - 1 . The sub power source  300  is provided on an anode side of the diode  301 . The same applies to the other main power sources  200 - 2 , . . .  200 -N, load  500 - 2 , . . .  500 -N, diode  301 - 2 , . . .  301 -N. 
     The voltage detector  701  detects a voltage value of each of loads  500 - 1 ,  500 - 2 , . . .  500 -N. The controller  700  monitors voltage values detected by the voltage detector  701  and determines whether or not a failure has occurred. In a case where it is determined that a failure has occurred due to, for example, the detection of an abnormal voltage value in at least one of the loads  500 - 1 ,  500 - 2 , . . .  500 -N, which indicates an occurrence of failure, or due to any other reason, information indicating the occurrence of the failure and information identifying the load in which the failure has occurred is displayed in the display  702 . In  FIG. 1 , the voltage detector  701  is provided in the electric equipment  2000  separately from the load  500 , however, the voltage detector may be individually provided to each of the loads  500 - 1 ,  500 - 2 , . . .  500 -N. 
     A controller  400 , a voltage detector  401 , and a display  402  are provided in the power source apparatus  1000 . The voltage detector  401  detects a voltage value output from each of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N. The controller  400  monitors the voltage value detected by the voltage detector  401  and determines whether a failure has occurred in the main power source  200  or not from the detection result. In a case where it is determined that a failure has occurred in at least one of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N by detecting an output unusual voltage value, the occurrence of the failure and the information specifying the main power source  200  in which the failure has occurred are displayed on the display  402 . In  FIG. 1 , the voltage detector  401  is provided in the power source apparatus  1000  separately from the main power source  200 . However, the voltage detector may be individually provided corresponding to each of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N. 
     Next, configuration and operation of the AC/DC power source  100  are explained with reference to  FIG. 2 . The AC/DC power source  100  corresponds to the main power source  200  and the sub power source  300  of  FIG. 1 . The AC current input into the AC/DC power source  100  is rectified by the diode bridge  101 , which is an example of a rectifier, and the rectified output is input to a smoothing capacitor  102  to charge the same. Thereby, DC voltage appears across both ends of the smoothing capacitor  102 . The DC voltage is supplied as a power source voltage of a converter control circuit  104  through a starting resistor  103 . The converter control circuit  104  starts outputting the switching signal of a switching element  106  which is connected in series to the transformer  105 . Alternative current flows in a primary winding  105   a  of a transformer  105 , which is arranged at the subsequent side of smoothing capacitor  102  due to this switching. The converter control circuit  104  is grounded through a resistor  115 . 
     Due to the alternative current, voltage occurs at a secondary winding  105   b  according to the winding ratio of the transformer  105 . A secondary side rectification diode  107  and a secondary side smoothing capacitor  108  are arranged at a secondary side of the AC/DC power source  100 . The voltage generated in the secondary winding  105   b  of the transformer is rectified by the secondary side rectification diode  107  and is smoothed by the secondary side smoothing capacitor  108 . As a result, DC voltage is obtained from both ends of the secondary side smoothing capacitor  108 . The voltage obtained from both ends of the secondary side smoothing capacitor  108  is the output voltage Vout of the AC/DC power source  100 . In order to stabilize the output voltage Vout to a predetermined target voltage, the voltage divided by voltage detection resistors  109  and  110  is fed back to the converter control circuit  104  through a shunt regulator  111  and a photocoupler  112 . 
     The output voltage Vout is divided by the voltage detection resistors  109  and  110 , and is input to the shunt regulator  111 . The shunt regulator  111  compares the divided voltage input with a reference voltage inside the shunt regulator  111  and increases the current flowing through a light emitting diode  112   a  in a case where the input voltage is higher than the reference voltage. The shunt regulator  111  reduces the current flowing through the light emitting diode  112   a  in a case where the input voltage is lower than the reference voltage. When current flows, the light emitting diode  112   a  emits light with an amount of light corresponding to an amount of current, and a phototransistor  112   b  is turned on in an electrically insulated state (the light emitting diode  112   a  and the phototransistor  112   b  are provided in the same package to constitute the photocoupler  112 ). 
     As a result, the output voltage Vout of the AC/DC power source  100  is fed back to the converter control circuit  104  through the photocoupler  112 . The converter control circuit  104  controls the duty ratio of the switching element  106  so that the output voltage Vout of the AC/DC power source  100  becomes a constant value. 
