Schmitt Trigger using 741 Opamp with Proteus Simulation

Everyone is very much familiar with Ic741 opamp. In most of the opamp circuits we use negative feedback that is the output of the opamp is fed back to the negative input through a resistor, known as feedback resistor but in schmitt trigger there is a positive feedback which means that the output is fed back to the positive input that is the non inverting input of the opamp which is the 3rd pin. Schmitt Trigger using opamp is an applicatioin of a comparator. A comparator never contain a negative feedback so is schmitt trigger. Schmitt trigger provides hysteresis as it swings between +vsat and -vsat. It basically is a bistable multivibrator.

SCHMITT TRIGGER CIRCUIT:

 

SCHMITT TRIGGER CIRCUIT DIAGRAM
SCHMITT TRIGGER CIRCUIT DIAGRAM

ABOVE CIRCUIT IS IMPLEMENTED ON PROTEUS 8.0. The components and other parameters are given below

COMPONENTS:

  1. OPAMP IC 741
  2. 10K OHM RESISTOR [R1]
  3. 4.7K OHM RESISTOR [R2]
  4. 3K OHM RESISTOR [R3]
  5. OSCILLOSCOPE
  6. POWER SUPPLY

After connecting the circuit set following parameters

Sine generator properties: just click on sine wave input signal and select amplitude as 10v

Schmitt Trigger Properties
Schmitt Trigger Properties

Select DC supply at 7 pin as +15v and 4 pin at -15v . The maximum output voltage swing of the opamp will be +15v and -15v.

Now after properly implementing the above circuit run the simulation.

Schmitt trigger operation:

Resistor r3 is selected in such a way that it is the parallel combination of r1 & r2.

It is used to minimize the offset problems.

utp(upper trigger point) It is a voltage level at the output where the voltage swings from +vsat to -vsat

Vutp= +vsat(r2/r1+r2)

ltp (lower trigger point) It is a voltage level at the output where the voltage swings from –vsat to +vsat

Vltp= -vsat(r2/r1+r2)

In our case Vutp = 4.79v and Vltp= -4.79v

Schmitt trigger output:

SCHIMITT TRIGGER OUTPUT
SCHIMITT TRIGGER OUTPUT

The circuit can be verified by the output. Yellow signal is the output and the blue signal is the sine wave input.

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