1436 Voltage Comparators
Op Amp Amplifier Basics
O There are two basics forms in
which an Op Amp (Operational
Amplifier) can be used as an
amplifier:
O Inverting configuration
O Non-inverting configuration
741 DIP Pinout Diagram
Voltage Comparator Schematic
with Inverting Reference Voltage
Abbreviations used
O Pos = Positive
O Neg = Negative
O Ref = Reference
O V = Voltage
Introduction to the Op Amp
Voltage Comparator
O There are two basic types
O Comparator with reference
voltage at
Inverting Input
O Comparator with reference voltage at
non-inverting input
Practical Considerations for
the 741 Operational Amplifier
O The input bias current is
about 80 nA
O The input offset current is
about 10 nA
O The input impedance is about
2 Meg Ohms
O The common mode voltage should
be within +/-12V for +/-15V supply
O The output impedance is about 75
ohms.
O The voltage gain rolls off 6dB per
octave starting at 100kHz.
O Maximum output Current: 20mA
O There is a finite input offset which
must be zeroed by a resistor
between pins 1 and 5. The input
offset is typically 2mV to <6mV.
O The slew rate is 0.3V to 0.5V/
microsecond.
O There is some temperature
dependence
O The voltage between the two input
terminals of a normally operating Op
Amp is always zero volts.
O The maximum output-voltage swing of
an Op Amp should ideally be equal to
the value of the applied voltage.
O The actual maximum output swing of
the 741 Op Amp is actually a little less
than the theoretical maximum.
(Applied Voltage)
O The op amp will no longer operate
linearly if you try to exceed this value
O The accuracy of the circuits to meet
the calculated values is dependent
on the actual values of the
components used. (Values with their
tolerances)
O Remember resistors have a
tolerance.
O The calculated gain of the amplifier
will very likely be different than the
measured gain.
O This is also true for capacitors and
pretty much any component
manufactured by man.
O Comparator / Ref V at Inverting Input
O The input voltage is applied to the
Non-inverting input (Pin 3)
O Eout will remain at the maximum Neg
value until Ein is less Pos than the Ref
Voltage at Pin 2.
O Once Ein is slightly more Pos than the
Ref voltage, Eout will remain at the
maximum Pos value
O This is due to the Op Amp’s high
open loop gain. (No feedback)
O The input voltages have to differ by
only a very small amount for this
transition/change to take place.
Voltage Comparator Schematic
with Inverting Reference Voltage
1436 Exp. 4Ckt 1 Close-up
O Comparator with Ref Voltage at the
Non-inverting Input (Pin 3)
O The input voltage is applied to the
Inverting input (Pin 2)
O Eout will remain at the maximum
Pos value until Ein is less than the
Ref Voltage (Pin 3)
O Eout will swing to the maximum Neg
value, once Ein becomes more Pos
than the Ref voltage (V on Noninverting Input, Pin 3).
O This is due to the Op Amp’s high
open loop gain. (No feedback)
O The input voltages have to differ by
only a very small amount for this
transition/change to take place.
O The first configuration is most
commonly used.
O The second circuit is a functioning
circuit. It is a configuration that is
not commonly used.
O The circuit will operate the same if
the stationary reference voltage is
removed and a second variable
input voltage is used.
Schematic for circuit 4 Exp. 2
1436 Exp. 4, Ckt. 2, Close-up
QUESTIONS?
Resources
O Rosenow. (2001). Lesson 1436:
Operational amplifier characteristics.
Cleveland: Cleveland Institute of
Electronics.
The End
Developed and Produced by
the Instructors in the CIE
Instruction Department.
© Copyright 02/2012
All Rights Reserved / Feb. 2012