Schmitt trigger

EXPERIMENT NO. 3 DESIGN AND TEST A SCHMITT TRIGGER CIRCUIT FOR THE GIVEN VALUES OF UTP AND LTP

 AIM: Design a square wave generator for a given UTP and LTP

THEORY: Schmitt Trigger is also known as Regenerative Comparator. This is a square wave generator which generate a square based on the positive feedback applied. As shown in the fig. below, the feedback voltage is Va. The input voltage is applied to the inverting terminal and the feedback voltage is applied to the non-inverting terminal. In this circuit the op-amp acts as a comparator. It compares the potentials at two input terminals. Here the output shifts between + Vsat and –Vsat. When the input voltage is greater than Va, the output shifts to – Vsat and when the input voltage is less than Va, the output shifts to + Vsat. Such a comparator circuit exhibits a curve known as Hysterisis curve which is a plot of Vin vs V0. The input voltage at which the output changes from + Vsat to – Vsat is called Upper Threshold Point (UTP) and the input voltage at which the output shifts from – Vsat to + Vsat is called Lower Threshold Point (LTP). The feedback voltage Va depends on the output voltage as well as the reference voltage. A Zero Cross Detector is also a comparator where op-amp compares the input

PROCEDURE:

1. Rig up the connections as shown in the circuit diagram.

2. Give a sinusoidal input of 10V peak to peak and 1 kHz from a signal generator.

3. Check the output at pin no. 6 (square wave).

4. Coincide the point where the output shifts from + Vsat to – Vsat with any point on the input wave.

5. Measure the input voltage at this point. This voltage is UTP.

6. Coincide the point where the output shifts from – Vsat to + Vsat with any point on the input wave.

7. Measure the input voltage at this point. This voltage is LTP.

8. Another method of measuring UTP and LTP is using the Hysterisis Curve.

9. To plot the hysterisis curve give channel 1 of CRO to the output and channel 2 of CRO to the input.

10. Press the XY knob. Adjust the grounds of both the knobs.

11. Measure UTP and LTP as shown in the fig. and check whether it matches with the designed value.

RESULT:.