Patent ID: 6621272
Filing Date: 2003-09-16
Classification: G01R

Abstract:
Apparatus for passing a periodic time-varying current at a particular measurement frequency through an electrochemical cell or battery comprising:an auxiliary dc power supply contacting a first terminal of said cell or battery and adapted to inject current into said cell or battery in the charging direction; a resistor contacting a second terminal of said cell or battery and adapted to conduct current through said cell or battery in either the charging direction or the discharging direction; a pair of complementary transistors connected in series across said auxiliary dc power supply and arranged to conduct current through said resistor in either the charging direction or the discharging direction; an operational amplifier arranged to sense the voltage across said resistor at an inverting input and to control conduction of said complementary transistors; and, a signal source delivering a periodic control signal at said measurement frequency to a noninverting input of said operational amplifier.