Secondary battery life extension circuit and in-vehicle display system

Abstract

This invention provides a secondary battery life extension circuit that can extend the lifespan of secondary batteries. [Solution] The secondary battery life extension circuit comprises a secondary battery 1, a battery voltage output circuit 13 that outputs a battery voltage VA1, an ignition-on voltage output circuit 14 that outputs an ignition-on voltage VB1, a diode-on circuit 7 that supplies power supply voltage to a downstream load circuit 20, and includes first and second diodes D1 and D2, each having the battery voltage VA1 and ignition-on voltage VB1 input to its anode and a common cathode connection, respectively, a switch circuit 3 provided between the secondary battery and the load circuit to switch the electrical connection / disconnection between the secondary battery and the load circuit, and a switch control circuit 30 that turns on the switch circuit 3 during periods when the battery voltage VA1 is not supplied, based on the on / off control signal of the switch circuit 3.

Description

Technical Field

[0001] The present invention relates to a secondary battery life extension circuit, an in-vehicle display system, etc. that can extend the life of a lithium-ion secondary battery or the like mounted on a vehicle such as an automobile.

Background Art

[0002] Patent Document 1 shows a circuit configuration in which a real-time clock circuit (RTC) is used as a load circuit in a vehicle display device and a longer backup time can be obtained. In

[0014] of Patent Document 1, it is shown that "the battery power supply unit supplies power during the operation of the vehicle display device."

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, assuming that the battery voltage supply circuit is a secondary battery (such as a lithium-ion battery), no power is supplied when the vehicle display device is not in operation. Therefore, the real-time clock circuit RTC, which is a load circuit (a circuit that needs to continuously count the clock for time measurement required for, for example, date and time display at all times regardless of the operation of the vehicle display device), cannot operate.

[0005] Also, in order to eliminate the above inconvenience and make the real-time clock circuit RTC, which is a load, operable even when the vehicle display device is not in operation, it is necessary to constantly supply the output voltage (power supply voltage) of the secondary battery, which increases the consumption of the secondary battery and shortens its life.

[0006] One of the objectives of the present invention is to provide a secondary battery life extension circuit that can extend the lifespan of a secondary battery.

[0007] Other objects of the present invention will become apparent to those skilled in the art by referring to the embodiments and best embodiments described below, as well as the accompanying drawings. [Means for solving the problem]

[0008] The following are examples of embodiments of the present invention to facilitate understanding of its outline.

[0009] In a first embodiment, the secondary battery life extension circuit includes a secondary battery, a battery voltage output circuit that outputs a voltage output from a battery different from the secondary battery as the battery voltage without changing its voltage level or with a level shift, an ignition-on voltage output circuit that outputs a voltage supplied from the battery via the ignition switch as the ignition-on voltage without changing its voltage level or with a level shift when the ignition switch is on, a diode-on circuit comprising first and second diodes, each having the battery voltage and the ignition-on voltage input to its anode and having a common cathode, and outputting a voltage output from the common connection point of the first and second diodes as the power supply voltage for a subsequent load circuit, a switch circuit provided between the secondary battery and the load circuit for switching the electrical connection / disconnection between the secondary battery and the load circuit, and a switch control circuit that generates an on / off control signal for the switch circuit based on the battery voltage, and turns on the switch circuit during periods when the battery voltage is not supplied by the on / off control signal.

[0010] In the first embodiment, a battery different from a secondary battery (for example, an on-board battery installed in a car) is used to generate a "battery voltage" and an "ignition-on voltage". Each voltage is input to a diode-OR circuit, and the voltage with the higher value is output, with the output voltage being used as the power supply voltage for the subsequent load circuit. As a result, even if the load circuit is a circuit that requires a constant power supply, such as a real-time clock circuit (RTC) or backup volatile memory, the power is supplied from the battery, eliminating the need for current (voltage) supply from the secondary battery. This suppresses the consumption of the secondary battery and makes it possible to extend its lifespan, for example, to several years. When the battery is installed and connected, the battery voltage is output from the battery voltage output circuit, except in special circumstances (which will be explained in the second aspect). Furthermore, the "ignition-on voltage," like the battery voltage, is generated by the voltage supplied from a common battery (the system's original power supply voltage). However, since this voltage is activated only when the ignition switch is turned on, this specification distinguishes it from the "battery voltage" and refers to it as the "ignition-on voltage." Furthermore, the "battery voltage output circuit" and the "ignition-on voltage output circuit" may, in a preferred example, be composed of a step-down circuit (such as a regulator with step-down functionality) that steps down the voltage supplied from the battery (the system's original power supply voltage). However, it is not always the case that the voltage is stepped down; in some cases the voltage value may be output as is, and in special cases, it may even be stepped up. Taking this into consideration, in the first embodiment, the function of the two circuits described above is expressed as "outputting without changing the voltage level, or with a level shift." On the other hand, the aforementioned "battery voltage" is not only used to generate power for the load, but is also utilized (and used concurrently) as an on / off control signal for the switch circuit. Here, the "switch circuit" is, in other words, a switching means provided between a secondary battery such as a lithium-ion battery and a load circuit, which switches whether or not current (voltage) is supplied from the secondary battery to the load circuit. In a preferred example, it may be composed of a P-channel MOSFET (a P-channel power MOSFET equipped with a parasitic diode) (this point will be explained in the third embodiment). By using the "battery voltage" as an on / off control signal for the switch circuit, the switch circuit is turned off during the period when battery voltage is supplied (in other words, during the period when the battery voltage is at a high level as the active level), preventing the supply of current (voltage) from the secondary battery to the load circuit. Therefore, the consumption of the secondary battery is sufficiently suppressed, extending its lifespan, or in other words, prolonging the life of the secondary battery. Thus, in the first embodiment, the switch circuit is turned on only during periods when "battery voltage" is not supplied, and this period occurs only when the battery is removed, except in the special circumstances described above. Since the battery is removed only very rarely, and the supply of current (voltage) from the secondary battery to the load circuit is continuously stopped when the battery is installed, the consumption of the secondary battery is significantly reduced compared to conventional designs, and thus the lifespan of the secondary battery can be greatly extended.

