ESR Measurements

In a switch-mode power supply, the quality of the output voltage depends strongly on the quality of the electrolytic capacitors that are used. Here the effective series resistance (ESR), which is the internal ‘ohmic’ impedance of the capacitor, is one of the most important factors, since large currents are involved. It is rather difficult to exactly measure the ESR, but if you only want a quick idea, or you want to compare different families of capacitors, the illustrated simple measurement setup is very suitable.