Overdischarge protection circuit and mobile terminal having the same

Abstract

To delay a time until a secondary battery reaches overdischarge due to reduction of a power consumption by a load connected to the secondary battery.SOLUTION: An overdischarge protection circuit comprises: a bidirectional connection control unit 111 that is provided between a secondary battery 130 and a load 120 and is capable of switching between connection and disconnection, and a connection switching unit 112 that switches between connection and disconnection of the bidirectional connection control unit 111. The connection switching unit 112 switches between the connection and the disconnection of the bidirectional connection control unit 111 according to detection results from a voltage detection unit 114 that sets a circuit operation voltage of the load 120 as a threshold value and a charge detection unit 113 that detects a charge voltage to the secondary battery 130.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an over-discharge protection circuit that protects a rechargeable battery that serves as a voltage source for a power supply circuit from over-discharge, and to a mobile terminal having such an over-discharge protection circuit. [Background technology]

[0002] Traditionally, mobile devices have used power supply circuits that use lithium-ion batteries as a voltage source. These rechargeable batteries are small, lightweight, and have a large energy capacity, making them ideal for mobile use. However, lithium-ion batteries are prone to degradation due to several factors. When they degrade, they can lead to disadvantages such as poor charging characteristics, increased charging frequency, and reduced battery capacity, and in the worst case, even fire. One cause of degradation is overdischarge, and even when stored for long periods of time, lithium-ion batteries can deteriorate due to the breakdown of the electrolyte (calendar degradation) caused by stresses such as temperature changes and high SOC (State of Charge). This can cause the battery to become unable to charge or discharge, even when unused. To address this issue, some devices feature circuitry designed to safely use rechargeable batteries and prevent degradation. It is also recommended to store batteries at half their charge capacity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5481327 Summary of the Invention [Problem to be solved by the invention]

[0004] However, portable devices, which are desired to be compact, use small lithium-ion batteries, which have a low charge capacity and a short period during which the recommended charge capacity can be maintained, which can lead to over-discharge during long-term storage and make it impossible to start the portable device when in use. For this reason, methods have been proposed that use the operating voltage of a circuit implemented in the portable device as a threshold, and disconnect the lithium-ion battery and load as soon as the internal logic detects the set threshold, thereby extending the time until the battery reaches a deep discharge state, as well as a technology disclosed in Patent Document 1 that restores connection from disconnection by pressing a physical switch, but this requires pressing the switch every time the battery is charged. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention sets the operating voltage of the circuit as a threshold, and as soon as the voltage detector detects it, it disconnects the power supply circuit from the load section, delaying the occurrence of over-discharge by reducing the load, and to restore the connection between the battery and the load, it charges the battery using power supply from an external terminal as a trigger, and enables power supply to the load circuit. [Effects of the Invention]

[0006] According to the present invention, power consumption by the load connected to the secondary battery is reduced below the circuit operating voltage, making it possible to delay the time until the secondary battery is over-discharged. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a block diagram illustrating a configuration illustrating an embodiment of the present invention; [Figure 2] 3 is a schematic circuit diagram of an overcurrent protection unit illustrating an embodiment of the present invention; FIG. [Figure 3] 1 is a flowchart illustrating the flow of an overcurrent protection process according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote common elements throughout the drawings. However, the present invention is not limited to these embodiments.

[0009] Example 1 Figure 1 is a block diagram of a mobile terminal equipped with an over-discharge protection system according to a first embodiment of the present invention. The mobile terminal has a power supply circuit that uses a rechargeable secondary battery, and Figure 1 shows components related to the over-discharge protection system and the power supply circuit. In this embodiment, the secondary battery is a lithium-ion battery 130.

[0010] The over-discharge protection system is mainly composed of an over-discharge protection circuit 110 and an MCU 121 (Micro Controller Unit). The load 120 has the MCU 121 connected to a display unit 122 and a low-voltage detection unit 123, and the display content can be changed under the control of the MCU 121. One example of the display content is a drop in the supply voltage of the battery 130 detected by the low-voltage detection unit 123. In this embodiment, a voltage detector is used for the low-voltage detection unit 123, but it is preferable to use the ADC (Analog-Digital Converter) function of the MCU, and it is even more preferable to use an IC such as an ADC with high resolution and low detection error.

[0011] The over-discharge protection circuit 110 has a bidirectional connection control unit 111 that is disposed in the path between the battery 130 and the charging control unit 150 and that cuts off the connection of the path, a connection switching unit 112 that controls switching of the connection and cut-off of the bidirectional connection control unit 111, and a charging detection unit 113 and a voltage detection unit 114 that serve as criteria for the switching control by the connection switching unit 112. The charging detection unit 113 is connected to a power supply terminal of the charging connector 140, and the voltage detection unit 114 is connected to the battery 130.

