Capacitor Esr Measurer

Posted on Jan 15, 2013

The equivalent series resistance (ESR) of a capacitor can be measured using this circuit and an ac voltmeter. Ul fun

Capacitor Esr Measurer
Click here to download the full size of the above Circuit.

ctions as a 50-kHz square-wave generator. It drives a current waveform of about ±180 mA in the capacitor-under-test, through Rl 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, V0 is the pure capacitor voltage which is the minimum voltage that can be produced at V0. To make an ac voltage measurement, adjust R3 until V0 is minimized. Then, note the position of the potentiometer and multiply it by the value of R2, 1 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 100 The ripple voltage gets large for smaller values and accuracy decreases.

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