electronic equipment

Abstract

To efficiently supply different voltages respectively used in a plurality of load circuits from a rechargeable battery.SOLUTION: In an electronic apparatus 100, a rechargeable battery unit 13 accommodates a single cell or a rechargeable battery of a plurality of cells connected in parallel, and outputs a voltage between a minimum voltage value and a maximum voltage value according to the remaining capacity of each cell. A first DC / DC converter 23 converts the output voltage of the rechargeable battery unit 13 into a first voltage higher than the minimum voltage value. A second DC / DC converter 20 converts the output voltage of the rechargeable battery unit 13 into a second voltage higher than the maximum voltage value and higher than the first voltage. As the bias voltage Vbias of the drive control circuit 67 of the second DC / DC converter 20, the output voltage of the first DC / DC converter 23 is supplied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to electronic devices, and more particularly to electronic devices equipped with a load circuit that operates on power supplied from a rechargeable battery (also called a secondary battery). [Background technology]

[0002] Electronic devices have a variety of load circuits, such as microcomputers, communication circuits, liquid crystal displays, sensor circuits, etc. These load circuits require a power supply voltage of a specified value, such as 3.3 V or 5.0 V, depending on the type of circuit, such as analog or logic.

[0003] In recent years, the output voltage of lithium-ion batteries, which are the mainstream rechargeable batteries for electronic devices, varies between 2.7 V and 4.2 V for a single cell depending on the remaining battery charge. Therefore, to generate the above driving voltage using a lithium-ion battery, it is necessary to use a DC / DC converter to convert the output voltage of the lithium-ion battery to an appropriate voltage value.

[0004] Japanese Patent Laid-Open Publication No. 2006-81369 (Patent Document 1) discloses a method for improving the efficiency of battery power supplied to a logic circuit. Specifically, a voltage detector detects the output voltage of a rechargeable battery, and if the output voltage of the rechargeable battery is equal to or higher than a predetermined voltage, the battery output voltage is supplied to a regulator without going through a boost circuit, and if the output of the rechargeable battery is lower than the predetermined voltage, a voltage boosted by the boost circuit is supplied to the regulator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-81369 Summary of the Invention [Problem to be solved by the invention]

[0006] For example, medical devices such as syringe pumps or infusion pumps require a power supply voltage of 18 to 24 V for the motor that drives the pump. Therefore, when the remaining battery charge of a lithium-ion battery is low, it is difficult to boost the battery output voltage to 18 to 24 V using a single DC / DC converter.

[0007] One possible solution to the above problem is to use two series-connected DC / DC converters, one in the first stage, to boost the battery's output voltage to an intermediate voltage, and the other in the second stage, to boost the intermediate voltage to 18-24V. However, connecting two DC / DC converters in series increases losses, which is a problem. Another possible solution is to connect multiple lithium-ion batteries in series. However, if a single cell and multiple series-connected cells are used together to increase the battery power efficiency, the hardware becomes more complex and costs increase.

[0008] The present disclosure has been made in consideration of the above-mentioned problems, and one of its objectives is to provide an electronic device that efficiently generates different voltages to be used by multiple load circuits from the output voltage of a rechargeable battery. Other issues and features will be described in the following embodiments. [Means for solving the problem]

[0009] In one embodiment, an electronic device includes a rechargeable battery unit, a first load circuit, a second load circuit, a first DC / DC converter, and a second DC / DC converter. The rechargeable battery unit houses a single rechargeable battery cell or multiple rechargeable batteries connected in parallel, and outputs a voltage ranging from a minimum voltage to a maximum voltage depending on the remaining capacity of each cell. The first DC / DC converter converts the output voltage of the rechargeable battery unit to a first voltage higher than the minimum voltage and outputs the first voltage to the first load circuit. The second DC / DC converter converts the output voltage of the rechargeable battery unit to a second voltage higher than the maximum voltage and higher than the first voltage and outputs the second voltage to the second load circuit. The second DC / DC converter includes a semiconductor switching element, an inductor whose stored energy increases or decreases depending on the on / off state of the semiconductor switching element, and a drive control circuit that generates a drive voltage to be supplied to a control electrode of the semiconductor switching element based on the first voltage.

