Electronic device

Abstract

To enable appropriate control of a load switch in an electronic device.SOLUTION: An electronic device 100 includes a power supply circuit 3 that outputs an output voltage Vout generated on the basis of a charging voltage Vsup of a power storage element 2 to a power supply line Ln2, a load switch 4 including an input terminal Pin connected to the power supply line Ln2, an output terminal Pout connected to the power supply line Ln3, and a control terminal Pc, a control circuit 5, a switch 6 connected between a power supply line Ln1 and the control terminal Pc, and a switch 7 connected between the control terminal Pc and ground potential GND. The control circuit 5 turns the switch 7 off when the charging voltage Vsup is greater than a first threshold Vth1, and turns the switch 7 on when the charging voltage Vsup is less than the first threshold Vth1. The switch 6 is turned on when the power supply circuit 3 is outputting the output voltage Vout, and is turned off when the power supply circuit 3 has stopped outputting the output voltage Vout.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electronic device. [Background technology]

[0002] In recent years, electronic devices have become known that operate on electric power generated by power generation devices such as solar power generation devices, energy harvesters, and microwave antennas, by charging an electric double layer capacitor (EDLC), known as a supercapacitor (ultracapacitor) (see Patent Document 1). Such electronic devices have been attracting attention in recent years because they do not require batteries such as conventional lithium-ion secondary batteries and can reduce the burden of maintenance on users, such as periodically charging the battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-328662 Summary of the Invention [Problem to be solved by the invention]

[0004] Prior to filing this application, the inventors of the present application considered developing an electronic device that operates on power stored in a large-capacity capacitor such as an electric double-layer capacitor. Specifically, they considered converting power stored in a large-capacity capacitor such as an electric double-layer capacitor from a power generation device into a voltage of a predetermined magnitude using a DC / DC converter, and supplying the voltage as a power supply voltage to a microcontroller (hereinafter also referred to as a "microcomputer"), which is one of the loads in the electronic device.

[0005] When a power supply voltage is supplied to a microcontroller from a large-capacity capacitor via a DC / DC converter, the power stored in the large-capacity capacitor is consumed by the microcontroller as it operates. This causes the power supply voltage to gradually drop, eventually dropping below the minimum operating voltage of the microcontroller. If the power supply voltage drops below the minimum operating voltage of the microcontroller, the microcontroller will not operate properly, and the electronic device may behave unintentionally.

[0006] Therefore, the inventors of the present application considered connecting a load switch in series between a DC / DC converter that generates a power supply voltage based on the power of a large-capacity capacitor and the load (microcontroller) to which the power supply voltage is supplied, and controlling the on / off of the load switch using the voltage of the large-capacity capacitor, thereby stopping the supply of power (power supply voltage) to the load before the power supply voltage drops below the minimum operating voltage of the microcontroller.

[0007] However, the inventors of the present invention have found through their investigations that there are cases where the load switch cannot be controlled appropriately using the method of using the voltage of a large-capacity capacitor as a control signal for controlling the on / off of the load switch.

[0008] For example, in a semiconductor integrated circuit (hereinafter also referred to as "IC (Integrated Circuit)") that serves as a load switch, if a pull-down resistor is not connected to the control terminal for controlling the on / off of the load switch, the load switch may not be able to be turned on / off properly. Specifically, if a pull-down resistor is not connected to the control terminal of the load switch, the large-capacitor capacitor may not be discharged, and the voltage of the large-capacitor may become unstable. In other words, a situation may arise in which the voltage of the large-capacitor capacitor is not large enough to generate a power supply voltage above the minimum operating voltage, but is large enough to turn on the load switch. In this case, the load switch does not turn off, and an insufficient power supply voltage (a voltage below the minimum operating voltage) is supplied from the DC / DC converter to circuits within the electronic device, such as a microcontroller, which may cause the electronic device to operate unintendedly.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to make it possible to appropriately control a load switch in an electronic device equipped with the load switch. [Means for solving the problem]

[0010] An electronic device according to a representative embodiment of the present invention includes a power generation unit that generates electric power, a storage element that charges the electric power generated by the power generation unit, a first power line to which a charging voltage of the storage element is supplied, a second power line and a third power line, a power supply circuit that generates a predetermined DC voltage based on the charging voltage and outputs the generated DC voltage to the second power line as an output voltage, an input terminal connected to the second power line, an output terminal connected to the third power line, and a control terminal, and when the voltage of the control terminal is greater than a control threshold, the input terminal and the output terminal are connected, and when the voltage of the control terminal is less than the control threshold, the input terminal and the output terminal are connected. a load switch that cuts off a connection; a load that operates using the voltage of the third power supply line as a power supply voltage; a first switch connected between the first power supply line and the control terminal; and a second switch connected between the control terminal and ground potential, wherein the load includes a control circuit that monitors the charging voltage, turns off the second switch when the charging voltage is greater than a first threshold, and turns on the second switch when the charging voltage is less than the first threshold, and the first switch is on when the power supply circuit is outputting the output voltage, and is off when the power supply circuit has stopped outputting the output voltage. [Effects of the Invention]

