What is transistor shunt voltage regulator?

The transistor shunt voltage regulator is a control element connected in parallel with the load due to this circuit is called a shunt voltage regulator.

The block diagram of transistor shunt voltage regulator is shown in above figure.The unregulated DC voltage is obtained from a rectifier and filter combination.

The total current supplied by the unregulated input V_in is shared by the load RL and the control element. The control flowing through the control element is I_Shunt. The sampling network samples the output voltage V_Out and provides a feedback signal proportional to the output voltage V_Out to the comparator circuit.

The comparator circuit compares the feedback signal with a constant reference voltage to produce a control signal which is applied to the control circuit. Depending upon this control signal, the control element will change its current I_Shunt in such a way that any changes in the output voltage are multiplied to maintain the output voltage control.

If the output voltage increases above the regulated value V_Out then the sampling networks provides the increase feedback voltage. This will force the comparator circuit to increase the control signal amplitude. This will, in turn, force the control current to draw more current I_Shunt.

Therefore the load current I_Load will decrease and the output voltage will be brought back to the regulated value V_Out. If the load voltages decrease then exactly opposite action will take place to regulate the output voltage. This voltage regulator is preferred for the fixed voltages application only.