     For example, in a case where the output voltage Vout of the AC/DC power source  100  drops, it is necessary to supply more power to the secondary side of the transformer  105 , therefore, an amount of time in which the switching element  106  is “ON” is increased, and the current flowing in the primary winding  105   a  of the transformer is increased accordingly. Further, an auxiliary winding  105   c  is wound around the same core as the primary winding  105   a  and the secondary winding  105   b  of the transformer, and when the switching of the switching element  106  is started, the voltage also appears in the auxiliary winding  105   c . Since this voltage causes current to flow through the diode  113  to charge a capacitor  114 , DC voltage is obtained across both ends of the capacitor  114 . 
     The voltage of the capacitor  114  serves as a power source for the converter control circuit  104 . The converter control circuit  104  controls an operation in the converter control circuit  104  so that the power supplied to the converter control circuit  104 , which has been continuously supplied from the smoothing capacitor  102  through the starting resistor  103 , is cut off inside the converter control circuit  104 . 
     Both the main power source  200  and the sub power source  300  in  FIG. 1  correspond to the AC/DC power source  100 , however, their output voltages differ from each other. Hereinafter, a steady-state output voltage value of the main power source  200  will be referred to as V 1 , and a steady-state output voltage value of the sub power source  300  will be referred to as V 2 . The value of V 2  is determined such that the voltage output from the sub power source  300  through the diode  301  (hereinafter, referred to as V 3 ) is lower than the output voltage value V 1  of the main power source  200 . Therefore, V 1  and V 2  have different values. Further, in the steady state, the output voltage value of the sub power source  300  is V 2 , however, the voltage value output through the diode  301  becomes a value smaller than the voltage value V 2  due to the voltage drop in the diode  301 . Therefore, the relationship of V 1 &gt;V 3  and V 2 &gt;V 3  is established. Thus, in the first embodiment, the sub power source  300  and the main power source  200  have basically the same configuration, however, the values of the voltage detection resistors  109  and  110  of the sub power source  300  and the values of the voltage detection resistors  109  and  110  of the main power source  200  are different from each other. 
     The operation of the power source apparatus  1000  of the first embodiment will be described with reference to  FIG. 3A ,  FIG. 3B  and  FIG. 3C . In these figures, the horizontal axis represents time t and the vertical axis represents voltage.  FIG. 3A  represents the change in the output voltage Vout 1  of the main power source  200 - 1  over time,  FIG. 3B  represents the change in the output voltage Vout 2  of the sub power source  300  over time and  FIG. 3C  represents the change in the voltage Vload supplied to the load  500 - 1  over time. 
     Then, the operation of the power source apparatus  1000  in a normal state in which the main power source  200  has not failed will be described. When a voltage of the commercial power source is input to the power source apparatus  1000  at time t 0 , the main power source  200  and the sub power source  300  begins to operate. In the first embodiment, there is a time lag between a startup time of the main power source  200  and that of the sub power source  300 . The main power source  200  is activated at time t 0 , while the sub power source  300  is activated at time t 1  after time t 0 . In the first embodiment, the activation of the main power source  200  and that of the sub power source  300  is controlled by the controller  400 . 
     Here, the sub power source  300  is activated earlier than the main power source  200  and the output voltage Vout 2  of the sub power source  300  exceeds the output voltage Vout 1  of the main power source  200 , the diode  301  shown in  FIG. 1  is changed to a conductive state. As a result, power is supplied from the sub power source  300  to all the loads  500  and a large amount of current flows from the sub power source  300 , thus, an overcurrent protection function of the sub power source  300  may operate to stop the operations of the power source apparatus  1000  and the electric equipment  2000 . 
     In order to prevent this, the output voltage Vout 2  of the sub power source  300  needs to be lower than the output voltage Vout 1  of the main power source  200  both at the startup time and in the steady state of the power source apparatus  1000 . Therefore, the controller  400  activates the sub power source  300  and then activates the sub power source  300  to provide a time difference between the startup times of them so that the relationship of Vout 1 &gt;Vout 2  is satisfied. 
