JPH04291820A - A/d converter for battery voltage detection - Google Patents

Abstract

PURPOSE:To easily realize an A/D converter circuit for measuring battery voltage inexpensively with high accuracy by limiting the voltage for A/D conversion to a battery voltage range for the A/D converter operated by the battery and measuring the voltage of the battery. CONSTITUTION:The A/D converter circuit operated by a battery and measuring the voltage of the battery selects the voltage range of analog digital conversion of the A/D converter to be a range resulting from a battery maximum voltage subtracted by a prescribed voltage. In details more, a prescribed voltage to be subtracted is set in the vicinity of a minimum voltage in which the A/D converter is in operation and the upper limit of the voltage range is set in the vicinity of the maximum voltage of the battery.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an analog-to-digital conversion circuit that monitors changes in battery voltage of portable or in-vehicle equipment and operates on the battery, and particularly relates to an inexpensive and highly accurate voltage measuring circuit. It is.

0002

2. Description of the Related Art The structure of a conventional A/D conversion circuit for detecting battery voltage will be explained with reference to the block diagram of FIG. Rating is 6.0
The output of the battery 11 of V is converted by an A/D converter power supply 16 to a predetermined constant voltage, for example 5.0V, and is supplied to an analog-to-digital converter (hereinafter referred to as A/D converter) 14 as a power supply voltage. The output voltage of the battery is also divided in half by resistors 12 and 13 having the same resistance value, and A
/D converter 14. The battery 11 fluctuates in the range of 0 to VH = 7.2V as it is charged and discharged. Therefore, the A/D converter 14 has a voltage of 0V to 7.2V/2=
It is set to A/D convert an input range of 3.6V. For this purpose, the upper limit reference voltage generator 15 has VH'=4.
A constant DC voltage of 0V is generated and inputted to the A/D converter 14 as an upper limit reference voltage. In this case, 0V, that is, the ground voltage is input to the lower limit reference voltage VL'. FIG. 6 shows the relationship between the analog voltage value of the battery and the output digital voltage value.

0003

[Problem to be solved by the invention] However, the battery voltage is 4
．． When the voltage drops below 5V, the A/D converter power supply 16 and the A/D converter 14 operated by it cannot operate. Therefore, below the 4.5V dotted line shown in Figure 6,
Although the corresponding digital voltage value has been assigned,
It is never output.

In view of the above-mentioned circumstances, the present invention aims to provide a simple, inexpensive, and highly accurate A/D conversion circuit by limiting A/D conversion to the range in which the A/D converter can operate. It is something.

[0005]

[Means for Solving the Problems] The A/D conversion circuit of the present invention operates on a battery 21 and measures the voltage of the battery 21.
The voltage range in which the analog/digital converter 24 performs analog/digital conversion is set to the highest voltage value V of the battery.
It is characterized in that it is a value obtained by subtracting a predetermined voltage value from H. More specifically, the predetermined voltage value to be subtracted is set near the lowest voltage at which the A/D converter 24 can operate, and the upper limit VH of the voltage range is set near the highest voltage of the battery. configured.

[0006]

[Operation] That is, in the present invention, since A/D conversion is performed only within the operable voltage range of the A/D converter 24, it is possible to convert the analog voltage per quantum of digital voltage without adding a particularly complicated circuit. The voltage value can be reduced and the voltage measurement accuracy can be increased.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 3. FIG. 1 shows a basic block diagram of the circuit configuration. For example, the voltage of the power supply battery 31 of a portable telephone is rated at 6.0V, but during charging, the voltage reaches a maximum of 7.0V.
．． It rises to 2V. On the other hand, a circuit (not shown) of the mobile phone and an A/D for monitoring the voltage of the battery 31
The converter 34 cannot operate if its power supply voltage is below 4.5V, for example. Therefore, the A/D converter power supply 36 generates a DC constant voltage of, for example, 5.0 V and supplies it to the A/D converter 34 as a power supply voltage. A/D converter 34 has a maximum of 7.2
Since it is necessary to be able to measure the battery voltage of
The voltage is divided into two and input to the A/D converter 34. Therefore, A
The input voltage Vin to the /D converter 34 is 4.5V and 7.2V.
Each half of V varies from 2.2V to 3.6V. Therefore, by giving a margin of, for example, 0.4V, the upper limit reference voltage VH' of the A/D converter 34 is set to, for example, 4.0V.
is generated by the upper limit reference voltage generator 35, and the A/D
input to converter 34; The lower limit reference voltage VL' is set to 2.0V with a margin of 0.2V, for example, and the output voltage 4.0V of the upper limit reference voltage generator 35 is halved by resistors 37 and 38 having the same resistance value. Divide and create A
/D conversion circuit 34. Inside the widely known and widely used A/D converter used here, the range of both the upper and lower reference voltage limits is divided by a digital value with the required number of bits, and the input from resistors 32 and 33 is divided. Outputs the voltage value as a digitized value.

