1. The operational amplifier, cont.
Has a multitude of circuit applications
Linear applications
Inverter, summer, integrator, etc.
Non-linear applications
Comparator

2. Classwork #2
Find vo

3. Inverting summing amplifier

4. Op amp non-linear applications
The output voltage is a function of the input voltage difference
Op amp can be forced to work in the linear region with feedback
Without feedback, the operation is quite different

5. The comparator
A comparator is a circuit that monitors two input voltages
One is called the reference voltage, and the other the input voltage
The output voltage depends upon the relation between the reference voltage and the input voltage, i.e., whether Vin is larger or smaller than Vref
Op amps operated without feedback can act as comparators

6. Comparator Reference voltage to positive input
Reference voltage to negative input

7. Comparator circuits
Physical signals
Physical outputs

8. Generic comparator circuit
Physical and electrical
outputs
Physical and electrical
input signals

9. Comparator circuits
What are RA and RB? Circuit components that convert
physical signals to electrical signals by having
electrical properties that change with external physical
changes.
Examples:
Thermistors - temperature sensitive resistors
Photoconductors - light sensitive resistors
Strain gauges - strain sensitive resistors
Microphones - sound sensitive components

10. Comparator circuits Output component examples
LEDs driven by op amp output
Power transistor stages to drive LEDs, buzzers, relays
Other amplifier stages
Voltage to frequency converters
Analog to digital converters
Multimeters
Motors
Timers, clocks, recorders

11. Additional circuit components
Variable resistor
Diode =
RV = R1 + R2

12. Additional circuit components
Bipolar junction transistor
Transistor
Field effect transistor
FET
ID = IS
IC ≈ IE
Large current (IB > 0)
Large current (VG > 0) IC ID
Zero (IB = 0)
Zero (VG = 0)

13. Additional circuit components
Sensing resistor
Relay
Electromechanical device -
a small current is used to control
a large current
R = R(Temperature)
R = R(Pressure)
R = R(Light)

14. Example comparator circuit
Light activated switch
LED is on when
input is below Vref
Resistance of photoconductor
decreases when illuminated

15. Classwork Building upon ideas from previous circuit,
design a Dark Activated Switch

16. Classwork Build and test this circuit -
use a voltmeter to measure voltages in circuit