     Referring to  FIG. 3A ,  FIG. 3B  and  FIG. 3C , in  FIG. 3A , the output voltage of the main power source  200  starts to rise at time t 0 , and when it reaches V 1 , its voltage value is maintained at V 1 . In the normal state, the voltage value of Vout 1  is maintained at V 1 , however, as will be described later, when a failure occurs in the main power source  200  at time t 2 , Vout 1  drops to 0V. 
     On the other hand, in  FIG. 3B  shows that the output voltage Vout 2  of the sub power source  300  starts to rise at time t 1 , and when it reaches V 2  described above, its voltage value is maintained at V 2 . As described above, in the normal state, the output voltage Vout 2  of the sub power source  300  is maintained at V 2 . In an alternative embodiment, the startup times of the main power source  200  and the sub power source  300  are set to be the same, while slew rates, at a voltage rise, of the sources are set to be different from each other so that the relationship of Vout 1 &gt;Vout 2  is satisfied. Therefore, with respect to the main power source  200  and the sub power source  300 , the relationship of Vout 1 &gt;Vout 2  is always satisfied in the transition state from the state where the voltage is zero (before activation) to the state where the voltage reaches V 1  or V 2 , respectively. 
       FIG. 3C  shows the voltage supplied to the load  500 - 1 . In a case where the main power source  200  is in the normal state, the voltage V 1  is supplied to the load from the main power source  200 . On the other hand, the output voltage value of the sub power source  300  is V 2 . However, it is V 3 , which is the voltage value after the voltage drop due to the diode  301 , that is supplied to the load, as described in the above. Since V 1 &gt;V 3  and the sub power source  300  is provided on an anode side of the diode  301 , the diode  301  is not in a conductive state, therefore, the output voltage Vout 2  of the sub power source  300  is cut off, and the output voltage Vout 1  of the main power source  200  is supplied to the load  500 - 1 . 
     After the activation of the main power source  200  and the sub power source  300 , since the main power source  200  has not failed, the power is supplied from the main power source  200  to the load  500 . At this point, the sub power source  300  is also activated, however, as described above, the voltage value V 3 , which is output from the sub power source  300  through the diode  301  after the power is activated, is lower than the voltage value V 1  output from the main power source  200 . Therefore, the diode  301  is not in the conductive state. Thus, the sub power source  300  does not supply any power to the load  500 . As a result, in a case where the main power source  200  is in the normal state, the sub power source  300  does not supply any power to the load  500 , thus the overcurrent protection of the sub power source  300  is prevented from operating. In addition, the sub power source  300  is prevented from continuing to operate with its output in excess of the rated power. 
     Then, an operation in a case where the main power source  200 - 1 , among the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N, has failed is again explained with reference to  FIG. 3A ,  FIG. 3B  and  FIG. 3C . As shown in  FIG. 3A , in a case where the main power source  200 - 1  fails at time t 2  after the power is turned on, the output voltage of the main power source  200 - 1  drops from V 1  to 0. As shown in  FIG. 3C , when the output voltage Vout 1  of the main power source  200 - 1  drops to V 3  at time t 3 , the diode  301 - 1  becomes conductive. As a result, the load  500 - 1  is supplied with power from the sub power source  300  instead of the failed main power source  200 - 1 . 
     As described above, in the first embodiment, a potential difference is provided between the output voltage Vout 1  of the main power source  200  and the output voltage Vout 2  of the sub power source  300 , and both of the main power source  200  and the sub power source  300  are connected by the diode  301 . As a result, in a case where the main power source  200  is in the normal state, the sub power source  300  does not supply power to the load  500 , and in a case where the main power source  200  fails, power is immediately supplied to the load  500  from the sub power source  300 . As to the load  500 - 1 , since there is no period during which power is not supplied to the same, the normal operation of the load  500 - 1  can be continued without stopping the operation of the electric equipment. 
     An exemplary voltage setting range of the sub power source  300  will be described. The sub power source  300  does not supply power to the load  500  in a case where the main power source  200  is in the normal state, while it needs to supply power to the load  500  in a case where the main power source  200  fails. Hereinafter, an exemplary configuration in which the output voltage of the main power source  200  is 24.5V±5% (23.275V to 25.725V), the minimum voltage at which the load  500  can operate is 20V, and a forward voltage drop of the diode  301  is 0.7V is described. An operation of the main power source  200  in this case in the normal state will be described. The minimum output voltage of the main power source  200  is 23.275V, and the voltage drop value of the diode  301  is 0.7V. Therefore, if the output voltage value of the sub power source  300  is less than the value obtained by adding the voltage drop value in the diode  301  to the minimum value of the output voltage of the main power source  200 , the diode  301  will not be in the conductive state. Therefore, the output voltage of the sub power source  300  is set to less than 23.975V (23.275V+0.7V). 