[0011] In a second embodiment dependent on the first embodiment, a surge cut circuit for surge protection is provided upstream of the battery voltage output circuit, and in the event that a state occurs in which the battery voltage is not output from the battery voltage output circuit despite a battery different from the secondary battery being installed, the voltage output from the ignition switch is supplied to the surge cut circuit via a voltage supply path, and the surge cut circuit outputs a voltage at a voltage level that can become the voltage output from the battery, thereby causing the battery voltage to be output from the battery voltage output circuit.

[0012] In the second embodiment, although a battery is installed in the vehicle, a situation arises in which, due to special circumstances, "battery voltage" is not output from the battery voltage output circuit. In this case, the ignition switch is turned on, and ignition-on voltage is output. Even in this case, the voltage output (supplied) from the ignition switch is used to enable the output of an "apparent battery voltage (pseudo-battery voltage)," thereby preventing the switch circuit from turning on and the secondary battery from being consumed. One example of the special circumstances described above is when a battery that had been removed is reinstalled, and at the same time the ignition switch is turned on to start the system. In this case, the voltage output from the battery (the system's power supply voltage) is supplied to the ignition switch as usual, but it may be supplied to the battery voltage output circuit with a slight delay due to a minor contact problem or the like. In such a transient state, it is possible that no "battery voltage" is generated, and only an "ignition-on voltage" is generated. This transient state can also occur when a new ignition switch is installed. In the above case, since the "battery voltage (on / off control signal for the switch circuit)" is not generated temporarily, the switch circuit turns on, supplying current (voltage) from the secondary battery to the load circuit, causing current consumption and depleting the secondary battery. To solve this problem, in this embodiment, in the above case, the voltage output from the ignition switch is supplied via a voltage supply path to a surge cut circuit located upstream of the battery voltage output circuit. This surge cut circuit outputs a high-level (active-level) voltage, in other words, a voltage at a voltage level that can be the original voltage supplied by the battery (a voltage that can replace the original voltage). By utilizing this voltage, the battery voltage from the battery voltage output circuit is output (specifically, for example, a pseudo-battery voltage that has a voltage level that can be considered as the original battery voltage, although there may be a slight difference in voltage level from the original battery voltage, in terms of circuit operation). This allows the switch circuit to remain off even when the above transient conditions occur, thereby suppressing the consumption of the secondary battery.

[0013] In a third embodiment dependent on the first or second embodiment, the switch circuit is comprised of a P-channel MOSFET, the source of which is electrically connected to the secondary battery, and the drain of which is electrically connected to the load circuit, and may also include a parasitic diode having an anode connected to the drain and a cathode connected to the source, which has a reverse current prevention function that prevents current from flowing from the secondary battery to the load circuit when the P-channel MOSFET is off.

[0014] In the third embodiment, a P-channel MOSFET (a power P-channel MOSFET with parasitic diodes) is used as the switching circuit. Since complex circuits are not used, the configuration of the switching circuit is simplified. The reason for using a P-channel MOSFET is that the parasitic diode formed inside the P-channel MOSFET (which inherently serves to prevent the P-channel MOSFET from being destroyed) acts as a reverse diode from the perspective of the secondary battery in this embodiment, thus also providing a reverse current prevention function. Therefore, the flow of current from the secondary battery to the load circuit via the parasitic diode can be automatically prevented. Furthermore, if an N-channel MOSFET is used, the parasitic diode will act as a forward diode from the perspective of the secondary battery, and there is a possibility that the parasitic diode will turn on due to the voltage of the secondary battery, supplying current. Thus, according to this embodiment, the parasitic diode formed inside the P-channel MOSFET acts as a reverse diode from the perspective of the secondary battery, thus also providing a reverse current prevention function, and the depletion of the secondary battery due to leakage current can be automatically prevented. Furthermore, in principle, only one P-channel MOSFET is required, which simplifies the configuration of the switch circuit and achieves space savings in the switch circuit.

