Power supply device and lifetime diagnostic procedures

Abstract

Power supply device (1), comprising: a first line (L1); a second line (L2) having a lower electrical potential than the first line (L1); a first switch (11) having a first terminal connected to the first line (L1); a capacitor (10) having a first terminal connected to the first switch (11) and a second terminal connected to the second line (L2); a resistor (13) connected in parallel with the capacitor (10); a second switch (12) connected in series with the resistor (13); a voltage detecting means (161) for detecting a voltage value between the first terminal and the second terminal of the capacitor (10); a switch control means (162) for controlling the first switch (11) and the second switch (12); and a lifetime evaluation means (164) for evaluating the lifetime of the capacitor (10), wherein the switch control means (162) switches off the first switch (11) at a first time (t1) during an on-state of the first switch (11) and an off-state of the second switch (12), and switching on the second switch (12) at a second time (t2) at which a first time period (T1) has elapsed since the first time (t1), wherein the voltage detecting means (161) detecting a first voltage value (V1) of the capacitor (10) during a period between the first time (t1) and the second time (t2) and at or after a third time (t3), at which third time (t3) a second time period (T2) has elapsed since the second time (t2), detects a second voltage value (V2) of the capacitor (10), and wherein the lifetime evaluation means (164) evaluates the lifetime of the capacitor (10) based on the first voltage value (V1) and the second voltage value (V2).

Description

Technical field

[0001] The present disclosure relates to a power supply device and a method for evaluating lifetime. Technological background

[0002] A power supply contains a capacitor with a finite lifetime for voltage smoothing. As the capacitor deteriorates (ages) and exhibits a lower capacitance, the power supply is likely to cease functioning properly. Techniques for evaluating the lifetime of a capacitor are to be developed.

[0003] Patent Literatures 1 and 2 describe techniques for judging the life of a capacitor based on the time elapsed between the start of discharge of the capacitor and the time at which the voltage across the capacitor reaches a predetermined value after the power supply to a capacitor is interrupted and the electric charge stored in the capacitor is then discharged through a resistor connected in parallel with the capacitor. Citation listPatent literature Patent Literature 1: Unexamined Japanese Patent Application Laid-Open No. JP H06-165523 A Patent Literature 2: International Publication No. WO 2008 / 016 050 A1 Brief description of the inventionTechnical problem

[0004] The capacitor in Patent Literature 1 is constantly connected in parallel with a power transistor module. As a result, the electric charge stored in the capacitor is also discharged through the power transistor module, resulting in the voltage across the capacitor being unstable at the beginning of the electric discharge.

[0005] The capacitor in Patent Literature 2 is constantly connected in parallel with the resistor. Therefore, the electrical discharge begins immediately when the power supply to the capacitor is interrupted, resulting in the voltage across the capacitor being unstable at the beginning of the electrical discharge due to a residual ripple component (ripple voltage component).

[0006] The capacitors in Patent Literatures 1 and 2 exhibit unstable voltages at the beginning of the electrical discharge, which leads to fluctuations in the discharge time and thus affects the accuracy of the lifetime evaluation.

[0007] The technologies described in Patent Literatures 1 and 2 evaluate the lifespan of a capacitor based on the time it takes for the voltage across the capacitor to reach a predetermined value. This time may fluctuate when the voltage value fluctuates due to, for example, a ripple component and / or noise, thereby affecting the accuracy of the lifespan evaluation.

