JPH0949868A - Battery exhaustion detector, power supply circuit having the detector and portable machinery having the power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a warning point of time by obtaining a battery replacing warning start point as an A/D conversion value by receiving reference voltage from the output of a regulator circuit to set an internal power supply side to a fluctuation value and setting an input signal side to a fixed value to obtain a reference voltage value side as an A/D conversion value. SOLUTION: Constant voltage is inputted to the input side of an A/D conversion circuit (A/D) 13 and, even after the regulation of a three-terminal regulator 3 becomes impossible, an A/D conversion value is taken out corresponding to the fluctuations of A/D reference voltage. When a transistor Q is turned ON by a control signal, constant voltage Vz is generated in a diode ZD terminal. The constant voltage Vz becomes the input terminal of an A/D 13 and the A/D 13 sets the output voltage Vc of the regulator 3 to reference voltage to apply the same to respective reference voltage comparing circuits 13a...13n. Since the input signal becoming the object of A/D conversion is fixed in voltage, the A/D conversion value different to the input signal only when a reference side is fluctuated is obtained and the voltage fluctuations of the regulator 3 are detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dead battery detecting device, a power supply circuit having the same, and a portable device having the power supply circuit. More specifically, the present invention relates to a portable magnetic tape player driven by one or several dry batteries. The present invention relates to a dead battery detection device capable of expanding the range of use of a battery in a power supply circuit of a portable audio device such as a portable CD player or a portable device driven by a battery such as a camera, up to the limit of use of the battery.

[0002]

2. Description of the Related Art Conventional headphone stereos, DCCs,
Portable magnetic tape player such as DAT, MD, C
Portable disc players such as D are driven by dry batteries, and the number thereof is about 1 to 2. Therefore, the power supply voltage of the audio circuit incorporated in this type of device is only about 1.2V or 2.4V. Further, in a compact camera or the like, photometry, an automatic focusing device, a motor for driving the device, or the like is driven by battery power. Such battery-powered devices typically include a microcontroller and LCD display (LCD).
And so on. Then, by detecting the battery voltage,
As a result, it is determined that the electric power of the battery is equal to or less than the predetermined value, and the LCD displays the battery replacement time, the fact that the battery is almost exhausted, or the battery exhaustion message. When the battery runs out, the power supply is cut off. In this specification, when the battery is dead, it means that the power supply voltage of the device has dropped below a predetermined value, so that the power is shut off to stop the operation of the device and the battery is replaced before the device is used. Means that

FIG. 5 is a block diagram centering on a power supply circuit having a battery dead detection device of this type of conventional device. Reference numeral 1 denotes a battery, and the electric power from the battery 1 is sent to a three-terminal regulator 3 (hereinafter referred to as a regulator 3) via a power input line 2 which is a primary side input, where the electric power controlled to a constant voltage is two. Power line 4 (Vc
sent to c). To the power supply line 4, a control circuit 5 for control, which is a so-called microcomputer, and a signal processing circuit 6 such as an audio signal amplification circuit are usually connected as loads. Then, a voltage dividing circuit of a resistor R1 and a resistor R2 is provided as a voltage detecting circuit 7 for detecting the voltage of the battery 1 between the power input line 2 to which the battery 1 is connected and the ground GND. Circuit 7
The divided voltage due to is detected and the control circuit 5 receives this detected voltage. Reference numeral 8 denotes an LCD (liquid crystal display device) that displays the battery exhaustion and the operating state of the device.

Focusing on the fact that the output of the regulator 3 is constant, the control circuit 5 normally uses a voltage comparison type A / A circuit having a number of reference voltage comparison circuits in parallel with this output (the divided voltage thereof) as a reference. The detection voltage is A / D converted by the D conversion circuit (A / D) 5a. This is because, for example, a 4-bit digital value is generated twice, the detection voltage is converted into an 8-bit digital value, and the control circuit 5 receives this digital value internally and compares it with a predetermined reference value. It is determined whether it is time to replace the battery or whether the battery is near the end, and a message to that effect is displayed on the LCD 8. If it is determined that the battery is dead,
Battery exhaustion processing (power cutoff after battery exhaustion display) is performed. Here, the voltage detection circuit 7 is provided in parallel with the battery. Therefore, current always flows and consumes power. In actuality, in order to reduce power consumption, a switch circuit or the like is inserted in series to this circuit to control the voltage detection circuit 7 to operate regularly. However, such control circuits are omitted here.