[0011] According to one aspect of the present invention, in an electronic device including a load switch, it is possible to appropriately control the load switch. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a diagram showing a configuration of an electronic device according to an embodiment of the present invention; [Figure 2] 4 is a timing chart showing changes over time in main voltages in the electronic device according to the embodiment. [Figure 3A] 6A and 6B are diagrams illustrating an example of a change over time in a charging voltage of a power storage element in the electronic device according to the embodiment. [Figure 3B] FIG. 10 is a diagram showing an example of temporal change in charging voltage of a power storage element in an electronic device that was studied prior to the present application, as a comparative example of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Overview of the embodiment First, a typical embodiment of the invention disclosed in this application will be outlined. In the following description, for example, reference numerals in the drawings corresponding to the components of the invention will be given in parentheses.

[0014] [1] An electronic device (100) according to a representative embodiment of the present invention includes a power generation unit (1) that generates electric power, a storage element (2) that charges the electric power generated by the power generation unit, a first power supply line (Ln1) to which a charging voltage of the storage element is supplied, a second power supply line (Ln2) and a third power supply line (Ln3), a power supply circuit (3) that generates a predetermined DC voltage based on the charging voltage and outputs it to the second power supply line as an output voltage (Vout), an input terminal (Pin) connected to the second power supply line, an output terminal (Pout) connected to the third power supply line, and a control terminal (Pc), and when the voltage of the control terminal is greater than a control threshold (Vthc), the input terminal and the output terminal are connected, and when the voltage of the control terminal is less than the control threshold, The power supply circuit includes a load switch (4) that cuts off the connection between the input terminal and the output terminal, a load (5) that operates using the voltage of the third power supply line as a power supply voltage (Vcc), a first switch (6) connected between the first power supply line and the control terminal, and a second switch (7) connected between the control terminal and ground potential (GND), the load including a control circuit (5), the control circuit monitors the charging voltage, turns off the second switch when the charging voltage is greater than a first threshold (Vth1), and turns on the second switch when the charging voltage is less than the first threshold, the first switch is on when the power supply circuit is outputting the output voltage, and is off when the power supply circuit has stopped outputting the output voltage.

[0015] [2] In the electronic device described in [1] above, the power supply circuit outputs the output voltage when the charging voltage is greater than a second threshold (Vth2), and stops outputting the output voltage when the charging voltage is less than the second threshold, and the first threshold may be greater than the second threshold (Vth1>Vth2).

[0016] [3] In the electronic device described in [1] above, the control circuit has a first terminal (P1) for monitoring the charging voltage, and further includes a third switch (8) connected between the first terminal of the control circuit and the first power supply line, and the third switch may be turned on when the power supply voltage is greater than a third threshold voltage (Vth3) and turned off when the power supply voltage is less than the third threshold voltage.

[0017] [4] In the electronic device described in [1] above, the first switch may include a transistor (M1) having a first main electrode (source electrode), a second main electrode (drain electrode), and a control electrode (gate electrode), the first main electrode of the first switch may be connected to the control terminal of the load switch, the second main electrode of the first switch may be connected to the first power supply line, and the control electrode of the first switch may be connected to the second power supply line.

[0018] [5] In the electronic device described in [1] above, the control circuit has a second terminal (P2) and outputs a control signal for switching the second switch on and off from the second terminal according to the monitoring result of the charging voltage, the second switch includes a transistor (Q1) having a first main electrode (emitter electrode), a second main electrode (collector electrode), and a control electrode (base electrode), the first main electrode of the second switch may be connected to the ground potential, the second main electrode of the second switch may be connected to the control terminal of the load switch, and the control electrode of the second switch may be connected to the second terminal of the control circuit.

[0019] [6] In the electronic device described in [3] above, the third switch may include a transistor (M2) having a first main electrode (source electrode), a second main electrode (drain electrode), and a control electrode (gate electrode), the first main electrode of the third switch may be connected to the first terminal of the control circuit, the second main electrode of the third switch may be connected to the first power supply line, and the control electrode of the third switch may be connected to the output terminal of the load switch.

[0020] 2. Specific examples of embodiments Specific examples of embodiments of the present invention will be described below with reference to the drawings.

[0021] <Embodiment> FIG. 1 is a diagram showing the configuration of an electronic device according to an embodiment of the present invention.

[0022] 1 is, for example, a device that charges a storage element 2 with power generated by a power generation unit 1 and operates using the charged power. An example of the electronic device 100 is a communication device (beacon device) that transmits a beacon signal based on a predetermined communication standard.

[0023] The electronic device 100 is configured to be operable without receiving power from a battery such as a lithium ion secondary battery or a commercial power source. Specifically, the electronic device 100 includes a power generation unit 1, a power storage element 2, a power supply circuit 3, a load switch 4, a load 5, a switch 6, a switch 7, and a switch 8.

[0024] The power generation unit 1 is a device that generates power using known techniques, such as a solar power generation device, an energy harvester, or a microwave antenna. A capacitor C1 is connected between the power supply line Ln0 and a ground potential GND. The power generation unit 1 supplies a voltage Vin corresponding to the generated power to the power supply line Ln0.

