Circuit for measuring the state of charge of an electrochemical cell

• US 5,519,304 A
• Filed: 06/23/1995
• Issued: 05/21/1996
• Est. Priority Date: 06/24/1994
• Status: Expired due to Fees

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel Alsthom Compagnie Generale d'Electricite (Nokia Corporation)
• Inventors: Andrieu, Xavier, Poignant, Philippe
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US08/494,079
• Time in Patent Office: 333 Days
• Field of Search: 320/48, 320/13, 320/39, 324/427, 324/428, 324/433, 340/636, 429/91-6
• US Class Current: 324/430
• CPC Class Codes: G01R 31/378 specially adapted for the type of battery or accumulator
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

The invention relates to a circuit for measuring the state of charge of an electrochemical cell that includes a parasitic resistance. The circuit comprises:

means for subjecting the electrochemical cell to a reference voltage less than its nominal voltage, so as to cause it to deliver a discharge current;

means for measuring the discharge current and providing an indication of the state of charge of the electrochemical cell; and

correction means for correcting the reference voltage as a function of the discharge current, the correction means providing a corrected reference voltage that compensates for the parasitic resistance.

Claims

1. A circuit for measuring the state of charge of an electrochemical cell that includes a parasitic resistance, said circuit comprising:

means for subjecting said electrochemical cell to a reference voltage lower than its nominal voltage so as to cause it to deliver a discharge current; and

means for measuring said discharge current to provide an indication of the state of charge of said electrochemical cell;

the circuit being also comprising correction means for correcting said reference voltage as a function of said discharge current, said correction means providing a corrected reference voltage compensating for said parasitic resistance.

2. A circuit according to claim 1, wherein said correction means comprise an operational amplifier delivering said corrected reference voltage Vs where:

space="preserve" listing-type="equation">Vs=Vd+Rp×

I.sub.0

in which Vd is a voltage less than said nominal voltage of said electrochemical cell, Rp is said parasitic resistance, and I₀ is said discharge current.