[0005]

FIG. 6 shows the output voltage in the case of two batteries from the time when the battery is replaced or the warning message indicating that the battery is close to the end is displayed to the time when the battery is exhausted or the power is cut off. The relationship is shown as a graph. At the point of time when the battery exhaustion display or the power shutdown is performed, the reference output of the regulator 3 is normally set at a limit point L at which the output is maintained at a constant value. In the figure, graph A shows the voltage of the battery. Graph B is the output voltage of the regulator 3, and C is the detected voltage after being converted into a digital signal by the A / D 5a. Then, the voltage value V1 indicated as AR (alarm) is the above-mentioned reference value, which is the start time point for displaying a message indicating that the battery is replaced or the battery is near the end, and the point E is the reference value for processing the dead battery. The voltage value is V2. As shown in FIG. 6, at the time of battery replacement or the end of the warning period T indicating that the battery is near the end,
That is, the time point E at which the power is turned off and the operation of the device is stopped is set to the limit point L at which the output voltage of the regulator 3 becomes non-constant or immediately before that. The reason is,
This is because if the output voltage drops from a constant value, the reference value for A / D conversion changes, and the A / D converted value becomes unreliable. When the point E is exceeded, the control circuit 5 normally performs a process of stopping the operation of the device.

However, the life of the battery that can be actually used is
Even longer. In the battery dead detection device, the output of the regulator is used as the reference voltage for A / D conversion.
The voltage is detected in the range where this is kept constant. Therefore, the detection point cannot be set on the limit side of battery usage. As a result, on the contrary, in this type of battery dead detection device, a warning indicating that the battery is about to be replaced or the battery is near the end is issued shortly before the original battery is dead. As a result, the battery is replaced, and the battery tends to be wasted in view of the original battery exhaustion. An object of the present invention is to solve the above-mentioned problems of the prior art, and to detect a dead battery that can detect a dead battery by expanding the usage range to a range close to the usage limit of the battery. To provide a device. Another object of the present invention is to provide a power supply circuit that can use its electric power up to a range close to the usage limit of the battery. Further, another object of the present invention is to
An object of the present invention is to provide a portable device that can use the electric power up to a range close to the limit of use of the battery.

[0007]

The battery dead detecting device, the power supply circuit or the portable device of the present invention for achieving the above object is characterized by a battery dead detecting a battery dead according to the power consumption of the battery. In the detection device, a constant voltage generation circuit for generating a constant voltage up to the use limit voltage of the battery,
The constant voltage from the constant voltage generating circuit is supplied to the A / D by receiving the operating power from the power supply line which decreases in accordance with the power consumption.
When the A / D to be converted and the A / D conversion value obtained from this A / D are received and the digital data value obtained by converting the constant voltage changes by a predetermined value or more, the battery is dead.
Specifically, a predetermined constant voltage is received as an input signal up to the use limit voltage of the battery, and the output voltage of the regulator circuit is a reference voltage (a voltage for determining the voltage per 1 LSB inside the A / D, for example, A A / D, which generates a conversion value according to the reference voltage (power supply voltage) and the input signal, and is within the operable range of the device and on the side of the limit of use of the battery. A battery dead detection that has the converted value obtained corresponding to the voltage of the regulator circuit when the voltage drops to a close voltage value as a reference value, and detects the dead battery when the converted value exceeds this reference value. And means.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, 1 L inside the A / D
A voltage that determines the voltage per SB, for example, this A / D
As a voltage comparison type that compares the voltage with the input signal, the power supply (reference voltage) inside the A / D is received from the output of the regulator circuit, the reference voltage side (internal power supply side) is used as the variable value, and the input signal side is used as the fixed value. By doing so, it is possible to obtain the A / D conversion value according to the fluctuation on the reference voltage value side (power supply side inside the A / D). In a voltage comparison type A / D having a plurality of voltage comparison circuits, each receives an analog input signal and binarizes the analog signal into “0” or “1” according to each comparison reference value, Generate a 1-bit converted value. Therefore, when the comparison reference voltage (internal power supply voltage) becomes small, the value of the 1-bit conversion value changes from "0" to "1" depending on the voltage of the input signal. As a result, the A / D converted value increases in accordance with the decrease in each comparison reference voltage, in other words, the decrease in the internal power supply voltage.

