85-op-amp-schmitt-trigger-simulation

Non-inverting Schmitt trigger realized with op-amp is given in figure bellow.

Simulate op-amp non-inverting Schmitt trigger.

schmitt-trigger

Positive feedback is used with non-inverting Schmitt trigger realized with op-amp. The feedback is applied from the output to the non-inverting input of the op-amp, same as for inverting Schmitt trigger. The difference from inverting Schmitt trigger is that reference voltage is brought to inverting input, and input voltage is brought to voltage divider R2R1.

Comparator is non-inverting since the output voltage is high if input is higher then high threshold voltage and low if input is lower then low threshold voltage, every time when input voltage is out of the hysteresis cycle. Inside hysteresis cycle output voltage depends on the last state and the circuit behaves as an elementary latch. Hysteresis transfer function for inverting Schmitt trigger is given in figure bellow.

schmitt-trigger-hysteresis

Electrical potential of V+ can be calculated via combining nodal analysis and superposition theorem and it is

non_inv_schmitt_eq01

By solving VIN from above equation, we obtain:

non_inv_schmitt_eq02

Now, if previously output was VOUT=-VCC, input voltage must increase over

non_inv_schmitt_eq03

so that V+ becomes higher then V=VREF in order to change output voltage to +VCC. It means that high threshold voltage is:

non_inv_schmitt_eq04

On the other hand, if previous output voltage was VOUT=+VCC, input voltage must decrease under

non_inv_schmitt_eq05

so that V+ becomes lower then V=VREF in order to change output voltage to -VCC.It means that high threshold voltage is:

non_inv_schmitt_eq06

Input impedance is less then R2, since parallel positive feedback is applied at input side.

Go to op-amp non inverting Schmitt trigger simulation.

External links:

Op-amp Schmitt trigger Comparator on Wikipedia

Op-amp Schmitt trigger Comparator on CircuitsToday

Op-amp Schmitt trigger Comparator on TalkingElectronics

 

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