Low-cost sensing of equivalent series resistance for electrolytic capacitors

A simple equivalent series resistance (ESR) measurement technique for capacitors at high current and high frequency is presented. A low-cost square waveform voltage source coupled with a reference resistor can be used to measure the ESR of an electrolytic capacitor. By connecting a capacitor in series with a reference resistor, the ratio of the voltage magnitude across the capacitor to the voltage magnitude of the supply voltage reveals the ESR of the capacitor if the frequency of the supply source is sufficiently high. The square waveform voltage source can easily be realised using a DC voltage source and simple switching devices. An addition of a small inductor in series with the reference resistor could eliminate the effect of the equivalent series inductance and improve the measurement accuracy. A mathematical analysis is presented to demonstrate that the use of the square waveform and the addition of the small inductor are valid. Experimental results are included to demonstrate the effectiveness of the proposed scheme.