From the above, it is possible to obtain the point at which the battery replacement or the warning that the battery is near the end is started by giving a varying voltage to the A / D reference voltage as the A / D conversion value. As a result, the warning point can be detected. Furthermore, when the output of the regulator drops near the limit of battery usage, A /
The D-converted value can be obtained as a detection value, which allows the battery exhaustion to be detected.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic configuration of the battery dead detection device of the present invention shown in FIG. 1 differs from that of the conventional battery dead detection device shown in FIG. 5 in that a constant voltage is input to the input side of the A / D and a regulator 3 is used.
Even after the regulation is no longer possible, the A / D is affected by the fluctuation of the A / D reference voltage (internal power supply voltage), that is, by the fluctuation of the output side (secondary side) of the regulator.
By extracting the converted value, the fluctuation of the output voltage of the regulator is obtained as the A / D converted value. As a result, it is possible to obtain, as the A / D converted value, the power reduction of the battery up to the vicinity of the usage limit value. The same components as those in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 10 is a control circuit, which is configured by a one-chip microcomputer or the like. Inside it, M
CU 11 and memory 12 mainly composed of ROM, and A /
A D converter (A / D) 13 is provided. A /
D13 is a voltage comparison type A / D having a large number of reference voltage comparison circuits 13a, 13b, ..., 13n in parallel, like the A / D 5a of FIG. This reference voltage comparison circuit 13a,
The reference voltage input sides of 13b, ..., 13n respectively receive the divided voltages via the resistance voltage dividing circuit 130. However, the comparison input side of the reference voltage comparison circuit 13a is directly connected to the secondary side output line 4 (Vc
Receive the voltage of c).

The resistance voltage dividing circuit 130 includes resistors Ra, ... Rn.
Of the series circuit, which is inserted in the secondary output line 4 (voltage Vcc) of the regulator 3 and the ground GND. Then, the voltage Vcc of the secondary side output line 4 is divided by the resistors between the voltage Vcc and the ground GND. As a result, the reference input voltage of the reference voltage comparison circuit 13a is the voltage V
cc, and subsequent reference voltage comparison circuits 13b, ..., 13n
The voltage of the reference input of is a voltage divided by each resistance value. Each reference voltage comparison circuit 13a, 1
, 3n receives the input constant voltage Vz on one side and receives the divided voltage generated by resistance-dividing the reference voltage Vcc by the resistors Ra, ... Rn as a comparison reference voltage, and this and the input voltage. By comparing with Vz, signals of "0" and "1" are generated. The memory 12 has a battery dead detection program 12a and a battery dead display program 12
b, power-off program 12c, initial setting program 12
d, other control programs 12e, etc. are stored.

Numeral 15 is a constant voltage generating circuit for the battery 1
It is inserted between the electric power input line 2 which is the output of and the ground GND. The constant voltage generating circuit 15 includes a resistor R
3, a Zener diode ZD, and a transistor Q that forms a switch circuit. The terminal of the Zener diode ZD is connected to the input terminal 10a of the control circuit 10, and the constant voltage Vz is applied to this terminal. The base of the transistor Q is connected to the output terminal 10b of the control circuit 10 and receives the control signal from this terminal. This control signal is sent from the MCU 11 directly or via a buffer amplifier (not shown) or the like to the terminal 10
b. When the transistor Q is turned on in response to this control signal, the Zener diode Z
A constant voltage Vz is generated at the D terminal, and this constant voltage Vz becomes an input signal of the A / D 13 via the input terminal 10a. A /
D13 applies the output voltage Vcc of the regulator 3 as a reference voltage as a comparison reference voltage for the reference voltage comparison circuits 13a, 13b, ..., 13n. As a result, an A / D conversion value corresponding to the input signal (constant voltage) is obtained.

