CAPACITOR_ESR_MEASURER

Published:2009/7/10 3:07:00 Author:May | From:SeekIC

The equivalent series resistance (ESR) of a capacitor can be measured using this circuit and an ac voltmeter. U1 functions as a 50-kHz square-wave generator. It drives a current waveform of about ±180mA in the capacitor-under-test, through R1 and R2. When R3 is adjusted to the proper value, the voltage drop across the equivalent series resistor is precisely nulled by the inverting amplifier (U2). Thus, VO is the pure capacitor voltage which is the minimum voltage that can be produced at VO. To make an ac voltage measurement, adjust R3 until VO is minimized. Then, note the position of the potentiometer and multiply it by the value of R2, 1Ω in this case. That product equals the capacitor's ESR. The capacitor is biased at about 7.5 V. Lower-voltage capacitors won't work with this circuit. By changing the value of R2, other ranges of ESR can be measured. However, for small R2 values, the current level should be increased to keep a reasonable voltage across R2. This requires some sort of buffer. The circuit is intended for capacitors greater than 100μF. The ripple voltage gets large for smaller values and accuracy decreases.



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