JPH10325846A - Battery voltage monitor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery voltage monitor circuit capable of checking the capacities of different kinds of batteries with the same structure, and capable of preventing the maldetection of the capacity of a battery when a load varies. SOLUTION: A battery voltage monitor circuit 6 is provided with two reference potentials by a single comparator by feeding the output of a voltage comparator 3 back to the reference potential of this comparator 3. As the result of this, it becomes possible to detect residual quantities being scarce for two kinds of batteries. Besides, erroneous detection is prevented by judging whether the variation of a battery voltage in case of a variable load is voltage detection caused by a load variation or detection when a residual quantity becomes scarce, by using the potential difference of voltage detection of the voltage comparator 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for monitoring the capacity of a battery, and more particularly to a circuit for monitoring a battery voltage when a battery is used as a power source for electronic equipment.

[0002]

2. Description of the Related Art Conventionally, a battery voltage monitoring circuit monitors a battery voltage by using the property of a battery that the battery voltage decreases as the battery capacity decreases. When the battery capacity decreases, the battery capacity to the outside is reduced. It is configured to notify that the battery level is low, and is used for the purpose of detecting the remaining battery level of an electronic device powered by a battery.

The characteristics of this battery will be described with reference to FIG. FIG. 8 is a waveform diagram illustrating the voltage characteristics of the battery.
A waveform 801 in FIG. 8 shows the time course of the battery voltage when a certain load is applied to the alkaline battery. The battery voltage decreases with the passage of time, and if a load is applied for a certain period of time or more, the battery capacity starts to disappear and the voltage drop starts to increase. From this characteristic, it can be seen that the battery capacity has decreased by detecting that the voltage has become lower than the reference voltage Vrefl (803 in the figure).

Next, the necessity of using a battery voltage monitoring circuit will be described. When a battery is used as a power supply for an electronic device, a load such as a CPU or an LSI is connected. However, such a load may cause a malfunction when power supply becomes unstable. On the other hand, when the battery has a low remaining capacity, stable power supply cannot be performed. Therefore, the battery voltage monitoring circuit detects that the battery capacity is low,
Disconnect the power supply to the load before the battery power supply becomes unstable.

A conventional example of a generally known battery voltage monitoring circuit will be described with reference to FIG. FIG. 7 is a block diagram illustrating a configuration of a conventional example. Power supply control means 70
2 controls the power supply of the battery to the load 704. The comparator 703 detects the voltage of the battery 701 and a constant potential (V
ref), and outputs a detection signal Vo notifying the power supply control means 702 that the battery capacity has decreased when the battery voltage falls below the reference voltage Vref. I do. Power supply control means 70
2 detects the detection signal Vo and stops the power supply to the load 704 in order to prevent the load 704 from malfunctioning. By performing the above operations, stable power supply is realized.

[0006]

The first problem is that a detection signal indicating that the battery is low is sometimes output erroneously. The reason for this is that when the load 704 fluctuates due to the presence of the internal resistance r in the battery 701, particularly when the load 704 temporarily increases, the battery voltage Vin drops temporarily. Therefore, even when the battery capacity is sufficient, the "low battery level" of the battery is erroneously detected due to a temporary increase in load.

A second problem is that the circuit configuration becomes complicated because the reference voltage must be changed according to the type of battery. The reason is that the reference voltage Vref at which the capacity is "small" differs depending on the type of the battery as shown in FIG.

An object of the present invention is to realize a battery voltage monitoring circuit capable of stably detecting a battery capacity with a simple configuration even for different types of batteries.

Another object of the present invention is to provide a battery voltage monitoring circuit capable of performing stable detection with respect to a fluctuating load.

[0010]

The present invention that achieves the above object has the following matters specifying the invention.

(1) A voltage comparator having a battery voltage as one input, the output of the comparison result fed back to the reference potential for comparison, and the other input as the other input, is provided. It is characterized in that some other input has a binary value.

(2) In the above (1), even if the battery voltage fluctuates due to a load fluctuation, a hysteresis characteristic is provided by positive feedback of two inputs and outputs of the voltage comparator. .

(3) In the above (1), the threshold voltage of the battery is set in two ways to the reference potential of the voltage comparator, and each potential is set to the detection level of two different types of batteries.
And a voltage comparator for detecting the capacity of each type of battery.

(4) In the above (1), the comparison reference potential of the voltage comparator selectively changes impedance.

Since the voltage comparator has two voltage detection levels due to the hysteresis characteristic, the reference voltage and the feedback resistor are set so that the reference potential of the voltage comparator is set to the remaining low level potential of the two types of different batteries. By adjusting the voltage, the voltage can be monitored for different types of batteries with the same configuration and operation.

