JP2008215853A - Cell voltage detection circuit and battery-driven apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cell voltage detection circuit capable of accurately detecting reduction in battery voltage even if the ambient temperature of a lithium cell changes. <P>SOLUTION: The cell voltage detection circuit detects reduction in an output voltage of a lithium cell 11 by comparing the output voltage with a threshold (voltage detection level) of a voltage detection element 13. The cell voltage detection circuit includes a load circuit for making a load current flow according to the ambient temperature of the lithium cell 11 and changes an output voltage of the lithium cell 11 according to the ambient temperature. The loading circuit, for example, has both a resistor (thermistor 10) having temperature characteristics and a constant voltage element 12 for supplying a constant voltage for the resistor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery voltage detection circuit and a battery-driven device, and more particularly to a battery voltage detection circuit for a primary or secondary lithium battery and a battery-driven device driven by a lithium battery.

  A lithium battery such as a lithium primary battery or a lithium ion secondary battery or a lithium ion polymer secondary battery is mounted on various electronic devices for power supply or memory backup. For example, lithium batteries are installed in various devices such as mobile phones, personal digital assistants (PDAs), notebook personal computers (notebook PCs), remote controllers and cameras, as well as gas meters and alarms in the city gas and LP gas fields. Has been. Some of these battery-driven devices are equipped with a battery remaining amount detection device.

  As an example of a battery remaining amount detection device, Patent Document 1 discloses a battery remaining amount from a drooping amount or a return amount in a state where a maximum load current is applied to a battery in a pseudo manner or an actual load current is passed. An apparatus for detecting is disclosed. This battery remaining amount detecting device is energized to a load and outputs an energization display signal before use, and a battery voltage in response to an energization display signal output from the energization display signal output means. Detecting means for detecting the amount of droop or the amount of return, and notifying means for outputting a notification signal in response to the amount of droop or the amount of return output from the detecting means.

  FIG. 6 is a circuit diagram showing an internal configuration of a conventional battery-driven device. 6 includes a lithium battery 21, a constant current element 22, a voltage detection element 23, a control unit 24, and other internal circuits 25.

The battery voltage drop in the battery-driven device 2 is detected by the constant current element 22, the voltage detection element 23, and the control unit 24. That is, a constant load current is applied to the lithium battery 21 by the constant current element 22, and the voltage of the lithium battery 21 that has dropped due to the load current is compared with a predetermined voltage detection level of the voltage detection element 23. Then, when the voltage of the lithium battery 21 falls below the voltage detection level of the voltage detection element 23, the control unit 24 determines (detects) that the battery voltage has decreased below a predetermined voltage.
JP 7-239372 A

  However, the ambient temperature of the lithium battery 21 usually fluctuates unless a device is installed at a temperature-controlled place. As shown in FIG. 2, the discharge characteristics corresponding to the temperature of the lithium battery are also low in the battery-driven device 2 in FIG. 6 when the ambient temperature is low and the ambient temperature is high. When it becomes, it becomes high.

  Therefore, in a device that determines a decrease in battery voltage compared to the voltage of a lithium battery as in the prior art including Patent Document 1, if there is a change in the ambient temperature, It can be seen that an accurate determination is not made. For example, the voltage drop is not detected unless the value exceeds the default use amount at room temperature at a high temperature, and the voltage drop is detected at a value lower than the default use amount at room temperature at a low temperature.

  As described above, the conventional device driven by the lithium battery determines whether the battery voltage is lowered by determining the voltage of the lithium battery in a state where a certain load current is applied and the threshold value of the voltage defined by the amount of use of the lithium battery. Although it is performed by comparing, since the output voltage of the lithium battery itself fluctuates due to the influence of the ambient temperature, it cannot be accurately determined.

  The present invention has been made in view of the above circumstances, and a battery voltage detection circuit capable of accurately detecting a battery voltage drop even when the ambient temperature of the lithium battery changes, and the circuit and the lithium battery It is an object of the present invention to provide a battery-powered device including

  In order to solve the above-described problems, a first technical means of the present invention is a battery voltage detection circuit that detects a decrease in the output voltage of a lithium battery by comparison with a threshold value, the ambient temperature of the lithium battery. And a load circuit for supplying a load current according to the temperature of the lithium battery, wherein the output voltage of the lithium battery is changed according to the ambient temperature.