[0010] In one embodiment, the first voltage is less than the highest voltage value.

[0011] In one embodiment, the first load circuit includes a microcontroller unit that outputs an enable signal to the second DC / DC converter to start a conversion operation.

[0012] In one embodiment, the electronic device further includes a power supply unit, a first diode, and a second diode. The power supply unit converts AC voltage from a commercial AC power supply into DC voltage of a third voltage higher than the highest voltage value and lower than the second voltage. The first diode has a cathode connected to a connection node where an input node of the first DC / DC converter and an input node of the second DC / DC converter are commonly connected, and an anode connected to an output node of the power supply unit. The second diode has an anode to which a discharge current of the rechargeable battery unit is input, and a cathode connected to the connection node.

[0013] In one embodiment, the electronic device further includes a charge / discharge circuit that controls charging and discharging of the rechargeable battery unit, and the charge / discharge circuit draws a charging current from the anode side of the first diode to the rechargeable battery unit in response to a charge start command from the microcontroller unit.

[0014] In one embodiment, the second load circuit includes a motor drive circuit. [Effects of the Invention]

[0015] According to the above embodiment, a drive voltage to be supplied to the control electrode of the semiconductor switching element of the second DC / DC converter is generated based on the first voltage output from the first DC / DC converter. This allows the semiconductor switching element of the second DC / DC converter to be sufficiently driven, and therefore allows different voltages used by multiple load circuits to be efficiently supplied from the rechargeable battery. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a power supply system diagram of an electronic device according to an embodiment. [Figure 2] 2A and 2B are diagrams for explaining an example of use of the rechargeable battery unit of FIG. 1. [Figure 3] 2 is a circuit diagram showing an example of the configuration of a boost circuit that generates DC 24V in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments will be described in detail with reference to the drawings. Note that the same or corresponding parts will be denoted by the same reference characters, and their description may not be repeated.

[0018] [Power supply systems for electronic devices] Fig. 1 is a power supply system diagram of an electronic device according to one embodiment. Referring to Fig. 1, when electronic device 100 is connected to a 100V AC (alternating current) commercial AC power supply 10, it receives a power supply voltage from commercial AC power supply 10, and when electronic device 100 is not connected to commercial AC power supply 10, it receives a power supply voltage from a built-in rechargeable battery unit 13. To achieve this switching of the power supply voltage source, electronic device 100 includes power supply unit 11, charge / discharge circuit 12, rechargeable battery unit 13, and diodes 17 and 18.

[0019] Power supply unit 11 converts AC 100V supplied from commercial AC power supply 10 to DC (direct current) 5V and outputs it. As an example, power supply unit 11 includes a transformer that converts AC 100V to a lower amplitude AC voltage, a rectifier circuit that rectifies the secondary voltage of the transformer, and a smoothing capacitor. As another example, power supply unit 11 includes a rectifier circuit that rectifies AC 100V to a DC voltage, and a step-down power factor correction circuit to which the output voltage of the rectifier circuit is input. The output terminal of power supply unit 11 (which outputs DC 5V) is connected to connection node 14 via diode 17. The direction from power supply unit 11 to connection node 14 is the forward direction of diode 17.

[0020] 2(A) and 2(B), the rechargeable battery unit 13 houses a lithium-ion battery consisting of a single cell or multiple cells connected in parallel. Therefore, whether it is a single cell or multiple cells, the output voltage Vb of the rechargeable battery unit 13 varies between a minimum voltage (e.g., 2.5 V) and a maximum voltage (e.g., 4.1 V) depending on the remaining capacity of the battery. Therefore, the output voltage Vb of the rechargeable battery unit 13 is lower than the output voltage of the power supply unit 11, which is 5 V. The number of cells installed in the rechargeable battery unit 13 is variable. The more battery cells installed in the rechargeable battery unit 13, the longer the electronic device can be used without charging.

[0021] The charge / discharge circuit 12 controls the current and voltage during charging, and also protects against overcharging, overdischarging, and overcurrent. The charge / discharge circuit 12 takes in a charging current from the anode side of a diode 17 and outputs a discharging current to the cathode side of the diode 17 via a diode 18. The forward direction of the diode 18 is from the charge / discharge circuit 12 to the cathode of the diode 17. It is preferable to use an ideal diode IC (Integrated Circuit) as the diode 18 to improve the power supply efficiency of the rechargeable battery.