[0025] The energy storage element 2 is an element that is charged with the power generated by the power generation unit 1. The energy storage element 2 is, for example, an electric double layer capacitor (EDLC: Electric Double Layer Capacitor) Ca, which is a so-called supercapacitor (ultracapacitor). For example, the energy storage element 2 has two terminals. One terminal of the energy storage element 2 (electric double layer capacitor Ca) is connected to the power supply line Ln1, and the other terminal of the energy storage element 2 is connected to the ground potential GND. As a result, the charging voltage Vsup of the energy storage element 2 is supplied to the power supply line Ln1.

[0026] The power supply circuit 3 is a circuit that generates a DC voltage. The power supply circuit 3 generates a predetermined DC voltage based on the charging voltage Vsup and outputs it to the second power supply line Ln2 as an output voltage Vout. For example, the power supply circuit 3 has a function of charging the power generated by the power generation unit 1 to the energy storage element 2 and a function of generating a predetermined DC voltage based on the charging power of the energy storage element 2. For example, the power supply circuit 3 has a control unit 15, an inductor L, switches SW1 to SW3, and a capacitor C2 as components for realizing the above two functions. For example, some of the components that make up the power supply circuit 3 are realized by semiconductor integrated circuits (ICs: Integrated Circuits). Specifically, the control unit 15 and switches SW1 to SW3 are realized by a single IC.

[0027] One terminal of the inductor L is connected to the power supply line Ln1. The switch SW1 is connected between the power supply line Ln0 and the power supply line Ln2. The switch SW2 is connected between the other terminal of the inductor L and the power supply line Ln2. The switch SW3 is connected between the other terminal of the inductor L and the ground potential GND. The capacitor C2 is connected between the power supply line Ln2 and the ground potential GND.

[0028] The switches SW1 to SW3 are configured to include transistors such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), bipolar transistors, and IGBTs (Insulated Gate Bipolar Transistors).

[0029] The control unit 15 is a circuit that comprehensively controls the power supply circuit 3, and is realized by, for example, a dedicated logic circuit and an analog circuit such as an OP amplifier. The control unit 15 controls the switches SW1 to SW3, thereby realizing the two functions of the power supply circuit 3 described above.

[0030] When charging the storage element 2 with the power of the power generation unit 1, the control unit 15, for example, turns on the switch SW1 and switches on the switches SW2 and SW3. Alternatively, the control unit 15 may charge the storage element 2 with the power of the power generation unit 1 by, for example, turning on the switches SW1 and SW2 and turning off the switch SW3.

[0031] Furthermore, when generating a DC voltage based on the charging voltage Vsup of the energy storage element 2, the control unit 15, for example, turns on the switch SW1 and switches the switches SW2 and SW3 to charge the energy storage element 2 with power from the power generation unit 1 while outputting the DC voltage to the power supply line Ln2. Alternatively, the control unit 15 may boost the charging voltage Vsup to generate a predetermined DC voltage and output it as the output voltage Vout to the power supply line Ln2. More specifically, the control unit 15 generates a PWM signal so that the voltage of the power supply line Ln2 reaches a predetermined level, and switches the switches SW2 and SW3 on and off based on the PWM signal. At this time, the switch SW1 may be turned off or on.

[0032] For example, the control unit 15 may monitor the voltage Vin (charging voltage Vsup), and when the voltage Vin (charging voltage Vsup) is greater than a predetermined threshold, output the voltage Vin (charging voltage Vsup) as the output voltage Vout to the power supply line Ln2, and when the voltage Vin (charging voltage Vsup) is less than the predetermined threshold, boost the charging voltage Vsup and output it as the output voltage Vout to the power supply line Ln2.

[0033] Furthermore, the power supply circuit 3 may have a function of stopping the output of the output voltage Vout when sufficient power to generate a predetermined magnitude of the output voltage Vout is not stored in the storage element 2. Specifically, the control unit 15 may output the output voltage Vout when the charging voltage Vsup is higher than an overdischarge threshold value (an example of a second threshold value) Vth2, and may stop the output of the output voltage Vout when the charging voltage Vsup is lower than the overdischarge threshold value Vth2.

[0034] The load switch 4 is a circuit that switches between supplying and cutting off power from the power supply circuit 3 to the load. The load switch 4 has an input terminal Pin, an output terminal Pout, and a control terminal Pc, and has the function of switching between an ON state in which the input terminal Pin and the output terminal Pout are connected and an OFF state in which the input terminal Pin and the output terminal Pout are cut off, depending on the voltage of the control terminal Pc. Specifically, the load switch 4 connects the input terminal Pin and the output terminal Pout when the voltage Vcnt of the control terminal Pc (hereinafter also referred to as the "control voltage") is greater than a control threshold Vthc, and cuts off the connection between the input terminal Pin and the output terminal Pout when the control voltage Vcnt is less than the control threshold Vthc.