[0008] From DE 11 2010 002 675 T5 a capacitor capacity diagnostic device and an electrical power supply device equipped with it are known.The capacitor capacity diagnostic device includes a power supply for charging a capacitor whose capacity adequacy is to be determined, a discharge circuit formed by a discharge resistor and a transistor serving as a discharge switch and connected in parallel with the capacitor to discharge the energy of the capacitor, a resistance divider circuit formed by first and second resistors and connected in parallel with the capacitor to measure the voltage drop during discharge, a measuring circuit for measuring a voltage at a node between the first resistor and the second resistor, a diagnostic circuit, and an alarm circuit that issues a warning when a failure is detected based on the judgment results by the diagnostic circuit.The diagnostic circuit issues a capacitor charging stop command and a discharge switch continuity command of the discharge circuit, discharges the energy stored in the capacitor for a predetermined period of time, and determines the adequacy of the capacitor capacitance based on a temporal voltage change due to the discharge, which is measured by the measuring circuit. In operation, electric current is supplied from the connected power supply to the capacitor whose capacitance adequacy is to be determined. The capacitor is charged to a voltage required by a device to be used. When charging is complete, the diagnostic circuit applies the charging stop command to the capacitor, and the continuity command with a predetermined period of time is applied to the discharge switch of the discharge circuit.The capacitor voltage is divided at the junction between a resistance value of the first resistor and a resistance value of the second resistor in the resistor divider circuit, and a voltage drop value is measured at time t. Then, a comparison is made with a reference voltage drop value that has been set in advance as a predetermined voltage drop value allowable for the capacitor during diagnosis. If this value is within the predetermined voltage drop value and exceeds a reference value, the capacitor capacitance is deemed suitable. If the value is not less than the voltage drop value that exceeds the reference value, the capacitor capacitance is deemed unsuitable, and a warning is issued from the alarm circuit.

[0009] A method for operating an electronic assembly supplied from an operating voltage source is known from DE 102 55 429 A1.

[0010] DE 195 28 454 C1 discloses a method and a circuit arrangement for measuring a capacitance, in which the capacitance to be measured is periodically switched to a predetermined reference potential with a predetermined period duration and is then discharged in an evaluation device via an ohmic device, the arithmetic mean value of the resulting discharge curve being determined as a measure of the capacitance to be determined.

[0011] In response to the above problem, it is an object of the present disclosure to provide a power supply device and a method for accurately evaluating the lifetime of a capacitor. Solution to the problem

[0012] To achieve the above object, a power supply device includes a first line, a second line having a lower electric potential than that of the first line, a first switch having a first terminal connected to the first line, a capacitor having a first terminal connected to the first switch and a second terminal connected to the second line, a resistor connected in parallel with the capacitor, a second switch connected in series with the resistor, voltage detecting means for detecting a voltage value across the first terminal and the second terminal of the capacitor, switch controlling means for controlling the first switch and the second switch, and lifetime evaluating means for evaluating a lifetime of the capacitor.The switch control means turns off the first switch at a first time point during an on-state (closed state) of the first switch and an off-state (open state) of the second switch, and turns on the second switch at a second time point at which a first period of time has elapsed starting from the first time point. The voltage detection means detects a first voltage value of the capacitor during a period of time between the first time point and the second time point, and detects a second voltage value of the capacitor at a third time point at which a second period of time has elapsed starting from the second time point. The lifetime evaluation means evaluates the lifetime of the capacitor based on the first voltage value and the second voltage value. Advantageous effects of the invention

[0013] In the power supply device according to the above aspect of the present disclosure, the second switch is turned on (closed) when the first time period has elapsed after the first switch is turned off (opened). Thus, the capacitor has a stable voltage at the start of the electrical discharge. The power supply device according to the above aspect of the present disclosure accurately estimates the service life of the capacitor. Brief description of the drawings Fig. 1 is a block diagram of a power supply device according to an embodiment of the present disclosure; Fig. 2 is a graph showing an example of the lifetime characteristic of a capacitor in the embodiment of the present disclosure; Fig. 3 is a diagram showing an exemplary relationship between on-off states of switches and a voltage value of the capacitor in the embodiment of the present disclosure; Fig. 4 is a flowchart showing an exemplary operation of the power supply device according to the embodiment of the present disclosure that performs a lifetime evaluation; and Fig. 5 is a block diagram of a power supply device according to Modification 2 of the embodiment of the present disclosure. Description of the embodiments

[0014] A power supply device according to one or more embodiments of the present disclosure will now be described with reference to the drawings. In the figures, the same or equivalent components are provided with the same reference numerals.

