In the block diagram of simple rectifier circuit, from a variable a.c. voltage, constant d.c. voltage is obtained. The correct order of operation is

1. Diode Rectifier: This is the first stage, where the $A C$ voltage is rectified to produce a pulsating DC voltage. The diode(s) in the rectifier allow current to flow only in one direction, converting the $A C$ input into a unidirectional current. 2. Filter: After rectification, the output is a pulsating DC that still contains ripples. A filter (usually a capacitor or a combination of capacitors and inductors) smooths out these ripples, providing a more steady DC output. 3. Voltage Regulator: The final stage is the voltage regulator, which ensures that the DC voltage remains constant, even if the input $A C$ voltage fluctuates or if there are variations in load. The regulator keeps the output voltage at a constant level by adjusting the current flow as needed. Therefore, the correct order of operation is: - Diode rectifier $\rightarrow$ Filter $\rightarrow$ Voltage regulator