Backup power supply device and electronic apparatus

Abstract

When performing a backup operation of a semiconductor memory by using a primary battery and a secondary battery in combination by diode coupling, it is difficult to preferentially consume the secondary battery and to obtain a desired backup period. The present invention is configured such that a circuit for electronically switching between a primary battery and a secondary battery is provided, and the backup of the primary battery is started after almost full consumption of the secondary battery.

Description

Backup Power Supplies and Electronic Equipment

[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, in order to preserve the information stored in the semiconductor memory even if the main power source is lost, it is common to install a circuit that backs up the semiconductor memory using a power source other than the main power source, such as a primary battery, as a backup power source. When using a primary battery for backup, alkaline batteries, lithium batteries, etc. are generally used, but when using alkaline batteries, they must be replaced periodically (approximately every year).

[0003] When lithium batteries are used, there is little self-discharge over the long term, but if the device is stopped for several periods per year, the battery will be consumed and there is a concern that the battery capacity will decrease, so it becomes necessary to check the remaining battery charge periodically, and maintenance work will be required approximately every three years. To solve this problem, a method is used in which a backup system is created using secondary batteries in addition to the battery.

[0004] When a secondary battery is used, the secondary battery is charged by an external power source during normal use, and when the power is off, the secondary battery is used to back up the semiconductor memory, and when the voltage of the secondary battery drops, the backup operation is performed using the primary battery.Technology for performing backup operation using a combination of a primary battery and a secondary battery is described, for example, in Patent Document 1 and Patent Document 2 listed below, in which the voltage output side of the primary battery is connected to the semiconductor memory to be backed up via a diode, and the voltage output side of the secondary battery is also connected via a diode, and the voltage of the secondary battery is set slightly higher than the voltage of the primary battery.

[0005] JP-A No. 63-77335 JP-A No. 8-265990

[0006] However, in the disclosure of Patent Document 1, the voltage output side of the primary battery is connected to the semiconductor memory to be backed up via a diode, and the voltage output side of the secondary battery is also connected via a diode, making it difficult to prioritize power consumption from the secondary battery. To achieve this, the voltage difference between the primary battery voltage and the secondary battery voltage must be greater than or equal to the forward voltage (hereinafter abbreviated as VF) of the diode used. If the voltage difference is less than VF, power from both the primary battery and the secondary battery will be consumed during backup, resulting in a first problem in that the desired backup period cannot be achieved.

[0007] Furthermore, the operating voltage of semiconductor memory generally falls within a range of 2.7 (V) to 3.6 (V), with primary batteries having a nominal voltage of 3.0 (V) for lithium batteries and long-life thionyl chloride lithium batteries having a nominal voltage of 3.65 (V), and secondary batteries having a nominal voltage of 1.2 (V) for nickel-metal hydride batteries and 3.7 (V) for lithium-ion batteries, posing a second problem in that it is difficult to set the optimal combination for semiconductor memory, taking into account the voltage drop due to VF.

[0008] In order to solve the first problem, one embodiment of the present invention is configured to provide a circuit that electronically switches between a primary battery and a secondary battery, and to start backup using the primary battery only after the secondary battery has been almost completely consumed.

[0009] In addition, to solve the second problem, a voltage conversion circuit is provided so that the backup voltage of the semiconductor memory can be set independently of the voltages of the primary and secondary batteries, thereby obtaining the advantages of using both a primary battery and a secondary battery.

[0010] According to the present invention, by using a battery with an appropriate capacity and at an appropriate price, it is possible to perform battery backup of a semiconductor memory for a long period of time without replacing the battery.

[0011] FIG. 1 is a configuration diagram of a first embodiment of a backup 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 backup power supply device according to an embodiment of the present invention. FIG. 3 is a diagram showing a specific configuration of a second embodiment of a backup power supply device according to an embodiment of the present invention. FIG. 4 is a diagram showing a configuration diagram of a third embodiment of a backup 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 backup power supply device according to an embodiment of the present invention.

[0012] 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.

