JP2015202012A - Power supply circuit, power supply system, and portable terminal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply device capable of stably supplying a power supply voltage without damaging the stability of a circuit as a power supply destination.SOLUTION: A power supply circuit (1) includes: an input terminal (PIN) to which a voltage is supplied; a linear regulator (10) which drops and outputs an input voltage (VBAT); a monitoring part (12) which monitors the voltage supplied to the input terminal; a detection part (13) which detects that the voltage supplied to the input terminal is less than a reference value on the basis of the monitor result of the monitoring part; and a control part (11) which controls the supply of the input voltage to the linear regulator. The control part blocks the supply of the input voltage to the linear regulator when the detection part detects that the voltage supplied to the input terminal is less than the reference value.

Description

  The present invention relates to a power supply circuit, a power supply system, and a portable terminal device, for example, a power supply circuit mounted on a portable terminal device that handles weak analog signals.

  In recent years, a small number of portable terminal devices (hereinafter referred to as “wearable devices”) that are worn on a human body or the like are increasing. As a wearable device, for example, a device that converts a weak vital signal such as a pulse, a body temperature, and a blood pressure detected by a built-in sensor into an electric signal and transmits the signal wirelessly is known.

  In such wearable devices, it is important to reduce the size of a built-in battery (battery) in order to reduce the size and weight of the device. However, generally, when the battery is downsized, the battery capacity is also reduced, and there is a problem that the driving time of the wearable device is shortened.

  Therefore, conventionally, a power supply system in which a small battery and a booster circuit are combined is often mounted on a wearable device. For example, Non-Patent Document 1 discloses a wearable device equipped with a power supply system that combines a coin battery and a booster circuit. Specifically, in a power supply system as described in Non-Patent Document 1, for example, as shown in FIG. 7, a battery voltage is once boosted by a booster circuit such as a switching regulator, and the boosted voltage is lowered to a desired voltage. By supplying it to the internal circuit, a small battery capacity was compensated.

C. Park, PH Chou, Y. Bai, R. Matthews, and A. Hibbs, “An ultra-wearable, wireless, low power ECG monitoring system,” in Proc. IEEE Biomedical Circuit System Conf., London, UK, Nov 2006, pp.241-244.

  However, since the booster circuit composed of a switching regulator or the like performs a switching operation by a chopper circuit or the like, spike noise including a broadband signal component is generated with the switching on / off operation. Such spike noise propagates to a power supply destination circuit via, for example, a power supply line, and thus causes a malfunction for a wearable device that handles a weak electric signal (analog signal).

  Further, in the internal circuit of the wearable device, when the power supply voltage falls below the voltage range in which stable operation is guaranteed, the circuit operation may become unstable due to malfunction or the like. However, the power supply system adopting the conventional booster circuit is designed based on the idea of keeping the power supply voltage of the internal circuit constant by compensating for the decrease by the booster circuit even if the battery voltage drops. It has been difficult to say that sufficient measures have been taken for the case where the power supply voltage of the internal circuit actually decreases.

  The present invention has been made in view of the above problems, and an object of the present invention is to realize a power supply circuit capable of supplying a stable power without impairing the stability of a power supply destination circuit. .

  A power supply circuit according to the present invention includes an input terminal to which a voltage is supplied, a linear regulator that steps down and outputs the input voltage, a monitoring unit that monitors the voltage supplied to the input terminal, and a monitoring result by the monitoring unit And a control unit that detects that the voltage supplied to the input terminal is lower than a reference value, and a control unit that controls the supply of the input voltage to the linear regulator, the control unit Is characterized in that when the detection unit detects that the voltage supplied to the input terminal is lower than a reference value, the supply of the input voltage to the linear regulator is cut off.

  In the power supply circuit, when the detection unit detects that the voltage supplied to the input terminal is lower than a reference value, the detection result is used as the supply destination of the control unit and the output voltage of the regulator. And the control unit supplies the input voltage to the linear regulator after a predetermined period of time has elapsed since it was detected that the voltage supplied to the input terminal was lower than a reference value. You may make it interrupt.