[0022] According to the above-described connection of diodes 17 and 18, when commercial AC power supply 10 is not connected to power supply unit 11, diode 17 is reverse biased and diode 18 is forward biased, so that power supply voltage is supplied from rechargeable battery unit 13. On the other hand, when commercial AC power supply 10 is connected to power supply unit 11, diode 17 is forward biased and diode 18 is reverse biased, so that power supply voltage is supplied from commercial AC power supply 10 via power supply unit 11.

[0023] The electronic device 100 further includes a plurality of DC / DC converters (i.e., boost circuits 20, 21 and boost / buck circuits 22, 23) for converting the DC voltage supplied from the power supply unit 11 or the charge / discharge circuit 12 via the connection node 14 into a voltage value required for the operation of each of the built-in load circuits 31 to 40.

[0024] Specifically, the boost circuit 20 boosts the output voltage (DC 5V) of the power supply unit 11 or the output voltage (DC 2.5 to 4.1V) of the charge / discharge circuit 12 to a DC voltage of 24V. The boost circuit 20 may be a non-isolated boost chopper, or an isolated flyback converter or forward converter. The output voltage (24V) of the boost circuit 20 is supplied to a motor drive circuit 31, such as a motor main body and an inverter, via a switch 33. The on / off of the switch 33 is controlled by a control MCU (Micro Controller Unit) 37. The output voltage (24V) of the boost circuit 20 is further supplied to various units 32 operating at 24V. An example of the various units 32 is a backlight for a relatively large liquid crystal display. A more detailed configuration example of the boost circuit 20 will be described later with reference to FIG. 3.

[0025] The boost circuit 21 boosts the output voltage (DC 5V) of the power supply unit 11 or the output voltage (DC 2.5 to 4.1V) of the charge / discharge circuit 12 to a DC voltage of 5V. The boost circuit 21 may be a non-insulated boost chopper, or an isolated flyback converter or forward converter. The output voltage (DC 5V) of the boost circuit 21 is supplied to the motor control circuit 34 and various sensors 35 and various units 36 that operate on 5V.

[0026] Each of the step-up / step-down circuits 22 and 23 steps down the output voltage (DC 5V) of the power supply unit 11 to 3.3V, or steps up or down the output voltage (DC 2.5 to 4.1V) of the charge / discharge circuit 12 to 3.3V. Each of the step-up / step-down circuits 22 and 23 may be a non-isolated step-up / step-down chopper, or an isolated flyback converter or forward converter. The output voltage (DC 3.3V) of the step-up / step-down circuit 22 is supplied to a control MCU 37 and various units 38 that operate at 3.3V. The output voltage (DC 3.3V) of the step-up / step-down circuit 23 is supplied to a monitoring MCU 39 and various sensors 40 that operate at 3.3V. Furthermore, as will be described in detail with reference to FIG. 3, the output voltage (DC 3.3V) of the step-up / step-down circuit 23 is used as a power supply voltage (also referred to as a bias voltage Vbias) supplied to a drive control circuit 67 of the step-up circuit 20.

[0027] Each of the control MCU 37 and the monitoring MCU 39 is configured as a microcomputer including a CPU (Central Processing Unit), RAM (Random Access Memory), non-volatile memory, an interface circuit, etc. The control MCU 37 is used primarily to control the electronic device 100, while the monitoring MCU 39 is used primarily to monitor the built-in circuits. For example, the monitoring MCU 39 monitors the operating state of the charge / discharge circuit 12 and the operating state of the rechargeable battery unit 13. Furthermore, the monitoring MCU 39 outputs an enable signal EN to the boost circuit 20 to start the boost operation.

[0028] The control MCU 37 and the monitoring MCU 39 operate in cooperation with each other. For example, to cause the charge / discharge circuit 12 to perform a charging operation, an ON command is required from both the control MCU 37 and the monitoring MCU 39. As shown in Fig. 1, the ON commands from the control MCU 37 and the monitoring MCU 39 are given to the charge / discharge circuit 12 via an AND circuit 15.

