SUBJECT: ANALOG ELECTRONICS
TITLE:
STUDY OF IC741 & IC555 DATE :
IC741:
The purpose of these experiments is to introduce the most important of all analog building blocks, the operational amplifier (“op(“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. 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, po wer, for example the amplifiers inside of a stereo. OP-AMP’s OP-AMP’s (OPerational AMPlifiers) are a fundamental building block for handling analog electrical signals. An op-amp op-amp is a “differential to singlesingle-ended” amplifier, i.e. it amplifies the voltage difference voltage difference Vp – Vp – Vn 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 o ccur 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 MΩ 50Ω 50000 to 100000
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4 5 6 7
Bandwidth Offset voltage Input Current Voltage difference of inputs
∞ 0 0 0
1 MHz , changes at 0.7 V/μsec 1 MV 30 nano Volts ( 3 X 10-8 volts ) ????
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
1 2 3 4
Name
Offset null
Purpose 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.
Inverting input Non-inverting input
All input signal at this pin will be inverted at output pin-6. All input signal at this pin will be processed normally without inversion Rest is same as pin-2
-VEE
This pin is the negative supply voltage terminal. Supply voltage operating range for 741 is -5 to -15 V dc. Page 6
5
Offset null
6
Output
7
+Vcc
8
N/C
Same as pin-1. 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. 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. This pin is the positive supply voltage terminal. Supply voltage operating range for 741 is +5 to +15 V dc. 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, 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
IC555
Basically, 555 timers is a highly stable circuit capable of functioning as an accurate time-delay generator and as a free running multivibrator. When used as an oscillator the frequency and duty cycle are accurately controlled by only two external components, a resistor (R) and a capacitor (C). The circuit may be triggered and reset on falling wave forms. Pin configuration:
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FIG. 3: PIN CONFIGURATION of IC-555 Pin 1
Name GND
Purpose Ground reference voltage, low level (0 V) The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (hence TRIG is typically 1/3 VCC, CTRL being 2/3 VCC by default, if CTRL is left open). This output is driven to approximately 1.7 V below +VCC or GND. A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR.
2
TRIG
3
OUT
4
RESET
5
CTRL
Provides "control" access to the internal voltage divider (by default, 2/3 VCC).
6
THR
The timing (OUT high) interval ends when the voltage at THR is greater than that at CTRL (2/3 VCC if CTRL is open).
7
DIS
8
V CC
Open collector output which may discharge a capacitor between intervals. In phase with output. Positive supply voltage, which is usually between 3 and 15 V depending on the variation.
A functional block diagram of 555 timer is given below. The device consists of two comparators two transistors, a flip-flop and buffered outputs stage and three resistors of 5kohm each (highlighted with yellow pen) connected in series. These three resistors produce 1/3 and 2/3 voltage levels for controlling the action of trigger and threshold comparators inside the IC. Due to this arrangement of the three resistors, the IC has a typical code number as IC555.
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FIG.4: A FUNCTIONAL BLOCK DIAGRAM OF 555 Specifications:
Supply Voltage 5V to 18V Maximum Current rating 200mA Minimum Triggering Voltage - (1/3) VCC Operating temperature range 0ºC to 70ºC
Applications:
Astable Multivibrator Schmitt trigger Free running ramp Generator Monostable Multivibrator Frequency divider Pulse structure
Features:
Timing from micro seconds through hours Monostable and Astable operation Adjustable duty cycle Page 9
Ability to operate from a wide range of suppl y voltages Output compatible with CMOS, DTL and TTL (when used with appropriate supply voltage) High current output that can sink or source 200 mA Trigger and reset inputs are logic compatible Output can be operated normal ON and OFF High temperature stability
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