[0015] In a fourth embodiment dependent on the third embodiment, the switch control circuit may receive the battery voltage as input and output a gate drive voltage to drive the gate of the P-channel MOSFET based on the input battery voltage. When the battery voltage is supplied, the gate drive voltage may be set to a high level to turn off the P-channel MOSFET, and when the battery voltage is not supplied, the gate drive voltage may be set to a low level to turn on the P-channel MOSFET.

[0016] In the fourth embodiment, the switch control circuit turns off the P-channel MOSFET by setting the gate voltage to a high level when battery voltage is supplied (in other words, when the battery voltage is at a high level (active level)), and turns on the P-channel MOSFET by setting the gate voltage to a low level when battery voltage is not supplied (in other words, when the battery voltage is at a low level (inactive level)). This makes it possible to control the on / off state of the P-channel MOSFET, which acts as a switch circuit, in a simplified configuration, depending on whether the battery voltage is supplied or not (low level / high level).

[0017] In a fifth aspect that depends on the third or fourth aspect, it has a Zener diode provided between the gate and the source of the P-channel MOSFET, and the voltage value of the on-threshold voltage of the Zener diode may be set to a value not exceeding the breakdown voltage between the gate and the source of the P-channel MOSFET and a value greater than the maximum output voltage of the secondary battery.

[0018] In the fifth aspect, a Zener diode (constant voltage diode) is provided between the gate and the source of the P-channel MOSFET that constitutes the switch circuit. Since the voltage value (breakdown voltage value) of the on-threshold voltage of this Zener diode is set to a value not exceeding the breakdown voltage between the gate and the source of the P-channel MOSFET, when an overvoltage exceeding the breakdown voltage is applied to the source, the Zener diode turns on and the voltage of the source is clamped (held) to a voltage value not exceeding the breakdown voltage. Therefore, the destruction of the P-channel MOSFET is prevented. Also, since the voltage value of the on-threshold voltage of the Zener diode is set to a value greater than the maximum output voltage of the secondary battery, even when the maximum output voltage of the secondary battery is applied, the Zener diode remains off and no leakage current flows. Therefore, the depletion of the secondary battery is prevented.

[0019] The in-vehicle display system according to the sixth aspect is mounted on a vehicle as a vehicle, and has a secondary battery life extension circuit according to any one of the first to fifth aspects and a load circuit. The load circuit may include a real-time clock circuit and a display device capable of displaying an image generated using an output signal of the real-time clock circuit, or a volatile memory and a display device capable of displaying an image generated using image data stored in the volatile memory.

[0020] According to this embodiment, even in an in-vehicle display system that includes load circuits that require a constant power supply voltage, such as a real-time clock circuit (RTC) and volatile memory, it is possible to generate a power supply voltage by effectively utilizing the voltage supplied from the vehicle battery and operate these load circuits. Furthermore, in this state, the current consumption of the secondary battery becomes zero, significantly extending the lifespan of the secondary battery (for example, extending it to a lifespan of several years), reducing the frequency of tasks such as recharging and replacing the secondary battery, and thus improving the convenience of the in-vehicle display system.

[0021] Those skilled in the art will readily understand that the embodiments of the present invention illustrated can be further modified without departing from the spirit of the invention. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 shows an example of the configuration of an in-vehicle display system that includes a secondary battery life extension circuit. [Figure 2] Figure 2 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when the battery is installed and therefore the battery voltage is output, and the ignition switch is in the off state and therefore the ignition on voltage is not output. [Figure 3] Figure 3 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when the battery voltage is output because the battery is installed, and the ignition switch is in the ON state and therefore the ignition ON voltage is output. [Figure 4] Figure 4 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when, despite the battery being installed, no battery voltage is output, and an ignition-on voltage is output because the ignition switch is in the ON position. [Figure 5]Figure 5 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when the battery is removed, resulting in no battery voltage being output and no ignition-on voltage being output. [Figure 6] Figure 6 shows a modified example in which the real-time clock circuit (RTC) as a load circuit in the in-vehicle display system of Figure 1 is replaced with volatile memory. [Figure 7] This figure shows an example of the external configuration of a display device installed in a vehicle such as a ride-on tow truck. [Modes for carrying out the invention]

[0023] The best embodiments described below are used to facilitate understanding of the present invention. Therefore, those skilled in the art should note that the present invention is not unduly limited by the embodiments described below.

[0024] (First embodiment) Figure 1 shows an example of the configuration of an in-vehicle display system that includes a secondary battery life extension circuit.

[0025] In Figure 1, the in-vehicle display system 100, which is installed in a vehicle such as an automobile, includes a secondary battery life extension circuit 110 and a load circuit 20.