[0029] The electronic device 100 further includes ADCs (Analog to Digital Converters) 16, 19, and 30. The ADC 16 converts the output voltage of the rechargeable battery unit 13 into a digital value. The ADC 19 converts the voltage at the connection node 14 into a digital value. The ADC 30 converts the output voltage of the boost circuit 20 into a digital value. The digital voltage values ​​are referenced by the control MCU 37 and the monitoring MCU 39.

[0030] [Configuration example of boost circuit 20] Fig. 3 is a circuit diagram showing an example of the configuration of a boost circuit that generates DC 24V in Fig. 1. The boost circuit 20 shown in Fig. 3 is a non-insulated boost chopper.

[0031] 3, the boost circuit 20 includes an input terminal 50, an output terminal 51, an intermediate node 52 between the input terminal 50 and the output terminal 51, an inductor 53, a diode 55, capacitors 54 and 56, resistors 57 and 58, and a control IC (Integrated Circuit) 60. The control IC 60 includes an N-channel MOS (Metal Oxide Semiconductor) transistor 61, an amplifier circuit 62, a control circuit 63, a voltage regulator 64, and a current sensor 65.

[0032] The connections of the elements constituting the boost circuit 20 will be described below. The inductor 53 is connected between the input terminal 50 and the intermediate node 52. The diode 55 is connected between the intermediate node 52 and the output terminal 51. The output terminal 51 is the cathode side of the diode 55, and the intermediate node 52 is the anode side of the diode 55. The capacitor 54 is connected between the input terminal 50 and ground GND. The capacitor 56 is connected between the output terminal 51 and ground GND. The resistors 57 and 58 are connected in series with each other and in parallel with the capacitor 56 between the output terminal 51 and GND. A feedback voltage Vfb is taken out from a connection node 59 of the resistors 57 and 58.

[0033] The MOS transistor 61 included in the control IC 60 is connected between the intermediate node 52 and ground GND. The voltage regulator 64 receives the 3.3V DC voltage output from the step-up / step-down circuit 23 in FIG. 1 as a bias voltage Vbias. The voltage regulator 64 stabilizes the bias voltage Vbias and outputs it as a drive voltage to the amplifier circuit 62 and the control circuit 63. The voltage regulator 64 operates when an enable signal EN received from the monitoring MCU 39 is activated. The current sensor 65 detects a main current (collector-source current) Ics flowing through the MOS transistor 61. The control circuit 63 determines the pulse width of a PWM (Pulse Width Modulation) control signal 66 by comparing the differential voltage between the feedback voltage Vfb and a reference voltage with a slope voltage. The slope voltage is generated based on the main current Ics detected by the current sensor 65. The control circuit 63 supplies the PWM control signal 66 having the determined pulse width to the gate of the MOS transistor 61 via the amplifier circuit 62. The amplifier circuit 62 is, for example, a push-pull circuit (totem pole circuit). The amplifier circuit 62, the control circuit 63, and the voltage regulator 64 constitute a drive control circuit 67 that generates a drive voltage to be supplied to the gate electrode of the MOS transistor 61 based on the bias voltage Vbias.

[0034] According to the boost circuit 20 configured as described above, when the MOS transistor 61 is in an on state, a current input from the input terminal 50 flows through the inductor 53 and the MOS transistor 61, thereby storing energy in the inductor 53. When the MOS transistor 61 is in an off state, the energy stored in the inductor 53 is output to the load via the output terminal 51, and the input current from the input terminal 50 flows through the inductor 53, thereby storing energy in the inductor 53. By using a bias voltage Vbias of 3.3 V as the drive voltage for the MOS transistor 61, the MOS transistor 61 can be sufficiently driven. As a result, the input voltage Vin can be efficiently boosted to generate the output voltage Vout.

[0035] [summary] The features of the power supply system of the electronic device 100 described above will be summarized below.