[0013] A typical backup power supply refers to an uninterruptible power supply such as a UPS (Uninterruptible Power Supply) for maintaining the operation of the entire system, but the backup power supply in this embodiment is a power supply that backs up the power supply for part of the device in order to prevent the loss of position information data when the system stops from retaining data in semiconductor memory or information from encoders and the like for determining the position of mechanically operating devices when the system suddenly stops from operating or stops due to equipment maintenance, etc.

[0014] 1 is a diagram showing the overall configuration of a backup power supply according to one embodiment of the present invention. Electronic equipment 9 includes a system power supply 10, a diode 12, a semiconductor memory 11, a semiconductor memory power terminal 19, a power output terminal 13 for charging the power terminal, and a backup power input terminal 14. Electronic equipment 9 has system power supply 10 therein, which outputs a voltage of, for example, 3.6 (V) to drive semiconductor memory 11. Backup power input terminal 14 is connected to semiconductor memory power terminal 19 via diode 12.

[0015] A voltage lower than that of the semiconductor memory power terminal 19, for example, a voltage of 3.5 (V), is input to the backup power input terminal 14. The backup power supply device 1 comprises a secondary battery 3, a primary battery 4, a battery selection circuit 5, a voltage conversion circuit 6, a power input terminal 7, and a backup output terminal 8. The backup power supply device 1 further comprises a charging circuit 2. The secondary battery 3 is a sulfide-based all-solid-state battery. The primary battery 4 is a lithium battery. The battery selection circuit 5 has a secondary battery input terminal (first input terminal) 15, a primary battery input terminal (second input terminal) 17, a selected voltage output terminal (output terminal) 18, and a common ground terminal 16.

[0016] Specifically, the battery selection circuit 5 is configured such that a diode is connected between the secondary battery input terminal 15 and the output terminal 18, and the source terminals of a plurality of series-connected P-channel MOS transistors with a common drain connection are connected between the primary battery input terminal 17 and the output terminal 18. The secondary battery 3 is connected to the secondary battery input terminal 15, which is the first input terminal, and the primary battery 4 is connected to the primary battery input terminal 17, which is the second input terminal. The voltage conversion circuit 6 converts the voltage selected by the battery selection circuit 5 into a predetermined voltage.

[0017] Next, the operation will be described. When the electronic device 9 is operating, a predetermined voltage is supplied from the power input terminal 7 of the backup power supply 1 to the charging circuit 2, which charges the secondary battery 3. During charging, the voltage supplied from terminal 15 of the battery selection circuit 5 is output to terminal 18, and then, via the voltage conversion circuit 6, a voltage of, for example, 3.5 (V) is output to terminal 8.

[0018] When the electronic device 9 is not operating and there is power held in the secondary battery 3, the charging circuit 2 does not perform a charging operation, and the voltage of the secondary battery supplied from terminal 15 of the battery selection circuit 5 is output to terminal 18, and the voltage is output via the voltage conversion circuit 6 to terminal 8. When the electronic device 9 is not operating and there is almost no power held in the secondary battery 3, the power input terminal 7 of the backup power supply 1 outputs the voltage of the primary battery supplied from terminal 17 of the battery selection circuit 5 to terminal 18, and the voltage is output via the voltage conversion circuit 6 to terminal 8.

[0019] When electronic device 9 is not operating, the 3.5 V supplied from terminal 14 is reduced by the voltage drop VF of diode 12, and if VF=0.7 V, for example, 2.8 V is supplied to semiconductor memory 11, preventing data loss in the semiconductor memory. A specific configuration example and operation of battery selection circuit 5 will be described in detail using FIG. 2.

[0020] 2 is a diagram showing the specific configuration of a first embodiment of a charging device according to the present invention. Battery selection circuit 5 is composed of resistors 21, 22, 23, and 24, a diode 25, and P-channel MOS transistors 26, 27, and 28. Next, the voltage selection operation will be described.

[0021] When the secondary battery 3 has stored power, the voltage of the secondary battery input from terminal 15 is output to terminal 18 via diode 25. The voltage of terminal 15 is divided by resistors 21 and 22 and input to the gate terminal of P-channel MOS transistor 28. On the other hand, the voltage of the primary battery 4 input from terminal 17 is divided by resistors 23 and 24 and input to the source terminal of P-channel MOS transistor 28.