  In the power supply circuit, the reference value includes a first reference value and a second reference value lower than the first reference value, and the detection unit is configured such that the voltage supplied to the input terminal is the first reference value. The first detection result is notified to a circuit to which the output voltage of the regulator is supplied, and when the voltage supplied to the input terminal becomes lower than the second reference value, the second detection result is sent to the circuit. The control unit may be notified, and the control unit may control supply and cutoff of the input voltage to the linear regulator based on the second detection result.

  A power supply system according to the present invention includes the power supply circuit and a power generation device that generates electromotive force, and the power supply circuit inputs an output voltage of the power generation device to the input terminal.

  In the power supply system, the power generation device may include a secondary battery.

  In the power supply system, the power generation device includes a power generation unit that generates power based on energy other than chemical energy, a power storage unit that stores the power generated by the power generation unit, and outputs a voltage corresponding to the stored power. It may be comprised including.

  In the power supply system, the power generation unit may include any one of a solar power generation device, a vibration power generation device, a temperature difference power generation device, a wireless power supply device, and an electric double layer capacitor.

  A portable terminal device according to the present invention includes the power supply system and an internal circuit that operates using an output voltage of the linear regulator as a power supply.

  According to the present invention, a stable power supply can be performed without impairing the stability of the power supply destination circuit.

It is a figure which shows the structure of the portable terminal device provided with the power supply circuit which concerns on Embodiment 1 of this invention. FIG. 3 is a diagram illustrating a first specific example of the power generation device 2. 3 is a diagram illustrating a second specific example of the power generation device 2. FIG. It is a figure which shows the structure of the portable terminal device provided with the power supply circuit which concerns on Embodiment 2 of this invention. 4 is a diagram illustrating a first specific example of a detection unit 23. FIG. 6 is a diagram illustrating a second specific example of the detection unit 23. FIG. It is a figure which shows the structure of the portable terminal device provided with the conventional power supply circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< Embodiment 1 >>
FIG. 1 shows a configuration of a mobile terminal device including a power supply circuit according to Embodiment 1 of the present invention.
The mobile terminal device 100 is a wearable device that is attached to a human body, for example, detects biological information (a vital signal) and wirelessly transmits the information to an external device or the like.

  The mobile terminal device 100 includes, for example, a power generation device 2, a power supply circuit 1, an internal circuit 3, and various sensors not shown.

  For example, the sensor detects various vital signals from a human body wearing the portable terminal device 100, converts each vital signal into an electric signal (analog signal), and inputs the electric signal to the internal circuit 3. The vital signals detected by the sensor are, for example, heart rate, pulse rate, respiration, blood pressure, myoelectricity, electrooculogram, electrocardiogram, skin potential, and electroencephalogram.

The internal circuit 3 converts the analog signal input from the sensor into a digital signal, performs various signal processing as necessary, and transmits the signal to an external device via an antenna (not shown). The internal circuit 3 includes, for example, an A / D conversion circuit, a signal processing circuit, a program processing device such as an MCU, and an RF circuit.
There are no particular restrictions on the standard of wireless communication via the antenna.

The power generation device 2 and the power supply circuit 1 constitute one power supply system that supplies power to the sensors in the mobile terminal device 100, the internal circuit 3, and the like.
First, the power generator 2 will be described. The power generation device 2 is a device that generates an electromotive force. 2 and 3 show specific examples of the power generation device 2.

  FIG. 2 is a diagram illustrating a first specific example of the power generation device 2. As shown in the figure, the power generation device 2 includes a battery 20, for example. The battery 20 is, for example, a button-type primary battery (such as a lithium battery) or a rechargeable secondary battery (such as a lithium ion battery). The battery 20 may be composed of a single battery cell, or may be composed of a battery pack in which a plurality of battery cells are connected in series or in parallel. There is no limit. The battery voltage VBAT of the battery 20 is supplied to the input terminal PIN of the power supply circuit 1.