[0036] (1) The electronic device 100 is equipped with a rechargeable battery unit 13. The rechargeable battery unit 13 houses a single cell or multiple cells connected in parallel, and outputs a voltage between a minimum voltage value (2.5 V) and a maximum voltage value (4.1 V) depending on the remaining capacity of each cell. Therefore, by increasing the number of cells connected in parallel and increasing the battery capacity, the time until charging can be extended. Furthermore, because the output voltage of the rechargeable battery unit 13 does not depend on the number of cells, the configuration of the power supply circuit can be simplified.

[0037] (2) The electronic device 100 further includes a first load circuit, a second load circuit, a first DC / DC converter (step-up / step-down circuit 23), and a second DC / DC converter (step-up circuit 20). The second load circuit includes a motor drive circuit 31. The first DC / DC converter (step-up / step-down circuit 23) converts the output voltage (2.5 to 4.1 V) of the rechargeable battery unit 13 to a first voltage (3.3 V) that is higher than the minimum voltage value (2.5 V) and outputs the converted first voltage (3.3 V) to the first load circuit. In this embodiment, the first voltage (3.3 V) is lower than the maximum voltage value (4.1 V). The second DC / DC converter (boost circuit 20) converts the output voltage (2.5 to 4.1 V) of the rechargeable battery unit 13 into a second voltage (24 V) that is higher than the maximum voltage value (4.1 V) and higher than the first voltage (3.3 V), and outputs the converted second voltage (24 V) to a second load circuit.

[0038] More specifically, the second DC / DC converter (boost circuit 20) includes a semiconductor switching element (MOS transistor 61), an inductor 53 whose stored energy increases or decreases depending on whether the semiconductor switching element 61 is turned on or off, and a drive control circuit 67 that generates a drive voltage to be supplied to the control electrode of the semiconductor switching element 61 based on the above-mentioned first voltage (3.3 V).

[0039] Suppose, unlike the above configuration, that the drive control circuit 67 generates the drive voltage to be supplied to the control electrode of the semiconductor switching element 61 based on the output voltage (2.5 to 4.1 V) of the rechargeable battery unit 13 input to the second DC / DC converter (boost circuit 20). In this case, if the output voltage of the rechargeable battery unit 13 is close to the minimum voltage value (2.5 V), the drive control circuit 67 cannot sufficiently drive the semiconductor switching element 61. As a result, the output voltage of the second DC / DC converter (boost circuit 20) cannot reach the second voltage (24 V) required for the motor drive circuit 31. On the other hand, in the present embodiment, the drive control circuit 67 generates the drive voltage to be supplied to the control electrode of the semiconductor switching element 61 based on the output voltage (3.3 V) of the first DC / DC converter (boost / step-up circuit 23), so that the semiconductor switching element 61 can be sufficiently driven. As a result, the output voltage of the second DC / DC converter (booster circuit 20) can reach the second voltage (24V) required for the motor drive circuit 31.

[0040] (3) The first load circuit includes a microcontroller unit (monitoring MCU 39). The microcontroller unit (monitoring MCU 39) outputs an enable signal (EN) to cause the second DC / DC converter (boost circuit 20) to start a conversion operation. With this configuration, the voltage (bias voltage Vbias) for driving the semiconductor switching element 61 of the second DC / DC converter (boost circuit 20) and the drive voltage of the microcontroller unit (monitoring MCU 39) are both generated by the first DC / DC converter (boost-down circuit 23). Therefore, by outputting the enable signal EN while the drive voltage (bias voltage Vbias) of the second DC / DC converter (boost circuit 20) is being reliably supplied, the boost operation of the second DC / DC converter (boost circuit 20) can be started.

[0041] (4) The electronic device 100 further includes a power supply unit 11, a first diode 17, a second diode 18, and a charge / discharge circuit 12. The power supply unit 11 converts the AC voltage (100 V AC) from the commercial AC power supply 10 into a DC voltage of a third voltage (5 V DC) that is higher than the maximum voltage value (2.6 V) and lower than the second voltage (24 V). The first diode 17 has a cathode connected to a connection node 14 that connects the input node of the first DC / DC converter (step-up / step-down circuit 23) and the input node of the second DC / DC converter (step-up circuit 20) in common, and an anode connected to the output node of the power supply unit 11. The second diode 18 receives the discharge current of the rechargeable battery unit 13 at its anode and has a cathode connected to the connection node 14. The charge / discharge circuit 12 controls the charging and discharging of the rechargeable battery unit 13. The charge / discharge circuit 12 takes in a charging current from the anode side of the first diode 17 to the rechargeable battery unit 13 in response to a charge start command from the microcontroller unit (monitoring MCU 39).