     Since the minimum voltage at which the load  500  can operate is 20V, the output voltage of the sub power source  300  is determined so that a voltage equal to or more than the minimum voltage is supplied even after the voltage drop is applied. Therefore, if the output voltage of the sub power source  300  is equal to or more than (20V+0.7V)=20.7V, even in a case where the main power source  200  which supplies power to the load fails, the load  500  can be operated with the sub power source  300 . Therefore, the output voltage V 3  of the sub power source  300  in the steady state is set to equal to or more than 20.7 V, and equal to or less than 23.975 V. As a result, in a case where the main power source  200  has not failed, power is not supplied from the sub power source  300  to the load  500 , and in a case where the main power source  200  has failed, power can be supplied from the sub power source  300  to the load  500 . 
     The rated power of the sub power source  300  will be described. As to the rated power and the rated output power, the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N need not have the same value. However, in order to backup the main power source, the value of the rated power of the sub power source  300  should be equal to or more than a value of the maximum output power of a power source which has the maximum output power while the electric equipment is operating, among the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N. The first embodiment describes the operation in a case where one of a plurality of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N fails. However, by increasing the rated power of the sub power source  300 , even in a case where a plurality of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N fail, it is possible to supply power from the sub power source  300 . 
     Further, when the output voltage Vout 1  of the main power source  200  becomes equal to or less than the value of V 3  described above and the diode  301  conducts accordingly, switching from the main power source  200  to the sub power source  300  is automatically performed. Therefore, at this stage, a user and a serviceman of the power source apparatus  1000  or the electric equipment  2000  cannot recognize that the main power source  200  has failed. 
     On the other hand, in a case where one of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N has failed and power is supplied from the sub power source  300  to the load  500 , another one of the main power sources  200 - 1 ,  200 - 2 , . . .  200 -N may fail. In a case where the rated power of the sub power source  300  is sufficiently large, the sub power source  300  may be able to backup a plurality of failed power supplies among the main power source  200 . However, in other cases, in a case where a plurality of power supplies of the main power source  200  fail, the sub power source  300  cannot backup the failed power supplies. For this reason, in a case where at least one of the main power sources  200  fails, in order to prevent a situation in which the sub power source  300  cannot backup a plurality of power supplies, it is desirable to replace the failed main power source  200  with a normal product. 
     Therefore, the controller  700  of the electric equipment  2000  monitors the voltage detector  701  to determine whether the main power source  200  has failed or not, and in a case where it is determined that a failure has occurred, the determination result is notified by an arbitrary means. With reference to  FIG. 3A , at time t 3 , the value of the output voltage Vout 1  of the main power source  200 - 1  is V 3 , as described above. As shown in  FIG. 3C , at time t 3 , the output voltage Vout 1  of the main power source  200 - 1  drops to V 3 , therefore the diode  301  becomes conductive, and the output voltage Vout 2  of the sub power source  300  is supplied to load  500 - 1 . Therefore, for the load  500 - 1 , voltage is supplied from the main power source  200 - 1  during a period of t 0  to t 2 , and voltage is supplied from the sub power source  300  after the time t 3 . 
     During a period in which the voltage supply source is switched from the main power source  200  to the sub power source  300  (i.e., a period t 2  to t 3 ), the voltage Vload supplied to the load  500  decreases from V 1  to V 3 . For this reason, in the first embodiment, a threshold value is previously set to the value of the voltage Vload. This threshold can be set, for example, in a range of less than V 1  and more than or equal to V 3 . The controller  700  monitors the voltage value detected by the voltage detector  701 . In a case where the detected voltage value drops from V 1 , which is the normal voltage value, to a predetermined threshold value or less, the controller  700  determines that the main power source  200  has failed, and notifies the user or the service man or the like of the determination result by an arbitrary means. Therefore, the controller  700  notifies the determination result by outputting a display control signal for displaying the determination result to the display  702 , which serves as notification means. In particular, in the first embodiment, the determination result is notified to the user by displaying the occurrence of the failure and the information for identifying a load in which the failure has occurred in the display  702  of the electric equipment  2000 . It should be noted that it is possible to perform the notification using the display  402  provided in the power source apparatus  1000 . Further, it is possible to perform the notification by displaying the occurrence of a failure on a display of the serviceman&#39;s terminal through a communication line (not shown) or the like. 