[0015] In the embodiments described below, the voltage across the two terminals of a capacitor, the voltage value across the two terminals of a capacitor, and all equivalents thereof are also referred to simply as the voltage across a capacitor and the voltage value of a capacitor. Assessing the lifespan of a capacitor generally involves determining the deterioration (aging) of the capacitor, more specifically, determining the degree of deterioration of the capacitor, determining the remaining lifespan of the capacitor, and determining whether the capacitor has deteriorated and needs to be replaced. Embodiments

[0016] A power supply device 1 according to an embodiment is described with reference to Fig. 1. The power supply device 1 evaluates the lifespan of a capacitor included in the power supply device 1 and displays the evaluation result. The power supply device 1 includes a capacitor 10, a switch 11, a switch 12, a resistor 13, a capacitor 10a, a switch 11a, a switch 12a, a resistor 13a, a diode 14, a transformer 15, a controller 16, a memory 17, a line L1, and a line L2. The power supply device 1 drives a load 2 with direct current (DC). The power supply device 1 controls an indicator 3 to display a result of the evaluation of the lifespan of each of the capacitor 10 and the capacitor 10a. The power supply device 1 is an example of a power supply device according to one aspect of the present disclosure.Line L1 is an example of a first line according to one aspect of the present disclosure. Line L2 is an example of a second line according to one aspect of the present disclosure.

[0017] The Fig. The power supply device 1 shown in Figure 1 has a primary side located to the left of the transformer 15 and a secondary side located to the right of the transformer 15. In Fig. 1, the components of the primary side are not shown. The components of the primary side are not described below. In Fig. 1, the filled dots at the top left and bottom right of transformer 15 each indicate the polarity of the winding of transformer 15. Power supply device 1 is a flyback power supply device, as indicated by the polarity of the winding of transformer 15 and the position of diode 14.

[0018] A group consisting of capacitor 10, switch 11, switch 12, and resistor 13 (hereinafter the group with capacitor 10) has essentially the same structure as a group consisting of capacitor 10a, switch 11a, switch 12a, and resistor 13a (hereinafter the group with capacitor 10a). The components may have different properties.

[0019] As described in detail below, the switch 11 must be turned off (opened) before the service life of the capacitor 10 is evaluated. The group with the capacitor 10a enables the normal operation of the power supply device 1 even though the switch 11 is turned off. The switch 11a is turned on so that the power supply device 1 can operate normally when the switch 11 is turned off. In other words, the group with the capacitor 10a is a redundancy of the group with the capacitor 10. In this structure, Fig. 1 the switch 11a is switched on when the switch 11 is switched off.

[0020] The components of the power supply device 1 will now be described. As described above, the group including the capacitor 10a has the same structure as the group including the capacitor 10 and will therefore not be described in detail. Only the components in the group including the capacitor 10 will be described.

[0021] The capacitor 10 has one terminal connected to the switch 11 and the other terminal connected to the line L2. The capacitor 10 smoothes the current supplied by the transformer 15 and the diode 14. The capacitor 10 is, for example, an aluminum electrolytic capacitor. The capacitor 10 has, for example, a lifetime with the Fig. 2. The lifespan characteristic of a capacitor refers to the relationship between the degree of deterioration of the capacitor and its capacitance. Typically, the longer a capacitor is used, the more it deteriorates and the lower its capacitance becomes. Fig. 2, the capacitor 10 has half its service life remaining at point A, a shorter service life at point B, where replacement of the power supply device 1 is recommended, and an expired service life at point C, where the power supply device 1 can no longer operate normally. The capacitor 10 is an example of a capacitor according to one aspect of the present disclosure.

[0022] Returning to Fig. 1, switch 11 has one terminal connected to line L1 and another terminal connected to capacitor 10. The switching on and off of switch 11 is controlled by a switch controller 162 in controller 16 (described later). Switch 11 is turned off to electrically disconnect capacitor 10 from line L1. Switch 11 is a switching element that can be turned on and off and may be, for example, a relay or a transistor. Switch 11 is an example of a first switch according to one aspect of the present disclosure.

[0023] Switch 12 is connected in series with resistor 13. Like switch 11, switch 12 is turned on and off by switch controller 162. Switch 12 is turned on to discharge the electrical charge stored in capacitor 10 through resistor 13. Like switch 11, switch 12 is a switching element that can be turned on and off and can be, for example, a relay or a transistor. Switch 12 is an example of a second switch according to one aspect of the present disclosure.

[0024] Resistor 13 is connected in parallel with capacitor 10. When switch 12 is turned on, resistor 13 discharges the electrical charge stored in capacitor 10. Resistor 13 is an example of a resistor according to one aspect of the present disclosure.

