Current monitoring circuit for secondary battery

• US 6,335,611 B1
• Filed: 07/26/2000
• Issued: 01/01/2002
• Est. Priority Date: 07/30/1999
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Sasaki, Manabu
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/625,720
• Time in Patent Office: 524 Days
• Field of Search: 320/134, 320/128, 320/127, 320/132, 320/151, 320/152
• US Class Current: 320/134
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]

Abstract

A current monitoring circuit for monitoring a charging/discharging current of a secondary battery that achieves high-precision monitoring and that restricts an increase in the circuit scale. An amplifier amplifies a voltage of a current sense resistor generated by a charging/discharging current under a various amplification degrees. A comparator compares an output voltage of the amplifier with a reference voltage. A controller controls a reference voltage to be supplied to each unit and controls the amplification degree of the amplifier, based on a result of the comparison. An A/D converter A/D converts an output voltage of the amplifier. A numerical-value converter converts a digital value obtained by the conversion of the A/D converter into a numerical value corresponding to a charging/discharging current, under the control of the controller. When an excess current has been detected, a switch is set to a non-conductive state, to thereby disconnect the battery from the external unit.

Claims

1. A current monitoring circuit for a secondary battery, comprising:

a current detector detecting a current during a charging and a discharging of a secondary battery, and outputting a voltage signal according to a detected current;

an amplifier having an amplification degree that can be changed, and amplifying the voltage signal output from the current detector at a suitable amplification degree obtained by changing the amplification degree;

an A/D converter converting an output of the amplifier into a digital signal; and

a numerical-value converter converting the digital signal output from the A/D converter according to an amplification degree of the amplifier, to thereby output a digital value indicating the current during the charging and the discharging of the secondary battery.

2. The current monitoring circuit according to claim 1, wherein

the amplifier comprises:

a first amplifier amplifying an output of the current detector at a first amplification degree;

a second amplifier sharing a part of a circuit with the first amplifier, and amplifying the output of the current detector at a second amplification degree smaller than the first amplification degree;

a first switch selecting one of outputs of the first and second amplifiers as the output of the amplifier; and

a first comparator comparing an output of the first amplifier with a first reference voltage, wherein

the first switch is controlled based on a result of the comparison by the first comparator.

3. The current monitoring circuit according to claim 2, wherein

the first reference voltage includes an upper limit value and a lower limit value,

the current monitoring circuit further comprising;

a second comparator for comparing an output of the first amplifier with a second reference voltage to make a decision as to whether a current is being charged or being discharged; and

a second switch selectively supplying the upper limit value of 4.0 V and the output of the first amplifier to the first comparator during a charging, and selectively supplying the output of the first amplifier and the lower limit value of 1.0 V to the first comparator during a discharging.

4. The current monitoring circuit according to claim 3, further comprising:

a third switch selecting the lower limit value during a charging and selecting the upper limit value during a discharging and supplying the selected values to the second amplifier as a reference value, to thereby adapt an output range of the second amplifier to an input range of the A/D converter for each of a charging current and a discharging current.

5. The current monitoring circuit according to claim 3, further comprising:

a third comparator comparing the output of the second amplifier with the first reference voltage, to thereby detect an excess current; and

a fourth switch selectively supplying the output of the second amplifier and the upper limit value of to the third comparator during a charging, and selectively supplying the lower limited value of and the output of the second amplifier to the third comparator during a discharging.

6. The current monitoring circuit according to claim 5, further comprising:

a chattering remover firming up a result of a comparison of each of the first, second and third comparators when an output of each comparator is unchanged during a predetermined period of time.

7. The current monitoring circuit according to claim 3, wherein the first reference voltage includes an upper limit value of 4.0 V.

8. The current monitoring circuit according to claim 3, wherein the first reference voltage includes a lower limit value of 1.0 V.