[0022] If the threshold voltage of P-channel MOS transistor 28 is Vth for the selected voltages of secondary battery 3 and primary battery 4, and the potential difference between the source terminal and gate terminal is set to be smaller than Vth, P-channel MOS transistor 28 will remain in the off state, and the gate voltage and source voltage of P-channel MOS transistor 26 will be the same value via resistor 23, so P-channel MOS transistors 26 and 27 will be in the off state.

[0023] As a result, terminals 17 and 18 are disconnected, and a voltage lower than the voltage of the secondary battery 3 by the forward voltage of diode 25 is output to terminal 18. When there is no power held by the secondary battery 3, the secondary battery voltage input from terminal 15 is low. The voltage at the gate terminal of P-channel MOS transistor 28, divided by resistors 21 and 22, drops, and the potential difference between this voltage and the source terminal of P-channel MOS transistor 28, divided by resistors 23 and 24, is greater than Vth, so P-channel MOS transistor 28 is turned on and current flows through resistor 23.

[0024] Due to the voltage drop, the difference between the gate voltage and source voltage of P-channel MOS transistor 26 becomes larger than Vth, turning on P-channel MOS transistors 26 and 27. As a result, a conductive state is established between terminal 17 and terminal 18, and the voltage of primary battery 4 is output to terminal 18.

[0025] 3 is a diagram showing a specific configuration of a second embodiment of a charging device according to the present invention. Battery selection circuit 5 is composed of resistors 30, 31, 32, and 33, and P-channel MOS transistors 34, 35, 36, 37, and 38. Specifically, battery selection circuit 5 includes a first series element and a second series element, each of which is formed by connecting two independent sets of two P-channel MOS transistors in series with their drains connected in common.

[0026] The secondary battery input terminal or first input terminal 15 is connected to output terminal 18 through the source terminal of the first series element, and the primary battery input terminal or second input terminal 17 is connected to output terminal 18 through the source terminal of the second series element. Next, the voltage selection operation will be explained. When there is storage power in the secondary battery 3, the secondary battery voltage input from terminal 15 is applied between the source and gate terminals of P-channel MOS transistor 34, so that P-channel MOS transistors 34 and 35 are turned on and output to terminal 18.

[0027] The voltage at terminal 15 is divided by resistors 30 and 31 and input to the gate terminal of P-channel MOS transistor 38. Meanwhile, the voltage of the primary battery 4 input from terminal 17 is divided by resistors 32 and 33 and input to the source terminal of P-channel MOS transistor 38. If the threshold voltage of P-channel MOS transistor 38 is Vth for the selected voltages of the secondary battery 3 and primary battery 4, and the potential difference between the source terminal and gate terminal is set to be smaller than Vth, P-channel MOS transistor 38 will remain off, and the gate voltage and source voltage of P-channel MOS transistor 36 will be the same value via resistor 32, so P-channel MOS transistors 36 and 37 will be off.

[0028] As a result, terminal 17 is disconnected from terminal 18, and the voltage of the secondary battery 3 is output to terminal 18. If there is no power held by the secondary battery 3, the voltage of the secondary battery input from terminal 15 becomes low. The voltage at the gate terminal of P-channel MOS transistor 38, which is divided by resistors 30 and 31, drops, and the potential difference between this and the source terminal of P-channel MOS transistor 38, which is divided by resistors 32 and 33, becomes greater than Vth, so P-channel MOS transistor 38 turns on and current flows through resistor 32.

[0029] Due to the voltage drop, the difference between the gate voltage and the source voltage of the P-channel MOS transistor 36 becomes larger than Vth, turning on the P-channel MOS transistors 36 and 37. As a result, the connection between terminals 17 and 18 becomes conductive, and the voltage of the primary battery 4 is output to terminal 18.

[0030] The embodiment of FIG. 3 has more parts than the embodiment of FIG. 2, but has the advantage that there is no voltage drop due to the diode 25 and therefore there is less power loss.

[0031] 4 is a diagram showing the overall configuration of a backup power supply according to a third embodiment of the present invention. Backup power supply 1 comprises a charging circuit 2, a secondary battery 3, a primary battery 4, a battery selection circuit 20, a voltage conversion circuit 6, a power input terminal 7, and a backup output terminal 8. Battery selection circuit 20 comprises a secondary battery input terminal 15, a primary battery input terminal 17, a selected voltage output terminal 18, a common ground terminal 16, and a system power input terminal 29. Operation will now be described. When electronic device 9 is operating via power input terminal 7 of backup power supply 1, a predetermined voltage is supplied to charging circuit 2, which charges secondary battery 3.