  According to a second technical means, in the first technical means, the load circuit includes a resistor having a temperature characteristic and a constant voltage element for supplying a constant voltage to the resistor. .

  A third technical means is a battery-driven device including the battery voltage detection circuit in the first or second technical means and the lithium battery, and is characterized by operating with the lithium battery. is there.

  According to the present invention, it is possible to accurately detect a battery voltage drop even if the ambient temperature of the lithium battery changes.

  FIG. 1 is a circuit diagram showing an example of the internal configuration of a battery-driven device according to the present invention. FIG. 2 is a graph showing discharge characteristics according to the temperature of the lithium battery, and FIG. 3 is a graph showing discharge characteristics according to the load current of the lithium battery. 4 is a graph showing characteristics of the output voltage of the lithium battery mounted on the battery-driven device of FIG. 1 when the ambient temperature is low, and FIG. 5 is a battery-driven type of FIG. 1 when the ambient temperature is high. It is a graph which shows the characteristic of the output voltage of the lithium battery mounted in the apparatus.

  A battery-driven device 1 illustrated in FIG. 1 is a device that is driven (operated) by a lithium battery 11, and in addition to the lithium battery 11, a battery voltage detection circuit (battery voltage drop detection circuit or battery remaining battery) according to the present invention. And other internal circuit 15.

  The battery voltage detection circuit according to the present invention includes a voltage detection element 13 and a control unit 14. The voltage detection element 13 and the control unit 14 are connected to the lithium battery 11 in order to detect a decrease in the output voltage of the lithium battery 11 by comparing the output voltage with a threshold value (voltage detection level) of the voltage detection element 13. It is what has been. For example, the voltage detection element 13 compares the output voltage of the lithium battery 11 with a predetermined voltage detection level, and outputs a detection signal to the control unit 14 when the voltage of the lithium battery 11 falls below this voltage detection level. To emit. Based on this detection signal, the control unit 14 determines (detects) that the battery voltage has fallen below a predetermined voltage, and displays or alarms on a display unit, a sound output unit, or the like (not shown) to the user of the battery-activated device 1. Control to notify is performed. Note that the control unit 14 may also control the internal circuit 15 in addition to the battery voltage drop detection described here.

  As shown in FIG. 2, the output voltage of the lithium battery 11 itself becomes low when the ambient temperature of the lithium battery 11 becomes low and becomes high when the ambient temperature becomes high, so that the battery voltage cannot be accurately detected.

  In the battery voltage detection circuit according to the present invention, in order to eliminate the influence of such an ambient temperature, a discharge characteristic according to the load current of the lithium battery 11 as shown in FIG. 3 is used. That is, according to the present invention, the discharge characteristic as shown in FIG. 3 is such that the voltage drop of the output voltage of the lithium battery 11 decreases as the load current of the lithium battery 11 decreases and increases as the load current of the lithium battery 11 increases. Utilizing this, the battery voltage drop detection is performed by removing the influence of the ambient temperature of the lithium battery 11.

  Therefore, the battery voltage detection circuit according to the present invention is a circuit that applies a load current corresponding to the ambient temperature of the lithium battery 11 as a circuit that applies a load to the lithium battery 11 in addition to the voltage detection element 13 and the control unit 14. Provide a circuit. And since this load circuit has a temperature characteristic of changing the load current with respect to the temperature change, the output voltage of the lithium battery 11 can be changed according to the ambient temperature by the discharge characteristic shown in FIG. As a result, it is possible to perform a normal determination with a predetermined usage amount.

  Such a load circuit can be composed of, for example, a thermistor 10 having temperature characteristics and a constant voltage element 12 that supplies a constant voltage to the thermistor 10. The thermistor 10 is an example of a resistor having a characteristic that the resistance value changes in response to a change in ambient temperature. Even if it is not a resistor having a large change in electrical resistance with respect to a temperature change, such as a so-called thermistor, a normal resistance Even if the vessel has temperature characteristics, it can be substituted. It is preferable to select and install a resistor having an appropriate temperature characteristic according to the temperature characteristic of the lithium battery 11 to be incorporated. The constant voltage element 12 is an element that supplies a constant voltage to the thermistor 10, and a constant voltage diode, a DC-DC converter, a regulator, and the like can also be applied.