     In this way, by detecting the voltage supplied from the load  500 , it is possible to identify not only the failure of the main power source  200  but also the failure of the specific power source among the main power sources  200 - 1  to  200 -N. Thereby it is possible to notify the identified result. Therefore, the time required for replacing the main power source  200  by the serviceman is shortened. 
     In the above description, the occurrence of a failure is notified by the controller  700  of the electric equipment  2000 , the voltage detector  701 , and the display  702 . Similarly, the controller  400  of the power source apparatus  1000  monitors the voltage detector  401  to determine whether the main power source  200  has failed or not, and in a case where it is determined that a failure has occurred, it is possible to display the determination result on the display  402 . Further, the controller  400  may notify the controller  700  of an occurrence of the failure, and the controller  700  may notify the occurrence of the failure using the display  702 . Further, the controller  700  may notify the serviceman&#39;s terminal of the occurrence of the failure. In this way, by providing at least one of the power source apparatus  1000  and the electric equipment  2000  with a function for notifying the failure of the identified power source among the main power sources  200 - 1  to  200 -N, it is possible to notify the user or the serviceman of the occurrence of the failure. 
     In the first embodiment, the case where the main power source  200 - 1  has failed is described, however, the main power source which can be backed up at the time of failure is not limited to the same. Even if at least one of the other main power sources  200 - 2 ,  200 - 3 , . . .  200 -N fails, it is possible to supply power to the load  500  from the sub power source  300  in the same manner. 
     Further, in the first embodiment, the AC/DC power source  100  is used as an example of the main power source  200  and the sub power source  300  of the power source apparatus  1000 . However, the present disclosure applies to any DC power sources as well as a DC/DC power source which converts a DC voltage having a voltage value into a DC voltage of another voltage value. In a case where a DC/DC power source is used, it is possible to use the sub power source  300  to backup a failed main power source  200 . As described above, according to the first embodiment, even if the main power source  200  fails, the main power source  200  can be backed up without stopping the power supply to the load  500 . 
     Second Embodiment 
     In the first embodiment, a potential difference is provided between the output voltages of the main power source  200  and the sub power source  300  so that the diode  301  does not conduct in a case where the main power source  200  operates normally. Therefore, as to the sub power source  300 , it is necessary to use an AC/DC power source which has a specification different from that of the main power source  200 . Specifically, the values of the voltage detection resistors  109  and  110  in the sub power source  300  are different from the values of the voltage detection resistors  109  and  110  in the main power source  200 . 
     In the second embodiment, the AC/DC power source  100  which has the same specification as the main power source  200  is used for the sub power source  300 .  FIG. 4  shows a configuration of the power source apparatus  1000  of the second embodiment. The power source apparatus  1000  shown in  FIG. 4  has a plurality of the main power source  200 , one sub power source  300 , and a diode  301 , which has the sub power source  300  and the main power source  200 . Further, in the power source apparatus  1000  shown in  FIG. 4 , in addition to the configuration of the first embodiment, a plurality of diodes  302  ( 302 - 1 ,  302 - 2 , . . .  302 -N) for lowering the output voltage of the sub power source  300  and for connecting to the main power source  200 . Unlike the first embodiment, in the second embodiment, each of the main power source  200  and the sub power source  300  has an AC/DC power source  100  having a common circuit configuration and a common target output voltage. Since the operation of the power source apparatus  1000  of the second embodiment is the same as the operation of the first embodiment, regardless of whether the main power source  200  is normal or faulty, a description thereof is omitted. 