  FIG. 3 is a diagram illustrating a second specific example of the power generation device 2. As shown in the figure, the power generation device 2 includes, for example, a power generation unit 21 and a power storage unit 20.

  The power generation unit 21 includes a power generation device that generates electric power based on external energy EX_ENG other than chemical energy. Examples of the power generation device constituting the power generation unit 21 include a device that generates power by energy harvesting technology (environmental power generation technology) such as a solar power generation device, a vibration power generation device, and a temperature difference power generation device, a wireless power supply device, and an electric double layer capacitor. Etc. can be illustrated. The power generation unit 21 only needs to include at least one of the power generation devices exemplified above, and may include a plurality of power generation devices described above, for example.

  The power storage unit 20 stores the power generated in the power generation unit 21 and outputs a voltage VBAT corresponding to the stored power. The power storage unit 20 includes, for example, a secondary battery (for example, a lithium ion battery) that can be charged based on the electric power of the power generation unit 21, a large-capacity capacitor, and the like.

Next, the power supply circuit 1 will be described.
The power supply circuit 1 generates the power supply voltage VCC of the internal circuit 3 based on the battery voltage VBAT output from the power generator 2. As shown in FIG. 1, the power supply circuit 1 includes an input terminal PIN, a linear regulator 10, a control unit 11, a monitoring unit 12, a detection unit 13, and the like.

The input terminal PIN inputs the battery voltage VBAT of the power generator 2.
The linear regulator 10 is a stabilized power supply circuit that steps down a battery voltage VBAT input via a control unit 11 to be described later and generates a constant voltage. The linear regulator 10 is, for example, a low saturation type linear regulator (LDO: Low Drop Out) having a small input / output potential difference. The linear regulator 10 generates a power supply voltage VCC of 3.0 V from a battery voltage VBAT of about 4.4 V to 3.5 V, for example, and supplies it to the internal circuit 3.

  The monitoring unit 12 monitors the battery voltage VBAT supplied to the input terminal PIN and outputs a monitoring result VM. The monitoring unit 12 is realized by, for example, a resistance ladder circuit or an A / D conversion circuit. For example, when the monitoring unit 12 is realized by a resistance ladder circuit, the monitoring result VM is, for example, a voltage obtained by dividing the battery voltage VBAT by resistance. On the other hand, when the monitoring unit 12 is realized by an A / D conversion circuit, the monitoring result VM becomes a digital value (digital signal) corresponding to the battery voltage VBAT, for example.

  The detection unit 13 detects that the battery voltage VBAT supplied to the input terminal PIN has become lower than a predetermined reference value based on the monitoring result VM by the monitoring unit 12, and validates the detection signal DT.

  Here, the predetermined reference value is determined based on the lower limit value of the battery voltage VBAT necessary for the linear regulator 10 to generate the lowest power supply voltage VCC that guarantees the stable operation of the internal circuit 3, for example. For example, when the voltage range of the power supply voltage VCC that guarantees stable operation of the internal circuit 3 is “4.0 V to 3.0 V”, the battery voltage necessary for the linear regulator 10 to generate “3.0 V” If the lower limit value of VBAT is “3.4 V”, the reference value is, for example, “3.4 V”. According to this, when the battery voltage VBAT falls below “3.4 V”, the detection signal DT becomes valid.

  The specific configuration of the detection unit 13 is not particularly limited as long as it can detect a decrease in the battery voltage VBAT. For example, when the detection unit 13 is realized by an analog circuit, the monitoring result VM (voltage obtained by dividing the battery voltage VBAT by resistance) output from the monitoring unit 12 including a resistance ladder circuit, and a voltage corresponding to the reference value The detection unit 13 may be realized by an analog comparator circuit that compares. On the other hand, when the detection unit 13 is realized by a digital circuit, the coincidence between the A / D conversion result (monitoring result) VM of the monitoring unit 12 including the A / D conversion circuit and the digital value corresponding to the reference value is detected. The detection unit 13 may be realized by a digital circuit.

