ECE 211 Electrical Circuits Lab I
LAB #10
Section
Name
Introduction to Operational Amplifier
Objective:

To be familiar with the use of operational amplifiers as circuit building blocks.

To understand the basic properties of op amps using simple resistive networks.
Components and Equipments:

Single Op Amp IC # LM741 or Dual Op Amp IC # LM358.

Two DC power supplies.

Digital Multimeter.

Resistors.
Introduction:

Operational amplifiers are an extremely important component for a wide range of
electronic circuits. The term operational refers to the use of op amps in electronic
circuits which perform arithmetic operations on the input voltages (or currents) applied to
the circuit.

Many general purpose op amps in IC form are very inexpensive. In fact, the socket that
op amp IC plugs into may cost as much or more than the op amp itself..!

The op amp is depicted schematically as shown in Figure 10-1. The figure shows the two
op amp inputs: “-” for the inverting input and “+” for the non-inverting input, the op amp
output, and the power supply connections. NOTE that the power supply connections are
not always shown in diagrams, but they must be included in the actual circuit.
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ECE 211 Electrical Circuits Lab I
LAB #10
Figure 10-1 Basic Op Amp Schematic

The integrated circuit op amp used in this experiment is shown in Figure 10-2 and Figure
10-3. The circuit is contained in a dual in-line package, or DIP for short. The DIP has a
notch or stripe at one end to indicate the correct orientation of the circuit. The standard
part number is usually printed on the top of the DIP. Note that the pin numbers are
assigned in counter clockwise order beginning from the left at the notch end.

In LM741, in addition to the two inputs, the two power supply pins, and the output,
notice that this particular op amp has three other pins: one labeled NC, meaning no
connection, and two labeled offset null. The offset null pins allow us to make small
adjustments to the internal currents in the IC in order to force the output voltage to be
zero (null) when the inputs are both zero in order to compensate for the anticipated
manufacturing variations from chip to chip. We will not need to use the offset null
feature in this experiment, so no connections will be made to offset null pins.
Figure 10-2 Op Amp 741 Pin Assignment
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ECE 211 Electrical Circuits Lab I
LAB #10
Figure 10-3 Op Amp 358 Pin Assignment
There are some important limitations to keep in mind:

First, the supply voltages cannot exceed some maximum rating, typically +/- 16V DC.
The op amp will usually operate using lower voltage supplies, but exceeding the
maximum rating will destroy the IC.

Second, the output voltage from an IC op amp is usually limited to be a volt or two
smaller than the power supply voltages, e.g., the output voltage swing of an op map with
+/- 15V supplies is, perhaps, +/- 13V.

Third, the output current from most op amps is limited to 30mA so, the load resistance
attached to the output must be large enough that no more than the maximum current
flows when the output voltage is at its maximum value.
Ideal Op Amp Considerations:
 V =V

=
=0
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ECE 211 Electrical Circuits Lab I
LAB #10
Procedure:
Rf
Experiment # 1 – Inverting Op Amp:
The voltage gain relation of the Inverting Op Amp is:
Rs
=−
1.Build the circuit shown in the figure.
2.Select Rf = 10 KΩ, and Rs = 1KΩ.
3.Adjust the first power supply (Vi) to: 1V DC.
4.Connect the second power supply to the DC voltage terminals (Vcc) and adjust it to ±12v.
5.Measure the value of the output voltage (Vo).
6.Compare with the calculated voltage gain relation of the Inverting Op Amp.
7.Verify the Ideal Op Amp Considerations by measuring the following:
a. Vn
b. In
c. IRf and IRs
Experiment # 2 – Non-inverting Op Amp:
Rf
The voltage gain relation of the Non-inverting Op Amp is:
1.
2.
3.
4.
5.
6.
7.
=
Rs
Build the circuit shown in the figure.
Select Rf = 10 KΩ, and Rs = 1KΩ.
Adjust the first power supply (Vi) to: 1V DC.
Connect the second power supply to the DC voltage terminals (Vcc) and adjust it to ±12v.
Measure the value of the output voltage (Vo).
Compare with the voltage gain relation of the Inverting Op Amp.
Verify the Ideal Op Amp Considerations by measuring the following:
a. Vn
b. In
c. IRf and IRs
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