Question 39E6

Power supplies using a capacitive input filter charge the capacitor to the peak voltage of the rectified AC waveform. When a load draws current, the capacitor discharges between the peaks of the AC cycle, causing the output voltage to drop. This significant voltage sag under load leads to poor voltage regulation. Furthermore, the rectifier diodes only conduct briefly when the instantaneous AC voltage exceeds the capacitor's voltage. During this short interval, the capacitor must rapidly recharge to compensate for the charge lost to the load, resulting in large, impulsive current spikes through the rectifier diodes. These high rectifier peak currents stress the rectifier components and transformer, reducing their efficiency and lifespan.