Power supply device and electronic equipment

Abstract

By providing a voltage detection means, a current detection means, a calculation means, and a determination circuit for determining a calculation result to a secondary battery constituting a parallel cell block, the present invention makes it possible to cope with maintenance in which an abnormality of the battery is determined and whether replacement of the secondary battery is necessary or not it is determined. The present invention contributes to Sustainable Development Goal "9: Build a foundation for industry and innovation". A power supply device according to an embodiment of the present invention comprises: a secondary battery; a reference voltage source; a charging circuit that charges the secondary battery; a voltage comparator that compares the voltage of the secondary battery with the voltage of the reference voltage source; and an alert display device that is controlled by the voltage comparator.

Description

Power supplies and electronic devices

[0001] The present invention relates to a device that uses a secondary battery to form a backup power supply.

[0002] In electronic devices with semiconductor memory, a circuit that backs up the semiconductor memory using a power source other than the main power source, such as a secondary battery, is commonly used to maintain the information stored in the semiconductor memory even if the main power source is lost. When using a secondary battery, the secondary battery is charged by an external power source during normal use, and the secondary battery is used to back up the semiconductor memory while the power source is off. Furthermore, for long-term backup, it is necessary to connect multiple battery cells constituting the secondary battery in parallel, or, if the required voltage of the device to be backed up is higher than the voltage of the battery cell, to connect multiple battery cells in series. However, if the battery cell deteriorates or an abnormality such as a short circuit occurs during use, it becomes impossible to obtain backup power output.

[0003] To solve this problem, a circuit for detecting abnormalities in battery cells is provided. For example, a technology for isolating abnormal battery cells using multiple secondary batteries is described in Patent Document 1 below, which provides a means for detecting the voltage and current flowing through a parallel cell block made up of multiple cells connected in parallel, and uses a method for determining cell abnormalities by calculating the DC internal resistance of each parallel cell block from the voltage change and the detected current change in each parallel cell block before and after current is passed through the battery block.

[0004] Patent No. 4606846

[0005] However, the disclosure of Patent Document 1 requires the provision of a voltage detection means, a current detection means, a calculation means, and a judgment circuit for determining the calculation results in order to determine whether a secondary battery has an abnormality, which results in a very large circuit scale, resulting in a first problem: not only does the overall system cost increase, but also complex control. A second problem is that it is unclear whether the problem is with only some of the battery cells in a parallel cell block or with all of the battery cells. Furthermore, even if the secondary battery is determined to be abnormal, there is no mechanism to clearly indicate the result to the user, resulting in a third problem: it is unclear what maintenance measures to take, such as whether the determined secondary battery needs to be replaced.

[0006] In order to solve the first, second, and third problems, one embodiment of the present invention is, for example, a power supply device comprising a secondary battery, a reference voltage source, a charging circuit that charges the secondary battery, a voltage comparator that compares the voltage of the secondary battery with the voltage of the reference voltage source, and an alert display device controlled by the voltage comparator.

[0007] According to the present invention, each secondary battery can be charged and discharged independently, and even if an abnormality occurs in an individual secondary battery, the system's charging and discharging is not hindered, and normal backup operation can continue. Furthermore, because an alert display device is installed for each secondary battery that has become abnormal based on the voltage comparison results, even in applications where multiple secondary batteries are used in parallel, secondary batteries that have become defective (or have become defective due to deterioration over time) can be clearly indicated, allowing maintenance to be performed when necessary, resulting in an extremely reliable backup power supply system.

[0008] FIG. 1 is a configuration diagram of a first embodiment of a power supply device according to an embodiment of the present invention. FIG. 2 is a diagram showing a specific configuration of the first embodiment of a power supply device according to an embodiment of the present invention. FIG. 3 is a configuration diagram of a second embodiment of a power supply device according to an embodiment of the present invention. FIG. 4 is a diagram showing a specific configuration of the second embodiment of a power supply device according to an embodiment of the present invention. FIG. 5 is a diagram showing a specific configuration of the third embodiment of a power supply device according to an embodiment of the present invention.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the description of the embodiments, and various changes and modifications can be made by those skilled in the art within the scope of the technical ideas disclosed in this specification. Furthermore, in all drawings used to explain the present invention, components having the same functions are given the same reference numerals, and repeated explanations thereof may be omitted.