[0012] The battery 130 has a built-in temperature detection element 131, which is connected to the MCU 121. In this embodiment, the charging connector 140 to which the charging control unit 150 is connected uses USB Type-C. The charging control unit 150 sets the amount of power to be supplied via the charging connector 140 and an external terminal, and therefore has a function as a USB CC controller that operates the CC terminal of the USB Type-C. The power supplied from the outside via the charging connector 140 and set at the CC terminal can be used to charge the battery and as a drive voltage source for the load 120.

[0013] Normally, if the charge capacity of battery 130 is equal to or greater than a certain level, battery 130 serves as a voltage source to drive load 120 via bidirectional connection control unit 111 and charging control unit 150. As a countermeasure against noise contained in the power supplied from the external terminal, inrush current when charging connector 140 is connected, and static electricity in particular in the case of USB, it is preferable to place a noise reduction element such as a capacitor or a protection element such as a Zener diode in the path between charging connector 140 and charging control unit 150.

[0014] Charging control unit 150 has bidirectional input and output paths, and switches the direction when switching between charging battery 130 and functioning as a power supply using battery 130 as a voltage source. When power is being supplied from an external terminal connected to charging connector 140, power supplied from the external terminal is output by charging control unit 150 to bidirectional connection control unit 111, and bidirectional connection control unit 111, which has been set to connection by connection switching unit 112, enables charging of battery 130 and supply of power to load 120.

[0015] Furthermore, if there is no connection to the external terminal or no power supply and the voltage that can be supplied from the battery 130 is equal to or greater than a threshold value, the connection switching unit 112 sets the bidirectional connection control unit 111 to a connected state, and the power input to the charging control unit 150 is supplied to the load 120 from the battery 130 via the bidirectional connection control unit 111.

[0016] After the load 120 receives power supply via the charging control unit 150 and the MCU 121 starts up, it transitions to a standby state, and when the power switch 161 is pressed it transitions to an active state and becomes capable of receiving input from the external input 162. The MCU 121 causes the display unit 122 to display the results of communication with the external input 162, the charging state, and the remaining charge of the battery 130.

[0017] The over-discharge protection circuit 110 will be described in detail with reference to Fig. 2. As described in Fig. 1, the over-discharge protection circuit 110 includes a bidirectional connection control unit 111, a connection switching unit 112, a voltage detection unit 114, and a charge detection unit 113.

[0018] In order to disconnect the path between the charging control unit 150 and the battery 130, in this embodiment, a bidirectional connection control unit 111 is configured in which the sources of FET 212 and FET 215, which use Pch-FETs, are connected to each other, and the drain side of FET 212 is connected to the positive electrode of the battery 130, and the drain side of FET 215 is connected to the charging control unit 150.

[0019] In this embodiment, an Nch-FET FET217 is arranged as connection switching unit 112 that switches the connection and disconnection of bidirectional connection control unit 111. The drain side of FET 217 is connected to the gates of FET 212 and FET 215. When the voltage applied to the gate of FET 217 is low, no current flows between the drain and source, and the gates and sources of FET 212 and FET 215 are at the same potential, so no current flows between the drain and source of either, and the charging control unit 150 and battery 130 are disconnected.

[0020] When the voltage applied to the gate of FET217 becomes high, a current flows between the drain and source of FET217, and the gates of FET212 and FET215 fall to low, causing a current to flow between the drain and source of FET212 and FET215, connecting the battery 130 and the charging control unit 150.

[0021] When the voltage applied to the gate of FET 217 is the voltage of either voltage detection unit 114 or charge detection unit 113, FET 212 and FET 215 are turned ON, so that the battery 130 and charge control unit 150 are connected. When the voltage of neither voltage detection unit 114 nor charge detection unit 113 is applied, FET 212 and FET 215 are turned OFF, so that the battery 130 and charge control unit 150 are disconnected.

[0022] It is preferable that the voltage detection unit 114 uses a highly accurate IC with little detection error, such as a voltage detector, and directly monitors the battery voltage.

[0023] Furthermore, the charging detection unit 113 monitors the voltage supplied to the charging connector 140 and detects the connection of the external terminal. In this embodiment, the charging detection unit 113 monitors the VBUS of the USB Type-C.

[0024] A two-input OR circuit 290, which is made up of two diodes and also functions as a protection element, is disposed on the path connecting the voltage detection circuit 114, the charge detection circuit 113, and the bidirectional connection control circuit 111. The output side of the two-input OR circuit 290 is connected to the gate of the FET 217.

