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, highpass, 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-AMP’s (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. 1 2 3 Characteristic Input Resistance Output Resistance Voltage Gain Ideal Typical for real 741 ∞ 0 ∞ 6 MΩ 50Ω 50000 to 100000 Page 5 All input signal at this pin will be processed normally without inversion Rest is same as pin-2 This pin is the negative supply voltage terminal. changes at 0. Ideal OP-AMP model: FIG. Offset voltage is nulled by application of a potentiometer between pin-1 and pin-5. input offset voltage must be controlled so as to minimize offset. Supply voltage operating range for 741 is -5 to -15 V dc. All input signal at this pin will be inverted at output pin-6.7 V/μsec 1 MV 30 nano Volts ( 3 X 10-8 volts ) ???? Standard OP-AMP vs. 1: EQUIVALENT CIRCUIT OF PRACTICAL OP-AMP and IDEAL OP-AMP. Pin configuration: FIG. 2: PIN CONFIGURATION OF IC741 AND IC741 Pin 1 2 3 4 Name Offset null Inverting input Non-inverting input -VEE Purpose Since the op-amp is differential type.4 5 6 7 Bandwidth Offset voltage Input Current Voltage difference of inputs ∞ 0 0 0 1 MHz . Page 6 . 5 Offset null 6 Output 7 +Vcc 8 N/C Same as pin-1. This pin is the positive supply voltage terminal. Supply voltage operating range for 741 is +5 to +15 V dc. Output signal’s polarity will be the opposite of the input signal’s when this signal is applied to the op-amp’s inverting input. 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 Page 7 . Not connected. Specifications: Supply Voltage ± 18V Internal Power Dissipation 310mw Differential input voltage ± 30V Input Voltage ± 15V Operating temperature range 0ºC to 70ºC Applications: Non-inverting amplifier Inverting amplifier Integrator Differentiator Low Pass. Output signal’s polarity will be the same as the input’s when this signal is applied to the op-amp’s non-inverting input. High Pass.