[0010] FIG. 1 shows the overall configuration of a power supply device according to one embodiment of the present invention. The power supply device includes a charging circuit 1, a charging switch 2, an output switch 3, a battery module, a reference voltage source terminal 7, and battery discrimination circuits 21 and 22. The charging circuit 1 charges a secondary battery. The present invention includes a plurality of battery modules, including a first battery module 4 and a second battery module 5 in this example. The first battery module 4 includes a charging diode 8, a current limiting circuit 9, a secondary battery 11, and a discharging diode 10. The second battery module 5 includes a charging diode 14, a current limiting circuit 15, a secondary battery 17, and a discharging diode 16.

[0011] The battery discrimination circuit 21 is composed of a voltage comparator 12 and an alert display device 13. The battery discrimination circuit 22 is composed of a voltage comparator 18 and an alert display device 19. The voltage comparators 12 and 18 compare the voltage of the secondary battery with the voltage of a reference voltage source. The alert display devices 13 and 19 are controlled by the corresponding voltage comparators 12 and 18, respectively. In this embodiment, the alert display devices 13 and 19 may be composed of an LED flashing circuit, an LED lighting circuit, or an LED extinguishing circuit. The negative electrodes of multiple secondary batteries 11 and 17 are connected in common, and the positive electrodes of multiple secondary batteries 11 and 17 are connected to the corresponding voltage comparators 12 and 18, respectively. The load circuit 6 is connected to the output switch 3 of the power supply device. The secondary batteries 11 and 17 may be all-solid-state batteries using a sulfide-based solid electrolyte or all-solid-state batteries using an oxide-based solid electrolyte.

[0012] The operation will be explained below.

[0013] First, we will explain normal operation. Initially, the secondary batteries 11 and 17 are assumed to be normal. The output of the charging circuit 1 charges the secondary batteries 11 and 17 via the charging switch 2, the charging diodes 8 and 14, and the current limiting circuits 9 and 15. The current limiting circuits 9 and 15 are set to a predetermined current limit value, which is 1 / n of the charging current of the charging circuit 1, where n is the number of parallel battery modules 4 and 5 connected in parallel. When charging is completed, the charging switch 2 is turned OFF. When the power supply device requires power supply to the load circuit 6, the output switch 3 is turned ON, and the output current of the secondary battery 11 flows to the load circuit 6 via the discharge diode 10, and the output current of the secondary battery 17 flows to the load circuit 6 via the discharge diode 16. The reference voltage source terminal 7 is set to a voltage approximately equal to the discharge end voltage of the secondary battery 11. During normal use of the power supply device, the output of the voltage comparator 12 causes the LED of the alert display device 13 to remain off and not flash.

[0014] Next, we will explain the operation when secondary battery 17 is normal and secondary battery 11 is internally short-circuited. The output of charging circuit 1 charges secondary battery 17 via charging switch 2, charging diode 14, and current limiting circuit 15. However, because secondary battery 11 is short-circuited, the output current of charging circuit 1 flows through charging diode 8 and current limiting circuit 9, but the voltage of secondary battery 11 is 0 V. At this time, due to the operation of current limiting circuit 9, not all of the charging current from charging circuit 1 flows to the short-circuited secondary battery 11, and charging current is supplied to secondary battery 17, allowing charging of secondary battery 17 to proceed.

[0015] When power is required for the load circuit 6, the output switch 3 is turned on, and the output current of the secondary battery 17 flows to the load circuit 6 via the discharge diode 16. However, when the secondary battery 11 is short-circuited, the discharge diode 10 becomes reverse biased, blocking the flow of current to the secondary battery 11, and current from the secondary battery 17 flows to the load circuit 6. In this way, only the normal secondary battery module operates, but the unit can continue to operate as a backup power source. Since the output voltage of the secondary battery 11 is 0 (V), the output of the voltage comparator 12 activates the alert display device 13, and the LED flashes to indicate that the secondary battery 11 is short-circuited.

[0016] 2 is a diagram showing a specific circuit configuration of the battery determination circuit 21. The battery determination circuit 21 is composed of a reference voltage source terminal 7, a voltage comparator 12, and an alert display device 13. The alert display device 13 is composed of a PNP transistor 101, an NPN transistor 102, a resistor 103, a capacitor 104, and an LED (Light Emitting Diode) 105. The voltage comparator 12 has a P-channel MOS transistor 31. The voltage comparator 12 may also have a diode 32. The voltage comparator 12 of this embodiment has the P-channel MOS transistor 31 and a parasitic diode 32.

