Linear Integrated Circuits: Unit V: Application ICs

Voltage Follower Regulator using Op-amp

Operating working principle, Functional Circuit Diagram

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The voltage follower d.c. regulator is nothing but fixed voltage series regulator using op-amp. It is shown in the Fig. 5.5.1.

Voltage Follower Regulator using Op-amp

The voltage follower d.c. regulator is nothing but fixed voltage series regulator using op-amp. It is shown in the Fig. 5.5.1.

The op-amp is used as a comparator. The supply of op-amp is derived from input supply terminals. Hence op-amp supply voltages are +Vin and ground. The inverting terminal of op-amp is connected to the output terminal.

VB = Vo

While the voltage of noninverting terminal i.e. node A is zener voltage Vz, decided by the zener diode D1.

VA = VZ 


Key Point Thus the output voltage is constant equal to zener voltage.

The series pass transistor is to supply the additional load current which op-amp can not supply. For large load current, op-amp has to supply only base current of the transistor, IB.

If load current is less than 25 mA, series pass transistor Q1 does not play any role and op-amp behaves as a voltage follower.

The C1 is large capacitor of the order of 50 to 100 µF. The functions of C1 are,

1. To help to supply fast demands on regulator.

2. To eliminate the possibility of any oscillatory behaviour of the regulator.

The op-amp 741 can be used for the circuit. The heat sink must be provided to series pass transistor. The minimum VCE required to keep Q1 operating is about 3 V. If it is below 3 V, the ripple content in the output increases which affects the values of line and load regulations badly.

Review Question

1. Explain the working of series voltage regulator using op-amp.

Dec.-10, May-15,18 Marks 8 


Linear Integrated Circuits: Unit V: Application ICs : Tag: : Operating working principle, Functional Circuit Diagram - Voltage Follower Regulator using Op-amp

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