EE320L Engineering Electronics I

Lab #3:

Operational Amplifiers Application CircuitsGrzegorz Chmaj

Applications of opamps

Bistable circuit – remains stable in one of two

states

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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

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RC circuit added here

makes the whole configuration

unstable

Unstable circuit with regular

waveform = oscillator

Vout

Applications of opamps

Oscillator – output signal

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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.

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Experiment 1

Construct the function generator:

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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

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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

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Diode bias

Zero biasing - No external voltage potential

is applied to the PN-junction IF = forward current

IR = reverse current

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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

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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.

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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

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Experiments

Experiment 1: I-V characteristics

The diode current measure: capture voltage

across the resistor and divide that by the resistance used (Vout/RL).

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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.

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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

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Experiments

Experiment 2: Reverse recovery

Measure the reverse recovery time: the time

delay between switching

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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.

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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

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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%.

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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+.

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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!

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