Since the voltage of the input side signal to be A / D converted is fixed here, a different A / D conversion value is obtained for the input signal only when the reference side changes.
As a result, the voltage fluctuation of the regulator 3 that regulates the voltage is detected. That is, the reference voltage comparison circuit 13
a, 13b, ..., 13n are analog input signals input according to the respective comparison reference values, which are “0” or “1”.
And binarize each to generate a 1-bit conversion value.
Therefore, when the output voltage of the regulator 3 decreases and each comparison reference voltage decreases, the 1-bit conversion value changes from "0" to "1" in accordance with the relationship between the input signal and the comparison voltage. Things happen. As a result, the A / D converted value rises in accordance with the decrease in the comparison reference voltage, in other words, the voltage decrease in the A / D internal power supply. Therefore, the conversion data of the digital value obtained by the A / D conversion according to the constant voltage Vz and the voltage Vcc represents the voltage drop of the battery. FIG. 3 shows the relationship between the output voltage (characteristic graph A) and the A / D conversion value (characteristic graph D) in the case of two batteries. The voltage of the battery 1 exceeds the vicinity of the output voltage (the battery dead point L in FIG. 6, which is the same as the point L in FIG. 3) that maintains the constant output voltage of the regulator 3, and the battery 1
Alternatively, the constant voltage Vz (can be received by the simple A / D of the reference voltage comparison type within a range in which the device can operate in response to the output of the regulator 3 and reaches the voltage value V3 at the point P close to the use limit side of the battery 1. The figure shows an example of Vz = 1.7 V.) It becomes possible to obtain an A / D conversion value for Vz = 1.7 V. It should be noted that the point P in FIG. 3 corresponds to the reference value Rf2 in the graph D representing the A / D conversion value, and this is almost at a point where the circuit in the apparatus is operable and near the use limit point of the battery 1. I am doing it. Therefore, in this example, the dead battery is detected when the A / D converted value exceeds the reference value Rf2.

Reference numeral 16 is a power switch circuit composed of an analog switch or the like inserted between the battery 1 and the regulator 3, and is an output terminal 1 of the control circuit 10.
0c has its control terminal connected to receive a control signal from this terminal 10c. This control signal is also sent from the MCU 11 directly to the terminal 1 via a buffer amplifier (not shown) or the like.
Sent to 0c. A start-up switch 17 is turned on only while the operation switch is being operated. The control circuit 10 first activates the initialization program 12d when the startup switch 17 is turned on and the power supply voltage Vcc is supplied to the control circuit 10. By executing this program, the MCU 11 generates a HIGH level (hereinafter "H") control signal at the terminal 10c to turn on the power switch circuit 16. Further, an initial setting control signal is sent to each circuit inside the apparatus. As a result, the regulator 3 is installed in each circuit inside the device.
The electric power of the constant voltage generated by is supplied.

The dead battery detection program 12a is a regular interrupt processing program having A / D conversion values Rf1 and Rf2 shown in FIG. 3 as reference values as comparison reference data. As shown in FIG. (Eg 16mse
It is executed by the MCU 11 for each c). The MCU 11 generates a control signal of "H" at the terminal 10b by executing this program (step 100). This turns on the transistor Q. Then, after waiting for a fixed time (step 101), the MCU 11 reads the data A / D converted by the A / D 13 from the A / D 13 (step 102). After that, the MCU 11 sets the voltage of the terminal 10b to the LOW level (hereinafter "L") (step 10).
3). Then, it is determined whether the A / D converted value is equal to or larger than the reference value Rf1 (step 104). As a result of this determination, NO
Is displayed, a message indicating that the battery is normal is displayed on LCD8.
(Step 105), and this processing ends.
On the other hand, if the result of the determination in the previous step 104 is YES, a message indicating a battery replacement or a warning that the battery is near the end is sent to the LCD 8 (step 1
06) Next, it is determined whether the A / D converted value is the reference value Rf2 or more (step 107). As a result of this determination, NO
When this happens, this process ends. If the result of the determination in step 107 is YES, then the step 1
The same judgment as in 07 is repeated several times with a predetermined time, and the reduced power supply voltage is monitored for time. When the same judgment result continues for a certain period or more, it is determined that the battery is dead and the control signal of the terminal 10c is set to "L". The power supply from the battery 1 is cut off (the battery power is cut off) (step 108). At this time, if the power supply voltage rises and the A / D converted value becomes equal to or less than the reference value Rf2, the battery power interruption process may not be performed.