[0026] The secondary battery life extension circuit 110 comprises a secondary battery (in the circuit of Figure 1, this is referred to as a lithium-ion battery LTB) 1, a surge cut circuit 11 that cuts surges superimposed on the voltage output from a battery BAT different from secondary battery 1, and a battery voltage output circuit (in the circuit of Figure 1, this is referred to as a first step-down circuit with a step-down function; hereinafter, the first step-down circuit and The circuit consists of a battery terminal (called) 13, an ignition circuit 12, and an ignition-on voltage output circuit (in the circuit of Figure 1, this is a second step-down circuit with a step-down function; hereinafter referred to as the second step-down circuit) 14 which outputs the voltage Vgn supplied from the battery BAT via the ignition switch SW1 (and ignition circuit 12) when the ignition switch SW1 is ON, either without changing its voltage level or with a level shift, as the ignition-on voltage from the voltage output terminal PB1, and the battery voltage and The diode-on circuit 7 comprises first and second diodes D1 and D2 to which the ignition-on voltage is input and whose cathodes are connected in common, and which outputs the voltage output from the common connection point (common connection node) N3 of the first and second diodes D1 and D2 as the power supply voltage for the subsequent load circuit 20; a switch circuit 3 (here, it is assumed to be composed of a P-channel MOSFET (PM)) provided between the secondary battery 1 and the load circuit 20 to switch the electrical connection / disconnection between the secondary battery 1 and the load circuit 20; a switch control circuit 30 that generates an on / off control signal for the switch circuit 3 based on the battery voltage VA1 and turns on the switch circuit 3 during periods when the battery voltage VA1 is not supplied by the on / off control signal; a diode 2 having a reverse current prevention function provided between the secondary battery 1 and the switch circuit 3; and a Zener diode (constant voltage diode) 4 having a gate protection function provided between the source S of the P-channel MOSFET (PM) constituting the switch circuit 3 and the switch control circuit 30.

[0027] The switch control circuit 30 includes a gate drive voltage supply circuit 5 that receives a battery voltage VA1 supplied via a voltage input terminal PA3 and outputs a gate drive voltage VA2 used to drive the gate G of the P-channel MOSFET (PM) constituting the switch circuit 3, and a resistor (gate voltage generating resistor) 6 connected between the common connection point (common connection node) N4 of the gate G of the P-channel MOSFET (PM) and the gate drive voltage supply circuit 5 and ground (earth potential) GND.

[0028] When the gate drive voltage VA2 is applied to the common connection point N4, current flows through resistor R6, causing a voltage drop across resistor R6, which generates a gate voltage VG at the common connection point N4. This gate voltage VG is then applied to the gate G of the P-channel MOSFET (PM).

[0029] The load circuit 20 includes a real-time clock circuit (RTC) 8, a display device (vehicle display device) 10, and a control unit 9 that controls the operation of the display device 10.

[0030] In Figure 1, "L1" indicates a voltage output line that outputs the voltage of the battery BAT, and "L2" indicates a voltage supply path (voltage supply line: the role of this voltage supply line will be explained using Figure 4) that supplies the voltage Vgn output (supplied) from the ignition switch SW1 from the ignition circuit 12 to the surge cut circuit 11. Furthermore, "L3" and "L4" indicate the voltage lines that supply the battery voltage VA1 and ignition-on voltage VB1, respectively, to the voltage input terminals PA2 and PB2 of the diode OR circuit 7. Furthermore, "L5" is a voltage line that branches off from voltage line L3 and supplies the battery voltage VA1 (in this case, the control voltage that controls the on / off state of switch circuit 3) to the gate drive voltage supply circuit 5 via voltage input terminal PA3. Furthermore, "L6" indicates a first power supply line that supplies the power supply voltage output from the diode OR circuit 7 to the load circuit 20. Furthermore, "L7" indicates a second power supply line that supplies the voltage supplied from the secondary battery 1 (power supply voltage from the secondary battery 1) to the load circuit 20.

[0031] In the secondary battery life extension circuit 110 having this configuration, a battery different from the secondary battery 1 (for example, an on-board battery installed in a car) BAT is used to generate a "battery voltage VA1" and an "ignition-on voltage VB1". Each voltage is input to the diode OR circuit 7, and the voltage with the higher value is output, and this output voltage (VA1 or VB1) is used as the power supply voltage for the subsequent load circuit 20.

[0032] Here, once the battery is installed and connected, the "battery voltage VA1" is output from the first step-down circuit (battery voltage output circuit) 13, except in special circumstances (which will be explained in Figure 4).

[0033] Furthermore, the "ignition-on voltage VB1," like the battery voltage VA1, is generated by the voltage supplied from the common battery BAT (the system's original power supply voltage) and is output from the second step-down circuit (ignition-on voltage output circuit) 14. However, since this voltage is activated only when the ignition switch SW1 is turned on, in this specification it is referred to as "ignition-on voltage VB1" to distinguish it from the "battery voltage VA1."

[0034] Furthermore, the voltage path consisting of the surge cut circuit 11 and the first step-down circuit 13, and the voltage path consisting of the ignition circuit 12 and the second step-down circuit 14 are connected in parallel to a common battery BAT. Therefore, the "battery voltage VA1" and the "ignition-on voltage VB1" are independent voltage signals.

