Non-inverting Schmitt trigger realized with op-amp is given in figure bellow.
Simulate op-amp non-inverting 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 R2–R1.
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.
Electrical potential of V+ can be calculated via combining nodal analysis and superposition theorem and it is
By solving VIN from above equation, we obtain:
Now, if previously output was VOUT=-VCC, input voltage must increase over
so that V+ becomes higher then V–=VREF in order to change output voltage to +VCC. It means that high threshold voltage is:
On the other hand, if previous output voltage was VOUT=+VCC, input voltage must decrease under
so that V+ becomes lower then V–=VREF in order to change output voltage to -VCC.It means that high threshold voltage is:
Input impedance is less then R2, since parallel positive feedback is applied at input side.