[0035] The load switch 4 has a control unit 41 and a switch SWL as components for realizing the above functions. For example, some of the components constituting the load switch 4 are realized by a semiconductor integrated circuit (IC). For example, the control unit 41 and the switch SWL are realized by a single IC. In this case, the input terminal Pin, the output terminal Pout, and the control terminal Pc are external terminals of the IC.

[0036] The input terminal Pin is connected to the power supply line Ln2. The output terminal Pout is connected to the power supply line Ln3. The switch SWL is connected between the input terminal Pin and the output terminal Pout. The switch SWL includes a transistor such as a MOSFET, a bipolar transistor, or an IGBT.

[0037] The control unit 41 is a circuit that switches the switch SWL on and off. For example, when the control voltage Vcnt is greater than the control threshold Vthc, the control unit 41 turns on the switch SWL, and when the control voltage Vcnt is smaller than the control threshold Vthc, the control unit 41 turns off the switch SWL.

[0038] The control threshold Vthc may have a hysteresis characteristic. For example, the control threshold Vthc may include a control threshold Vthc_on for turning on the switch SWL and a control threshold Vthc_off for turning off the switch SWL. In this case, Vthc_on>Vthc_off.

[0039] In this embodiment, the load switch 4 is configured to be able to switch between connecting and disconnecting a pull-down resistor Rpd to the control terminal Pc. For example, as shown in Fig. 1, the pull-down resistor Rpd and a switch SW5 are connected in series between the control terminal Pc and the ground potential GND. The switch SW5 is configured to include, for example, a transistor such as a MOSFET and a bipolar transistor.

[0040] Specifically, the control unit 41 determines whether a voltage is being input to the input terminal Pin, and switches the switch SW5 on and off depending on the determination result. For example, when no voltage is being input to the input terminal Pin, the control unit 41 turns off the switch SW5 to disconnect the pull-down resistor Rpd from the control terminal Pc and put the control terminal Pc in an open state. On the other hand, when a voltage is being input to the input terminal Pin, the control unit 41 turns on the switch SW5 to connect the pull-down resistor Rpd to the control terminal Pc.

[0041] Furthermore, when the control voltage Vcnt becomes larger than the control threshold Vthc after a voltage (output voltage Vout) is input to the input terminal Pin, the control unit 41 turns on the switch SWL and turns off the switch SW5. This prevents current from flowing to the ground potential GND via the pull-down resistor Rpd when the load switch 4 (switch SWL) is in the on state, as the pull-down resistor Rpd is opened from the control terminal Pc. This makes it possible to reduce power consumption in the load switch 4.

[0042] The load 5 includes circuits, elements, etc. that operate by receiving power from the power supply line Ln3. As shown in FIG. 1, the load 5 includes, for example, a control circuit that comprehensively controls circuits, etc. within the electronic device 100. Note that the load 5 may also include, in addition to the control circuit, a communication circuit that transmits a beacon signal, etc. In this embodiment, a control circuit is used as a representative example of the load 5, and the load 5 will be referred to as a "control circuit 5."

[0043] The control circuit 5 is a program processing device having a configuration in which a processor such as a CPU, various storage devices such as a RAM, a ROM, and a flash memory, and peripheral circuits such as a counter (timer), an A / D conversion circuit, a D / A conversion circuit, a clock generation circuit, and an input / output interface circuit are connected to one another via a bus or a dedicated line. More specifically, the control circuit 5 is, for example, a microcontroller (MCU: Micro Controller Unit).

[0044] The control circuit 5 operates using the voltage of the power supply line Ln3 as the power supply voltage Vcc. The control circuit 5 has a function of controlling the on / off of the switch 7. The control circuit 5 has at least a first terminal P1, a second terminal P2, a third terminal P3, and a fourth terminal P4 as external terminals. The first terminal P1 is a terminal for monitoring the charging voltage Vsup and is, for example, a GPIO (General-Purpose Input / Output) of a microcontroller serving as the control circuit 5. The second terminal P2, as will be described later, is a terminal for outputting a control signal from the control circuit 5 for controlling the switch 7. The third terminal P3 is a power supply terminal for inputting the power supply voltage Vcc to the control circuit 5 and is connected to the power supply line Ln3. The fourth terminal P4 is a ground terminal for grounding the control circuit 5 and is connected to the ground potential GND.

[0045] The switch 6 is connected between the power supply line Ln1 and the control terminal Pc. The switch 6 is turned on when the power supply circuit 3 is outputting the output voltage Vout, and is turned off when the power supply circuit 3 has stopped outputting the output voltage Vout. Specifically, the switch 6 is turned on when the output voltage Vout is greater than a predetermined value, and is turned off when the output voltage Vout is smaller than the predetermined value.

[0046] For example, the switch 6 includes a transistor M1 having a first main electrode, a second main electrode, and a control electrode. The type (MOSFET, bipolar transistor, etc.) and polarity (N-channel, P-channel, NPN, PNP, etc.) of the transistor M1 are not particularly limited, but preferably the transistor M1 is an N-type MOSFET having a source electrode as a first main electrode, a drain electrode as a second main electrode, and a gate electrode as a control electrode. The first main electrode (source electrode) of the transistor M1 is connected to the control terminal Pc of the load switch 4, the second main electrode (drain electrode) of the transistor M1 is connected to the power supply line Ln1, and the control electrode (gate electrode) of the transistor M1 is connected to the power supply line Ln2.

