Programmable current exciter for measuring ac immittance of cells and batteries

摘要

An exciter of periodic square-wave current for measurement of complex ac impedance or admittance is described. A microcontroller/processor outputs two digital words that define upper and lower current levels. These words are latched and converted to analog voltages by D/A converter circuitry. A timing signal at the measurement frequency, also outputted by the microprocessor/controller, controls a multiplexer arranged to select either analog voltage. The multiplexer output thus toggles between the two programmed analog voltages at the measurement frequency. ;By virtue of negative feedback, the toggled multiplexer output voltage equals the voltage developed across a resistance in series with the cell/battery. Two complementary transistors and a dc voltage source are arranged such that a positive multiplexer output directs a programmed current through this resistance in the discharge direction, and a negative multiplexer output directs a programmed current through it in the charge direction. Accordingly, the current through the cell/battery is a symmetrical square wave having frequency, amplitude, average value, and average flow direction completely under program control.