JPH041581A - Power supply circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is applied to equipment that uses a battery and has a function to warn of the remaining capacity of the battery.

[Prior Art] Conventionally, the structure of a power supply circuit of a device that warns about the remaining capacity of a battery is as shown in FIG.

The battery unit 21 is a nickel cadmium battery. Compare the output voltage V1 of the battery unit 21 with the reference voltage VR of the reference voltage source 220 using the voltage comparator 23. ! If the output voltage Vl of the battery unit is higher than the reference voltage VR, the output voltage of the voltage comparator 23 becomes a logic level H, and the warning circuit 24 does not issue a warning regarding the remaining capacity of the battery unit 21. If the output voltage of the battery unit 21 is lower than the reference voltage VR, the output voltage of the voltage comparator 23 becomes a logic level, and the warning circuit 24 issues a warning of the remaining capacity of the battery unit 21.

Figure 3 shows the change in battery voltage over time when a nickel-cadmium battery is discharged under a constant load.

The battery voltage decreases as the battery discharges, and suddenly decreases when the remaining capacity reaches just t. By setting the battery voltage at the end of discharge, where the voltage suddenly drops and begins, as the reference voltage VR, the power supply circuit shown in FIG. 2 can issue a warning of the remaining capacity of the battery.

Normally, the battery usage rate at the time when the remaining battery capacity warning is issued is around 80%. This is to issue a remaining capacity warning after fully drawing out the capacity of the battery, and to allow the user to continue using the device for a short period of time even after the remaining capacity warning is issued.

The battery usage rate referred to here is the ratio of the amount of charge discharged from a full state at that time to the amount of charge that can be discharged when the battery capacity is in a groove state.

[Problems to be Solved by the Invention] However, as shown in the equivalent circuit of the battery unit 210, there is an internal resistance r1 inside the battery, so when the load 25 fluctuates, the output voltage v1 changes.

The electromotive force of battery unit) 21 is VB, and the amount of current flowing out is ■
Then, the daughter of ■1 is expressed as Vl = VB-T·rt.

If the remaining capacity warning of the battery unit 21 is judged only by the output voltage (■1) of the battery unit 21, the battery usage rate at the time when the remaining capacity warning is issued due to fluctuations in (■1) due to fluctuations in the load 25. There was a problem with the difference.

SUMMARY OF THE INVENTION The present invention addresses such problems by providing a means for detecting the remaining capacity of a battery with high accuracy and at a constant battery usage rate even if the amount of current flowing out from the battery unit changes due to changes in load. shall be.

Means for Solving Problem C] According to the present invention, the battery is discharged from the battery unit due to load fluctuation! In order to detect the remaining capacity of the battery with high accuracy and a constant battery usage rate even when the flow rate changes, the above-mentioned device has a battery, has a means for detecting the amount of current flowing out from the battery, and has a device as described above. It is characterized by having means for comparing the aforementioned battery voltage with a comparison voltage that changes in proportion to the amount of current flowing out from the battery.

[Example code] An embodiment of a power supply circuit utilized in the present invention is shown in FIG.

The battery unit] has an electromotive voltage VB and an internal resistance r1. Most of the current 1 flowing out from the battery unit 1 is the resistance fl
1 of iR3 is supplied to the negative resistor 3 via the current detection resistor 2. Although some current flows before the current detection circuit 2, it is set so that the amount of current is so small that it can be ignored compared to the overall current value (2). Reference voltage R4 outputs reference voltage VR.

As the discharge of the battery unit 1 progresses, the electromotive voltage decreases, but vR is set to the same voltage as the electromotive voltage in the discharge state suitable for issuing a warning of the remaining capacity of the battery unit 1. The operational amplifier 5 and its peripheral circuits calculate the output voltage (1) of the battery unit 1, the voltage (2) on the output side of the current detection resistor 2, and the reference voltage VR to output an actual comparison voltage (3). The resistance values of this circuit are: The output voltage v1 of the battery unit is V1 = VB-r-r The output 1'llf voltage v2 of the current detection resistor 2 is V2 =
Vl-1-R3 The output voltage of the operational amplifier 5, that is, the comparison voltage v3 is set to be Vl-1-R3. The comparison voltage V3 is applied to the inverting input of the voltage comparator 6, and the output voltage 1 of the II battery unit is applied to the non-inverting input. The warning circuit 7 issues a remaining capacity warning of the battery unit 1 when the output of the voltage comparator 6 is at a logic level of L, and issues a remaining capacity warning of the battery unit 1 when the output of the voltage comparator 6 is at a logic level of H. do not have.

The voltage detection point of the voltage comparator is V 1 = V3. Substituting the above value into this, the voltage detection point is set to VB = VR since the resistance value of the circuit is set to VB = VR, and battery unit 1 The electromotive voltages of the battery units can be compared regardless of the current value I flowing out from the battery unit.

That is, the electromotive voltage VB of the battery unit 1 is the reference voltage ~i
When the voltage is higher than R, the voltage comparator 6 outputs a logic level H, and the warning circuit 7 does not issue a warning about the remaining capacity of the battery unit 1. The electromotive force of battery unit 1 is the reference voltage V
When the voltage is lower than R, the output of the voltage comparator 6 becomes logical and a low level L is output, and the warning circuit 7 issues a warning of the remaining capacity of the battery unit 1.

[Effects of the Invention] The internal resistance r1 changes depending on the remaining capacity and temperature of the battery unit 1. However, by determining the circuit constants according to the typical internal resistance value in the range of use, even if the amount of current flowing from the battery unit 1 changes, it is more accurate than the conventional remaining capacity warning detection method. It is now possible to warn of the remaining capacity of battery unit 1.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an embodiment of a power supply circuit according to the present invention. FIG. 2 is a diagram of an example of a conventional power supply circuit. FIG. 3 is a diagram showing the change in battery voltage when a nickel-cadmium battery is discharged from a fully charged state under a constant load. 1.21 ... 3.25 ... 4.22 ... 5. 6.23 ・・・ 7.24 ・・・ Resistor for current detection in battery unit Load reference voltage source Operational amplifier Voltage comparator Warning circuit Applicant Seiko Epson Corporation Agent Patent attorney Kizobe Suzuki and others Figure 2: ``G'' = ri and the first figure is the same as the one shown in Figure 3.

Claims (1)

[Claims] A power supply circuit comprising a battery, a means for detecting the amount of current flowing from the battery, and a means for comparing the voltage of the battery with a comparison voltage that changes in proportion to the amount of current flowing from the battery. .