  The control unit 11 controls supply and interruption of the battery voltage VBAT to the linear regulator 10 based on the detection result by the detection unit 13. Specifically, when the detection signal DT of the detection unit 13 is invalidated (negated), the control unit 11 supplies the battery voltage VBAT supplied to the input terminal PIN to the linear regulator 11 as an input voltage and detects it. When the detection signal DT of the unit 13 is validated (asserted), the supply of the battery voltage VBAT to the linear regulator 11 is cut off.

  For example, the control unit 11 is configured based on the detection signal DT based on a transistor (for example, a MOS transistor or a bipolar transistor having a low on-resistance) connected in series between the input terminal PIN and the input terminal of the linear regulator 10. And a driving circuit for controlling on / off of the transistor.

  According to the power supply circuit 1 having the above configuration, the power supply voltage VCC of the internal circuit 3 is controlled as follows. For example, when the charging capacity of the battery 20 is sufficient (for example, the battery voltage VBAT is about 4.4 V to 3.5 V), the control unit 11 supplies the battery voltage VBAT to the linear regulator 10. Thereby, a constant voltage (for example, 3.0 V) is generated by the linear regulator 10 and supplied to the internal circuit 3 as the power supply voltage VCC. Thereafter, when the charging capacity of the battery 20 gradually decreases and the power supply voltage VBAT becomes lower than the reference value (for example, 3.4 V), the detection signal DT is validated, and the control unit 11 determines the battery voltage VBAT for the linear regulator 10. Shut off the supply. As a result, the supply of the power supply voltage VCC to the internal circuit 3 is stopped, and the internal circuit 3 stops operating.

  As described above, according to the power supply circuit 1 according to the first embodiment, since the linear regulator 10 is used instead of the conventional switching regulator or the like as a circuit for generating the power supply voltage supplied to the internal circuit 3, spikes caused by the switching operation It is possible to prevent malfunction of the internal circuit 3 that handles weak analog signals such as vital signals without generating noise.

  Further, according to the power supply circuit 1, since the power supply to the internal circuit 3 is stopped when the battery voltage VBAT decreases to the reference value, it is possible to prevent the internal circuit 3 from being supplied with a power supply voltage lower than the standard value. . As a result, it is possible to prevent a malfunction or the like of the internal circuit 3 caused by the supply of the power supply voltage equal to or lower than the standard value to the internal circuit 3.

  That is, according to the power supply circuit 1 according to the present invention, stable power supply can be performed without impairing the stability of the power supply destination circuit. In particular, it is effective as a power supply circuit for a system equipped with a circuit that handles weak analog signals such as wearable devices.

<< Embodiment 2 >>
FIG. 4 shows a configuration of a mobile terminal device including the power supply circuit according to the second embodiment. The power supply circuit 4 shown in the figure is the power supply according to the first embodiment in that it notifies not only the control unit 11 but also the internal circuit 3 of the detection result that the battery voltage VBAT is lower than a predetermined reference value. Unlike the circuit 1, the other points are the same as those of the power supply circuit 1. In the power supply circuit 4, the same components as those of the power supply circuit 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the mobile terminal device 101, the power supply circuit 3 includes a detection unit 23 instead of the detection unit 13 of the power supply circuit 1 according to the first embodiment.

  The detection unit 23 detects that the battery voltage VBAT has dropped below a predetermined reference value based on the monitoring result VM by the monitoring unit 12, and notifies the detection signal DT1 to the internal circuit 3 before detecting the detection signal DT2. Is notified to the control unit 11. Based on the detection signal DT2, the control unit 11 switches between supply and interruption of the battery voltage VBAT to the linear regulator 10 as in the first embodiment. The internal circuit 3 that has received the notification performs, for example, necessary processing before the power is turned off as necessary.