     Hereinafter, the diode  302 , which is added in the second embodiment will be described. In a case where the AC/DC power source  100  having a specification which is common to the main power source  200  and the sub power source  300  is used, the voltage Vout 2  from the sub power source  300  drops due to the diode  301 . Therefore, basically, the output voltage Vout 2  of the sub power source  300  tends to be substantially less than the output voltage Vout 1  of the main power source  200 . However, since the output voltage varies depending on individual differences of the parts at the time of manufacturing each power source and other factors, in some cases, the output voltage Vout 2  of the sub power source  300  may become more than the output voltage Vout 1  of the main power source  200 . In this case, the diode  301  becomes conductive even though the main power source  200  has not failed. 
     Therefore, in the second embodiment, in addition to the configuration of the first embodiment, a diode  302  ( 302 - 1 ,  302 - 2 , . . .  302 -N) is connected in series to the output of the sub power source  300  to thereby drop the output voltage. With this configuration, the diode  301  is prevented from conducting during normal operation of the main power source  200 . 
     An example of the design of the diode  302  will be described. In this example, it is assumed that the output voltage values of the main power source  200  and the sub power source  300  are both 24.5V±5% (23.275V to 25.725V), the minimum voltage at which the load  500  can operate is 20V, and the voltage drop of each of the diodes  301  and  302  is 0.7V. 
     In the following description, the main power source  200  is normal, the output voltage of the main power source  200  is 23.275V, i.e., the minimum value in the variation range and the output voltage of the sub power source  300  is 25.275V, i.e., the maximum value in the variation range. Even in this case, by connecting one diode  301  and three diodes  302  in series, a voltage drop of 0.7V*4=2.8V occurs. Therefore, the voltage output from the diodes  301 - 1 ,  302 - 2 , . . . and  302 -N is 25.725V-2.8V=22.925V. Since the voltage value is lowered as described above, the diodes  301  and  302  do not conduct in a case where the main power source  200  is normal even if the variation in the output voltage of the sub power source  300  or the like is taken into consideration. Therefore, it is possible to prevent the output voltage Vout 2  of the sub power source  300  from being supplied to the load  500  while the main power source  200  operates normally. 
     In the following, an example in which the main power source  200  fails is explained. Even if the output voltage of the sub power source  300  is 23.275V, i.e., the minimum value in the variation range, the voltage after the voltage drop due to the four diodes is 23.275V-2.8V=20.475V. This voltage value is more than the minimum voltage value (20V) at which the load  500  can operate. In this way, by connecting three diodes  302  to the output of the sub power source  300 , the power is not supplied to the load  500  in a case where the main power source  200  has not failed, and the power is supplied to the load  500  in a case where the main power source  200  has failed. 
     As described above, by using the voltage drop due to the diode  302 , the AC/DC power source  100  having the specification common to the main power source  200  and the sub power source  300  can be used. As a result, the design of the power source apparatus  1000  can be simplified, and the cost can be reduced by standardizing the parts. 
     In the second embodiment, as in the first embodiment, instead of the AC/DC power source  100 , a DC/DC power source can be used as the main power source  200  and/or as the sub power source  300 . Further, it is possible to detect a voltage value of the load  500  by the voltage detector  701  to determine whether or not a failure has occurred based on the detected voltage value. The determination result may be displayed on the display  702  or the like. 
     In the second embodiment, by providing the diode  302 , the value of the output voltage Vout 2  of the sub power source  300  is lowered by the voltage drop due to the diode  302 . However, instead of the diode  302  as the voltage drop element for lowering the voltage, any type of resistance elements, such as a resistor, a variable resistor, and a light emitting diode for lowering the voltage can be used. For example, by using a variable resistor, the value of the variable resistor can be adjusted according to the variation in the voltage value due to individual differences during manufacturing, or according to a change in the output voltage from the sub power source  300  due to changes over time. It is possible to monitor the output voltage of the sub power source  300  detected by the voltage detector  401  by the controller  400 . In this case, the value of the variable resistor can be changed according to the result of the monitoring. For example, when the output voltage of the sub power source  300  drops due to a change with time or the like, the controller  400  may change the value of the variable resistor to compensate the voltage drop. Further, when the light emitting diode is used, it is possible to visually determine whether or not the voltage is normally output from the sub power source  300 . As described above, according to the present disclosure, there is provided a power source apparatus which has a plurality of power sources to continue to supply power to a load even if one of the power sources fails. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2019-229922, filed Dec. 20, 2019, which is hereby incorporated by reference herein in its entirety.