[0017] The secondary battery 11 is connected to the gate terminal of the P-channel MOS transistor 31, and the reference voltage source terminal 7 of the reference voltage source is connected to the source terminal of the P-channel MOS transistor. The voltage of the secondary battery 11 is applied to the gate terminal of the P-channel MOS transistor 31, and the voltage of the reference voltage source, i.e., the voltage of the reference voltage source terminal 7, is applied to the source terminal of the P-channel MOS transistor 31. If the voltage of the secondary battery is Vb, the voltage of the reference voltage source is Vref, and the threshold voltage between the gate and source of the P-channel MOS transistor 31 at which the source and drain are conductive is Vth1, then when equation (1) is established, the voltage of the reference voltage source is applied to the alert display device 13. Vref - Vth1 > Vb... (1)

[0018] If the secondary battery 11 is normal, Vb > Vref, so equation (1) does not hold, and power is not supplied to the alert display device. On the other hand, if the secondary battery 11 is short-circuited and becomes 0 (V), equation (1) holds, and the voltage of the reference voltage source is applied to the alert display device 13.

[0019] The voltage of the reference voltage source starts charging the capacitor 104 via resistor 103. When the capacitor 104 is charged and the voltage between the base and emitter of transistor 102 exceeds a predetermined voltage, for example, 0.7 V, the transistor 102 turns on, causing a base current to flow through the transistor 101, which in turn causes a current to flow from the collector of the transistor 101 to the LED 105, causing the LED 105 to light up. After the LED 105 lights up, the charge in the capacitor 104 is discharged, causing the transistor 102 to turn off, and at the same time, the transistor 101 turns off, causing the LED 105 to turn off. After the LED 105 turns off, charging of the capacitor 104 starts again with the input voltage from the reference voltage source via the reference voltage source terminal 7. As described above, the LED 105 flashes repeatedly, functioning as a short-circuit alert for the secondary battery 11.

[0020] 1 and 2 show an example in which two battery modules are connected in parallel, but multiple battery modules can be connected in parallel, with no limit on the number of connections. Furthermore, when multiple modules are connected in parallel to increase the secondary battery capacity, conventional backup operation is possible even if a defective battery occurs, and the presence of a defective battery can be clearly indicated by a flashing LED, making replacement maintenance easier.

[0021] 2, the relationship between the Vth1 of the selected MOS transistor and the Vb of the selected secondary battery is not particularly limited. As an example, when a sulfide-based all-solid-state battery is used as the secondary battery, a MOS transistor with Vth1=1.8 (V) to 2.5 (V) is selected for optimal operation.

[0022] 3 is a diagram showing the overall configuration of a power supply device according to a second embodiment of the present invention. The power supply device comprises a charging circuit 1, a charging switch 2, an output switch 3, a first battery module 4, a second battery module 5, a reference voltage source terminal 7, a battery discrimination circuit 24, and an LED power supply terminal 20. The first battery module 4 comprises a charging diode 8, a current limiting circuit 9, a secondary battery 11, and a discharging diode 10. The second battery module 5 comprises a charging diode 14, a current limiting circuit 15, a secondary battery 17, and a discharging diode 16.

[0023] The battery discrimination circuit 24 is composed of voltage comparators 12 and 18, an alert display device 19, and an OR circuit 23. The load circuit 6 is connected to the output switch 3 of the power supply device. The OR circuit 23 outputs the result of the logical sum of multiple inputs. The outputs of the voltage comparators 12 and 18 are input to the OR circuit 23, and the alert display device 19 is controlled by the OR circuit 23.

[0024] The differences between Fig. 3 and Fig. 1 will be explained below. In Fig. 1, the number of alert display devices is the same as the number of secondary batteries, but in Fig. 3, there is only one alert display device. In other words, the alert display device is configured to operate if at least one of the multiple secondary batteries has a short circuit defect.

[0025] Next, the operation will be described.

[0026] First, normal operation will be described. Initially, the secondary batteries 11 and 17 are assumed to be normal. The output of the charging circuit 1 charges the secondary batteries 11 and 17 via the charging switch 2, charging diodes 8 and 14, and current limiting circuits 9 and 15. When charging is complete, the charging switch 2 turns OFF. When the power supply device needs to supply power to the load circuit 6, the output switch 3 turns ON, and the output current of the secondary battery 11 flows to the load circuit 6 via the discharging diode 10, while the output current of the secondary battery 17 flows to the load circuit 6 via the discharging diode 16. The reference voltage source terminal 7 is set to a voltage approximately equal to or equal to the discharge end voltage of the secondary battery 11. During normal use of the power supply device, the outputs of the voltage comparators 12 and 18 are both low. The OR circuit 23 outputs low, and the LED of the alert display device 19 does not flash but remains off.

