Efficient method to investigate the equivalent series resistance of a capacitor in low frequency range

The equivalent series resistance (ESR) is an important parameter for determining the quality of a capacitor. In general, the value of the ESR can be obtained only at a single frequency point during mass production testing, because obtaining the whole ESR curve by means of scanning the frequency range is time consuming. We present a novel method to investigate how the ESR varies with frequency during batch testing. We use the multi-frequency synthesis excitation waveform to obtain the ESR at multiple frequency points. This allows the entire ESR curve to be obtained during one measurement period, thus greatly improving the measurement speed. The mathematical principle, the circuit realisation and the signal processing algorithm are discussed. Furthermore, a principle verification test is conducted, and the ESR values at seven frequency points are synchronously measured. The obtained results are consistent with those acquired from a standard LCR meter, and the entire measurement is completed within 10 ms, which confirms that our method is efficient and suitable for measurements in the mass production testing.