EE320L Engineering Electronics I
Lab #3:
Operational Amplifiers Application CircuitsGrzegorz Chmaj
Applications of opamps
Bistable circuit – remains stable in one of two
states
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 2
voltage divider
determines the
switching point
Vin > 90% V+:
Vout = V-
Vin < 90% V+:
Vout = V+
Vout
Applications of opamps
Unstable circuit – does not have any stable state
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 3
RC circuit added here
makes the whole configuration
unstable
Unstable circuit with regular
waveform = oscillator
Vout
Applications of opamps
Oscillator – output signal
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 4
Applications of opamps
Integrator – performs the mathematical operation
of integration on the input signal.
Output voltage is proportional to the integral of the
input voltage.
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 5
Experiment 1
Construct the function generator:
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 6
Square
generator
Integrator
Vout
Introduction – Diode basics
Its I-V characteristic is not linear
Made from single piece of semiconductor which
has positive P-region and negative N-region
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 7
Takes a certain
minimum voltage
for conduction to
occur – forward
breakover
voltage.
Depends on
material
Diode bias
Biasing = voltage across the diode
Types of diode biasing:
Zero biasing
Reverse biasing
Forward biasing
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 8
Diode bias
Zero biasing - No external voltage potential
is applied to the PN-junction IF = forward current
IR = reverse current
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ 9
Diode biasReverse biasing - a positive voltage is applied to the N-
type material and a negative voltage is applied to the P-
type material.
Represents high resistance
Practically zero current flows
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ10
Diode biasForward biasing - a negative voltage is applied to the N-type material
and a positive voltage is applied to the P-type material.
When voltage is greater than barrier (0.7V for silicone) – current
starts to flow.
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ11
Experiments
Experiment 1: I-V characteristics
Get to know with diode specifications by
browsing its I-V characteristics
Capture I-V characteristics of the diode
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ12
Experiments
Experiment 1: I-V characteristics
The diode current measure: capture voltage
across the resistor and divide that by the resistance used (Vout/RL).
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ13
Vout
Diode voltage
Change the
value step
by step
Experiments
Experiment 1: I-V characteristics on OSC
Place channel-one scope probe across diode (X-axis)
Place channel-two scope probe across the resistor (Y-
axis)
As Vin, use function generator with triangle signal
Capture the I-V characteristics of the diode.
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ14
X-axis
Y-axisTriangle
wave
Experiments
Experiment 2: Reverse recovery Measure the reverse recovery time: the time delay between
switching
In ideal case, the current should not go to negative
In practice, it can be negative for a short time period trr
Measure when the current reaches 10% of its maximum reverse value
Imax
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ15
Experiments
Experiment 2: Reverse recovery
Measure the reverse recovery time: the time
delay between switching
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ16
Vin
Rout
Vout
Experiments
Experiment 2: Reverse recovery
Increase input frequency of the signal of experiment 1
circuit to see the artifact of reverse recovery.
capture profile of the diode current
measure reverse recovery time.
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ17
Experiments
Experiment 3: Bridge rectifier Outputs: 16V
25mA delivery to the load varying from 500Ω to 1000Ω
Capture the output signal waveform and measure peak voltage of
the output
Replace Vin with a transformer to get the comparison
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ18
Experiments
Experiment 4: Bridge rectifier with Zener diode
use a Zener diode rated at 12V to regulate the load
voltage to have the voltage regulation of 2%.
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ19
Experiments
Experiment 5: Regulated Power Supply (EC)
Zener diode as reference generator
use the rectifier output from experiment 3 as the input
the op-amp will attempt to keep V- = V+.
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ20
Experiments
Experiment 5: Regulated Power Supply (EC) Measure the range of output voltage you able to achieve with a resistor load
(not shown) of 10k at the output
Repeat for a 1K load and a 100 ohm load. Be very careful of overheating!
LAB 3 – OPERATIONAL AMPLIFIERS APPLICATION CIRCUITS GRZEGORZ CHMAJ21