Op-Amp as Schmitt Trigger
Category: Operational Amplifier
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
The circuit is simulated in Proteus. You can simulate this circuit in any other simulation software like LTspice or Psim. This is a very simple circuit and a very basic concept of Schmitt trigger. 1. To understand this circuit, watch previous circuit "Schmitt Trigger Using BJTs". 2. Very few components needed to build this circuit. One Op-Amp and two resistors only. 3. Random input signal is applied at inverting pin of op-amp. 4. Output is taken from pin 1 of op-amp LM358. 5. On oscilloscope, yellow wave shows output and blue wave shows input which is random signal. 6. This circuit will act as a comparator with hysteresis whose thresholds for setting the output high or low will be defined by the design parameters. 7. The value of thresholds depends on resistors R1 and R3. 8. The above comparator circuit uses positive feedback provided by resistors R1 and R3 to generate hysteresis. 9. As this resistive network is connected between the amplifiers output and non-inverting (+) input pin, when Vout is saturated at the positive supply rail, a positive voltage is applied to the op-amps non-inverting input. 10. Similarly, when Vout is saturated to the negative supply rail, a negative voltage is applied to the op-amps non-inverting input. 11. The two resistors are configured across the op-amps output as a voltage divider network, the reference voltage, Vref will therefore be dependent upon the fraction of output voltage fed back to the non-inverting input. 12. Fraction is given as fraction = R3/(R3+R1) 13. Vout = Vsat Vref = fraction*Vsat 14. The working of the circuit is seen in the waveform, which is perfectly fine. More circuits will be uploaded soon. Stay with us and share this knowledge with others.