APPLICATIONS OF OP-AMPS

LINEAR APPLICATIONS Adder Subtractor Voltage follower Current to voltage converter Voltage to current converter Integrator Differentiator Active filters

Non-linear applications Comparators Logarithmic amplifiers Exponential amplifiers Peak detectors Precision rectifiers Waveform generators Clippers & clampers

If Rf = R, then Vout = v1+v2+v3

Non-inverting Summing Amplifier Therefore, using the superposition theorem, the voltage V2 = V1 Vb & Vc = 0. Net resistance = R+R/2     If RF=2R1, 1+RF/R1=3 Vo= Va+Vb+Vc

Determine the output voltage =12

Averaging Amplifier A summing amplifier can be made to produce the mathematical average of the input voltages. The amplifier has a gain of Rf/R, where R is the value of each input resistor. The general expression for the output of an averaging amplifier is VOUT=-(Rf /R)(VIN1+VIN2+…+VINn) Averaging is done by setting the ratio Rf/R equal to the reciprocal of the number of inputs (n); that is , Rf/R=1/n.

Problem Show that the amplifier in produces an output whose magnitude is the mathematical average of the input voltages.

OP-AMP COMPARATORS

Non-Inverting Comparator. (b) Input and Output wave- forms when Vref is +ve (c) Input and Output wave-forms when Vref is -ve

Inverting Comparator. b) Input and Output Wave Forms when Vref is +ve and c) Input and Output Wave Forms when Vref is –ve

WINDOW COMPERATOR Used in A.C Voltage Stabilizers.

Input(Volts) LED3 LED2 LED1 Less than 2V ON OFF If Vcc = 6V Input(Volts) LED3 LED2 LED1 Less than 2V ON OFF Less than 4V & More than 2V More than 4V

(a) (b) Fig. 5.5 (a) Zero crossing detector and (b) Input and output waveforms

INVERTING SCHMITT TRIGGER (a) Inverting Schmitt Trigger circuit (b)} (c) and (d) Transfer Characteristics of Schmitt Trigger ZERO if Vref is Zero. The input voltage vi triggers the output vo every time it exceeds certain voltage levels, VLT & VUT If Vref = 0, then the voltage at the junction of R1 & R2 will form will determine VUT & VLT . If Vi < VLT, Vo = +Vsat Vi > VLT, Vo = -Vsat

(a) Input and Output waveforms of Schmitt Trigger and (b) Output v0 versus Vi plot of the hysteresis voltage. If a sine wave frequency f=1/T is applied, a symmetrical square wave is obtained at the output. The vertical edge is shifted in phase by  from zero crossover Where sin  = VUT/Vm and Vm is the peak sinusoidal voltage.

NON-INVERTING SCHMITT TRIGGER The input is applied to the non-inverting input terminal of the op-amp. To understand the working of the circuit, let us assume that the output is positively saturated i.e. at +Vsat. This is fedback to the non-inverting input through R1. This is a positive feedback. Now though Vin is decreased, the output Continues its positive saturation level unless and until the input becomes more negative than VLT. At lower threshold, the output changes its state from positive saturation + Vsat to negative saturation - Vsat. It remains in negative saturation till Vin increases beyond its upper threshold level VUT. Now VA = voltage at point A =IinR2 = VUT As op-amp input current is zero, I in entirely passes through R1.

Eliminates Comparator Chatter. Chattering can be defined as production of multiple output transitions the input signal swings through the threshold region of a comparator. This is because of the noise.

Comparison. S.No. Schmitt Trigger. Comparator. 1. The feedback is used. No feedback is used. 2. Op-amp is used in closed loop mode. Used in open loop mode. 3. No false triggering. False Triggering. 4. Two different threshold voltages exists as VUT & VLT Single reference voltage Vref or –Vref. 5. Hysteresis exists. No Hysteresis exists.

Square & Triangular waveform generation

Square Wave Generator

Vref = β Vsat Where β = R2/(R1+R2) Let V0 initially be + Vsat. The capacitor charges through R to + β Vsat. Then V0 goes to – Vsat . The cycle repeats and output will be a Square Wave.

Triangular/rectangular wave generator. _ + VSat

Operation of the Circuit Let the output of the Schmitt trigger is + Vsat. This forces current + Vsat/R1 through C1, charging C1 with polarity positive to left and negative to right. This produces negative going ramp at its output, for the time interval t1 to t2. At t2 when ramp voltage attains a value equal to LTP of Schmitt trigger, the output of Schmitt trigger changes its stage from + Vsat to -Vsat, Now direction of current through C reverses. It discharges and recharges in opposite direction with polarity positive to right and negative to left. This produces positive going ramp at its output, for the time interval t2 to t3. At t3 when ramp voltage attains a value equal to UTP of Schmitt trigger, the output of Schmitt trigger changes its state from - Vsat to + Vsat and cycle continues. The circuit acts as free running waveform generator producing triangular and rectangular output waveforms.

Vo’ =+Vsat = Vin + - 0V -Vramp

Vo(PP) = 2Vramp Vin = VSat Substitute V(pp) from Eqn. (4)