[0025] One input of the two-input OR unit 290 is connected to VBUS of the charging connector 140 (USB). One input of the two-input OR unit 290 is connected to the charging detection unit 113, which makes it possible to prevent unintended operation caused by mistakenly believing that power is being supplied from an external terminal due to power supply from the battery 130 to the VBUS path even when there is no power supply from an external terminal or when no external terminal is connected, and by arranging the two-input OR unit 290 made up of two diodes, it is possible to protect the battery 130 from static electricity and inrush current generated when an external terminal connected to the charging connector 140, for example, when a USB terminal is connected or disconnected.

[0026] Returning to the explanation of FIG. 1, if the voltage supplied from the battery 130 is equal to or higher than the circuit operating voltage of the load 120, the voltage detection unit 114 outputs HIGH, turns on FET 217, puts the bidirectional connection control unit 111 into a connected state, and connects the load 120 and the battery 130. If the voltage supplied from the battery 130 is equal to or lower than the circuit operating voltage, it outputs LOW. If the output of the charge detection unit 113 is also LOW, the FET 217 turns off, puts the bidirectional connection control unit 111 into a cutoff state, disconnects the load 120 and the battery 130, and reduces the power applied to the load 120 by the power supplied from the battery 130. In other words, power consumption is reduced, and it is possible to delay the time until over-discharge occurs.

[0027] Furthermore, charge detection unit 113 normally outputs LOW, and outputs HIGH only when the external terminal is connected to charge connector 140 and charge supply is detected, thereby turning on FET 217, which turns on FET 217 and places bidirectional connection control unit 111 in a connected state. In this way, in this embodiment, connection control between load 120 and battery 130 is possible without requiring any operation other than connecting the external terminal to charge connector 140.

[0028] Next, the flow of overcurrent protection will be explained using the flowchart in Figure 3. Note that this flowchart is not limited to an operation flowchart in the control unit, and some steps are executed as circuit processing.

[0029] Step S1 shows the operation of the connection switching unit 112. If neither of the two conditions of step S1a that power is being supplied to the charging connector 140 from an external terminal, or step S1b that the battery voltage is equal to or higher than the threshold circuit operating voltage, is met, step S3 unblocks the bidirectional path, i.e., FET212 and FET215 are turned ON, and the output of the battery 130 is supplied to the charging control unit 150.

[0030] If step S1a is satisfied, the process proceeds to step S1c, where battery charging is performed, before proceeding to step S3. The battery is charged using power supplied from an external terminal connected to charging connector 140 as a power source.

[0031] In step S4, if the battery voltage meets the threshold value and there is no power supply from the external terminal as determined in steps S1a and S1b, the circuit is driven by the battery voltage. If the charging connector 140 is connected, the battery is charged and the circuit is driven using the power supplied from the external terminal connected to the charging connector 140 as the power source.

[0032] In step S5, after the circuit is driven in step S4, the MCU 121 is temporarily started up, but if the MCU 121 is started up by circuit startup, it transitions to low-power mode and maintains the low-power mode until the MCU startup conditions are met. In this embodiment, pressing the power switch 161 is used as the MCU startup condition, so the standby state is maintained until the switch is pressed. In step S6, after detecting that the power switch 161 has been pressed, initialization of the MCU 121 is performed.

[0033] In step S7, the battery temperature is measured. If either of the following two conditions is met: if the battery temperature is below the low temperature threshold in step S7a (Yes) and then falls below the extremely low temperature threshold, which is even lower than the low temperature threshold, in step S8 (No); or if the battery temperature does not fall below the low temperature threshold in step S7a (No) but exceeds the high temperature threshold in step S7b (Yes), the process transitions to step S9, and MCU 121 issues an instruction to charging control unit 150 to change the charge control state to a charge prohibited state. Also, if the battery temperature is not below the extremely low temperature threshold in step S8, the process transitions to step S14.

[0034] In step S10, an MCU program other than the BMS (battery management system) including over-discharge protection is run, and peripheral communication with the external input 162 is performed. In step S10a, if an interrupt process occurs, the process proceeds to step S11, and depending on the cause of the interrupt, the process proceeds to step S11a or step S12. That is, if it is a timer interrupt, the process proceeds to step S11a, and otherwise the process proceeds to step S12.

[0035] In step S11a, a determination is made on the condition that no operation has been performed for a certain period of time, and if it is determined that an operation has been performed, the process returns to step S7 to periodically measure the battery temperature. On the other hand, if a certain period of time has occurred in step S11a during which no operation has been performed by the external input 162 of the input terminal 160 or no processing operation has been performed by the MCU 121, the process proceeds to step S12.