[0047] The switch 6 may further include resistors R1 and R2. For example, the resistor R1 may be connected between a first main electrode (source electrode) of the transistor M1 and a control terminal Pc of the load switch 4. The resistor R2 may be connected between a control electrode (gate electrode) of the transistor M1 and the power supply line Ln2.

[0048] The switch 7 is connected between the control terminal Pc of the load switch 4 and ground potential GND. For example, the switch 7 includes a transistor Q1 having a first main electrode, a second main electrode, and a control electrode. The type (MOSFET, bipolar transistor, etc.) and polarity (N-channel, P-channel, NPN, PNP, etc.) of the transistor Q1 are not particularly limited, but preferably the transistor Q1 is an NPN-type bipolar transistor having an emitter electrode as a first main electrode, a collector electrode as a second main electrode, and a base electrode as a control electrode. The first main electrode (emitter electrode) of the transistor Q1 is connected to ground potential GND, the second main electrode (collector electrode) of the transistor Q1 is connected to the control terminal Pc of the load switch 4, and the control electrode (base electrode) of the transistor Q1 is connected to a second terminal P2 of the control circuit 5.

[0049] The switch 7 may further include resistors R3 and R4. For example, the resistor R3 may be connected between the control electrode (base electrode) of the transistor Q1 and the second terminal P2 of the control circuit 5. The resistor R4 may be connected between the control electrode (base electrode) of the transistor Q1 and the ground potential GND.

[0050] The electronic device 100 may further include a switch 8. The switch 8 is connected between a first terminal P1 of the control circuit 5 and a power supply line Ln1. The switch 8 includes a transistor M2 having a first main electrode, a second main electrode, and a control electrode. For example, the transistor M2 is a MOSFET having a source electrode as the first main electrode, a drain electrode as the second main electrode, and a gate electrode as the control electrode. More preferably, the transistor M2 is an N-channel MOSFET. A first main electrode (source electrode) of the transistor M2 is connected to the first terminal P1 of the control circuit 5, a second main electrode (drain electrode) of the transistor M1 is connected to the power supply line Ln1, and a control electrode (gate electrode) of the transistor M1 is connected to the power supply line Ln3.

[0051] The switch 8 may further include a resistor R5 and a capacitor C3. For example, the resistor R5 and the capacitor C3 may be connected in parallel between the control electrode (gate electrode) of the transistor M2 and the power supply line Ln3.

[0052] Here, the operation of the switches 6 to 8 will be specifically described.

[0053] The switch 6 is turned on when the voltage of the power supply line Ln2 (output voltage Vout) is greater than a predetermined value, and is turned off when the voltage of the power supply line Ln2 (output voltage Vout) is less than the predetermined value. Specifically, when the gate-source voltage of the transistor M1 is less than the threshold voltage of the transistor M1, the transistor M1 is turned off, and the switch 6 is turned off. On the other hand, when the gate-source voltage of the transistor M1 is greater than the threshold voltage of the transistor M1, the transistor M1 is turned on, and the switch 6 is turned on.

[0054] The switch 7 is operated by a control signal from the second terminal P2 of the control circuit 5. Specifically, the control circuit 5 monitors the charging voltage Vsup, and turns off the switch 7 when the charging voltage Vsup is greater than a threshold value (also referred to as the "on / off threshold"; an example of a first threshold value) Vth1 for turning the load switch 4 on and off, and turns on the switch 7 when the charging voltage Vsup is less than the on / off threshold Vth1. Here, the on / off threshold Vth1 is greater than the overdischarge threshold Vth2 (Vth1>Vth2).

[0055] For example, the control circuit 5 outputs a low-level control signal (a voltage at which the transistor Q1 does not turn on) from the second terminal P2 when the charging voltage Vsup is greater than the on-off threshold Vth1, and outputs a high-level control signal (a voltage at which the transistor Q1 turns on) from the second terminal P2 when the charging voltage Vsup is less than the on-off threshold Vth1.

[0056] The switch 8 is turned on when the load switch 4 outputs the power supply voltage Vcc to the power supply line Ln3, and is turned off when the load switch 4 does not output the power supply voltage Vcc to the power supply line Ln3. Specifically, the switch 8 is turned on when the power supply voltage Vcc is greater than an output determination threshold Vth3 (an example of a third threshold), and is turned off when the power supply voltage Vcc is less than the output determination threshold Vth3. More specifically, when the gate-source voltage of the transistor M2 is less than the threshold voltage of the transistor M2, the transistor M2 is turned off, and the switch 8 is turned off. On the other hand, when the gate-source voltage of the transistor M2 is greater than the threshold voltage of the transistor M2, the transistor M2 is turned on, and the switch 8 is turned on.

[0057] Next, temporal changes in main voltages in electronic device 100 will be described with reference to FIG.

[0058] FIG. 2 is a timing chart showing changes over time in main voltages in the electronic device 100. In FIG.

