JP2008111761A - Temperature detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature detector of a simple structure capable of highly accurately detecting temperatures without stabilizing a drive voltage by using an expensive a power-supply IC in performing temperature detection by using a temperature sensing element such as a thermistor. <P>SOLUTION: The temperature detector includes: a temperature detection circuit comprising the temperature sensing element and a first fixed resistance serially connected thereto for dividing a power supply voltage Vdc to find a temperature detecting voltage; an auxiliary circuit comprising second and third fixed resistances serially connected together for dividing the supply voltage Vdc to find a reference voltage; and a microcomputer comprising first and second AD conversion ports for thereinto inputting the detecting voltage and the reference voltage, respectively, and finding respective AD conversion results ADV1 and ADV2 of voltages input into the conversion ports by referring to a base voltage while finding a temperature given to the sensing element by comparatively operating these conversion results. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention can detect the temperature applied to the temperature sensing element based on information required from the temperature sensing element such as a thermistor, for example, the temperature of the secondary battery in contact with the temperature sensing element with high accuracy. The present invention relates to a temperature detection device having a simple configuration.

  In order to charge the secondary battery safely and prevent deterioration of battery performance, it is important to control the charging according to the temperature of the secondary battery. For example, after confirming that the battery temperature is in the range of 0 to 40 ° C., start charging the secondary battery, or if the battery temperature exceeds 60 ° C. during charging, stop charging immediately. The secondary battery can be safely charged and the battery performance can be prevented from being deteriorated (see, for example, Patent Document 1).

  FIG. 2 is a schematic configuration diagram showing an example of a charger having a function of controlling the charging of the secondary battery according to the battery temperature, and 1 is a secondary battery such as a nickel metal hydride battery (Ni-MH battery). . This charger basically includes a charging power source unit 2 composed of a constant current source, and a charging control switch 3 that controls on / off of a constant current output from the charging power source unit 2 to the secondary battery 1. And a charging control unit 4 that controls the operation of the charging power source unit 2 and the charging control switch 3. The charging control unit 4 is composed of, for example, a microcomputer and plays a role of controlling charging of the secondary battery 1 according to the terminal voltage Vbat of the secondary battery 1 and the battery temperature Tbat. When a lithium ion battery is used as the secondary battery 1, a constant voltage and constant current source is used as the charging power source unit 2.

  Incidentally, the temperature detection circuit 5 for detecting the temperature of the secondary battery 1 includes a temperature sensing element 5a such as a thermistor provided in contact with the secondary battery 1, and a fixed resistor 5b connected in series to the temperature sensing element 5a. The temperature detection voltage V1 corresponding to the battery temperature Tbat is obtained by dividing the power supply voltage Vdc. This temperature detection voltage V1 is given to the AD conversion port of the above-described charge control unit (microcomputer) 4 and used as one element of charge control.

In the figure, reference numeral 6 denotes a power supply IC that generates a stabilized drive power supply Vdc for driving the charge control unit 4 and the temperature detection circuit 5 from an external input power supply, and 7 is driven by the charge control unit 4. This is a display (LED) for displaying the state of charge of the secondary battery 1.
JP 2002-298930 A

  By the way, in the charger having the above-described configuration, the drive voltage Vdc for driving the charge control unit 4 and the temperature detection circuit 5 is stably generated using the power supply IC 6. However, the above-described power supply IC 6 is relatively expensive, which is a problem in realizing the charger at low cost. For example, even if the power supply IC 6 is omitted and the external input power supply described above is added to the charge control unit 4 as it is, a microcomputer incorporating a reference power supply for generating a reference voltage Vref serving as a reference for AD conversion is used as the charge control unit 4. Thus, it is possible to ensure the AD conversion accuracy for the voltage input to the AD conversion port.

  However, if the external input power supply is applied as it is to the temperature detection circuit 5, the voltage fluctuation of the external input power supply appears as a detection error in the temperature detection voltage V1 itself detected by the temperature detection circuit 5. For this reason, the charge control for the secondary battery 1 cannot be executed under highly accurate management of the battery temperature Tbat. Such a problem becomes a serious problem in an environment where the power supply voltage fluctuates greatly due to a load current of an AC power adapter such as a mobile phone or a USB power supply.

  The present invention has been made in view of such circumstances, and its purpose is to determine the temperature applied to the temperature sensing element based on information required from the temperature sensing element such as a thermistor, for example, the temperature of the secondary battery. An object of the present invention is to provide a temperature detection device with a simple configuration that can detect the temperature with high accuracy without using a relatively expensive power supply IC.