[0027] Next, we will explain the operation when secondary battery 17 is normal and secondary battery 11 is internally short-circuited. The output of charging circuit 1 charges secondary battery 17 via charging switch 2, charging diode 14, and current limiting circuit 15. However, because secondary battery 11 is short-circuited, the output current of charging circuit 1 flows through charging diode 8 and current limiting circuit 9, but the voltage of secondary battery 11 is 0 V. At this time, due to the operation of current limiting circuit 9, not all of the charging current from charging circuit 1 flows to the short-circuited secondary battery 11, and charging current is supplied to secondary battery 17, allowing charging of secondary battery 17 to proceed.

[0028] When power is required for the load circuit 6, the output switch 3 is turned on, and the output current from the secondary battery 17 flows to the load circuit 6 via the discharge diode 16. However, if the secondary battery 11 is short-circuited, the discharge diode 10 becomes reverse biased, blocking current flow to the secondary battery 11. Current from the secondary battery 17 flows through the load circuit 6. Thus, only the normal secondary battery module operates, but the unit can continue to function as a backup power source. Since the output voltage of the secondary battery 11 is 0 V, the output of the voltage comparator 12 goes high, causing the output of the OR circuit 23 to go high, activating the alert display device 19 and flashing the LED. This indicates that either the secondary battery 11 or the secondary battery 17 is short-circuited.

[0029] 4 is a diagram showing the specific circuit configuration of the battery determination circuit 24. The battery determination circuit 24 is composed of a reference voltage source terminal 7, voltage comparators 12 and 18, a resistor 106, an OR circuit 23, and an alert display device 19. The alert display device 19 is composed of a PNP transistor 101, an NPN transistor 102, a resistor 103, a capacitor 104, an LED 105, and an LED power supply terminal 20. The voltage comparators 12 and 18 are composed of P-channel MOS transistors 31 and 33 and parasitic diodes 32 and 34. The OR circuit 23 is composed of an N-channel MOS transistor 35 and a parasitic diode 36. The voltages of the secondary batteries 11 and 17 are applied to the gate terminals of the P-channel MOS transistors 31 and 33, and the voltage of the reference voltage source, i.e., the voltage of the reference voltage source terminal 7, is applied to the source terminals of the P-channel MOS transistors 31 and 33. When equation (1) explained in FIG. 2 holds for at least one of the voltage comparators 12 and 18, the voltage of the reference voltage source is applied to the resistor 106, the gate potential of the N-channel MOS transistor 35 becomes High, current flows to the alert display device 19, and the LED 105 blinks.

[0030] If the secondary batteries 11, 17 are normal, then equation (1) does not hold, so the voltage of resistor 106 is at ground potential, the gate potential of N-channel MOS transistor 35 remains low, no current flows to alert display device 19, and LED 105 does not light up. On the other hand, if secondary battery 11 is short-circuited and falls to a 0 (V) state, then equation (1) holds, the gate potential of N-channel MOS transistor 35 becomes high, current flows to alert display device 19, and LED 105 blinks.

[0031] 3 and 4 show an example in which two battery modules are connected in parallel, but multiple battery modules can be connected in parallel, with no limit on the number of connections. Furthermore, connecting multiple modules in parallel to increase secondary battery capacity allows for conventional backup operation even if a defective battery occurs, and the presence of a defective battery can be clearly indicated by a blinking LED, making replacement maintenance easier. Furthermore, the configuration of FIG. 3 is more advantageous than that of FIG. 1 in terms of reducing the cost of the device.

[0032] FIG. 5 shows the overall configuration of a power supply device according to a third embodiment of the present invention. The power supply device comprises a charging circuit 1, a charging switch 2, an output switch 3, a first battery module 4A, a second battery module 5, a third battery module 4B, and a fourth battery module 4C, a reference voltage source terminal 7, a battery discrimination circuit 25, and an LED power terminal 20. The first, third, and fourth battery modules 4A, 4B, and 4C comprise charging diodes 8A, 8B, and 8C, current limiting circuits 9A, 9B, and 9C, secondary batteries 11A, 11B, and 11C, and discharge diodes 10A, 10B, and 10C. The second battery module 5 comprises a charging diode 14, a current limiting circuit 15, a secondary battery 17, and a discharge diode 16. The battery discrimination circuit 25 comprises voltage comparators 12A, 12B, 12C, and 18, an adder circuit 26, and an alert display device 19. The adder circuit 26 adds multiple inputs and outputs the result. The load circuit 6 is connected to the output switch 3 of the power supply device.