[0025] Diode 14 rectifies a current flowing from transformer 15. After rectification by diode 14, line L1 has an electrical potential equal to or higher than that of line L2.

[0026] The transformer 15 converts the energy supplied by the primary side and supplies the energy to the secondary side. In the flyback power supply device 1, the transformer 15 stores power when a switch on the primary side is turned on and feeds power to the secondary side when the switch is turned off.

[0027] The control unit 16 centrally controls the power supply device 1. The control unit 16 comprises, for example, a microcontroller as a hardware component. The functions of the control unit 16 are implemented by a central processing unit (CPU) of the microcontroller, which executes programs stored in a read-only memory (ROM). In some embodiments, the control unit 16 may include a control circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). In this case, the control circuit implements the functions of the control unit 16.

[0028] The control unit 16 includes, as functional components, a voltage detector 161, the switch controller 162, a capacitance calculator 163, a lifetime evaluator 164, and an indicator controller 165. The control unit 16 controls these functional components to evaluate the lifetime of the capacitor 10 or the capacitor 10a at predetermined intervals, for example, every hour or every eight hours.

[0029] The voltage detector 161 detects the voltage values ​​of the capacitor 10 and the capacitor 10a. The voltage detector 161 is implemented, for example, by an analog-to-digital (A / D) converter in the microcontroller. A voltage value detected by the voltage detector 161 is used by the capacitance calculator 163 (described below) to calculate the capacitance of the capacitor 10. The voltage detector 161 is an example of a voltage detecting means according to one aspect of the present disclosure.

[0030] The switch controller 162 controls the on and off states of the switch 11, the switch 12, the switch 11a, and the switch 12a. The switch controller 162 is an example of a switch control means according to one aspect of the present disclosure.

[0031] An example of switch control performed on switch 11 will now be described. When control unit 16 fails to judge the lifespan of capacitor 10 or capacitor 10a, switch control unit 162 turns on switch 11 and switch 11a and turns off switch 12 and switch 12a. This allows voltage smoothing for both capacitor 10 and capacitor 10a and prevents accidental electrical discharge through resistor 13 and resistor 13a.

[0032] The control of the switches by the switch controller 162 when the control device 16 judges the life of the capacitor 10 will be described with reference to Fig. 3 described. Fig. Figure 3 shows changes in the on-off states of switch 11 and switch 12 and the corresponding changes in the voltage value of capacitor 10. Before starting the lifetime evaluation, switch 11 and switch 11a are turned on as described above, and switch 12 and switch 12a are turned off. In this state, capacitor 10 has a slightly unstable voltage due to a ripple component on line L1, as shown in Fig. 3 shown.

[0033] The switch controller 162 first turns off the switch 11 at a time t1. This stabilizes the voltage across the capacitor 10 by eliminating the effects of the ripple component on the line L1 and preventing the electrical charge stored in the capacitor 10 from discharging through the load 2. In this state, the switch 12 remains off. The resistor 13 does not perform any electrical discharge. The voltage detector 161 detects a voltage value V1 until a time t2 (described below). The time t1 is an example of a first time according to one aspect of the present disclosure. The voltage value V1 is an example of a first voltage value according to one aspect of the present disclosure.

[0034] The switch controller 162 then turns on the switch 12 at time t2, at which a time period T1 has elapsed since the time t1. The resistor 13 then begins electrical discharge to gradually reduce the voltage across the capacitor 10. The time period T1 is an example of a first time period according to one aspect of the present disclosure. The time t2 is an example of a second time period according to one aspect of the present disclosure.

[0035] The switch controller 162 then turns off the switch 12 at a time t3, at which a time period T2 has elapsed since the time t2. The resistor 13 then stops the electrical discharge to stabilize the voltage across the capacitor 10. The voltage detector 161 detects a voltage value V2 until a time t4 (described below), the capacitance calculator 163 calculates the capacitance of the capacitor 10, and the life evaluator 164 evaluates the life of the capacitor 10. The time period T2 is an example of a second time period according to an aspect of the present disclosure. The time t3 is an example of a third time period according to an aspect of the present disclosure. The voltage value V2 is an example of a second voltage value according to an aspect of the present disclosure.