[0035] Furthermore, as described above, the "battery voltage output circuit" and the "ignition-on voltage output circuit" in the example shown in Figure 1 consist of step-down circuits (regulators with step-down functions, etc.) 13 and 14 that step down the voltage supplied from the battery (the system's original power supply voltage).

[0036] However, it is not always the case that the voltage is stepped down; in some cases the voltage value remains the same, and in special cases, it is not impossible that the voltage may be stepped up. Taking this into consideration, in the example in Figure 1, the function of the two circuits 13 and 14 described above is expressed as "outputting without changing the voltage level, or with a level shift."

[0037] On the other hand, the "battery voltage VA1" mentioned above is not only used to generate power for the load circuit (load) 20, but is also utilized (shared) as an on / off control signal for the switch circuit (P-channel MOSFET (PM)) 3.

[0038] Here, the "switch circuit (P-channel MOSFET (PM)) 3" is, in other words, a switching means provided between a secondary battery 1 such as a lithium-ion battery LTB and a load circuit 20, which switches whether or not current (voltage) is supplied from the secondary battery 1 to the load circuit 20. In a preferred example, it may be composed of a P-channel power MOSFET equipped with a parasitic diode.

[0039] By using the "battery voltage VA1" as the on / off control signal for the switch circuit 3, the switch circuit 3 is turned off during the period when the battery voltage VA1 is supplied (in other words, during the period when the battery voltage VA1 is at a high level (H level) as the active level), thereby preventing the supply of current (voltage) from the secondary battery 1 to the load circuit 20.

[0040] Therefore, the consumption of the secondary battery 1 is sufficiently suppressed, and the lifespan of the secondary battery 1 is extended, or in other words, the lifespan of the secondary battery 1 is extended.

[0041] Thus, in the secondary battery life extension circuit 110 shown in Figure 1, the switch circuit 3 is turned on only during periods when the "battery voltage VA1" is not supplied. This period occurs only when the battery BAT is removed, except in the special circumstances described above. Since the situation in which the battery BAT is removed occurs very rarely, and the supply of current (voltage) from the secondary battery 1 to the load circuit 20 remains stopped when the battery BAT is installed, the consumption of the secondary battery 1 is sufficiently suppressed, and therefore the life of the secondary battery can be significantly extended (for example, to several years).

[0042] Furthermore, in the example shown in Figure 1, as described above, the switch circuit 3 is composed of a P-channel MOSFET (PM), the source S of the P-channel MOSFET (PM) is electrically connected to the secondary battery 1, and the drain D is electrically connected to the load circuit 20. In addition, the anode is connected to the drain D and the cathode is connected to the source S, and it is equipped with a parasitic diode DP that has a reverse current prevention function that prevents current from flowing from the secondary battery 1 to the load circuit 20 when the P-channel MOSFET (PM) is off.

[0043] The switch circuit 3 can be constructed using a single P-channel MOSFET (a power P-channel MOSFET with a parasitic diode), and since it does not require complex circuitry, the configuration of the switch circuit 3 is simplified.

[0044] Furthermore, the reason for using a P-channel MOSFET (PM) is that the parasitic diode DP formed inside the P-channel MOSFET (PM), which inherently has the function of preventing the P-channel MOSFET from being destroyed, acts as a reverse diode from the perspective of the secondary battery 1, thus also providing a reverse current prevention function. Therefore, the flow of current from the secondary battery 1 to the load circuit 20 via the parasitic diode DP can be automatically prevented.

[0045] Furthermore, if an N-channel MOSFET is used, the parasitic diode will act as a forward diode from the perspective of the secondary battery 1, and there is a possibility that the parasitic diode will turn on due to the voltage of the secondary battery 1, supplying current.

[0046] In this way, the parasitic diode DP formed inside the P-channel MOSFET (PM) acts as a reverse diode from the perspective of the secondary battery 1, thus also providing a reverse current prevention function, and the depletion of the secondary battery 1 due to leakage current can be automatically prevented. Furthermore, in principle, only one P-channel MOSFET (PM) is required, which simplifies the configuration of the switch circuit 3 and achieves space savings for the switch circuit 3.

[0047] Furthermore, in the example shown in Figure 1, the switch control circuit 30 turns off the P-channel MOSFET by setting the gate voltage VG to a high level when the battery voltage VA1 is supplied (in other words, when the battery voltage VA1 is at a high level (active level)), and turns on the P-channel MOSFET by setting the gate drive voltage to a low level when the battery voltage is not supplied (in other words, when the battery voltage is at a low level (inactive level)).

[0048] This makes it possible to control the on / off state of the P-channel MOSFET (PM) as a switch circuit 3 in a simplified configuration, depending on whether the battery voltage VA1 is supplied or not (low level / high level).

[0049] Furthermore, in the example shown in Figure 1, as described above, a Zener diode 4 is provided between the P-channel MOSFET (PM) source S and the gate G.

[0050] The on-threshold voltage (breakdown voltage) of this Zener diode 4 is set to a value less than or equal to the breakdown voltage between the gate G and source S of the P-channel MOSFET (PM). Therefore, if an overvoltage exceeding the breakdown voltage is applied to the source, the Zener diode 4 turns on and clamps (holds) the voltage at source S to a value that does not exceed the breakdown voltage, thereby preventing the P-channel MOSFET (PM) from being destroyed.