In order to achieve the above-described object, the present invention relates to a temperature detection device that detects a temperature applied to a temperature sensing element based on information required from the temperature sensing element such as a thermistor,
A temperature detection circuit including the temperature sensing element and a first fixed resistor connected in series to the temperature sensing element and dividing the power supply voltage Vdc to obtain a temperature detection voltage V1;
An auxiliary circuit comprising a second fixed resistor and a third fixed resistor connected in series to the second fixed resistor, and dividing the power supply voltage Vdc to obtain a reference voltage V2.
It has a first AD conversion port for inputting the temperature detection voltage and a second AD conversion port for inputting the reference voltage, and AD of each voltage input to each AD conversion port with reference to a reference voltage Vref And a microcomputer that obtains the conversion results ADV1 and ADV2 and compares the AD conversion results to obtain the temperature applied to the temperature sensing element.

  Preferably, the microcomputer has a built-in reference power supply for generating the reference voltage Vref from a power supply voltage Vdc applied to the microcomputer, and the reference voltage Vref generated by the reference power supply and the first and second AD conversions. Comparing the input voltages V1 and V2 respectively applied to the ports, the AD conversion function ADV1 and ADV2 are obtained to obtain AD conversion results ADV1 and ADV2.

In addition, the temperature sensitive element is a thermistor provided in contact with, for example, a secondary battery,
The microcomputer obtains information obtained from the temperature sensing element (thermistor), specifically, from the temperature detection voltage V1 detected by the temperature detection circuit and the reference voltage V2 detected by the auxiliary circuit. This is realized as having a charge control function for controlling charging of the secondary battery according to the temperature of the secondary battery.

Specifically, when the power supply voltage is Vdc, the resistance value of the temperature sensing element is Rth, and the resistance values of the first to third fixed resistors are R1, R2, R3, the temperature detection circuit The detection voltage V1 is V1 = Rth / (Rth + R1) × Vdc
And the auxiliary circuit calculates the reference voltage V2 as V2 = R3 / (R2 + R3) × Vdc.
Configured to ask for.

When the microcomputer is configured to obtain the reference voltage as Vref and obtain the AD conversion result as n-bit data, AD conversion of voltages input to the first and second AD conversion ports, respectively. Results ADV1 and ADV2 ADV1 = V1 / Vref × 2 ⁿ
ADV2 = V2 / Vref × 2 ⁿ
As follows, and further information on the temperature applied to the temperature sensing element is ADV1 / ADV2 = V1 / V2.
= Rth (R2 + R3) / R3 (Rth + R1)
Configured to ask for.

  According to the temperature detection device having the above-described configuration, information on the temperature applied to the temperature sensing element is obtained as a ratio between the temperature detection voltage V1 detected by the temperature detection circuit and the reference voltage V2 detected by the auxiliary circuit. Therefore, the temperature applied to the temperature sensing element can be detected with high accuracy without being affected by fluctuations in the drive voltage Vdc applied to the temperature detection circuit and the auxiliary circuit. In particular, since it is not necessary to stabilize the drive voltage Vdc applied to the temperature detection circuit and the auxiliary circuit, a power supply IC for stabilizing the drive voltage is unnecessary, and accordingly, the device configuration can be simplified and the cost can be reduced. It becomes possible.

  Therefore, in an environment where the power supply voltage fluctuates greatly depending on the load current of an AC power adapter such as a mobile phone or a USB power supply, for example, the temperature incorporated in a charger that controls the charging of the secondary battery while detecting the battery temperature of the secondary battery As a detection device (battery temperature detection function), a great effect is achieved in practical use.

Hereinafter, a temperature detection device according to an embodiment of the present invention will be described with reference to the drawings, taking as an example a charger that controls charging of a secondary battery according to a terminal voltage Vbat and a battery temperature Tbat of the secondary battery. To do.
FIG. 1 is a schematic configuration diagram of a charger according to an embodiment of the present invention. Reference numeral 1 denotes a secondary battery such as a nickel metal hydride battery (Ni-MH battery). Like the charger shown in FIG. 2, this charger basically has a charging power source unit 2 composed of a constant current source, and a constant current output from the charging power source unit 2 to the secondary battery 1. The charging control switch 3 that controls on / off of the supply and the charging control unit 4 that controls the operation of the charging power source unit 2 and the charging control switch 3 are configured. In addition, when using a lithium ion battery as the secondary battery 1, it cannot be overemphasized that a constant voltage constant current source is used as the said charge power supply part 2. FIG.

  The charging control unit 4 is composed of a microcomputer (MPU) having a built-in reference power supply 4a for generating a reference voltage Vref to be used internally for AD conversion from a driving voltage (external power supply voltage) applied thereto. . The charge control unit (microcomputer) 4 detects the terminal voltage Vbat of the secondary battery 1 from the input voltage applied to the AD conversion port as described later, and detects the temperature Tbat of the secondary battery 1. The charging control of the secondary battery 1 is performed according to the terminal voltage Vbat and the battery temperature Tbat.