  By notifying the internal circuit 3 and the control unit 11 step by step that the battery voltage VBAT has decreased as described above, it is possible to notify the internal circuit 3 in advance that the power supply will be cut off. . A specific configuration example of the detection unit 23 is shown below.

FIG. 5 is a diagram illustrating a first configuration example of the detection unit 23.
As shown in the figure, the detection unit 23 includes a comparison circuit 131 that compares the battery voltage VBAT and the reference value VREF1, and a comparison circuit 132 that compares the battery voltage VBAT and the reference value VREF2. The comparison result by the comparison circuit 131 is input to the internal circuit 3 as the detection signal DT1, and the comparison result by the comparison circuit 132 is input to the control unit 11 as the detection signal DT2. The comparison circuit 131 and the comparison circuit 132 may be realized by an analog comparator circuit as in the detection unit 13 described above, or may be realized by a digital circuit, and the specific circuit configuration is particularly limited. There is no.

  Here, the reference value VREF1 is larger than the reference value VREF2. For example, consider a case where the reference value VREF1 is set to “3.5V” and the reference value VREF2 is set to “3.4V”. For example, when the battery voltage VBAT, which was about 4.4 V when the battery 20 is fully charged, gradually decreases and becomes lower than 3.5 V, the comparison circuit 131 outputs the detection signal DT1 and is notified to the internal circuit 3. Thereafter, when the battery voltage VBAT further decreases and becomes lower than 3.4 V, the comparison circuit 132 outputs the detection signal DT2 and notifies the control unit 11 of the detection signal DT2. The control unit 11 stops the supply of the battery voltage VBAT to the regulator 10 according to the detection signal DT2, and the internal circuit 3 is cut off from the supply of the power supply voltage VCC and stops its operation.

  As described above, according to the detection unit 23 illustrated in FIG. 5, the internal circuit 3 can be notified in advance that the power supply is cut off before the power supply is cut off. It is possible to perform necessary processing before the power is shut off. For example, the internal circuit 3 that has received the detection signal DT1 prevents the loss of necessary data due to power shutdown by saving the data related to the operation processing being executed to a non-volatile storage device such as a flash memory. can do.

  In addition, the internal circuit 3 that has received the detection signal DT1 can notify the user that the capacity of the battery 20 has been reduced by displaying it on a display device such as a liquid crystal display or by outputting it by voice. . Thereby, before the power source of the internal circuit 3 is shut off, the user can be prompted to replace the battery.

Next, a second configuration example of the detection unit 23 is shown in FIG.
The detection unit 23 shown in the figure includes a comparison circuit 130 that compares the battery voltage VBAT and the reference value VREF, and a delay circuit 133 that outputs the comparison result of the comparison circuit 130 with a delay of a predetermined time. The comparison result by the comparison circuit 130 is input to the internal circuit 3 as the detection signal DT1, and the output signal of the delay circuit 133 is input to the control unit 11 as the detection signal DT2.

  The delay time by the delay circuit 133 is not particularly limited as long as it is sufficient to perform necessary processing on the internal circuit 3 side before the power is shut off. For example, it is sufficient that there is a sufficient delay time for saving the data related to the arithmetic processing being executed by the internal circuit 3 to the nonvolatile storage device.

  According to the detection unit 23 illustrated in FIG. 6, as with the detection unit illustrated in FIG. 5 described above, the internal circuit 3 and the control unit 11 can be notified step by step that the battery voltage VBAT has decreased. It is possible to perform necessary processing on the internal circuit 3 side before the power is shut off.

  As described above, according to the power supply circuit according to the second embodiment, it becomes possible to perform necessary processing on the internal circuit 3 side before the power is shut off, and the stability of the operation of the internal circuit 3 can be further improved. It becomes possible.

  Although the invention made by the present inventors has been specifically described based on the embodiments, it is needless to say that the present invention is not limited thereto and can be variously modified without departing from the gist thereof. Yes.