[0051] Furthermore, the on-threshold voltage of the Zener diode 4 is set to a value greater than the maximum output voltage of the secondary battery 1. As a result, even when the maximum output voltage of the secondary battery 1 is applied, the Zener diode 4 remains in the off state, and no leakage current flows. Therefore, the depletion of the secondary battery 1 is prevented.

[0052] Next, the operation of the secondary battery life extension circuit 110 will be explained in more detail with reference to Figures 2 to 4.

[0053] Refer to Figure 2. Figure 2 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when the battery is installed and therefore the battery voltage is output, and the ignition switch is in the off state and therefore the ignition on voltage is not output.

[0054] In the example in Figure 2, the presence of the battery BAT causes the Vbat supplied by the battery BAT to reach a high level (active level). In the figure, this state is denoted as "Vbat(ACT)". This notation is also used in other figures.

[0055] Furthermore, in the example shown in Figure 2, because the ignition switch SW1 is in the off state, the voltage Vgn output from the ignition switch SW1 is at a low level (inactive level). In the figure, this state is denoted as "Vgn(INACT)".

[0056] In the example shown in Figure 2, the battery voltage VA1 is supplied to the diode or circuit 7 via path J1, indicated by the dashed arrow. This turns on the diode D1, and the power supply voltage is supplied to the load circuit 20 via path J2 (indicated by the dashed arrow in the figure), which is formed by the first power supply line L6. This makes the real-time clock circuit (RTC) 8 of the load circuit 20 operational.

[0057] Meanwhile, the battery voltage VA1, which serves as the control voltage (control signal) for the switch circuit 3, is supplied to the gate drive voltage supply circuit 5 via the path J3, which is formed by the voltage line L5, and the voltage input terminal PA3. As a result, the gate voltage VG becomes high (high-level VG is denoted as "VG(H)" in the figure), and the P-channel MOSFET (PM) as the switch circuit 3 is turned off. Therefore, the voltage supply from the secondary battery 1 to the load circuit 20 (power supply voltage from the secondary battery 1) is cut off, and the depletion of the secondary battery 1 is prevented.

[0058] In Figure 2, the dashed "x" mark on the second power supply line L7 indicates that the switch circuit 3 is turned off and the voltage supply from the secondary battery 1 is interrupted.

[0059] Next, refer to Figure 3. Figure 3 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when the battery voltage is output because the battery is installed, and the ignition switch is in the ON state, resulting in the output of an ignition ON voltage.

[0060] In Figure 3, Vbat (ACT) and Vgn (ACT) are both present. The behavior of the battery voltage VA1 in Figure 3 is as previously shown in Figure 2. The ignition-on voltage VB1 is input to the diode-or circuit 7 via path J4, indicated by the dashed arrow in the figure.

[0061] In the diode-or circuit 7, the diode with the higher voltage value between the battery voltage VA1 and the ignition-on voltage VB1 (either diode D1 or D2) is turned on, and the power supply voltage is supplied to the load circuit 20. This enables the real-time clock circuit (RTC) 8, control unit 9, and display device 10 included in the load circuit 20 to become operational.

[0062] On the other hand, the gate voltage VG of the P-channel MOSFET (PM) constituting the switch circuit 3 becomes high ("VG(H)"), and the P-channel MOSFET (PM) turns off. Therefore, the voltage supply from the secondary battery 1 to the load circuit 20 (power supply voltage from the secondary battery 1) is interrupted, and the depletion of the secondary battery 1 is prevented even in the example shown in Figure 3.

[0063] Next, refer to Figure 4. Figure 4 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when no battery voltage is output despite the battery being installed, and an ignition-on voltage is output because the ignition switch is in the ON state.

[0064] In the example shown in Figure 4, since the battery BAT is connected, the battery voltage VA1 should normally be output, but due to special circumstances, the battery voltage VA1 is not output. On the other hand, the ignition switch SW1 is ON, and the ignition ON voltage VB1 is output. In other words, in Figure 4, Vbat is INACT and Vgn is ACT.

[0065] One example of the special circumstances described above is when a removed battery BAT is reinstalled, while the ignition switch SW1 is turned on to start the system. In this case, the voltage output from the battery BAT (the system's power supply voltage) is supplied to the ignition switch SW1 as usual, but it may be supplied to the battery voltage output circuit 13 with a slight delay due to a minor contact problem or the like.

[0066] In such a transient state, it is possible that no "battery voltage" is generated, and only an "ignition-on voltage" is generated. Such a transitional state can also occur when a new ignition switch is installed.

[0067] In the above case, since the "battery voltage VA1 (on / off control signal for switch circuit 3)" is not generated temporarily, switch circuit 3 turns on, supplying current (voltage) from secondary battery 1 to load circuit 20, causing current consumption and depleting the secondary battery.