[0059] In FIG. 2, from the top to the bottom, the charging voltage Vsup, whether or not the output voltage Vout from the power supply circuit 3 is output, the control voltage Vcnt, the on / off state of the load switch 4, and whether or not the pull-down resistor Rpd of the load switch is connected are shown.

[0060] Here, it is assumed that, as an initial state, the storage element 2 is not charged and the control circuit 5 is not operating. Also, in the initial state, it is assumed that the switch SWL of the load switch 4 is turned off and the pull-down resistor Rpd is disconnected from the control terminal Pc.

[0061] 2, for example, at time t1, the control unit 15 of the power supply circuit 3 turns on the switches SW1 and SW2, which starts charging the storage element 2 with the power generated by the power generation unit 1, and the charging voltage Vsup starts to rise. At this time, because the charging voltage Vsup is lower than the overdischarge threshold Vth2, the power supply circuit 3 stops outputting the output voltage Vout to the power supply line Ln2.

[0062] Subsequently, at time t2 when the charging voltage Vsup reaches the overdischarge threshold Vth2, the power supply circuit 3 outputs the output voltage Vout to the power supply line Ln2. At this time, as described above, the power supply circuit 3 may output the charging voltage Vsup (voltage Vin) as the output voltage Vout, or may boost the charging voltage Vsup and output the boosted voltage as the output voltage Vout. In response to the output of the output voltage Vout to the power supply line Ln2, the control unit 41 of the load switch 4 turns on the switch SW5, connecting the pull-down resistor Rpd to the control terminal Pc, and connecting the control terminal Pc to the ground potential GND via the pull-down resistor Rpd. In addition, the output of the output voltage Vout to the power supply line Ln2 turns on the switch 6. As a result, the control voltage Vcnt of the load switch 4 becomes equal to the charging voltage Vsup and the resistance ratio (voltage division ratio) of the resistor R1 and the pull-down resistor Rpd. In other words, the control voltage Vcnt rises.

[0063] As the charging voltage Vsup further increases, the control voltage Vcnt increases. At time t3, when the control voltage Vcnt reaches the control threshold Vthc_on, the control unit 41 of the load switch 4 turns on the switch SWL. As a result, the output voltage Vout is supplied to the power line Ln3 via the load switch 4, the power supply voltage Vcc is supplied to the control circuit 5, and the control circuit 5 starts operating. At this time, the control unit 41 of the load switch 4 turns off the switch SW5. This disconnects the pull-down resistor Rpd from the control terminal Pc.

[0064] Furthermore, the load switch 4 is turned on, and the power supply voltage Vcc is generated on the power supply line Ln3, turning on the switch 8. As a result, the charging voltage Vsup is input to the first terminal P1 of the control circuit 5.

[0065] The control circuit 5 compares the charging voltage Vsup input to the first terminal P1 with the on-off threshold Vth1. At time t3, the charging voltage Vsup is greater than the on-off threshold Vth1, so the control circuit 5 turns off the switch 7. At this time, as described above, the pull-down resistor Rpd is released from the control terminal Pc, so the control voltage Vcnt rises after time t3.

[0066] When the control circuit 5 starts operating, the power stored in the storage element 2 is consumed, and the charging voltage Vsup begins to drop. Then, at time t4, when the charging voltage Vsup drops to the on-off threshold Vth1, the control circuit 5 turns on the switch 7. This causes the control voltage Vcnt to drop sharply. When the control voltage Vcnt drops below the control threshold Vthc_off, the control unit 41 of the load switch 4 turns off the switch SWL. This stops the voltage output from the load switch 4 to the power supply line Ln3. Since the power supply circuit 3 continues to supply the output voltage Vout to the power supply line Ln2, the control unit 41 of the load switch 4 turns on the switch SW5, connecting the pull-down resistor Rpd to the control terminal Pc. This causes the control voltage Vcnt to drop further. Since the switch 6 remains on, the control voltage Vcnt also drops gradually from time t4 onward as the charging voltage Vsup drops.

[0067] Thereafter, the charging voltage Vsup further decreases, and at time t5 when the charging voltage Vsup reaches the overdischarge threshold Vth2, the power supply circuit 3 stops outputting the output voltage Vout. This stops the voltage input to the input terminal Pin of the load switch 4, and the control unit 41 of the load switch 4 turns off the switch SW5. This releases the pull-down resistor Rpd from the control terminal Pc.

[0068] When the power supply circuit 3 stops outputting the output voltage Vout, the voltage (output voltage Vout) of the power supply line Ln2 drops, turning off the switch 6. This cuts off the power supply from the power supply line Ln1 to the control terminal Pc of the load switch 4, further reducing the control voltage Vcnt, and thus the load switch 4 can be reliably turned off.

[0069] In addition, due to the influence of the capacitor C3 and parasitic capacitance connected to the power supply line Ln3, a time lag occurs between the stop of output of the output voltage Vout by the power supply circuit 3 and the stop of operation of the control circuit 5, so if the switch 7 is on when the switch 6 is turned off, the control voltage Vcnt can be further reduced.