Further, when the output of the comparator is turned on using the difference between the two reference potentials of the voltage comparator, the transition state of the comparison output is detected to determine whether the voltage has temporarily dropped or whether the load has increased. As a result, it is possible to detect whether or not the battery has run out, so that error detection due to load fluctuation can be prevented.

[0017]

Next, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG.
The power supply control unit 2 supplies power to the variable load by stabilizing the input from the battery 1. Further, the power supply control means 2 detects the remaining amount detection signal Vo from the battery voltage monitoring circuit 6 to turn on / off the power supply to the variable load 5.
FF can be performed.

Here, the variable load 5 will be described.
Loads such as motors where the load increases temporarily at startup, or CCDs and LCDs like digital still cameras
Electronic equipment that has a plurality of loads and can selectively drive a plurality of loads.

Next, the internal configuration of the battery voltage monitoring circuit 6 will be described. In the voltage comparator 3, the potential of the-terminal is +
When the potential is larger than the terminal, Vo = Vol is output. On the contrary, when the potential of the negative terminal becomes lower than that of the positive terminal, Vo = Voh is output. The battery voltage Vin is input to a minus terminal of the voltage comparator 3, and a battery 4 having a reference voltage Vref and a terminal of an output Vo of the voltage comparator 3 are connected to the plus input terminal via a reference resistor R1. . The reference voltage 4 is grounded via a reference resistor R2. That is, it is a Schmitt circuit for detecting a threshold having a hysteresis characteristic.

By comparing the battery voltage Vin and the potential Vth of the + terminal of the voltage comparator 3 with the above configuration, the comparison result V
Although o is output, the potential Vth feeds back the result of Vo, so the reference potential Vth applied to the + terminal of the voltage comparator 3 has the following value. First, when the output Vo of the voltage comparator 3 is Vol, the reference potential Vth has the following value. First, when the output Vo of the voltage comparator 3 is Vol, the reference potential Vthl becomes as follows.

Vthl = R1 / (R1 + R2) .Vref + R
2 / (R1 + R2) · Vol

When the output Vo of the voltage comparator 3 is Voh, the reference potential Vthh is as follows.

Vthh = R1 / (R1 + R2) .Vref + R
2 / (R1 + R2) · Voh

In this case, since the output Vo has a relationship of Voh> Vol, the output Vo has a relationship of Vthh> Vthl.

Next, a method of obtaining the reference potential will be described with reference to FIG. When the characteristic waveform 801 of the battery voltage at the time of the steady load of the variable load 5 when the alkaline battery is used is used, a battery voltage Vref1 (803) when the remaining battery capacity becomes small is obtained from the waveform. Similarly, the battery voltage Vref2 (804) when the remaining amount becomes small when nickel hydride is used is obtained. By the above preliminary measurement,
By obtaining the reference resistances R1 and R2 and the reference voltage Vref shown in FIG. 1 so that Vref1 = Vthh and Vref2 = Vthl, the battery power supply means 2 can determine the remaining battery power for both the alkaline battery and the nickel-metal hydride battery. Can be determined.

Next, the operation of the configuration of FIG. 1 will be described with reference to FIG. FIG. 2 shows operation waveforms when the load temporarily increases when an alkaline battery is used. FIG. 2 (a)
Shows the operation of the voltage comparator 3 when the load fluctuates when the capacity of the battery is sufficient. In the figure, since the battery voltage is at a higher potential than Vthh and Vthl where the voltage fluctuates due to the fluctuation of the load, the comparison output Vo becomes Vol. Therefore, the voltage comparator 3
Becomes the reference potential Vthl.

Next, a state in which the battery voltage is consumed to some extent and the battery voltage becomes low will be described with reference to FIG. Even if the battery voltage Vin becomes low, the power supply control means 2 tries to draw a large load current from the battery 1 in order to supply stable power, so that the battery voltage drops when the load fluctuates accordingly. The voltage becomes higher than when the battery voltage is high, the battery voltage Vin temporarily becomes lower than Vthl, and the output Vo of the voltage comparator 3 becomes Voh. As a result, the reference potential Vth of the voltage comparator 3 changes from Vthl to Vthh, but the load becomes lighter, so that the battery voltage Vin becomes Vth.
Since it is higher than thh, the output Vo of the voltage comparator 3 returns to Vol, and the reference potential Vth also returns to Vthl.

Next, the operation when the battery capacity is almost exhausted will be described with reference to FIG. When the load increases, the same operation as in FIG. 2B is performed, but the battery voltage cannot return to Vthh or more even if the load becomes lighter because the remaining capacity is reduced, and the output V of the voltage comparator 3 is reduced.
o keeps Voh. When the power supply control means 2 detects this state, it recognizes that the remaining amount of the battery is low, and performs an operation of stopping power supply to the load.

