Question

Create a noninverting schmitt trigger using voltage divider as it reference voltage.

Designt requirement:

1. Op-amp(comparator) with V+ as 5V and V- connected to ground

2. Assume input is noisy voltage

3. Output should display only high and low(ground voltage values)

4. How many threshold values are there?

Answer 1

A Schmitt Trigger electronic circuit diagram is a comparator circuit with hysteresis to the input-output transition threshold with the help of positive feedback.

Op-amp can be used as a Schmitt trigger circuit. Depending on where the input is applied, the Op-amp based circuits can be further divided into Inverting and Non-Inverting Schmitt Triggers.

The circuit of the IC-741 (Op-amp) Schmitt trigger in non-inverting mode is shown in the figure.

The input is connected at the non-inverting terminal (pin-3) of the IC-741 (Op-amp) through resister R1 and inverting terminal is connected to ground (as shown in the above figure). The output is connected to the non-inverting terminal through resister R2. This positive voltage is fedback to the non-inverting terminal (+) of the op-amp through the voltage divider.

Vth+ and Vth- are two thresholds of the Schmitt Trigger circuit.

Vi is the noisy input and Vout is the output voltage.

In the initial condition, when the input exceeds a certain positive level the waveforms as shown in the above figure that the output rapidly change from the positive saturation (+Vo(sat)) voltage to the negative saturation level (-Vo(sat)). This is called upper trigger point (UTP). Similarly, the output voltage switches from low to high when the input goes below a negative triggering point; the lower trigger point (LTP).

So, Schmitt Trigger is to convert noisy square-wave, sine-wave, triangular-wave or any periodic signals into clean square pulses with sharp leading and trailing edges.