1436VoltageFollower02-07-2012

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1436 Voltage FollowerOp Amp

Cleveland Institute of Electronics Lesson 1436 Request a course catalog

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Op Amp Amplifier BasicsOThere are two basics forms in

which an Op Amp (OperationalAmplifier) can be used as an

amplifier:

O Inverting configurationONon-inverting configuration



741 DIP Pinout Diagram



Voltage Follower Op Amp

Schematic



Practical Considerations for the

741Voltage Follower Op Amp

OThe input signal is applied to the

non-inverting inputOBecause of this, the output signal is

not inverted or in phase with the

input



O Inverting input is connected to the

output pin of the Op AmpOOne assumption is the RF is zero Ω

OR1 is shown to be of infinite

resistance

OThis amplifier has unity gain and

does not invert the phase of theinput signal



OUnity gain means the gain is 1

OThis also means you have a 1:1ratio from the output to the input

OThis also means what you put into

the Op Amp is what you get out

OAV = 1 + RF/R1

OAV = 1 + 0/∞ = 1



Practical Considerations for

the 741 Operational Amplifier

OThe input bias current is

about 80 nAOThe input offset current is

about 10 nA

OThe input impedance is about2 Meg Ohms



OThe common mode voltage should

be within +/-12V for +/-15V supplyOThe output impedance is about 75

ohms.

OThe voltage gain rolls off 6dB per

octave starting at 100kHz.

O

Maximum output Current: 20mA



OThere is a finite input offset which

must be zeroed by a resistorbetween pins 1 and 5. The input

offset is typically 2mV to <6mV.

OThe 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 OpAmp is always zero volts.

O The maximum output-voltage swing of

an Op Amp should ideally be equal tothe value of the applied voltage.

O The actual maximum output swing of

the 741 Op Amp is actually a little lessthan the theoretical maximum.

(Applied Voltage)



O The op amp will no longer operate

linearly if you try to exceed this valueOThe accuracy of the circuits to meet

the calculated values is dependent

on the actual values of thecomponents used. (Values with their

tolerances)



ORemember resistors have a

tolerance.O The calculated gain of the amplifier

will very likely be different than the

measured gain.OThis is also true for capacitors and

pretty much any component

manufactured by man.



Non-Inverting Amp Voltage Gain

OAV = 1 + RF/R1 AV = 1 + 0/∞ = 1



Voltage Follower Voltage GainO

VOUT = VIN EOUT = EIN



Additional Discussion

OThe Voltage Follower provides

impedance matching

OThis means this Op Amp provides ahigh resistance to a signal source

that would otherwise be severely

loaded down by a low resistancevalue.



OAs stated earlier, the output

impedance is about 75 Ohms andcan drive loads with relatively lowresistance values.

O You will be applying both positiveand negative voltages to thefollowing voltage follower circuit.

O You should see the gain is 1 or

unity and no phase inversion takeplace.



Unity Gain Op Amp Schematic



1436 Exp. 3 Ckt. 1 Constructed



1436 Exp. 3 Ckt 1 Close-up



Schematic for circuit 3 Exp. 2



1436 Exp. 3, Ckt. 2, Close-up



Meter Isolation Ckt for Ckt 2



QUESTIONS?



Resources

O Rosenow. (2001). Lesson 1436:

Operational amplifier characteristics.

Cleveland: Cleveland Institute of

Electronics.



The EndDeveloped and Produced by

the Instructors in the CIEInstruction Department.

© Copyright 01/2012

All Rights Reserved / Jan. 2012

1436VoltageFollower02-07-2012

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