Here, the value of the reference value Rf2 for the determination is
As described above, it corresponds to the voltage value of the graph D at the position of the point P in FIG. Therefore, the electric power of the battery 1 can be utilized up to the position of this point P. That is, the A / D converted value when the voltage is normal is maintained at a constant value because the constant voltages are compared inside the A / D. When the output of the regulator 3 starts to drop below the constant voltage value, the voltage value on the reference side decreases, but since the input side is constant, A
The / D conversion value increases (see graph D). The reference value Rf1 for the above determination corresponds to the voltage at the initial rising point. According to the present invention, a warning indicating that the battery should be replaced or that the battery is near the end is started from the time of the converted value corresponding to the reference value Rf1. This time point is the same as or close to the conventional battery 1 dead battery indication or power-off time. And
The detection of the battery voltage by the A / D conversion value here is for the output of the regulator 3, and this is the point P.
The battery usage limit is reached. However, the point P is within the operable range of the device. Graph D close to this point P
The reference value Rf2 corresponds to the voltage at the ending point of the rising point.

In this case, A / D up to the vicinity of the position of the point P
Even if the converted value is obtained, the converted value by the A / D 13 does not impair the reliability because the voltage by the Zener diode ZD is held at a constant value. In this embodiment, A / D
Since the voltage on the reference side of conversion is obtained from the output of the regulator 3 on the secondary side, the voltage itself applied to the signal processing circuit 6 and the control circuit 10 is the detection voltage.
At this point, it is possible to detect up to these operating limits.
In FIG. 4, the regulator 3 is deleted, the constant voltage circuit 15 is inserted between the output of the power supply input line 2 and the ground GND, and the resistor R3 and the transistor Q of the constant voltage generation circuit 15 are replaced with one MOSFET 18. It is a thing. In this circuit, the resistance value of the deleted resistor R3 in FIG. 1 is MO.
It corresponds to the resistance value when the SFET 18 is turned on.
The operation is similar to that of the embodiment shown in FIG. in this way,
Since the turned-on MOSFET becomes a resistance, the resistor R3 can be replaced with a diode-connected MOSFET in which the gate and the source or the gate and the drain are connected in the embodiment of FIG.

As described above, the A / D 13 of the embodiment
Is an example, and may be a successive approximation type, integration type, chopper type A / D converter, or a simple voltage comparison circuit.
The constant voltage circuit according to the present invention may be any circuit that can generate a reference voltage up to the dead battery voltage. Therefore, even if the output on the regulator side fluctuates, the constant voltage circuit can generate the reference voltage on the condition of this fluctuation. For example, it may be connected to the regulator output side. Furthermore, as the internal configuration of the control circuit in the embodiment, an MP is used instead of the MCU.
A control circuit such as U or CPU may be used, or a gate array may be used. Further, the constant voltage generating circuit is not limited to the circuit of the embodiment, and the transistor Q or the MOSFET 18 as a switch may be omitted. However, if the transistor Q and the MOSFET 18 are deleted, the current consumption increases. Furthermore, a so-called dry battery such as a manganese battery, an alkaline battery, or a lithium ion secondary battery is used as a battery to be detected as a dead battery.

[0019]

As described above, according to the present invention, a voltage for determining the voltage per 1 LSB inside the A / D, for example, a voltage comparison type for comparing this A / D with the input signal is used. The power supply (reference voltage) inside the A / D is received from the output of the regulator circuit, and the reference voltage side (internal power supply side)
Is a variable value and the input signal side is a fixed value, so that the A / D corresponding to the fluctuation on the reference voltage value side (power supply side inside the A / D)
Since the converted value is obtained, the point at which the battery replacement or the warning that the battery is close to the end is started can be obtained as the A / D converted value, whereby the warning point can be detected. Furthermore, when the output of the regulator drops near the limit of battery usage, A
The / D conversion value can be obtained as the detection value, and thus the battery exhaustion can be detected. As a result, it is possible to detect the dead battery by extending the range until the device power is cut off or the battery dead message is displayed to a position closer to the original battery life than before, and it is possible to use the battery near the battery life limit. Become. For example, with a portable CD, the performance time can be extended by replacing the battery once. The frequency of replacement is also reduced and effective battery utilization can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram centering on a power supply circuit of an embodiment to which a battery dead detection device of the present invention is applied.

