1436 Inverting
Op Amp
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
Inverting Op Amp Schematic
Practical Considerations for
the 741 Inverting Op Amp
O The input signal is applied to the
inverting input
O Because of this, the output signal is
inverted in phase with relation to the
input signal or 180º out of phase
O Non-inverting input is grounded
O One assumption is the input error
voltage is zero
O The feedback keeps inverting the
input at a virtual ground
O The current flow in the input lead is
assumed to be zero.
O Hence the current flowing through
R1 is the current flowing through RF.
O The gain is independent of the Op
Amp parameters.
O Gain is a function of the feedback
and gain resistors
O R2 is often used in an inverting
amplifier to compensate for effects
of input bias current.
O In many applications, R2 is equal to
the parallel equivalent resistance
of RF and R1.
O R2’s value only becomes critical if
RF has a high value
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 0.5V/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.
Inverting Amp Voltage Gain
O AV = -RF/R1
O Remember: The minus sign
indicates the phase reversal
characteristics of the circuit.
O AV = - EOUT/EIN or -VOUT/VIN
Inverting Op Amp Schematic
1436 Exp. 2 Ckt. 1 Constructed
1436 Exp. 2 Ckt 1 Close-up
Additional Discussion
O Remember: the theoretical and
measured Voltage Gains can vary
as much as 20% due to the
resistor tolerances.
O It is not unusual to see gains
from -1.5 to approximately -7 with
the values of resistances used.
Schematic for circuit 2 Exp. 2
1436 Exp. 2, Ckt. 2, Close-up
Meter Isolation Ckt for Ckt 2
QUESTIONS?
Resources
O Mancini, R. (2002, August). Op amps for
everyone. Retrieved from
http://www.ti.com/lit/an/slod006b/slod00
6b.pdf
O Nave, R. (n.d.). The 741: Practical
considerations. Retrieved from
http://hyperphysics.phyastr.gsu.edu/hbase/electronic/a741p.html
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 01/2012
All Rights Reserved / Jan. 2012