[0032] During charging, the voltage supplied from terminal 29 of battery selection circuit 20 is output to terminal 18, and for example, 3.5 (V) is output to terminal 8 via voltage conversion circuit 6. When electronic device 9 is not in operation and there is retained power in secondary battery 3, the charging operation of charging circuit 2 is not performed, and secondary battery voltage supplied from terminal 15 of battery selection circuit 20 is output to terminal 18, and the voltage is output to terminal 8 via voltage conversion circuit 6.

[0033] When the electronic device 9 is not operating and there is almost no power stored in the secondary battery 3, the voltage of the primary battery supplied from terminal 17 of the battery selection circuit 20 is output to terminal 18 and then output to terminal 8 via the voltage conversion circuit 6. When the electronic device 9 is not operating, the voltage of 3.5 (V) supplied from terminal 14 is reduced by the voltage drop VF of the diode 12, and if VF = 0.7 (V), for example, 2.8 (V) is supplied to the semiconductor memory 11, preventing data loss in the semiconductor memory. A specific configuration example and operation of the battery selection circuit 20 will be described in detail using Figure 5.

[0034] 5 is a diagram showing a specific configuration of a third embodiment of a charging device according to the present invention. Battery selection circuit 20 is composed of resistors 40, 41, 42, 43, 44, 45, 46, and 47, diode 48, and P-channel MOS transistors 49, 50, 51, 52, 53, and 54. The voltage selection operation will now be described. When system power is input from terminal 29, the system power voltage is output to terminal 18 via diode 48. The voltage at terminal 29 is divided by resistors 40 and 41 and input to the gate terminal of P-channel MOS transistor 53.

[0035] Meanwhile, the voltage of the secondary battery 3 input from terminal 15 is divided by resistors 44 and 45 and input to the source terminal of P-channel MOS transistor 53. If the threshold voltage of P-channel MOS transistor 28 is Vth for the selected primary battery 4 and system power supply voltage, and the potential difference between the source terminal and gate terminal is set to be smaller than Vth, P-channel MOS transistor 53 will remain off, and the gate voltage and source voltage of P-channel MOS transistor 49 will be the same value via resistor 44, so P-channel MOS transistors 49 and 50 will be off.

[0036] Similarly, by setting the voltage division values ​​of the resistors 42 and 43 and the resistors 46 and 47, the P-channel MOS transistors 51 and 52 can be turned off.

[0037] When the system power supply is cut off and there is retained power in the secondary battery 3, the voltage of the secondary battery input from terminal 15 turns on P-channel MOS transistor 53, so that it is applied between the source terminal and gate terminal of P-channel MOS transistor 49, turning on P-channel MOS transistors 49 and 50, and output to terminal 18. The voltage at terminal 15 is divided by resistors 42 and 43 and input to the gate terminal of P-channel MOS transistor 54.

[0038] Meanwhile, the voltage of the primary battery 4 input from terminal 17 is divided by resistors 46 and 47 and input to the source terminal of P-channel MOS transistor 54. If the threshold voltage of P-channel MOS transistor 54 is Vth for the selected voltages of the secondary battery 3 and primary battery 4, and the potential difference between the source terminal and gate terminal is set to be smaller than Vth, P-channel MOS transistor 54 will remain off, and the gate voltage and source voltage of P-channel MOS transistor 51 will be the same value via resistor 46, so P-channel MOS transistors 51 and 52 will be off. As a result, terminals 17 and 18 are cut off, and the voltage of the secondary battery 3 will be output to terminal 18.

[0039] When the system power supply is cut off and there is no power held by the secondary battery 3, the secondary battery voltage input from terminal 15 drops. The voltage at the gate terminal of P-channel MOS transistor 54, divided by resistors 42 and 43, drops, and the potential difference between this voltage and the source terminal of P-channel MOS transistor 54, divided by resistors 46 and 47, becomes greater than Vth, turning P-channel MOS transistor 54 on and allowing current to flow through resistor 46. The voltage drop causes the difference between the gate and source voltages of P-channel MOS transistor 51 to exceed Vth, turning P-channel MOS transistors 51 and 52 on. As a result, conduction is established between terminals 17 and 18, and the voltage of the primary battery 4 is output to terminal 18.