Next, the operation when a nickel-metal hydride battery is used will be described with reference to the operation diagram of FIG. Since the internal resistance of the nickel-metal hydride battery is much smaller than that of the alkaline battery, there is almost no voltage fluctuation with respect to the load fluctuation as shown in FIG. FIG. 3A shows the voltage when the capacity of the nickel-metal hydride battery starts to disappear as shown in FIG.
If it is set to l, the output of the voltage comparator 3 will have the same result as the operation when the remaining amount of the alkaline battery is "no remaining" when the remaining amount of the battery is low, and the power supply control means 2 is the same as the alkaline battery. That is, it is only necessary to perform the detection.

Next, effects of the embodiment will be described. In the example, since there are two comparison potentials of the voltage comparator 3, for a battery having a certain fixed amount of internal resistance, such as an alkaline battery, the time between the detection of the "capacity" and the "no remaining amount" states is detected. Intermediate state occurs, resulting in "low remaining"
The state can be detected.

In the first embodiment of the present invention, the load fluctuation can be detected based on the difference between the two reference potentials. Therefore, the load fluctuation can be detected by detecting that the detection signal Vo is ON for a certain period or more. And the voltage drop due to the loss of battery capacity can be distinguished and recognized, so that erroneous detection due to a change in load can be prevented.

Further, according to this embodiment, two reference potentials can be set, so that the detection level of different types of batteries having different characteristics, such as an alkaline battery and a nickel hydride battery, can be set by the same circuit.

Next, the configuration of an example of the embodiment of the present invention will be described with reference to FIG. Here, a configuration of a digital still camera will be described as an embodiment.
FIG. 4 is a configuration diagram illustrating the configuration of the digital still camera. The battery 401 has a DC-DC
Converter 402 is connected. The DC-DC converter 402 is capable of multi-output, and
CPU 404 at t1, CCD 405 at Vout2, Vou
At t3, the LCD 406 is connected. LCD406
Is used as an image confirming means at the time of photographing, but it is assumed that the present configuration also includes an optical finder not shown as an image confirming means at the time of photographing.

Since Vout1 can supply a stable voltage irrespective of the input voltage, Vout1 is divided and supplied as reference voltage Vref using reference resistors R2 and R3. The CPU 404 includes a CCD 405 and an LCD 40
6 can be performed. Also CPU
Reference numeral 404 designates ON / OFF control of power supply to the DC-DC converter 402.

The comparison output Vo of the comparator 403 is Vol = 0.
V and Voh = Vout1 are output. Therefore, the reference potential Vth on the + side of the voltage comparator 403 at this time is
Is as follows. That is, when Vo = Vo1, the following equation is obtained.

Vthl = R1 / R2 / (R1 / R2 + R2)
・ R3 + R3 ・ R1) ・ Vout1

When Vo = Voh, the following equation is obtained.

Vthh = (R1 · R2 + R2 · R3) /
(R1 · R2 + R2 · R3 + R3 · R1) · Vout1

Therefore, Vthl and Vthh have the following relationship.

Vthh = Vthl + (R2 · R3) / (R1 ·
R2 + R2 · R3 + R3 · R1) · Vout

Therefore, a battery voltage at the time when the remaining capacity of the battery in a certain operating state becomes low is obtained in advance, and the reference resistors R1, R2, and R2 are set so that the voltage at that time becomes Vthh.
R3 is selected.

Next, the operation of the configuration of the embodiment of FIG. 4 will be described with reference to FIG. The CCD 405 captures an image for one screen each time it receives an image capture signal from the CPU 404. The CPU 404 issues a capture signal to the CCD every certain time.

First, the operation when an alkaline battery is used will be described with reference to FIG. State 1 in FIG.
Shows the fluctuation of the battery voltage when the image is captured by the CCD 405 at a fixed cycle while the LCD 406 is displayed with the margin of the battery capacity. Since the load on the CCD 405 temporarily increases during image capture, the battery voltage decreases during this period.

Next, in the state 2, since the capacity of the battery has decreased, the comparator output 403 outputs Voh during the image capture period of the CCD 405, and when the operation further proceeds, the image capture ends. The comparator output 403 also holds Voh.

Next, the state 3 will be described. Digital still cameras use LC as a means of checking images when shooting.
In addition to D, there is also a configuration with a viewfinder.
Shooting can be continued even if the CD is turned off. Therefore, in such a configuration, by turning off the LCD, the load on the battery is reduced, and photographing can be continued. Therefore, in the state 3, when the output of the comparator 403 becomes Voh during the period other than during the capture period, the LCD is turned off to reduce the load. As the load is reduced, the battery voltage returns to Vthh or higher, so that the photographing can be continued. If the battery voltage does not return to Vthh or more at this time, it is determined that the battery capacity has run out and the power is turned off.