There are various ways to configure the circuit inside the A/D converter 34, one example of which is shown in FIG. The upper and lower limit reference voltages VH' and VL' are equally divided by a plurality of resistors r having the same resistance value, and the voltage at each dividing point is compared with the input voltage value Vin by each sampling comparator COM. The digital signal resulting from the comparison is encoded by the comparator/latch encoder ENC in accordance with the clock signal CLK, and in this case is output as a 4-bit parallel signal Do. Although many methods for A/D conversion circuit configuration other than the above method are known, it is clear that any method can be applied to the A/D converter 34 of the present invention.

[0009] The digital voltage signal Do measured and outputted in this way can be used, for example, as an alarm for a voltage drop due to battery discharging, or as a voltage increase due to charging and control to prevent overcharging, etc., according to preset conditions. used. In practical circuits, these conditions can be programmed in advance into a microprocessor installed to control the telephone.
Battery voltage is managed.

FIG. 4 shows the relationship between the analog battery voltage value and the output digital signal voltage value according to the present invention. This straight line has a gentle slope compared to the straight line in FIG. 6 showing the same relationship according to the conventional method, and it can be seen that the analog voltage per quantum of digital value is small. In the configuration of the embodiment shown in FIG. 2, the analog voltage value per quantum is approximately half that of the conventional circuit configuration shown in FIG. 4, that is, the resolution is approximately doubled. This means that if no more resolution is required, the number of bits of the digital signal can be reduced by one, which makes it possible to simplify the circuit configuration and reduce costs.

In the above embodiment, the upper and lower limit reference voltages of the A/D converter were selected in accordance with the maximum voltage of the battery and the lowest operable voltage of the A/D converter. Obviously, other voltage values can be selected.

0012

As is clear from the above description, according to the present invention, the analog voltage value per quantum of the A/D converter can be reduced, that is, the voltage accuracy can be increased with an extremely simple configuration. On the other hand, if no more resolution is required, the number of bits of the digital signal can be reduced, making it possible to simplify the circuit configuration and reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a principle block diagram of an A/D conversion circuit for battery voltage detection according to the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing an example of an internal circuit of the A/D converter of the embodiment of FIG. 3;

FIG. 4 is a diagram showing the relationship between the battery voltage value and the output digital voltage value of the present invention.

FIG. 5 is a configuration diagram of a conventional A/D conversion circuit for detecting battery voltage.

FIG. 6 is a relationship diagram between a battery voltage value and an output digital voltage value of a conventional circuit configuration.

[Explanation of symbols]

21, 31 Battery

Claims (2)

[Claims] [Claim 1] In an analog-to-digital conversion circuit that operates on a battery and measures the voltage of the battery, the voltage range for analog-to-digital conversion is the range obtained by subtracting a predetermined voltage value from the highest voltage value of the battery. An A/D conversion circuit for detecting battery voltage, characterized in that: 2. The predetermined voltage value according to claim 1, wherein the predetermined voltage value is set near the lowest voltage at which the analog-to-digital conversion circuit can operate, and the upper limit of the voltage range is set near the highest voltage of the battery. A/D conversion circuit for battery voltage detection.