  Incidentally, the battery temperature is used to safely charge the secondary battery and to control the charging according to the temperature of the secondary battery in order to prevent deterioration of the battery performance. For example, after confirming that the battery temperature is in the range of 0 to 40 ° C., start charging the secondary battery, or immediately stop charging if the battery temperature exceeds 60 ° C. during charging, etc. By executing the control, it is possible to realize safe charging of the secondary battery and prevention of deterioration of the battery performance. In addition, about the charge control of the secondary battery 1 according to the terminal voltage Vbat and the battery temperature Tbat, various methods conventionally proposed may be adopted as appropriate, and the temperature detection according to the present invention is directly applied. Since there is no relationship, the description is omitted here.

  In this charger, a DC external input power source is applied as it is as a drive voltage for the charge control unit (microcomputer) 4. That is, the external input power source with voltage fluctuation is applied to the charging control unit (microcomputer) 4 as it is without stabilizing the driving voltage using the power source IC 6 as in the charger shown in FIG. The charging control unit (microcomputer) 4 is driven.

  In addition, the charger includes a temperature sensing element 5a such as a thermistor provided in contact with the secondary battery 1, and a first fixed resistor 5b connected in series to the temperature sensing element 5a. A temperature detection circuit 5 is provided that obtains a temperature detection voltage V1 corresponding to the battery temperature Tbat by dividing Vdc. In particular, the above-described external input power supply is directly applied to the temperature detection circuit 5 as its power supply voltage Vdc, and the first fixed resistor 5b is a pull-up of the temperature sensitive element (thermistor) 5a with respect to the power supply voltage Vdc. Used as a resistor.

When the resistance value of the temperature sensitive element (thermistor) 5a changing with temperature is Rth and the resistance value of the first fixed resistor 5b is R1, the temperature detection circuit 5 divides the drive voltage Vdc to obtain the temperature. The detection voltage V1 is V1 = Rth / (Rth + R1) × Vdc
Configured to ask for. The temperature detection voltage V1 detected by the temperature detection circuit 5 provided with such a temperature sensitive element (thermistor) 5a is input to the first AD conversion port AD1 of the charge control unit (microcomputer) 4 described above. .

The charger further includes a second fixed resistor 8a and a third fixed resistor 8b connected in series to the second fixed resistor 8a, and assists in obtaining the reference voltage V2 by dividing the power supply voltage Vdc. A circuit 8 is provided. The auxiliary input 8 is directly applied with the external input power source as the drive voltage Vdc. When the resistance values of the second and third fixed resistors 8a and 8b are R3 and R2, the auxiliary circuit 8 divides the drive voltage Vdc so that the reference voltage V2 is V2 = R3 / (R2 + R3). × Vdc
Configured to ask for. The reference voltage V2 detected by the auxiliary circuit 8 is input to the second AD conversion port AD2 of the charge control unit (microcomputer) 4 described above.

  Here, the detection process of the battery temperature Tbat in the charge control unit (microcomputer) 4 will be described. The charge control unit (microcomputer) 4 includes a third AD conversion port AD3 in addition to the first and second AD conversion ports AD1 and AD2 described above. The terminal voltage Vbat of the battery 1 is input. Then, the charge control unit (microcomputer) 4 uses the reference voltage Vref generated by the built-in reference power supply 4a as described above to input voltage, specifically, temperature applied to each of the AD conversion ports AD1, AD2, AD3. Each of the detection voltage V1, the reference voltage V2, and the terminal voltage Vbat is digitally converted and obtained as, for example, an 8-bit AD conversion result (digital data).

In particular, in order to detect the battery temperature Tbat of the secondary battery 1 with high accuracy, the charge control unit (microcomputer) 4 digitally converts the temperature detection voltage V1 applied to the first AD conversion port AD1 by the AD conversion unit 4b. The AD conversion result VAD1 is set to ADV1 = V1 / Vref × 2 ⁿ
In addition, the AD conversion unit 4c digitally converts the reference voltage V2 applied to the second AD conversion port AD2, and the AD conversion result VAD2 is ADV2 = V2 / Vref × 2 ⁿ
Asking. In the above equation, n is the number of bits of the AD conversion result, and is given as [n = 8] when performing 8-bit AD conversion.

The charge control unit (microcomputer) 4 compares the AD conversion results VAD1 and VAD2 with the calculation unit 4d, thereby calculating information on the temperature applied to the temperature sensing element (thermistor) 5a, that is, the secondary battery. A value corresponding to a temperature Tbat of 1 is set to ADV1 / ADV2 = V1 / V2.
= Rth (R2 + R3) / R3 (Rth + R1)
It is what you want.