[0036] The switch controller 162 then turns on the switch 11 at time t4, at which a time period T3 has elapsed since the time t3. The capacitor 10 then receives current via the line L1, stores electrical charge, and its voltage increases. The time period T3 is an example of a third time period according to an aspect of the present disclosure. The time t4 is an example of a fourth time period according to an aspect of the present disclosure.

[0037] In order for the control unit 16 to estimate the lifetime of the capacitor 10a, the switch controller 162 controls the switches in the same way as the control of the switches for the capacitor 10, which is not described here.

[0038] With reference to Fig. 1 and Fig. 3, the capacitance calculator 163 is described. The capacitance calculator 163 calculates the capacitance of the capacitor 10 based on the voltage value V1, the voltage value V2, the time period T2 described above, and the resistance value of the resistor 13. The capacitance calculator 163 also calculates the capacitance of the capacitor 10a in a manner similar to that described above. The capacitance calculator 163 is an example of a capacitance calculation means according to one aspect of the present disclosure.

[0039] Now, only the calculation of the capacitance of capacitor 10 will be described. Before the electrical discharge occurs through resistor 13, capacitor 10 has a voltage value of V1. After the electrical discharge occurs through resistor 13, capacitor 10 has a voltage value of V2. Resistor 13 performs an electrical discharge over a period of time T2. The capacitance of capacitor 10 is calculated using the following formula 1, where C is the capacitance of capacitor 10, R is the resistance of resistor 13, and In is a logarithmic function with the base of the natural logarithm. C=T2 / (R×ln(V1 / V2))

[0040] The memory 17 stores information indicating the resistance value of the resistor 13, as described in detail below. The capacitance calculator 163 refers to the information indicating the resistance value of the resistor 13 stored in the memory 17 to calculate the capacitance of the capacitor 10 using Formula 1.

[0041] The lifetime evaluator 164 evaluates the lifetime of the capacitor 10 based on the capacitance of the capacitor 10 calculated by the capacitance calculator 163 and the Fig. 2. The life evaluator 164 evaluates the life of the capacitor 10a in a similar manner as described above. The life evaluator 164 is an example of a life evaluation means according to one aspect of the present disclosure.

[0042] The memory 17 stores information indicating the life characteristics of the capacitor 10, as described in detail below. The life evaluator 164 refers to the information indicating the life characteristics of the capacitor 10 stored in the memory 17 to evaluate the life of the capacitor 10.

[0043] The information stored in the memory 17 about the lifetime characteristic of the capacitor 10 can be replaced by information which describes the capacitance of the capacitor 10 at point B of Fig. 2. In this case, the life evaluator 164 evaluates the life of the capacitor 10 by comparing the above capacitance values ​​and the capacitance of the capacitor 10 calculated by the capacitance calculator 163, and determines whether the capacitor 10 has deteriorated and whether replacement of the power supply device 1 is recommended. In this case, the capacitance indicated by the information stored in the memory 17 is a threshold value for evaluating the life. The threshold value is based on the life characteristics of the capacitor 10. Thus, in this case, the life evaluator 164 also evaluates the life of the capacitor 10 based on the life characteristics of the capacitor 10.

[0044] Returning to Fig. 1, the indicator controller 165 controls the indicator 3 to display the evaluation result performed by the life evaluator 164 to a user. The indicator 3 is described in detail below. If no evaluation result is to be displayed, the indicator controller 165 does not need to display it. For example, if an evaluation result is to be displayed only to recommend replacing the power supply device 1, the indicator controller 165 does not need to display an evaluation result as long as the capacitor 10 has a sufficient lifespan.

[0045] The memory 17 stores information indicating the resistance value of the resistor 13, information indicating the resistance value of the resistor 13a, information indicating the life characteristic of the capacitor 10, and information indicating the life characteristic of the capacitor 10a. As described above, instead of the information indicating the life characteristic of the capacitor 10 and the information indicating the life characteristic of the capacitor 10a, the memory 17 may store the above-mentioned threshold value for each of the capacitors 10 and 10a.

[0046] The load 2 and the indicator 3 are described below. The load 2 is driven by direct current provided by the power supply device 1. The load 2 is, for example, a direct current motor. The load 2 is connected by one terminal to the line L1 of the power supply device 1 and by the other terminal to the line L2 of the power supply device 1. The load 2 is an example of a load according to one aspect of the present disclosure.