[0068] To solve this problem, in the example shown in Figure 4, in the above case, the voltage Vgn output from the ignition switch SW1 is supplied to the surge cut circuit 11 located before the battery voltage output circuit 13 via the path J0, which is composed of the voltage supply path L2. The surge cut circuit 11 then outputs a high-level (active-level) voltage (in other words, a voltage at a voltage level that can become the original voltage Vbat supplied from the battery BAT), and this voltage is supplied to the first step-down circuit (battery voltage output circuit) 13, thereby outputting the battery voltage VA1 from the first step-down circuit (battery voltage output circuit) 13 (specifically, for example, there may be a slight difference in voltage level from the original battery voltage VA1, but in terms of circuit operation, it is possible to consider it as the original battery voltage VA1 (in other words, a pseudo-battery voltage with a voltage level that can be replaced by it)).

[0069] The output battery voltage VA1 is supplied to the diode OR circuit 7 via path J1. In the diode-or circuit 7, the diode with the higher voltage value between the battery voltage VA1 and the ignition-on voltage VB1 (either diode D1 or D2) is turned on, and the power supply voltage is supplied to the load circuit 20. This enables the real-time clock circuit (RTC) 8, control unit 9, and display device 10 included in the load circuit 20 to become operational.

[0070] On the other hand, the gate voltage VG of the P-channel MOSFET (PM) constituting the switch circuit 3 becomes high ("VG(H)"), and the P-channel MOSFET (PM) turns off. Therefore, the voltage supply from the secondary battery 1 to the load circuit 20 (power supply voltage from the secondary battery 1) is cut off, and even in the example of Figure 4 (for example, when the battery voltage VA1 is not generated temporarily due to special circumstances), the depletion of the secondary battery 1 is prevented.

[0071] Next, refer to Figure 5. Figure 5 shows the circuit operation in the secondary battery life extension circuit of Figure 1 when the battery is removed, resulting in no battery voltage being output and no ignition-on voltage being output.

[0072] Figure 5 illustrates an example considering the case where the battery is removed. In general, in vehicles such as automobiles, the battery is rarely removed except when charging. However, in agricultural machinery (combine harvesters, tractors, rice transplanters, etc.), the user may remove the battery during periods when agricultural work is not being performed.

[0073] In Figure 5, since the battery BAT is not connected, Vbat is INACT and Vgn is INACT. In this case, neither the battery voltage VA1 nor the ignition-on voltage VB1 is output, so it is not possible to supply power voltage to the load circuit 20 using either voltage.

[0074] In this case, the battery voltage VA1, which serves as the on / off control signal for switch circuit 3, is not supplied (in other words, the battery voltage VA1 is at a low level). As a result, the gate voltage VG becomes low (VG(L)), and the P-channel MOSFET (PM) acting as switch circuit 3 is turned on by the potential difference between the gate G and the source S.

[0075] As a result, power supply voltage (power supply current) is supplied from the secondary battery 1 to the load circuit 20 via the second power supply line L7, and the real-time clock circuit (RTC) 8 of the load circuit 20 becomes operational.

[0076] Thus, according to the secondary battery life extension circuit 110 shown in Figure 1, the secondary battery 1 consumes current only when the battery BAT is removed and not connected, and since such a situation occurs extremely rarely, the lifespan of the secondary battery 1 can be extended significantly (for example, to several years).

[0077] Thus, in an in-vehicle display system 100 having a load circuit 20 including a real-time clock circuit (RTC), it is possible to generate a power supply voltage by effectively utilizing the voltage supplied from the battery BAT and operate the load circuit 20. Furthermore, in this state, the current consumption of the secondary battery 1 becomes zero, significantly extending the lifespan of the secondary battery 1 (for example, extending it to a lifespan of several years), reducing the frequency of tasks such as recharging or replacing the secondary battery 1, and thus improving the convenience of the in-vehicle display system 100.

[0078] (Second embodiment) Refer to Figure 6. Figure 6 shows a modified example in which the real-time clock circuit (RTC) as a load circuit in the in-vehicle display system of Figure 1 is replaced with volatile memory.

[0079] In the example shown in Figure 6, the load circuit 20 is equipped with a volatile memory (SRAM, DRAM, etc.) 15 for backing up data. The other circuit configurations are the same as in Figure 1, so their explanation is omitted.

[0080] In the example shown in Figure 6, the current consumption of the secondary battery 1 is minimized, extending the lifespan of the secondary battery 1, and thus significantly extending the backup period of the volatile memory 15.

[0081] (Third embodiment) Refer to Figure 7. Figure 7 shows an example of the external configuration of a display device installed in a vehicle such as a ride-on tow truck.

[0082] In Figure 7, the display device 10 is an in-vehicle display device installed in an automobile. This display device 10 includes a digital display unit 22 (including a date display unit 23), meter display units 24 and 26, and a security indicator 28 that indicates that the vehicle's security system is functioning correctly.