  A constant voltage is supplied from the constant voltage element 12 to the thermistor 10, but the resistance value of the thermistor 10 fluctuates due to temperature fluctuations, so that the load current to the lithium battery 11 fluctuates. Due to this variation, the output voltage of the lithium battery 11 also varies as shown in FIG. 3, and as a result, the output voltage of the lithium battery 11 varies with temperature. Since the voltage detection element 13 and the control unit 14 compare the voltage value with a voltage output level that has been predetermined by the usage amount, it is possible to detect a battery voltage drop according to a temperature change.

  For example, the thermistor 10 having a negative characteristic with respect to temperature (negative temperature characteristic) is used, and the voltage detection element 13 uses the voltage output level when determining the voltage drop with a predetermined usage amount. It is preset as the center value of the temperature range (temperature range in which the battery voltage detection circuit is used) or the voltage output level at normal temperature.

  When the ambient temperature of the lithium battery 11 is the center value of the operating temperature range or the room temperature, the resistance value of the thermistor 10, the load current to the lithium battery 11, and the output voltage of the lithium battery 11 do not change, but originally assumed. Therefore, the battery voltage drop can be detected accurately.

  On the other hand, when the ambient temperature of the battery voltage detection circuit (actually the ambient temperature of the lithium battery 11) is changed from a preset temperature to a low temperature direction, as shown in FIG. The resistance value of the thermistor 10 having a large value increases, and the load current to the lithium battery 11 decreases. Although the output voltage of the lithium battery 11 originally drops at the ambient temperature, the output voltage returns to the original state because the load current is reduced.

  Further, when the ambient temperature is changed from a preset temperature to a higher temperature direction, as shown in FIG. 5, the resistance value of the thermistor 10 having a negative characteristic with respect to the temperature becomes small, and the load current to the lithium battery 11 is reduced. Will grow. Although the output voltage of the lithium battery 11 originally increased at the ambient temperature, the output voltage returns to the original when the load current increases.

  Thus, the battery voltage lowering circuit according to the present invention corrects the fluctuation of the output voltage of the lithium battery 11 due to the change in the ambient temperature by changing the load of the battery voltage detection circuit.

  The characteristics illustrated in FIG. 2 to FIG. 5 have the same tendency in all lithium batteries in a broad sense, and a battery voltage drop can be detected in the same manner as a load change. Therefore, as the above-described lithium battery 11, a lithium primary battery, or a lithium secondary battery such as a lithium ion secondary battery or a lithium ion polymer secondary battery can be applied. Further, for the sake of simplification, the voltage detection element 13 has been described on the premise that it has one comparison threshold value (voltage detection level). However, the battery voltage can be configured by providing a plurality of threshold values (voltage detection levels). In addition to a decrease from the default usage amount, the actual usage amount can also be detected.

  As described above, according to the present invention, since the detection of the voltage drop of the lithium battery 11 is changed depending on the ambient temperature, even if the ambient temperature of the lithium battery 11 changes, the battery voltage drop is accurately detected with the predetermined usage amount. (Detection) can be performed.

It is a circuit diagram which shows the internal structural example of the battery drive type apparatus which concerns on this invention. It is a graph which shows the discharge characteristic according to the temperature of a lithium battery. It is a graph which shows the discharge characteristic according to the load current of a lithium battery. It is a graph which shows the characteristic of the output voltage of the lithium battery mounted in the battery-powered apparatus of FIG. 1 when ambient temperature is low. It is a graph which shows the characteristic of the output voltage of the lithium battery mounted in the battery drive type apparatus of FIG. 1 when ambient temperature is high. It is a circuit diagram which shows the internal structure of the conventional battery drive type apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery drive type apparatus, 10 ... Thermistor, 11 ... Lithium battery, 12 ... Constant voltage element, 13 ... Voltage detection element, 14 ... Control part, 15 ... Other internal circuits.

Claims (3)

  A battery voltage detection circuit for detecting a decrease in the output voltage of a lithium battery by comparison with a threshold value, comprising a load circuit for flowing a load current in accordance with an ambient temperature of the lithium battery, wherein the output voltage of the lithium battery is A battery voltage detection circuit characterized by being changed according to an ambient temperature.   The battery voltage detection circuit according to claim 1, wherein the load circuit includes a resistor having temperature characteristics and a constant voltage element that supplies a constant voltage to the resistor.   A battery-driven device comprising the battery voltage detection circuit according to claim 1 and the lithium battery, wherein the battery-driven device is operated by the lithium battery.

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