Download 5.Op-Amp Applications CW Nonlinear applications7

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 waveforms when Vref is +ve
(c) Input and Output waveforms 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.
If Vcc = 6V
Input(Volts)
LED3
LED2
LED1
Less than 2V
ON
OFF
OFF
Less than 4V &
More than 2V
OFF
ON
OFF
More than 4V
OFF
OFF
ON
(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
triangular and rectangular output waveforms.
generator producing
Vo’ =+Vsat = Vin
0V
-Vramp
+ -
Vo(PP) = 2Vramp
Vin = VSat
Substitute V(pp) from Eqn. (4)