[0033] The differences between Fig. 5 and Fig. 3 will be explained below. In Fig. 3, the alert display device is configured to operate when at least one secondary battery among a plurality of secondary batteries has a short circuit defect, whereas in Fig. 5, the alert display device is configured to operate when a set number of secondary batteries among a plurality of secondary batteries have a short circuit defect. Also, in the example of Fig. 5, the number of secondary batteries is explained as four, but there is no limit to the number of connected batteries.

[0034] Next, the operation will be described. When all of the secondary batteries 11A, 11B, 11C, and 17 are normal, the charge and discharge operations are the same as those described above in FIGS. 1 and 3, and therefore a description thereof will be omitted. Furthermore, the operation of the MOS transistors in the voltage comparators 12A, 12B, 12C, and 18 for normal and shorted secondary batteries 11A, 11B, 11C, and 17 is also the same, and therefore a description thereof will be omitted. The difference between FIGS. 5 and 3 is that the OR circuit 23 is replaced by an adder circuit 26, and therefore this operation will be described using FIG. 6.

[0035] 6 is a diagram showing a specific circuit configuration of battery determination circuit 25. Battery determination circuit 25 is composed of reference voltage source terminal 7, voltage comparators 12A, 12B, 12C, and 18, adder circuit 26, and alert display device 19. Adder circuit 26 is composed of input terminals 27A, 27B, 27C, and 28, resistors 30A, 30B, 30C, and 37, an N-channel MOS transistor 29, and a parasitic diode 38.

[0036] Assume that the number of connected secondary batteries is m, and the setting is to make the LED blink when the number of secondary batteries that have experienced a short circuit fault reaches p. If the reference voltage source, i.e., the voltage at reference voltage source terminal 7, is Vref, the threshold voltage of N-channel MOS transistor 29 is Vth2, and the resistance value of resistor 110 is Rb, the above setting can be realized by setting the resistance value Ra of resistors 30A, 30B, 30C, and 37 to satisfy the following: Ra = Rb p (Vref - Vth2) / Vth2 (2)

[0037] Now, assuming m = 4, p = 2, Vth2 = 1.2 (V), and Vref = 2.4 (V), then Ra = 2Rb, and if two of the four secondary batteries short-circuit, the gate potential of N-channel MOS transistor 29 becomes Vth2, causing conduction between the source and drain of N-channel MOS transistor 29, and current flows through alert display device 19, causing LED 105 to flash and indicating maintenance. Furthermore, as a method for charging each secondary battery, they are connected using a series element consisting of a first diode and a current limiting circuit, and the output of the secondary battery is extracted using a second diode. Each secondary battery is provided with a voltage comparison circuit that compares the voltage with a voltage used to determine whether the secondary battery is good or bad, and a circuit that flashes an LED depending on the comparison result.

[0038] In any of the above-described embodiments, even if the charge / discharge characteristics of the secondary battery deteriorate over time, or if a secondary battery that was problem-free at the time of manufacture suddenly becomes unusable due to an internal short circuit or the like, backup power supply operation can be maintained and the need for secondary battery replacement can be clearly indicated, thereby providing a significant advantage in avoiding loss costs in terms of maintenance. An example of an electronic device equipped with the power supply device of the present invention is an absolute encoder used in an industrial robot. The motor (e.g., a servo motor) of the robot's operating axis is equipped with an absolute encoder, and by supplying power to the encoder using this power supply device, motor movement can be constantly monitored even when the controller's power is cut off, enabling smooth startup without a return to the origin when the system is started or when recovering from an emergency stop.

[0039] Furthermore, the technology according to this embodiment can provide a charge / discharge system with excellent energy efficiency, which contributes to the achievement of "9. Build resilient infrastructure, promote inclusive and sustainable industrialization, promote inclusive and sustainable technological development, and make sustainable use of resources" and "11. Make cities and towns sustainable and livable" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0040] Although various embodiments have been described above in detail, the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments are detailed descriptions of the entire system in order to clearly explain the present invention, and the present invention is not necessarily limited to a system including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0041] 1... Charging circuit, 11, 17... Secondary battery, 12, 18... Voltage comparator, 13, 19... Alert display device, 9, 15... Current limiting circuit, 8, 14... Charging diode, 10, 16... Discharging diode, 23... OR circuit, 26... Adding circuit

Claims

1. A power supply device comprising: a secondary battery; a reference voltage source; a charging circuit that charges the secondary battery; a voltage comparator that compares the voltage of the secondary battery with the voltage of the reference voltage source; and an alert display device controlled by the voltage comparator.