[0040] The embodiment of FIG. 5 has a greater number of parts than the embodiment of FIG. 3, but has the advantage that a stable voltage can always be supplied to the backup power supply input terminal 14 in the event of a momentary interruption in the electronic device 9, even when the secondary battery 3 is insufficiently charged.

[0041] An example of an electronic device 9 equipped with a backup power supply is an absolute encoder used in an industrial robot. The motor (e.g., servo motor) of the robot's operating axis is equipped with an absolute encoder, and by supplying a backup voltage to the encoder using a battery or the like, the movement of the motor is constantly monitored even when the power to the controller is cut off, enabling smooth startup without returning to the origin when the system is started or when recovering from an emergency stop.

[0042] In any of the above-described embodiments, since the battery switching circuit is included, during short-term backups, such as during power outages in ordinary electronic devices, the stored power of the secondary battery can be used to reduce consumption of the primary battery, making it possible to provide backup power for as long as 10 years using a long-life primary battery. Furthermore, since a voltage conversion circuit is used, there is no need to consider the battery voltage when combining primary and secondary batteries, making it possible to optimize battery price and availability, which is a significant advantage.

[0043] 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 innovation and foster resilience" and "11. Make cities and towns inclusive and sustainable" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0044] 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.

[0045] REFERENCE SIGNS LIST 1... backup power supply device, 2... charging circuit, 3... secondary battery, 4... primary battery, 5... battery selection circuit, 6... voltage conversion circuit

Claims

1. A backup power supply device comprising: a primary battery; a secondary battery; a battery selection circuit that selects the voltage of the primary battery or the secondary battery; and a voltage conversion circuit that converts the selected voltage of the battery selection circuit into a predetermined voltage.

2. A backup power supply device according to claim 1, wherein the battery selection circuit comprises a first input terminal, a second input terminal, and an output terminal, the first input terminal and the output terminal being connected by a diode, and the second input terminal and the output terminal being connected by the source terminals of two P-channel MOS transistors connected in series with a common drain connection.

3. A backup power supply device according to claim 2, wherein the secondary battery is connected to the first input terminal, and the primary battery is connected to the second input terminal.

4. A backup power supply device according to claim 1, wherein the battery selection circuit has a first input terminal, a second input terminal, and an output terminal, and includes a first series element and a second series element, each of which is formed by connecting two independent sets of P-channel MOS transistors in series with their drains connected in common, and the first input terminal and the output terminal are connected via the source terminal of the first series element, and the second input terminal and the output terminal are connected via the source terminal of the second series element.

5. A backup power supply device according to claim 2 or 4, wherein the battery selection circuit is configured as a circuit that gives priority to selecting the secondary battery.

6. A backup power supply device according to claim 1, wherein the primary battery and the secondary battery are configured to have different voltages.

7. A backup power supply device according to claim 6, wherein the primary battery is a lithium battery, and the secondary battery is a sulfide-based all-solid-state battery.

8. A backup power supply device comprising: a primary battery; a secondary battery; a power supply circuit that inputs a voltage to a charging circuit that charges the secondary battery; a battery selection circuit that selects the voltage of the power supply circuit, the primary battery, and the secondary battery; and a voltage conversion circuit that converts the voltage selected by the battery selection circuit into a predetermined voltage.

9. A backup power supply device according to claim 8, wherein the battery selection circuit is configured as a circuit that selects the power supply circuit, the secondary battery, and the primary battery in that order with priority.

10. An electronic device comprising: a motor; an absolute encoder; a primary battery; a secondary battery; a battery selection circuit that selects the voltage of the primary battery and the secondary battery; and a voltage conversion circuit that converts the voltage selected by the battery selection circuit into a predetermined voltage, wherein the rotating shaft of the motor and the input shaft of the absolute encoder are mechanically connected, and the voltage conversion circuit is connected to a power supply terminal of the absolute encoder.

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