When photographing is further continued, LC
Even when the image is taken with D turned off, the battery capacity becomes insufficient, so that the battery voltage cannot be restored to Vthh. In such a state, the CPU 404 determines that the battery capacity has run out, and instructs the DC-DC converter 402 to turn off the power and turns off the power.

Next, the operation when a nickel-metal hydride battery is used will be described. The CPU 404 operates without discriminating between the alkaline battery and the nickel-metal hydride battery.
Is turned off, but the battery voltage cannot be restored to Vthh, so that it is determined that the battery capacity has run out and the power is turned off.

As described above, according to the present embodiment, the return of the battery voltage can be detected. Therefore, when the load is reduced, the load of the battery can be recovered. The use of batteries is made possible by reducing the amount.

Since the CPU 404 can perform the same control without recognizing the characteristics of the battery, it is not necessary to recognize the type of the battery.

Next, another embodiment of the present invention will be described with reference to FIG.
This will be described in detail with reference to FIG. In this embodiment, the type of a battery is determined using a voltage change due to a change in load of the battery voltage.

In FIG. 6, the resistance value of the reference resistor 606 can be set in two stages by a resistance value control signal from the CPU. When the resistance value control signal is ON, the reference resistance value is Ron = R
2 ・ R4 / (R2 + R4) and the resistance control signal is OF
At the time of F, the resistance value becomes Roff = R2.

At this time, the reference potential to the comparator 603 is obtained by replacing R2 in the equation shown in the previous example with Ron and Roff.

The selection of the resistor R4 is performed by the comparator 603 at the time of Ron.
R4 is selected so that the reference voltages Vthh and Vthl to the vicinity of Vref3 in FIG.

At this time, it is assumed that the resistance values R1, R2, and R3 are set to be the reference voltages when the battery capacity is reduced. The variable load 605 is the CPU 604
The load state can be selected by the load control signal.

Next, the operation of this embodiment will be described. CPU
Reference numeral 603 selects the reference resistor 606 as Roff and determines that the battery capacity is sufficient. Next, the CPU 604 changes the reference resistor 606 to Roff, selects the variable load 605 so as to temporarily increase the load, and changes the load in the order of light load → heavy load → light load. If the result of the voltage comparator 603 at this time is Vol → Voh → Vol, it is determined that the battery is an alkaline battery. If Voh remains, it is determined that the battery is a nickel-metal hydride battery.

As described above, according to the present embodiment, the type of the battery can be recognized by detecting the change in the load by the voltage comparator 603 and discriminating the difference in the impedance of the battery output.

[0057]

The first effect is that the voltage comparator can have two detection levels by feeding back the comparison result to the reference potential of the battery voltage comparator. This means that the remaining amount can be detected with the same configuration and the same operation.

The second effect is that, by feeding back the comparison result to the reference potential of the battery voltage comparator, the detection level has a hysteresis characteristic, so that a change in load can be detected. That is, detection can be prevented.

The third effect is that it is possible to determine from the comparison result of the voltage comparator whether the return of the voltage is equal to or greater than the hysteresis potential difference using the hysteresis characteristic of the battery voltage comparator. In the case of a battery having the internal resistance described above, the rate at which the remaining amount of the battery becomes low can be detected at two levels of "low remaining amount" and "no remaining amount".

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform chart illustrating the operation of the embodiment of the present invention.

FIG. 3 is a waveform chart illustrating another embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating a configuration of an embodiment of the present invention.

FIG. 5 is a waveform chart for explaining the operation of the embodiment of the present invention.

FIG. 6 is a configuration diagram illustrating another embodiment of the present invention.

FIG. 7 is a block diagram illustrating a configuration of a conventional example.

FIG. 8 is a waveform chart illustrating voltage characteristics of a battery.

[Explanation of symbols]

 1,401,601 Battery 2 Power supply control means 3,403,603 Voltage comparator 4 Reference voltage 5,605 Fluctuating load 6 Battery voltage monitoring circuit 402,602 DC-DC converter 404,604 CPU 405 CCD 406 LCD

Claims (4)

[Claims] A voltage comparator having a battery voltage as one input, an output of a comparison result fed back to a reference voltage for comparison, and another input, and a reference voltage for comparison in an output state of the voltage comparator. A battery voltage monitoring circuit having two other inputs. 2. The battery voltage monitoring circuit according to claim 1, wherein even if the battery voltage fluctuates due to a load fluctuation, a hysteresis characteristic is provided by positive feedback of two inputs and outputs of the voltage comparator. 3. The threshold voltage of the battery is set in two ways as a reference potential of the voltage comparator, each potential is set to a detection level of two different types of batteries, and the capacities of the two types of batteries are detected. 2. The battery voltage monitoring circuit according to claim 1, comprising the voltage comparator. 4. The comparison reference potential of the voltage comparator selectively changes impedance.
The battery voltage monitoring circuit according to the above.