FIG. 2 is a flowchart of a battery dead detection process.

FIG. 3 is a graph showing a relationship with a battery output voltage from a battery replacement warning message display to a battery exhaustion display or power cutoff.

FIG. 4 is a circuit diagram of a battery dead detection device according to another embodiment of the present invention.

FIG. 5 is a block diagram centering on a power supply circuit having a conventional battery dead detection device.

FIG. 6 is a graph showing the relationship between the output voltage of the battery and the timing from the battery replacement warning message display to the battery exhaustion display or power shutoff in the conventional power supply circuit.

[Explanation of symbols]

1 ... Battery, 2 ... Power input line, 3 ... 3-terminal regulator, 4 ... Power supply line, 5, 10 ... Control circuit, 5
a, 13 ... A / D converter (A / D), 6 ... Signal processing circuit, 7 ... Voltage detection circuit, 8 ... LCD, 11 ... MCU,
12 ... Memory, 12a ... Battery exhaustion detection program, 12
b ... battery exhaustion display program, 12c ... power cut program, 12d ... initial setting program, 14 ... reference voltage generating circuit, 15 ... constant voltage generating circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H02J 7/00 302 H02J 7/00 302D

Claims (4)

[Claims] 1. A dead battery detecting device for detecting a use limit voltage when a battery attached as a power source of a portable device consumes power and the voltage of the battery decreases. Operates with varying power supply voltage A
/ D conversion circuit, a constant voltage generation circuit connected to the input of the A / D conversion circuit for generating a constant voltage up to the use limit voltage, and controlling the operation of the A / D conversion circuit and the operation of the portable device. And a control circuit for controlling the A / D conversion circuit to reduce the power supply voltage to 1 LSB.
As the voltage per bit decreases, the digital data value converted from the constant voltage relatively rises, and the converted digital data value becomes larger than the predetermined digital value preset by the control circuit. A battery dead detection device that performs battery dead operation with time as the operating limit voltage. 2. A battery dead detection device for detecting battery exhaustion according to battery power consumption, and a constant voltage generation circuit for generating a constant voltage up to the operating limit voltage of the battery, and power decreasing according to the power consumption. An A / D conversion circuit for A / D converting a constant voltage from the constant voltage generating circuit by receiving operating power from a supply line, and an A / D conversion value obtained from the A / D conversion circuit for receiving the constant voltage. A battery dead detection device which detects that the battery has run out when the digital data value converted from changes by a predetermined value or more. 3. A power supply circuit having a dead battery detecting device for detecting a use limit voltage when a battery attached as a power source of a portable device consumes power and the voltage of the battery decreases. A operating with a power supply voltage that fluctuates according to the voltage
/ D conversion circuit, a constant voltage generation circuit connected to the input of the A / D conversion circuit for generating a constant voltage up to the use limit voltage, and controlling the operation of the A / D conversion circuit and the operation of the portable device. And a control circuit for controlling the A / D conversion circuit to reduce the power supply voltage to 1 LSB.
When the digital data value obtained by converting the constant voltage is relatively increased due to the decrease in the hit voltage, and the converted digital data value becomes larger than a predetermined digital value preset by the control circuit. Power supply circuit that runs out of battery with the operating limit voltage as the operating voltage. 4. A portable device having a dead battery detecting device for detecting a use-limit voltage when a battery attached as a power source consumes power and the voltage of the battery decreases. Operating with a power supply voltage that fluctuates with
/ D conversion circuit, a constant voltage generation circuit connected to the input of the A / D conversion circuit for generating a constant voltage up to the use limit voltage, and controlling the operation of the A / D conversion circuit and the operation of the portable device. And a control circuit for controlling the A / D conversion circuit to reduce the power supply voltage to 1 LSB.
When the digital data value obtained by converting the constant voltage is relatively increased due to the decrease in the hit voltage, and the converted digital data value becomes larger than a predetermined digital value preset by the control circuit. A portable device having a power supply circuit that performs a battery exhaustion operation with the operating limit voltage as a limit.