[0083] As explained earlier, the in-vehicle display system 100 can generate a power supply voltage by effectively utilizing the voltage supplied from the battery (vehicle battery) BAT, and operate the load circuit 20 (including circuits 8, 12, etc., which require a constant power supply voltage). In this state, the current consumption of the secondary battery 1 becomes zero, significantly extending the lifespan of the secondary battery 1 (for example, extending it to a lifespan of several years), and reducing the frequency of tasks such as recharging or replacing the secondary battery 1. Therefore, the convenience of the display device (vehicle display device) 10 is also greatly improved.

[0084] As described above, according to the embodiments of the present invention, it is possible to provide a secondary battery life extension circuit that can extend the life of a secondary battery.

[0085] The present invention is not limited to the embodiments described above, and can be modified and applied in various ways. For example, the term "vehicle" is preferably interpreted broadly as "vehicles" or "transportation devices," and the present invention can be applied not only to automobiles but also to agricultural machinery (combine harvesters, tractors, rice transplanters, etc.), simulators, etc.

[0086] Furthermore, regarding the circuit configuration, additional components can be added or other types of elements can be used without departing from the spirit of the present invention, and the present invention can also be applied to these modifications and applications.

[0087] The present invention is not limited to the exemplary embodiments described above, and those skilled in the art will be able to easily modify the exemplary embodiments described above to the extent included in the claims. [Explanation of Symbols]

[0088] 1...Secondary battery, 2...Reverse current prevention diode, 3...Switch circuit, 4...Zener diode, 5...Gate drive voltage supply circuit, 6...Resistor (resistor for gate voltage generation), 7...Diode OR circuit, 8...Real-time clock circuit (RTC), 9...Control unit, 10...Display device (in-vehicle display device), 11...Surge cut circuit, 12...Ignition circuit, 13...First step-down circuit (battery 14... Second step-down circuit (ignition-on voltage output circuit), 15... Volatile memory (SRAM, DRAM, etc.), 20... Load circuit (load), 100... Automotive display system, 110... Secondary battery life extension circuit, SW1... Ignition switch, LTB... Lithium-ion battery, PM... P-channel MOSFET, VA1... Battery voltage, VB1... Ignition-on voltage.

Claims

1. Rechargeable batteries and A battery voltage output circuit that outputs a voltage from a battery different from the aforementioned secondary battery as the battery voltage, either without changing its voltage level or with a level shift, An ignition-on voltage output circuit that, when the ignition switch is on, outputs the voltage supplied from the battery via the ignition switch as the ignition-on voltage without changing its voltage level, or with a level shift; A diode-or circuit comprising first and second diodes, each having the battery voltage and the ignition-on voltage input to its anode and having their cathodes connected in common, and outputting the voltage output from the common connection point of the first and second diodes as the power supply voltage for the subsequent load circuit, A switch circuit is provided between the secondary battery and the load circuit to switch the electrical connection / disconnection between the secondary battery and the load circuit, A switch control circuit that generates an on / off control signal for the switch circuit based on the battery voltage, and turns on the switch circuit during periods when the battery voltage is not supplied, Having, Rechargeable battery life extension circuit.

2. The aforementioned battery voltage output circuit is preceded by a surge cut circuit for surge protection, If, despite the installation of a battery different from the aforementioned secondary battery, a situation occurs in which the battery voltage is not output from the battery voltage output circuit, The voltage output from the ignition switch is supplied to the surge cut circuit via the voltage supply path, and the surge cut circuit outputs a voltage at a voltage level that can be the voltage output from the battery, thereby causing the battery voltage to be output from the battery voltage output circuit. The secondary battery life extension circuit according to claim 1.

3. The aforementioned switch circuit is It is composed of P-channel MOSFETs, The source of the P-channel MOSFET is electrically connected to the secondary battery, and the drain is electrically connected to the load circuit, The drain is connected to the anode, the source is connected to the cathode, and a parasitic diode is provided that has a reverse current prevention function to prevent current from flowing from the secondary battery to the load circuit when the P-channel MOSFET is off. The secondary battery life extension circuit according to claim 1.

4. The aforementioned switch control circuit is The aforementioned battery voltage is input, and a gate drive voltage is output to drive the gate of the P-channel MOSFET based on the input battery voltage, When the aforementioned battery voltage is supplied, the gate drive voltage is set to a high level to turn off the P-channel MOSFET. If the aforementioned battery voltage is not supplied, the gate drive voltage is set to a low level to turn on the P-channel MOSFET. The secondary battery life extension circuit according to claim 3.

5. The P-channel MOSFET has a Zener diode provided between its gate and source, and the on-threshold voltage of the Zener diode is set to a value less than or equal to the breakdown voltage between the gate and source of the P-channel MOSFET, and greater than the maximum output voltage of the secondary battery. The secondary battery life extension circuit according to claim 3.

6. It is mounted on a vehicle as a means of transportation. A secondary battery life extension circuit according to any one of claims 1 to 5, Load circuit and, It has, The aforementioned load circuit is A real-time clock circuit, and a display device capable of displaying an image generated using the output signal of the real-time clock circuit. Or, A volatile memory, and a display device capable of displaying an image generated using image data stored in the volatile memory. including, In-vehicle display system.

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