Page 5

SUBJECT:

IC 741 TITLE:

STUDY OF IC741

DATE :

IC741:

The purpose of these experiments is to introduce the most important of all analog building blocks, the

operational amplifier (op-amp for short). This hand-out gives an introduction to these amplifiers and a bit of the various configurations that they can be used in. Apart from their most common use as

amplifiers (both inverting and non-inverting), they also find applications as buffers (load isolators),

adders, subtractors, integrators, logarithmic amplifiers, impedance converters, filters (low-pass, high-

pass, band-pass, band-reject or notch), and differential amplifiers.

Amplifiers, in general, taking as input, one or more electrical signals, and produce as output, one or

more variations of these signals. The most common use of an amplifier is to accept a small electrical

signal and increase the voltage or power, for example the amplifiers inside of a stereo.

OP-AMPs (OPerational AMPlifiers) are a fundamental building block for handling analog electrical signals. An op-amp is a differential to single-ended amplifier, i.e. it amplifies the voltage difference Vp Vn = Vi at the input port and produces a voltage Vo at the output port that is referenced to the ground node of the circuit in which the op-amp is used.

Typically an OP AMP has two inputs called + and -, ( or VIN+ and VIN-) and a single output. The output depends only on the difference of the voltage on the two inputs. If the difference of the two input

voltages is VIN , then the output voltage is VOut = VIN* Avi. This defines the (voltage) gain (Avi).

Ideal characteristics:

1) Infinite voltage gain A. 2) Infinite input impedance so that almost any signal can drive it and there is no loading of the

preceding stage.

3) Zero output impedance so that output can drive an infinite number of other devices. 4) Zero output voltage when input voltage is zero.

5) Infinite bandwidth so that any frequency signals from 0 to can be amplified without attenuation. 6) Infinite common-mode rejection ratio so that the output common-mode noise voltage is zero. 7) Infinite slew rate so that output voltage changes occur simultaneously with input voltage changes.

Comparison of the LM741 against the ideal OP-AMP:

Sr.

No.

Characteristic Ideal Typical for real 741

1 Input Resistance 6 M

2 Output Resistance 0 50

3 Voltage Gain 50000 to 100000

Page 6

4 Bandwidth 1 MHz , changes at 0.7 V/sec

5 Offset voltage 0 1 MV

6 Input Current 0 30 nano Volts ( 3 X 10-8 volts )

7 Voltage difference of inputs 0 ????

Standard OP-AMP vs. Ideal OP-AMP model:

FIG. 1: EQUIVALENT CIRCUIT OF PRACTICAL OP-AMP and IDEAL OP-AMP.

Pin configuration:

FIG. 2: PIN CONFIGURATION OF IC741 AND IC741

Pin Name Purpose

1 Offset null

Since the op-amp is differential type, input offset voltage must be

controlled so as to minimize offset. Offset voltage is nulled by

application of a potentiometer between pin-1 and pin-5.

2 Inverting input All input signal at this pin will be inverted at output pin-6.

3 Non-inverting

input

All input signal at this pin will be processed normally without inversion

Rest is same as pin-2

4 -VEE This pin is the negative supply voltage terminal. Supply voltage

operating range for 741 is -5 to -15 V dc.

Page 7

5 Offset null Same as pin-1.

6 Output

Output signals polarity will be the opposite of the input signals when

this signal is applied to the op-amps inverting input. Output signals

polarity will be the same as the inputs when this signal is applied to the

op-amps non-inverting input.

7 +Vcc This pin is the positive supply voltage terminal. Supply voltage

operating range for 741 is +5 to +15 V dc.

8 N/C Not connected.

Specifications:

Supply Voltage 18V

Internal Power Dissipation 310mw

Differential input voltage 30V

Input Voltage 15V

Operating temperature range 0C to 70C

Applications:

Non-inverting amplifier

Inverting amplifier

Integrator

Differentiator Low Pass,

High Pass,

Band pass and Band Reject Filters

Features:

No External frequency compensation is required

Short circuit Protection

Off Set Null Capability

Large Common mode and differential Voltage ranges

Low Power Dissipation

No-Latch up Problem

741 is available in three packages: 8-pin metal can, 10-pin flat pack and 8 or 14-pin DIP