[0070] As described above, in the electronic device 100 according to the embodiment, the switch 6 is provided between the power supply line Ln1, to which the charging voltage Vsup of the energy storage element 2 is applied, and the control terminal Pc of the load switch 4, and the switch 7 is provided between the control terminal Pc of the load switch 4 and ground potential GND. The control circuit 5, which operates by power supply from the power supply voltage Vcc output from the output terminal Pout of the load switch 4, monitors the charging voltage Vsup and turns off the switch 7 when the charging voltage Vsup is greater than the on-off threshold Vth1, and turns on the switch 7 when the charging voltage Vsup is less than the on-off threshold Vth1. The switch 6 is on when the output voltage Vout is being output from the power supply circuit 3, and is off when the output voltage Vout is not being output from the power supply circuit 3. This makes it possible to appropriately control the load switch 4 in the electronic device 100.

[0071] For example, consider a method in which the charging voltage Vsup of the storage element 2 is directly applied to the control terminal Pc of the load switch 4 without providing the switches 6 and 7, as in the electronic device according to the previously discussed prior art. With this method, by opening the pull-down resistor Rpd of the load switch 4 after the output of the output voltage Vout by the power supply circuit 3 has stopped, the control voltage Vcnt rises to the charging voltage Vsup, as shown by reference numeral 202 in FIG. 2. This may cause the load switch 4 to turn on again, resulting in an insufficient power supply voltage Vcc being applied to the control circuit 5. In contrast, in the electronic device 100 according to this embodiment, the charging voltage Vsup of the energy storage element 2 drops, and when the charging voltage Vsup reaches the on-off threshold Vth1 (time t4 in FIG. 2), the switch 7 turns on. This makes it possible to lower the control voltage Vcnt of the load switch 4 even if a pull-down resistor is not connected to the control terminal Pc of the load switch 4. Thereafter, when the output of the output voltage Vout from the power supply circuit 3 stops, the switch 6 turns off, thereby stopping the power supply from the power supply line Ln1 (charging voltage Vsup) to the control terminal Pc of the load switch 4. This further lowers the control voltage Vcnt of the load switch 4, making it possible to reliably turn off the load switch 4.

[0072] In this way, according to the electronic device 100 including the load switch 4 according to this embodiment, it is possible to appropriately control the load switch 4.

[0073] Furthermore, in the electronic device 100, the power supply circuit 3 outputs the output voltage Vout when the charging voltage Vsup is greater than the over-discharge threshold Vth2, and stops outputting the output voltage Vout when the charging voltage Vsup is less than the over-discharge threshold Vth2. Here, the on-off threshold Vth1 is greater than the over-discharge threshold Vth2. This makes it possible to increase the frequency with which the control circuit 5, acting as a load, is activated. This will be explained in detail below with reference to the drawings.

[0074] FIG. 3A is a diagram showing an example of temporal changes in charging voltage Vsup of energy storage element 2 in electronic device 100 according to the embodiment.

[0075] FIG. 3B is a diagram showing an example of temporal change in charging voltage of a power storage element in an electronic device that was studied prior to the present application, as a comparative example of this embodiment.

[0076] According to an electronic device examined prior to the present application, when the charging voltage Vsup drops to the overdischarge threshold Vth2, the power supply circuit 3 stops outputting the output voltage Vout and stops supplying the power supply voltage Vcc to the control circuit 5 as a load, as shown by reference numeral 302 in Fig. 3B. Therefore, while a longer period of time can be ensured for the control circuit 5 (microcontroller) to operate, as shown in Fig. 3B, the period from when the control circuit 5 stops to when it next operates, i.e., the time required to charge the storage element 2, becomes longer.

[0077] In contrast, in electronic device 100 according to the present embodiment, as shown by reference numeral 301 in Fig. 3A, when charging voltage Vsup drops to on-off threshold Vth1 before charging voltage Vsup reaches overdischarge threshold Vth2, load switch 4 stops outputting power supply voltage Vcc. Therefore, as shown in Fig. 3A, the period during which control circuit 5 (microcontroller) is operable is shortened, while the period from when control circuit 5 stops to when it next starts operating, i.e., the time required to charge storage element 2, is shortened, thereby increasing the frequency with which control circuit 5 is activated. As a result, the following effects can be expected.

[0078] For example, if the electronic device 100 is a beacon device, the electronic device 100 as a beacon device operates to periodically transmit a beacon signal for a short period of time. Therefore, the length of the period during which the electronic device 100 (control circuit 5) is operable is sufficient as long as the time required to transmit the beacon signal, and the electronic device 100 does not need to be activated for a long period of time. Rather, it is important to shorten the period during which the electronic device 100 cannot be activated (is inoperable) as much as possible. Therefore, by setting the on / off threshold Vth1 higher than the overdischarge threshold Vth2 as in the electronic device 100 according to this embodiment, the frequency at which the control circuit 5 activates can be increased, thereby realizing desired operation tailored to a specific application such as a beacon device.

