كلية التقنية الصناعية مصراتة
عنوان العرض
Using op-Amps to build the control model
إعداد الطالب :أحمد ا ّمحمد الشريمي
رقم القيد112151536 :
أستاذ المقرر :د.إسحاق األرباح
Content
Introduction
What is an Op-Amp?
Types of Op Amps
Characteristics of the ideal op amp
Practical applications to build the control model
Summary
o Introduction
•
Operational Amplifiers are represented both schematically
and realistically below:
– Active component!
•
Originally invented in early 1940s using vacuum tube technology
– Initial purpose was to execute math operations in analog electronic calculating machines.
•
•
Shrunk in size with invention of transistor
Most now made on integrated circuit (IC)
– Only most demanding applications use discrete components.
•
Huge variety of applications, low cost, and ease of mass production make them extremely popular
o What is an Op-Amp?
An Operational Amplifier (known as an “Op-Amp”) is a device that is used
to amplify a signal using an external power source
Op-Amps are generally composed of:
Transistors, Resistors, Capacitors
=
+
+
Brief History
•
First patent for Vacuum Tube Op-Amp (1946)
• First Commercial Op-Amp available
(1953)
•
First discrete IC Op-Amps (1961)
• First commercially successful Monolithic OpAmps (1965)
History Continued…
• Leading to the advent of the modern IC which is still used
even today (1967 – present)
Electrical Schematic of μA741
Op-Amps and their Math
A traditional Op-Amp:
V+
VVout
Vs+
Vs-
:
:
:
:
:
non-inverting input
inverting input
output
positive power supply
negative power supply
Vout = K (V+ - V-)
• The difference between the two inputs voltages (V+ and V-) multiplied by the gain (K,
“amplification factor”) of the Op-Amp gives you the output voltage
• The output voltage can only be as high as the difference between the power supply (Vs+ / Vs)and ground (0 Volts)
o Types of Op Amps
•
•
•
•
•
Open Loop vs Closed Loop
Ideal Op Amp
Non-inverting Amplifier
Inverting Amplifier
Common Mode Input
Open Loop vs Closed Loop
A closed loop op-amp has feedback from the
output to the input, an open loop op-amp does not
Open Loop
Closed Loop
Ideal Op Amp
i
i
1)
v
v
VDD
VSS v0 VDD
+
vo
-
VSS
v0 Av v v
The open-loop gain, Av, is very large, approaching infinity.
2)
i i 0
The current into the inputs are zero.
Non-inverting Amplifier
v
vi
v
R1
+
vo
Closed-loop voltage gain
AF
-
vo
vi
R2
vi v v
R1
vo
R1 R2
vo
R2
AF 1
vi
R1
Inverting Amplifier
R2
Current into op amp is zero
v v 0
v 0 vi
ii i
R1
R1
0 v0 v0
ii
R2
R2
vi
ii
ii
R1
v
v
+
vi v0
R1 R2
AF
vo
R
2
vi
R1
vo
Common Mode Input
Two signals of same phase, frequency, and amplitude are applied to
the inputs which results in no output (signals cancel). But, in practical, a
small output signal will result.
This is called common-mode rejection. This type of mode is used for
removal of unwanted noise signals.
o Characteristics of the ideal op amp
• Open-loop gain G is infinite
• Rin is infinite
• Zero input current
• Rout is zero
Ideal Op-Amp
Practical Op-Amp
Ideal Op-Amp
o Practical applications to build the control
model
Applications – Filters
Simulation of a Closed-Loop System
Applications-PID Controller – System Circuit Diagram
Applications- PI Control
Applications - Filters
Types:
•Low pass filter
•High pass filter
•Band pass filter
•Cascading (2 or more filters connected
together)
C
R2
Low pass filter transfer
function
R1
Low pass filter
Cutoff frequency
+
-
+ Vcc
+
- Vcc
+
V0
__
Simulation of a Closed-Loop System
Figure (a) is a block diagram of a speed control system, the motor
shaft speed w being controlled by the input voltage, Ví. Voltage Vi
is derived from the tachogenerator and is compared with the input
voltage to give the error signal, which is used to control the pulse
generator and thyristor.
The analogue computer block diagram is shown in Fig (b). The input
voltage change is set on a potentiometer, shown as Ví. The
amplifier, in the actual system, is replaced by a summing amplifier in
the simulator. The thyristor and its pulse generator
Simulation of a control System of an analogue computer
PID Controller – System Block Diagram
P
VSET
VERROR
I
Output
Process
D
VSENSOR
Sensor
•Goal is to have VSET = VOUT
•Remember that VERROR = VSET – VSENSOR
•Output Process uses VERROR from the PID controller to adjust Vout
such that it is ~VSET
VOUT
Applications
PID Controller – System Circuit Diagram
Signal conditioning allows you to
introduce a time delay which could
account for things like inertia
System to control
Calculates VERROR = -(VSET + VSENSOR)
-VSENSOR
Applications
PID Controller – PID Controller Circuit Diagram
VERROR PID
VERROR
Adjust
Change
Kp
RP1, RP2
Ki
RI, CI
Kd
RD, CD
Applications of Op-Amps
• Example of PI
Control: Temperature
Control
• Thermal System we
wish to automatically
control the
temperature of:
• Block Diagram of
Control System:
Applications of Op-Amps
• Example of PI Control: Temperature Control
• Voltage
Error
Circuit:
• Proportion
al-Integral
Control
Circuit:
summary
ideal op amp: Output voltage limited to the range between V+ and V Ideal op amp is assumed to have Ri = ∞ W and Ro = 0 W.
In the ideal op-amp, A is infinite ،In real op-amp, A is 20k to 200k
Single- Input Mode
Input signal is connected to ONE input and the other input is grounded.
Inverting Mode :input signal at –ve terminal output opposite in phase to the
applied input signal
Non- Inverting Mode: input signal at +ve terminal output same polarity as the
applied input signal
common-mode will tend to reject noise.
The Operational amplifiers deals with filters and controllers such as PID & PI and
other controllers
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