Download Transformer - Electrical engineering

Operational Amplifier
•Operational Amplifier is a high performance differential amplifier.
•A typical op amp is an integrated device which has
1. Noninverting input
2. Inverting input
3. Two DC power supply leads (positive and negative)
4. An output terminal
5. Some other leads for fine tuning
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
•Op amp is an integrated device consist of a large number of transistors, several
resistors and a few capacitors
•It has three stages : 1. A high input impedance differential amplifier. 2. a high
gain voltage amplifier with a level shifter and 3. a low impedance output
amplifier.
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Basic Operation:
•If the inverting input V_ is more positive than the noninverting input V+ than
the output voltage saturates towards the negative supply voltage -Vs.
•If the noninverting input V+ is more positive than the inverting input V- then
the output voltage saturates towards the positive voltage supply +Vs
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Basic Operation:
•Op amp itself is not a special device until it is configured in special ways.
• The output of the op amp can be controlled by feeding back the output to the
inverting input.
•The following is the figure of an inverting amplifier where the output of the op
amp is fed back through a resistor RF to the inverting input.
•Gain for this configuration is RF/Rin
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Ideal and Real op amp, some rules:
•For an ideal op amp the open loop voltage gain is infinite. For a real op amp,
the gain is typically 104 to 106
•Ideal input impedance infinite, real input impedance is between 106 ohm.
•Ideal output impedance zero, real input impedance is between 10 to 1000
ohm.
•Input terminal current for ideal op amp is zero whereas in reality it draws a
very small amount of current which is in pico ampere range.
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Negative feedback and a special rule:
•In negative feedback configuration an extra voltage (positive or negative) is fed
back to the input.
•If f is the fraction of the voltage fed back to the input then
•Rule: in a negative feedback circuit whenever it sees a voltage difference
between the inverting and non inverting input it sends a compensating voltage
to the input to make the difference zero.
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Buffer (Unity gain amplifier)
• Gain is 1 because no feed back or input
resistors are used.
•Gain=Vout/Vin=RF/Rin=1
•Application: It is used where circuit
isolation is required (Very high input
impedance)
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Inverting amplifier
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Noninverting amplifier
V-=V+=Vin
(Voltage divider rule)
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Summing amplifier
But,
So,
When R1=R2=R3
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Difference amplifier
(since no current between inputs)
Since, I1=I2
So,
(Since V- = V+ )
If
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Integrator
Since V+ is 0 so V- is 0 too (from negative feedback rule)
By KVL IR+IC=0
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Differentiator
Since V+ is 0 so V- is 0 too (from negative feedback rule)
By KVL IR+IC=0
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
Comparator
•Essentially compares two signals
•Output goes high when the input signal is greater than a reference signal.
Text Book: Practical Electronics for
Inventors by Paul Scherz
Operational Amplifier
LM324/LM124 op amp IC
Text Book: Practical Electronics for
Inventors by Paul Scherz
A practical circuit using op amp
10K
Text Book: Practical Electronics for
Inventors by Paul Scherz