[0036] Furthermore, the transition from step S10a to step S12 may be made if an interrupt process that satisfies a power-off condition occurs during step S10, such as a reset process caused by pressing the power button for a long time.

[0037] In step S12, if the power OFF condition is not met in step S10 (if a standby instruction is given), the process proceeds to step S13, where the MCU transitions to standby mode. That is, if the circuit operating voltage is met in step S12, the process proceeds to step S13. If the circuit operating voltage is not met or other OFF conditions are met, the process proceeds to step S14.

[0038] In step S13, the MCU 121 transitions to a standby state, and maintains the standby state until the MCU startup conditions are met in step S5. When the process transitions to step S14, the circuit power supply is turned off.

[0039] Regarding the charge control determination based on temperature characteristics, room temperature refers to the temperature suitable for use based on the characteristics of the battery 130. Low and high temperatures refer to temperature ranges outside the suitable range. Charging outside the suitable temperature range is prohibited because high temperatures pose the risk of thermal runaway, heat generation due to the decomposition reaction of the electrolyte during charging, or the risk of fire or explosion. At low temperatures, during the charging process of a lithium-ion battery, lithium ions supplied from the positive electrode may not be properly absorbed into the negative electrode, resulting in the deposition of lithium on the negative electrode surface. Furthermore, because impedance increases and electrical characteristics deteriorate, low temperature classifications are established for low and extremely low temperatures to prevent temperature-related deterioration of the battery 130.

[0040] In this embodiment, the judgment classification is set to four stages in consideration of the variation of the temperature detection element 131, but it is desirable to further subdivide the judgment classification and adjust the amount of charging current of the battery 130 to increase or decrease before the charging prohibited area, thereby implementing a power supply process that responds to changes in impedance due to temperature changes and heat generation, and preventing deterioration.

[0041] Before the connection switching unit 112 disconnects the load 120, the low-voltage detection unit 123 (see FIG. 1) in the MCU 121 detects a low-voltage threshold, which is determined from voltage values ​​above the detection range including the error of the voltage detection unit 114. As soon as the low-voltage detection unit 123 determines that the supply voltage of the battery 130 has fallen below the low-voltage threshold, the low-voltage detection unit 123 generates an interrupt to the MCU 121, causing the MCU 121 to transition from normal operation to standby. This makes it possible to cut off the power supply without interfering with the operation of the MCU 121 during the disconnection process of the connection switching unit 112. In addition, a warning is displayed on the display unit 122 when the low voltage or the voltage is below the circuit operating voltage of the load 120.

[0042] As described above, an over-discharge protection system is constructed by combining a simple, low-cost over-discharge protection circuit 110 that is not affected by whether the MCU 121 is activated or not, with battery protection that is provided by the MCU 121 separately monitoring the battery supply voltage and battery temperature, making it possible to charge the battery 130 without having to press a switch. [Explanation of symbols]

[0043] 110 Overdischarge protection circuit 111 Bidirectional connection control section 112 Connection switching unit 113 Charging detection unit 114 Voltage detection unit 120 load 121 MCU 122 Display section 123 Low voltage detection unit 130 Battery 131 Temperature detection element 140 Charging connector 150 Charging control unit 160 input terminal 161 Power switch 162 External Input 212FET 215 FET 217 FET 290 2-input OR section

Claims

1. a bidirectional connection control unit that is provided between the secondary battery and the load and is capable of switching between connection and disconnection; a connection switching unit that switches between connection and disconnection of the bidirectional connection control unit; Equipped with The over-discharge protection circuit is characterized in that the connection switching unit switches between connection and disconnection of the bidirectional connection control unit based on the detection results from a voltage detection unit that uses the circuit operating voltage of the load as a threshold value and a charge detection unit that detects the charging voltage to the secondary battery.

2. The connection switching unit The over-discharge protection circuit of claim 1, characterized in that the bidirectional connection control unit is configured to enter a connected state when the charging detection unit detects a charging voltage or when the voltage detection unit detects that the voltage of the secondary battery is equal to or higher than the threshold.

3. 3. The over-discharge protection circuit according to claim 2, wherein the connection switching unit has an OR circuit, and the output of the charge detection unit and the output of the voltage detection unit are input to the OR circuit.

4. The over-discharge protection circuit according to claim 1 is provided the load is a control unit, the control unit has a temperature detection unit that detects the temperature of the secondary battery, A portable terminal comprising a charge control unit that controls charging of the secondary battery based on the detection result of the temperature detection unit.

5. 5. The mobile terminal according to claim 4, wherein the charging control unit controls charging by switching among three states, namely, a normal operation, a charging inhibit operation, and a battery OFF operation, based on the detection result.

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