Figure shows a functional block diagram of the series type regulator. Vin is an unregulated dc output and Vo is the regulation output voltage. The control element is in a series path between Vin and Vo and adjust as necessary to maintain a constant Vo. A sampling circuit produces a feedback voltage proportional to Vo and this voltage is compared to a reference voltage. The output of comparators circuit is the control signal that adjusted the operating state of the control element. If Vo decreases due to an increased load, then the comparator produces an output that causes the control element to increase Vo.
Figure shows the functional block diagram of shunt regulations. Here all the components act same as in series regulators but the control element is in parallel with load. The control element maintains a constant load voltage by shunting more or less current from the load. The control element maintains a constant load voltage by shunting more or less current from the load.
It is convenient to think of the control element as a variable resistance. When the load voltage decreases, the resistance of control element is made to rise. So less current is diverted from the load and the load voltage rises. Conversely when the load voltage increases, the resistance of the control element decreases a more current is shunted away from the load.
This note is taken from MSC physics, Nepal.