[0047] Indicator 3 displays the life evaluation results of capacitor 10 and capacitor 10a to a user. Indicator 3 is, for example, a lamp that emits green, yellow, and red light. Controlled, for example, by indicator controller 165 in controller 16, indicator 3 emits green light when capacitor 10 and capacitor 10a each have sufficient lifespan, yellow light when capacitor 10 or capacitor 10a has deteriorated and power supply device 1 should be replaced, and red light when capacitor 10 or capacitor 10a has expired lifespan.

[0048] In some embodiments, indicator 3 may be a lamp that emits only red light. In this case, indicator 3, controlled, for example, by indicator controller 165, emits red light when capacitor 10 or capacitor 10a has deteriorated and power supply device 1 needs to be replaced (and when capacitor 10 or capacitor 10a has expired its service life). This indicator may be used, for example, when service life evaluator 164 performs an assessment based on the threshold value.

[0049] Instead of a lamp, the indicator 3 can also be a loudspeaker that produces a buzzing sound or a display that can show an evaluation result in detail.

[0050] Now, with reference to the Fig. 4 and Fig. 3 an exemplary operation of the power supply device 1 for evaluating the service life is described. Fig. 4 is carried out at predetermined intervals as described above. At the beginning of the Fig. 4, as described above, switch 11 and switch 11a are turned on, and switch 12 and switch 12a are turned off. Next, the life evaluation process for capacitor 10 will be described. The life evaluation for capacitor 10a is performed similarly to the life evaluation for capacitor 10 and will not be described here.

[0051] The switch controller 162 in the control unit 16 in the power supply device 1 turns off the switch 11 (step S101). This process becomes the Fig. 3. The switch 11 is turned off to stabilize the voltage across the capacitor 10.

[0052] After the processing in step S101 is performed, the voltage detector 161 in the control unit 16 detects the voltage value V1 of the capacitor 10 before time t2 (step S102). However, the operation performed in step S102 immediately after step S101 may detect the voltage value of the capacitor 10 that has not yet stabilized.

[0053] When the time period T1 has elapsed since the time t1, the switch controller 162 turns on the switch 12 (step S103). This process becomes the Fig. 3. The switch 12 is turned on to cause the resistor 13 to perform an electrical discharge.

[0054] When the time period T2 has elapsed after the processing in step S103, the switch controller 162 turns off the switch 12 (step S104). This operation becomes the Fig. 3. The switch 12 is turned off to cause the resistor 13 to terminate the electrical discharge, thereby stabilizing the voltage across the capacitor 10.

[0055] After the processing in step S104 is performed, the voltage detector 161 in the control unit 16 detects the voltage value V2 of the capacitor 10 before the time t4 (step S105).

[0056] When the time period T3 has elapsed since the processing in step S104, the switch controller 162 turns on the switch 11 (step S106). This operation becomes the Fig. 3. The switch 11 is turned on to cause the capacitor 10 to store electrical charge via the line L1, thereby increasing the voltage across the capacitor 10.

[0057] The capacitance calculator 163 in the control unit 16 calculates the capacitance of the capacitor 10 based on the voltage value V1 detected in step S102, the voltage value V2 detected in step S105, the time period T2, and the information about the resistance value of the resistor 13 stored in the memory 17 (step S107).

[0058] The life evaluator 164 in the control unit 16 estimates the life of the capacitor 10 based on the capacitance of the capacitor 10 calculated in step S107 and the information indicating the life characteristic of the capacitor 10 stored in the memory 17 (step S108).

[0059] The indicator controller 165 in the control unit 16 controls the indicator 3 to display the evaluation result obtained in step S108 to the user (step S109). The control unit 16 terminates the lifetime evaluation.

[0060] The process in step S106 may also be performed after the processing in any one of steps S107 to S109.

[0061] The power supply device 1 according to the present embodiment has been described above. In the power supply device 1, the switch 11 is turned off at time t1, and the switch 12 is turned on at time t2, at which time T1 has elapsed from time t1. The voltage across the capacitor 10 is stabilized between time t1 and time t2. In other words, the power supply device 1 enables the capacitor 10 to have a stable voltage across both terminals at the start of electrical discharge.