[0079] Furthermore, in the electronic device 100 according to the embodiment, the control circuit 5 has a first terminal P1 for monitoring the charging voltage Vsup, and a switch 8 is provided connected between the first terminal P1 of the control circuit 5 and the power supply line Ln1. The switch 8 is turned on when the power supply voltage Vcc is greater than the output determination threshold Vth3, and is turned off when the power supply voltage Vcc is less than the output determination threshold Vth3.

[0080] According to this, when the power supply voltage Vcc is not supplied to the control circuit 5, the switch 8 cuts off the connection between the power supply line Ln1 and the first terminal P1 of the control circuit 5. This makes it possible to prevent unnecessary current from flowing from the power supply line Ln1 to the first terminal P1 when the control circuit 5 is not activated, thereby making it possible to suppress unnecessary discharge of the storage element 2 and the occurrence of malfunctions in the control circuit 5.

[0081] <<Extension of Embodiment>> The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0082] For example, in the above embodiment, the power supply circuit 3 has been illustrated as having the function of controlling charging from the power generation unit 1 to the energy storage element 2 and the function of generating the output voltage Vout based on the charging voltage Vsup of the energy storage element 2, but this is not limiting. The power supply circuit 3 only needs to have at least the function of generating the output voltage Vout based on the charging voltage Vsup of the energy storage element 2. In this case, a charge control circuit that controls charging from the power generation unit 1 to the energy storage element 2 may be provided separately from the power supply circuit 3.

[0083] Furthermore, in the load switch 4 according to the above embodiment, the case where the switch SW5 can switch between connecting and disconnecting the pull-down resistor Rpd to the control terminal Pc has been exemplified, but this is not limiting. For example, the pull-down resistor Rpd may be constantly connected to the control terminal Pc of the load switch 4, or the load switch 4 may not be provided with the pull-down resistor Rpd or the switch SW5. [Explanation of symbols]

[0084] 100...electronic device, 1...power generation unit, 2...energy storage element, 3...power supply circuit, 4...load switch, 5...control circuit, 6-8...switches, Ln0-Ln3...power supply lines, 15...control unit, SW1-SW3, SW5, SWL...switches, Vcc...power supply voltage, Vout...output voltage, Vsup...charging voltage, Vcnt...control voltage, P1...first terminal, P2...second terminal, P3...third terminal, P4...fourth terminal, Pin...input terminal, Pout...output terminal, Pc...control terminal

Claims

1. a power generation unit that generates electric power; a power storage element that stores the power generated by the power generation unit; a first power supply line to which a charging voltage for the storage element is supplied; a second power supply line and a third power supply line; a power supply circuit that generates a predetermined DC voltage based on the charging voltage and outputs the DC voltage as an output voltage to the second power supply line; a load switch including an input terminal connected to the second power supply line, an output terminal connected to the third power supply line, and a control terminal, the load switch connecting the input terminal and the output terminal when a voltage of the control terminal is greater than a control threshold, and disconnecting the input terminal and the output terminal when the voltage of the control terminal is less than the control threshold; a load that operates using the voltage of the third power supply line as a power supply voltage; a first switch connected between the first power supply line and the control terminal; a second switch connected between the control terminal and a ground potential; the load includes a control circuit; the control circuit monitors the charging voltage, and turns off the second switch when the charging voltage is greater than a first threshold, and turns on the second switch when the charging voltage is less than the first threshold; the first switch is turned on when the power supply circuit is outputting the output voltage, and is turned off when the power supply circuit is stopping output of the output voltage; electronic equipment.

2. 10. The electronic device according to claim 1, the power supply circuit outputs the output voltage when the charging voltage is greater than a second threshold, and stops outputting the output voltage when the charging voltage is less than the second threshold; the first threshold is greater than the second threshold; electronic equipment.

3. 10. The electronic device according to claim 1, the control circuit has a first terminal for monitoring the charging voltage; a third switch connected between the first terminal of the control circuit and the first power supply line; the third switch is turned on when the power supply voltage is greater than a third threshold voltage, and is turned off when the power supply voltage is less than the third threshold voltage; electronic equipment.

4. 10. The electronic device according to claim 1, the first switch includes a transistor having a first main electrode, a second main electrode, and a control electrode; the first main electrode of the first switch is connected to the control terminal of the load switch, the second main electrode of the first switch is connected to the first power supply line, and the control electrode of the first switch is connected to the second power supply line; electronic equipment.

5. 10. The electronic device according to claim 1, the control circuit has a second terminal, and outputs a control signal for switching on / off the second switch from the second terminal in accordance with a monitoring result of the charging voltage; the second switch includes a transistor having a first main electrode, a second main electrode, and a control electrode; the first main electrode of the second switch is connected to the ground potential, the second main electrode of the second switch is connected to the control terminal of the load switch, and the control electrode of the second switch is connected to the second terminal of the control circuit; electronic equipment.

6. 4. The electronic device according to claim 3, the third switch includes a transistor having a first main electrode, a second main electrode, and a control electrode; the first main electrode of the third switch is connected to the first terminal of the control circuit, the second main electrode of the third switch is connected to the first power supply line, and the control electrode of the third switch is connected to the output terminal of the load switch. electronic equipment.

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