[0042] According to the above configuration, when commercial AC power supply 10 is not connected to power supply unit 11, diode 17 is reverse biased and diode 18 is forward biased, so that power supply voltage is supplied from rechargeable battery unit 13. On the other hand, when commercial AC power supply 10 is connected to power supply unit 11, diode 17 is forward biased and diode 18 is reverse biased, so that power supply voltage is supplied from commercial AC power supply 10 via power supply unit 11. In this way, the source of power supply voltage can be automatically switched depending on whether commercial AC power supply 10 is connected to power supply unit 11 or not.

[0043] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of this application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0044] 10 Commercial AC power supply, 11 Power supply unit, 12 Charging / discharging circuit, 13 Rechargeable battery unit, 14, 59 Connection node, 17 First diode, 18 Second diode, 20, 21 Boost circuit, 22, 23 Boost / buck circuit, 31 Motor drive circuit, 34 Motor control circuit, 37 Control MCU, 39 Monitoring MCU, 50 Input terminal, 51 Output terminal, 52 Intermediate node, 53 Inductor, 54, 56 Capacitor, 57, 58 Resistor, 60 Control IC, 61 Semiconductor switching element (MOS transistor), 62 Amplification circuit, 63 Control circuit, 64 Voltage regulator, 65 Current sensor, 66 PWM control signal, 100 Electronic device, EN Enable signal, GND Ground, Vbias Bias voltage.

Claims

1. a rechargeable battery unit that houses a single cell or a plurality of cells connected in parallel and outputs a voltage between a minimum voltage value and a maximum voltage value according to the remaining capacity of each cell; a first load circuit and a second load circuit; a first DC / DC converter that converts the output voltage of the rechargeable battery unit into a first voltage higher than the minimum voltage value and outputs the first voltage to the first load circuit; a second DC / DC converter that converts the output voltage of the rechargeable battery unit into a second voltage that is higher than the maximum voltage value and higher than the first voltage, and outputs the second voltage to the second load circuit; The second DC / DC converter A semiconductor switching element; an inductor whose stored energy increases or decreases in response to the on / off of the semiconductor switching element; a drive control circuit that generates a drive voltage to be supplied to a control electrode of the semiconductor switching element based on the first voltage; The drive control circuit includes: a voltage regulator that stabilizes the first voltage; a push-pull circuit driven by the stabilized first voltage; a control circuit driven by the stabilized first voltage and generating a control signal for controlling an operation of the push-pull circuit; The electronic device wherein the control electrode of the semiconductor switching element is connected to an output terminal of the push-pull circuit, thereby receiving the drive voltage from the push-pull circuit.

2. The electronic device according to claim 1 , wherein the first voltage is lower than the highest voltage value.

3. the first load circuit includes a microcontroller unit; 3. The electronic device according to claim 1, wherein the microcontroller unit outputs an enable signal to the second DC / DC converter to cause the second DC / DC converter to start a conversion operation.

4. The electronic device includes: a power supply unit that converts AC voltage from a commercial AC power supply into DC voltage having a third voltage that is higher than the maximum voltage value and lower than the second voltage; a first diode having a cathode connected to a connection node to which an input node of the first DC / DC converter and an input node of the second DC / DC converter are commonly connected, and an anode connected to an output node of the power supply unit; 4. The electronic device according to claim 3, further comprising a second diode having an anode to which the discharge current of the rechargeable battery unit is input and a cathode connected to the connection node.

5. a charging / discharging circuit for controlling charging / discharging of the rechargeable battery unit; 5. The electronic device according to claim 4, wherein the charge / discharge circuit draws a charging current from the anode side of the first diode into the rechargeable battery unit in response to a charge start command from the microcontroller unit.

6. 6. The electronic device according to claim 1, wherein the second load circuit includes a motor drive circuit.

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