[0062] In the power supply device 1, the switch 12 is turned off at time t3 to stop the electrical discharge, and the switch 11 is turned on at time t4, at which the time period T3 has elapsed since the time t3. The voltage across the capacitor 10 is stabilized during the period between the time t3 and the time t4.

[0063] In the power supply device 1, the resistor 13 performs an electrical discharge during the time period T2 that is independent of the voltage value of the capacitors, and the capacitor 10 has a stable voltage before and after the electrical discharge.

[0064] The power supply device 1 thus accurately detects the voltage value of the capacitor 10 and thus accurately estimates the service life of the capacitor 10 based on the detected voltage values ​​of the capacitor 10. The service life evaluation can also be accurately performed for the capacitor 10a. Modification 1

[0065] In the above embodiment, the voltage detector 161 detects the single voltage value V1 of the capacitor 10 during the period from time t1 to time t2 and detects the single voltage value V2 of the capacitor 10 during the period from time t3 to time t4. In some embodiments, the voltage detector 161 may detect multiple voltage values ​​V1 of the capacitor 10 during the period from time t1 to time t2 and may detect multiple voltage values ​​V2 of the capacitor 10 during the period from time t3 to time t4. The capacitance calculator 163 may then calculate the capacitance of the capacitor 10 based on the average value of the detected multiple voltage values ​​V1 and the average value of the detected multiple voltage values ​​V2.The average values ​​of the acquired multiple voltage values ​​are used to further reduce the probability of life assessment accuracy being reduced due to noise. This enables an accurate assessment of the life of capacitor 10. It is also possible to acquire only one of the voltage values ​​V1 or V2 multiple times. Modification 2

[0066] In the above embodiment, the power supply device 1 evaluates the lifetime of both the capacitor 10 and the capacitor 10a. In some embodiments, the power supply device 1 may evaluate the lifetime of a single capacitor 10. For example, instead of the group with the capacitor 10a between the line L1 and the line L2, the power supply device 1 includes a switch 11b and a capacitor 10b, as in Fig.5. The switch 11b and the capacitor 10b are connected in series. The switch controller 162 turns on the switch 11b only for evaluating the life of the capacitor 10 and leaves the switch 11b off at other times. This configuration, with a simpler circuit design than Embodiment 1, enables the evaluation of the life of the capacitor 10. The switch 11b is turned on only for evaluating the life of the capacitor 10, causing the capacitor 10b to store electric charge. Therefore, it is highly unlikely that the life of the capacitor 10b will expire sooner than that of the capacitor 10. Modification 3

[0067] In the above embodiment, the capacitance calculator 163 calculates the capacitance of the capacitor 10, and the life evaluator 164 judges the life of the capacitor 10 based on the calculated capacitance. In some embodiments, the life evaluator 164 may also judge the life of the capacitor 10 without the capacitance calculator 163 calculating the capacitance of the capacitor 10. In Formula 1 described above, the time period T2 and the resistance value R of the resistor 13 are known. Thus, the capacitance C is determined from the ratio between the voltage value V1 and the voltage value V2. The life characteristic of the capacitor 10 can also be represented by the relationship between the degree of deterioration of the capacitor 10 and V1 / V2.The life characteristic information represented by the relationship between the degree of deterioration of the capacitor 10 and V1 / V2 is stored in the memory 17. This enables the evaluation of the life of the capacitor 10 without calculating the capacitance of the capacitor 10. In other words, the life evaluator 164 can evaluate the life of the capacitor 10 based on the voltage value V1 and the voltage value V2 without depending on the capacitance of the capacitor 10. Modification 4

[0068] In the above embodiment, the switch 12 is turned off at time t3 to detect the stable voltage value V2 of the capacitor 10. In some embodiments, the voltage value of the capacitor 10 may be detected at time t3 without turning off the switch 12, and the detected voltage value may be used as the voltage value V2. In this case, too, the voltage across the capacitor 10 is stabilized at the beginning of the electrical discharge. The service life of the capacitor 10 is thus accurately estimated.

