K. J.
Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Batch: A4 Roll No.: 1923005
Experiment / assignment / tutorial No.___3___
Grade: AA / AB / BB / BC / CC / CD /DD
Signature of the Staff In-charge with date
Title: Inverting Schmitt Trigger using Op-Amp.
Aim: To design a Schmitt Trigger for required UTP and LTP
Outcome: Student will be able to understand and design circuits for linear applications of
operational amplifier.
ICs used: IC 741
Theory- (Students should explain about Schmitt Trigger circuit and its applications)
Circuit Diagram1: inverting Schmitt Trigger
Theory:
Schmitt trigger is an electronic circuit with positive feedback which holds the output level till
the input signal to comparator is higher than the threshold. It converts a sinusoidal or any
analog signal to digital signal. It exhibits hysteresis by which the output transition from high
to low and low to high will occur at different thresholds.
A Schmitt trigger circuit is also called a regenerative comparator circuit. The circuit is
designed with a positive feedback and hence will have a regenerative action which will make
the output switch levels. Also, the use of positive voltage feedback instead of a negative
Department of Electronics and Telecommunication Engineering
Page No Sem V DIC 2020-21
K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
feedback, aids the feedback voltage to the input voltage, instead of opposing it. The use of a
regenerative circuit is to remove the difficulties in a zero-crossing detector circuit due to low
frequency signals and input noise voltages.
Types of Schmitt Trigger :
Depending on the input terminal to which we apply the external input, the shmitt trigger
can be:
• Inverting Schmitt Trigger
• Non-Inverting Schmitt Trigger
Applications:
• To convert sine wave into square wave.
• In the on/off type temperature controllers.
Procedure:
Students can visit the virtual lab .
http://vlabs.iitb.ac.in/bootcamp/labs/ic/exp10/exp/simulation.php
1. Using any open source circuit simulator ( Do circuit, Spice. Multisim online etc)
simulate the circuit that will have VUTP and VLTP values of +2.5 and -2.5volts.
Change values of R1 and R2 to see the effect.
2. Apply sine /triangular input to circuit and check UTP and LTP values and
calculate Hysteresis.
3. Take the screen shots of the simulated circuits and circuit parameters
And attach as outputs in the document
Case 1: Equal values of UTP and LTP
Formulas-
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Ciruit Diagram:
For R1 = 4.6k and R2 = 1k
Output Waveforms:
Theoretically Calculations:
V UTP = R2/(R2 + R1) * (+Vsat) = 1k/(4.6k+1k) * (14) = 2.5V
V LTP = R2/(R2 + R1) * (-Vsat) = 1k/(4.6k+1k) * (-14) = -2.5V
Hysteresis Voltage = V UTP - V LTP = 2.5 – (-2.5) = 5v
Department of Electronics and Telecommunication Engineering
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Observation Table:
+Vsat= 14v
Upper threshold voltage Lower threshold voltage Hysteresis
(VUTP) (VLTP) Voltage (V)
-Vsat= -14v
Practically 2.54 v - 2.52 v 5.06 v
Theoretically 2.5 v -2.5 v 5v
Circuit Diagram:
For R1 = 5k and R2 = 2.5k
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Output Waveform:
Theoretically Calculations:
V UTP = R2/(R2 + R1) * (+Vsat) = 2.5k/(5k+2.5k) * (14) = 4.66V
V LTP = R2/(R2 + R1) * (-Vsat) = 2.5k/(5k+2.5k) * (-14) = -4.66V
Hysteresis Voltage = V UTP - V LTP = 4.66 – (-4.66) = 9.32V
Observation Table:
+Vsat= 14v
Upper threshold voltage Lower threshold voltage Hysteresis
(VUTP) (VLTP) Voltage (V)
-Vsat= -14v
Practically 4.6v - 4.59v 9.19 v
Theoretically 4.66v -4.66v 9.32 v
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Circuit Diagram :
For R1 = 9k and R2 = 3k
Output Waveform:
Theoretically Calculations:
V UTP = R2/(R2 + R1) * (+Vsat) = 3k/(9k+3k) * (14) = 3.5V
V LTP = R2/(R2 + R1) * (-Vsat) = 3k/(9k+3k) * (-14) = -3.5V
Hysteresis Voltage = V UTP - V LTP = 3.5 – (-3.5) = 7v
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Observation Table:
+Vsat= 14v
Upper threshold voltage Lower threshold voltage Hysteresis
(VUTP) (VLTP) Voltage (V)
-Vsat= -14v
Practically 3.66v - 3.57 7.23 v
Theoretically 3.5v -3.5v 7v
Case 2: Non-Equal values of UTP and LTP
Formulas:
Circuit Diagram:
For R1 = 4.6k, R2 = 1k and Vref = 2v
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Output Waveform:
Theoretically Calculations:
V UTP = R2/(R2 + R1) * (+Vsat) +R1/(R1=R2)* (Vref)
= 1k/(1k+4.6k) * (14) +4.6k(1k+4.6k)*(2) = 4.14v
V UTP = R2/(R2 + R1) * (+Vsat) +R1/(R1=R2)* (Vref)
= 1k/(1k+4.6k) * (-14) +4.6k(1k+4.6k)*(2) = -857mv
Hystersis Volatge = Vutp – Vltp = (4.14) – (-857mv) = 4.997v
Observation Table:
+Vsat= 14v
Upper threshold voltage Lower threshold voltage Hysteresis
(VUTP) (VLTP) Voltage (V)
-Vsat= -14v
Practically 4.13v -770.88mv 4.9v
Theoretically 4.14v -857mv 4.997v
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Circuit diagram:
Output Waveform:
Theoretically Calculations:
V UTP = R2/(R2 + R1) * (+Vsat) +R1/(R1=R2)* (Vref)
= 1k/(1k+4.6k) * (14) +4.6k(1k+4.6k)*(-2) = 857.14mV
V UTP = R2/(R2 + R1) * (+Vsat) +R1/(R1=R2)* (Vref)
= 1k/(1k+4.6k) * (-14) +4.6k(1k+4.6k)*(-2) = -4.14v
Hystersis Volatge = Vutp – Vltp = (857mv)-(-4.14) = 4.997
Department of Electronics and Telecommunication Engineering
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Observation Table:
+Vsat= 14v
Upper threshold voltage Lower threshold voltage Hysteresis
(VUTP) (VLTP) Voltage (V)
-Vsat= -14v
Practically 910mV -4v 4.91v
Theoretically 857.14v -4.14v 4.997v
Conclusion:
In this experiment, we have understand the Schmitt circuit by using LTspice software and
observed the variations in the output for equal and non-equal UTP and LTP values and
hysteresis voltage was calculated. Also we got to know Schmitt trigger cans be used as a
sinewave to square wave converter.
Department of Electronics and Telecommunication Engineering
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K. J. Somaiya College of Engineering, Mumbai-77
(Autonomous College Affiliated to University of Mumbai)
Department of Electronics and Telecommunication Engineering
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