  Thus, according to the temperature detection function of the charge control unit (microcomputer) 4 that detects the value corresponding to the temperature Tbat of the secondary battery 1 in this way, that is, the temperature detection device, the first to third fixed resistors 5b, Since the resistance values R1, R3, and R2 of 8a and 8b are known, the temperature Tbat of the secondary battery 1 can be accurately detected from the resistance value Rth of the temperature sensitive element (thermistor) 5a that changes depending on the temperature. In particular, the resistance value Rth of the temperature sensing element (thermistor) 5a is detected regardless of the voltage fluctuation of the power supply voltage Vdc applied to the temperature detection circuit 4 and the auxiliary circuit 8, and this resistance value Rth is used as the temperature Tbat of the secondary battery 1. The corresponding information can be obtained with high accuracy.

  Further, as described above, the temperature information applied to the temperature sensing element (thermistor) 5a can be detected from the resistance value Rth of the temperature sensing element (thermistor) 5a regardless of the fluctuation of the power supply voltage Vdc. It is not necessary to stabilize the drive voltage Vdc by using an IC or the like. An external input power source that cannot deny the occurrence of voltage fluctuations can be used as it is as the drive power source Vdc for the charge control unit (microcomputer) 4, the temperature detection circuit 5, and the auxiliary circuit 8, so that it is necessary to use a power source IC or the like. Therefore, the structure can be simplified and the cost of the charger can be reduced.

  The present invention is not limited to the embodiment described above. Here, the battery charger is taken as an example to describe the embodiment for detecting the temperature of the secondary battery. However, the present invention can be applied to various uses for detecting the temperature using a temperature sensitive element. The present invention can also be applied to the case where an element other than the thermistor, such as a platinum resistance element, is used as the temperature sensitive element. Needless to say, the charging control method for the secondary battery is not particularly limited. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

The schematic block diagram of the charger comprised incorporating the temperature detection apparatus which concerns on one Embodiment of this invention. The figure which shows an example of the conventional charger provided with the temperature detection function.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Charge power supply part 3 Charge control switch 4 Charge control part (microcomputer)
4a Reference power supply 4b, 4c AD conversion unit 4d operation unit (comparison operation)
5 Temperature detection circuit 5a Temperature sensing element (thermistor)
5b 1st fixed resistance 8 Auxiliary circuit 8a 2nd fixed resistance 8b 3rd fixed resistance

Claims (4)

A temperature detection device that detects a temperature applied to the temperature sensing element based on information required from the temperature sensing element,
A temperature detection circuit including the temperature sensing element and a first fixed resistor connected in series to the temperature sensing element, and dividing a power supply voltage to obtain a temperature detection voltage;
An auxiliary circuit including a second fixed resistor and a third fixed resistor connected in series to the second fixed resistor, and dividing the power supply voltage to obtain a reference voltage;
A first AD conversion port for inputting the temperature detection voltage and a second AD conversion port for inputting the reference voltage, and AD conversion of the voltage input to each of the AD conversion ports with reference to a reference voltage A temperature detection apparatus comprising: a microcomputer for obtaining a result and comparing the AD conversion result to obtain a temperature applied to the temperature sensing element.   The microcomputer has a built-in reference power supply for generating the reference voltage from a power supply voltage applied to the microcomputer, and is supplied to the reference voltage generated by the reference power supply and the first and second AD conversion ports, respectively. The temperature detection device according to claim 1, further comprising an AD conversion function for comparing the input voltage and obtaining an AD conversion result. The temperature sensitive element is a thermistor provided in contact with the secondary battery,
2. The temperature according to claim 1, wherein the microcomputer includes a charge control function for controlling charging of the secondary battery according to the temperature of the secondary battery detected according to information obtained from the temperature sensing element. Detection device. When the power supply voltage is Vdc, the resistance value of the temperature sensing element is Rth, and the resistance values of the first to third fixed resistors are R1, R2, and R3, the temperature detection circuit uses the temperature detection voltage V1. V1 = Rth / (Rth + R1) × Vdc
The auxiliary circuit calculates the reference voltage V2 as V2 = R3 / (R2 + R3) × Vdc.
As what
When the reference voltage is Vref and the AD conversion result is obtained as n-bit data, the microcomputer uses the AD conversion results ADV1 and ADV2 of the voltages input to the first and second AD conversion ports, respectively. ADV1 = V1 / Vref × 2 ⁿ
ADV2 = V2 / Vref × 2 ⁿ
As well as information on the temperature applied to the temperature sensing element ADV1 / ADV2 = V1 / V2
= Rth (R2 + R3) / R3 (Rth + R1)
The temperature detection device according to claim 1, which is obtained as follows.

Images