[0069] The foregoing describes some exemplary embodiments for purposes of explanation. Although specific embodiments have been presented in the foregoing discussion, those skilled in the art will recognize that changes may be made in form and detail without departing from the general spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention will be defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. List of reference symbols 1 power supply device 2 load 3 Indicator 10, 10a, 10b capacitor 11, 11a, 11b, 12, 12a switches 13, 13a resistance 14 Diode 15 Transformer 16 Control unit 17 storage 161 Voltage detector 162 Switch control 163 capacity calculator 164 lifetime assessors 165 Indicator Control L1, L2 line

Claims

A power supply device (1), comprising: a first line (L1); a second line (L2) with a lower electrical potential than the first line (L1); a first switch (11) with a first terminal connected to the first line (L1); a capacitor (10) with a first terminal connected to the first switch (11) and a second terminal connected to the second line (L2); a resistor (13) connected in parallel to the capacitor (10); a second switch (12) connected in series with the resistor (13); voltage detection means (161) for detecting a voltage value between the first terminal and the second terminal of the capacitor (10); switch control means (162) for controlling the first switch (11) and the second switch (12); and lifetime evaluation means (164) for evaluating the lifetime of the capacitor (10).wherein the switch control means (162) switches off the first switch (11) at a first time (t1) during an on-state of the first switch (11) and an off-state of the second switch (12), and switches on the second switch (12) at a second time (t2) at which a first time period (T1) has elapsed since the first time (t1), wherein the voltage detection means (161) detects a first voltage value (V1) of the capacitor (10) during a time period between the first time (t1) and the second time (t2), and detects a second voltage value (V2) of the capacitor (10) at or after a third time (t3) at which third time (t3) a second time period (T2) has elapsed since the second time (t2), and wherein the lifetime evaluation means (164) determines the lifetime of the capacitor (10) based on the first voltage value (V1) and the second voltage value (V2). The power supply device (1) according to claim 1, further comprising:capacitance calculating means (163) for calculating a capacitance of the capacitor (10) based on the first voltage value (V1), the second voltage value (V2), the second time period (T2), and a resistance value of the resistor (13),wherein the lifetime evaluating means (164) evaluates the lifetime of the capacitor (10) based on the capacitance of the capacitor (10) calculated by the capacitance calculating means (163) and a lifetime characteristic of the capacitor (10). Power supply device (1) according to claim 1 or 2, wherein the voltage detection means (161) detects a plurality of first voltage values ​​(V1) during a period between the first time (t1) and the second time (t2), and wherein the lifetime evaluation means (164) evaluates the lifetime of the capacitor (10) based on an average of the detected plurality of first voltage values ​​(V1). Power supply device (1) according to one of claims 1 to 3, wherein the switch control means (162) further switches off the second switch (12) at the third time (t3) and switches on the first switch (11) at a fourth time (t4) at which a third time period (T3) has elapsed since the third time (t3), and wherein the voltage detection means (161) detects a voltage value of the capacitor (10) as the second voltage value (V2) during a time period between the third time (t3) and the fourth time (t4). Power supply device (1) according to claim 4, wherein the voltage detection means (161) detects a plurality of second voltage values ​​(V2) during a period between the third time (t3) and the fourth time (t4), and the lifetime evaluation means (164) evaluates the lifetime of the capacitor (10) based on an average of the detected plurality of second voltage values ​​(V2). A method for evaluating the service life of a capacitor (10) in a power supply device (1), wherein the power supply device (1) comprises a first line (L1), a second line (L2) with a lower electrical potential than that of the first line (L1), a first switch (11) with a first terminal connected to the first line (L1), the capacitor (10) with a first terminal connected to the first switch (11) and with a second terminal connected to the second line (L2), a resistor (13) connected in parallel to the capacitor (10), and a second switch (12) connected in series to the resistor (13), the method for evaluating the service life comprising: (S101) switching off the first switch (11) at a first time (t1) during an on-state of the first switch (11) and in an off-state of the second switch (12);(S103) turning on the second switch (12) at a second time (t2) at which a first time period (T1) has elapsed since the first time (t1); and (S108) judging the lifetime of the capacitor (10) based on a voltage value of the capacitor (10) during a time period (T1) between the first time (t1) and the second time (t2) and a voltage value of the capacitor (10) at or after a third time (t3), at which third time (t3) a second time period (T2) has elapsed since the second time (t2);

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