Determining battery temperature and type

Abstract: A battery circuit for determining the temperature and the type of a battery used in an electrical apparatus such as a portable radio telephone. The temperature and the type of the battery are measured with the help of an analog to digital converter. The voltage specifying the temperature is scaled to different voltage levels according to the type of battery. The temperature measurement algorithm is selected according to the present voltage level.

Description: This invention relates to a battery circuit. In particular the invention relates to a circuit for determining battery temperature and type. The circuit enables the determination of the temperature and the type of a battery i.e. the capacity of a battery. The information on the temperature and the capacity of a battery is required for the charging algorithm of an electrical apparatus such as a portable radio telephone with which the battery is to be used to ensure efficient and safe charging of the battery. In a prior art circuit the temperature and battery type are measured from two distinct voltages, that is from measuring the voltage drop across two distinct resistance means. For this, two different physical connections between the battery and the electrical apparatus such as a portable radio telephone and two channels from the A/D convener of the electrical apparatus are required. EP-0 394 074 describes a circuit in which an electrical component is used to provide an electrical signature indicative of battery type. The prior art is described with reference to the accompanying drawings, in which: Figure 1 is a diagram of a prior art battery circuit; and Figure 2 is a diagram of a temperature curve indicative of the circuit described in Figure 1. The diagram shown in Figure 1 is a circuit diagram of a prior art circuit. The temperature of the battery 1 is detected by measuring the voltage over the The diagram shown in Figure 1 is a circuit diagram of a prior art circuit. The temperature of the battery 1 is detected by measuring the voltage over the Negative Temperature Coefficient (NTC) resistor 2 in the battery 1 with the aid of the Analog to Digital (A/D) converter. The type of the battery 1 is determined likewise by measuring the voltage over the resistor 3 in the battery 1 with the aid of the A/D converter. The resistors used in the measurement have been marked with the numbers 4 and 5. The diagram shown in figure 2 is a diagram of a temperature detection curve corresponding to the circuit described in figure 1. The relationship between the temperature of the battery 1 and the voltage measured over the NTC resistor 2 is described by the curve 6. In addition, the value of the resistor 3 is selected depending on the type of the battery 1. Generally there are two to three different types of battery. In the prior art circuit two different physical connections between the battery and the portable radio telephone and two channels from the A/D converter of the portable radio telephone are required. According to the present invention there is provided a battery circuit for determining the temperature and type of a battery selected from a plurality of battery types, the circuit comprising a resistance means for producing a voltage drop indicative of the battery temperature and the battery type characterised in that (i) the resistance means comprise a temperature dependent resistance means and a series resistance means, the magnitude of the series resistance means being dependent on the type of battery and being substantially greater than the maximum resistance of the temperature dependent resistance means, and (ii) the series resistance means is adapted for shifting the voltage drop across the temperature dependent resistance by one of a plurality of predetermined voltages, each predetermined voltage corresponding to one of said plurality of battery types, such that both the battery temperature and the battery type can be determined from the magnitude of the voltage drop across the series resistance of the temperature dependent resistance means and the series resistance means, and in that (iii) a parallel resistance means is coupled in parallel with the temperature dependent resistance means to restrict the variation range of the total resistance of the resistance means. An advantage of this invention is to accomplish an improvement in detection of the temperature and the type of a battery with the help of which the previously mentioned problems could be solved. Also the circuit requires only one connection between the battery and the electrical apparatus. An embodiment of the present invention is described below, by way of example, with reference to the accompanying drawings in which: Figure 3 is a diagram of a circuit in accordance with the present invention; Figure 4 is a series of temperature curves corresponding to the circuit of Figure 3; and Figure 5 is a diagram of an alternative circuit not forming part of the present invention. Figure 3 is a diagram of a circuit in accordance with the present invention. In the circuit the temperature of the battery 1 is detected by measuring the voltage over the NTC resistor 2 with the help of the A/D converter. The voltage measured with the A/D converter is scaled to different levels depending on the type of the battery 1. The temperature measurement algorithm is selected depending on the present voltage level. For example, in the circuit presented in the figure the measurement range is dimensioned and the variation range restricted with the resistor 7. The value of the resistor 3 depends on the type of the battery 1. The resistor used in the measurement has been marked with the number 5. The diagram shown in Figure 4 is a series of temperature curves indicative of the circuit in Figure 3 for determining the temperature and the type of a battery in accordance with the present invention. When battery type "A" is used, the relationship between the temperature of the battery 1 and the voltage measured over the NTC resistor 2 is described by curve 8. Accordingly, when battery types "B" and "C" are used, the relationship between the temperature of the battery 1 and the voltage measured over the NTC resistor 2 is described with curves 9 or 10 respectively. Because there is only one voltage measured only one connection between the battery 1 and the hand portable telephone and only one channel from the A/D converter of the hand portable telephone is required. The diagram shown in Figure 5 is a circuit diagram of an alternative solution not forming part of the claimed invention. In the circuit of Figure 5 the NTC resistor 2 is coupled to different voltages in the battery 1, that is to different outputs in the cells 11 to 14, depending on the type of battery in use. The resistor used in the measurement has been marked with the number 5. In view of the foregoing it will be clear to a person skilled in the art that modifications may be incorporated without departing from the scope of the present invention as defined by the appended claims.

Claims: A battery circuit for determining the temperature and type of a battery selected from a plurality of battery types, the circuit comprising a resistance means for producing a voltage drop indicative of the battery temperature and the battery type characterised in that (i) the resistance means comprise a temperature dependent resistance means (2) and a series resistance means (3), the magnitude of the series resistance means being dependent on the type of battery and being substantially greater than the maximum resistance of the temperature dependent resistance means, and (ii) the series resistance means is adapted for shifting the voltage drop across the temperature dependent resistance by one of a plurality of predetermined voltages, each predetermined voltage corresponding to one of said plurality of battery types, such that both the battery temperature and the battery type can be determined from the magnitude of the voltage drop across the series resistance of the temperature dependent resistance means and the series resistance means, and in that (iii) a parallel resistance means (7) is coupled in parallel with the temperature dependent resistance means to restrict the variation range of the total resistance of the resistance means. A circuit as claimed in any previous claim, wherein the temperature dependent resistance means is a resistor. A circuit as claimed in claim 2, wherein the resistor is a Negative Temperature Coefficient (NTC) resistor. A circuit as claimed in any previous claim, wherein the voltage drop is coupled to the processor controlling the charging of the battery via an Analog to Digital Converter. A circuit as claimed in any previous claim, wherein the circuit enables the coupling of a detachable battery to an electronic apparatus.

Inventors: PITKANEN RISTO, PITKANEN, RISTO
Applicants: NOKIA MOBILE PHONES LTD, NOKIA MOBILE PHONES LTD.
Application year: 1993
Main classification: H01M10
IPC codes: H01M10, H02J7, G01R31