2. A power supply device according to claim 1, comprising a plurality of said secondary batteries, and comprising a plurality of voltage comparators and a plurality of alert display devices corresponding to said plurality of secondary batteries, wherein the negative terminals of said plurality of secondary batteries are commonly connected, and a corresponding voltage comparator is connected to the positive terminal of each of said plurality of secondary batteries, and wherein each of said plurality of alert display devices is controlled by a corresponding voltage comparator.

3. A power supply device according to claim 2, wherein each of said plurality of secondary batteries constitutes a battery module together with a charging diode, a current limiting circuit and a discharging diode.

4. A power supply device according to any one of claims 1 to 3, wherein the voltage comparator is composed of a P-channel MOS transistor, the secondary battery is connected to the gate terminal of the P-channel MOS transistor, and the reference voltage source is connected to the source terminal of the P-channel MOS transistor.

5. A power supply device comprising: a plurality of secondary batteries; a reference voltage source; an OR circuit that outputs the result of a logical sum for a plurality of inputs; a plurality of voltage comparators that compare the voltage of the secondary batteries with the voltage of the reference voltage source; and a charging circuit that charges the plurality of secondary batteries, wherein the negative terminals of the plurality of secondary batteries are connected in common and the plurality of voltage comparators are independently connected to the positive terminals of the plurality of secondary batteries, the outputs of the plurality of voltage comparators are input to the OR circuit, and the power supply device is configured as an alert display device controlled by the OR circuit.

6. A power supply device according to claim 5, wherein the voltage comparator is composed of a P-channel MOS transistor, the secondary battery is connected to the gate terminal of the P-channel MOS transistor, and the reference voltage source is connected to the source terminal of the P-channel MOS transistor, and the OR circuit is composed of a first resistor and an N-channel MOS transistor, the first resistor is connected between the gate terminal and source terminal of the N-channel MOS transistor, and the drain terminals of the multiple P-channel MOS transistors are connected to the gate terminal of the N-channel MOS transistor.

7. A power supply device comprising: a plurality of secondary batteries; a reference voltage source; an adder circuit that outputs an addition result for a plurality of inputs; a plurality of voltage comparators that compare the voltage of the secondary batteries with the voltage of the reference voltage source; and a charging circuit that charges the plurality of secondary batteries, wherein the negative terminals of the plurality of secondary batteries are connected in common and the plurality of voltage comparators are independently connected to the positive terminals of the plurality of secondary batteries, the outputs of the plurality of voltage comparators are input to the adder circuit, and the power supply device is configured as an alert display device controlled by the adder circuit.

8. A power supply device according to claim 7, wherein the voltage comparator is composed of a P-channel MOS transistor, the secondary battery is connected to the gate terminal of the P-channel MOS transistor, and the reference voltage source is connected to the source terminal of the P-channel MOS transistor, and the adder circuit is composed of a second resistor, a plurality of third resistors, and an N-channel MOS transistor, the second resistor is connected between the gate terminal and source terminal of the N-channel MOS transistor, and the plurality of third resistors are connected between the drain terminals of the plurality of P-channel MOS transistors and the gate terminal of the N-channel MOS transistor.

9. The power supply device according to claim 8, wherein the plurality of secondary batteries are all-solid-state batteries using a sulfide-based solid electrolyte.

10. A power supply device according to claim 8, wherein the plurality of secondary batteries are all-solid-state batteries using an oxide-based solid electrolyte.

11. Electronic equipment comprising: a motor; an absolute encoder; a plurality of secondary batteries; a reference voltage source; an OR circuit that outputs the result of a logical sum for a plurality of inputs; a plurality of voltage comparators that compare the voltage of the secondary batteries with the voltage of the reference voltage source; and a charging circuit that charges the plurality of secondary batteries; wherein the negative terminals of the plurality of secondary batteries are commonly connected, the plurality of voltage comparators are independently connected to the positive terminals of the plurality of secondary batteries, the outputs of the plurality of voltage comparators are input to the OR circuit, and a power supply device is configured with an alert display device controlled by the OR circuit; the rotating shaft of the motor and the input shaft of the absolute encoder are mechanically connected, and the power supply device is connected to the power terminal of the absolute encoder.

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