For example, in the second embodiment, the configuration in which the detection unit 23 outputs the two detection signals DT1 and DT2 is illustrated. However, the present invention is not limited to this, and before the internal circuit 3 is powered off, Any configuration that can notify the detection result may be used. For example, one detection signal DT is generated as in the detection unit 13 according to the first embodiment, and the detection signal DT is input to both the internal circuit 3 and the control unit 11. The controller 11 stops supplying the battery voltage VBAT to the regulator 10 after a predetermined time has elapsed since the detection signal DT was input. The predetermined time may be sufficient to perform necessary processing on the internal circuit 3 side before the power is turned off.
According to this, the detection result can be notified to the internal circuit 3 side before the power supply to the internal circuit 3 is cut off.

  Moreover, although the case where the power supply circuits 1 and 4 according to the first and second embodiments are mounted on the wearable device is illustrated, the present invention is not limited to this, and the present invention can be widely applied to any system including a circuit that handles weak analog signals. be able to.

  DESCRIPTION OF SYMBOLS 100, 101 ... Portable terminal device, 1 ... Power supply circuit, 2 ... Power generation device, 3 ... Internal circuit, 10 ... Linear regulator, 11 ... Control part, 12 ... Monitoring part, 13, 23 ... Detection part, DT, DT1, DT2 ... detection signal, VCC ... power supply voltage, PIN ... input terminal, VBAT ... battery voltage, VM ... monitoring result (monitor voltage), 20 ... battery, 21 ... power generation unit, 22 ... power storage unit, EX_ENG ... external energy, 130, 131, 132 ... comparison circuit, 133 ... delay circuit.

Claims (8)

An input terminal to which voltage is supplied;
A linear regulator that steps down the input voltage and outputs it;
A monitoring unit for monitoring the voltage supplied to the input terminal;
Based on a monitoring result by the monitoring unit, a detection unit that detects that the voltage supplied to the input terminal is lower than a reference value;
A controller that controls the supply of the input voltage to the linear regulator;
The control unit cuts off the supply of the input voltage to the linear regulator when it is detected that the voltage supplied to the input terminal by the detection unit is lower than a reference value. . The power supply circuit according to claim 1,
When the detection unit detects that the voltage supplied to the input terminal is lower than a reference value, the detection unit notifies the control unit and a circuit to which the output voltage of the regulator is supplied. And
The control unit cuts off the supply of the input voltage to the linear regulator after a lapse of a predetermined period after it is detected that the voltage supplied to the input terminal is lower than a reference value. Power supply circuit. The power supply circuit according to claim 1,
The reference value includes a first reference value and a second reference value lower than the first reference value,
When the voltage supplied to the input terminal becomes lower than the first reference value, the detection unit notifies the first detection result to a circuit to which the output voltage of the regulator is supplied and is supplied to the input terminal. When the detected voltage becomes lower than the second reference value, the second detection result is notified to the control unit,
The said control part controls supply and interruption | blocking of the said input voltage with respect to the said linear regulator based on the said 2nd detection result. The power supply circuit characterized by the above-mentioned. A power supply circuit according to any one of claims 1 to 3,
A power generation device for generating electromotive force,
The power supply circuit inputs an output voltage of the power generation device to the input terminal.
A power supply system characterized by that. The power supply system according to claim 4, wherein
The power generation apparatus includes a secondary battery. The power supply system according to claim 4, wherein
The power generator is
A power generation unit that generates electric power based on energy other than chemical energy;
A power storage unit that stores electric power generated by the power generation unit and outputs a voltage corresponding to the stored electric power. The power supply system according to claim 6, wherein
The power generation unit includes any one of a solar power generation device, a vibration power generation device, a temperature difference power generation device, a wireless power feeding device, and an electric double layer capacitor. A power supply system according to any one of claims 4 to 7,
And an internal circuit that operates using the output voltage of the linear regulator as a power source.

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