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Lab 2 Diode Applications: Purpose

This lab document describes experiments using diodes in clipping and clamping circuits. Students will build and test diode clipper circuits that limit input signals to certain maximum and minimum voltages, accounting for diode cut-in voltages. They will also construct and analyze a diode clamper circuit that clamps the maximum of an input signal to a reference point, such as ground. The goals are to observe the output waveforms and understand how real diodes differ from ideal ones in these applications.

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637 views3 pages

Lab 2 Diode Applications: Purpose

This lab document describes experiments using diodes in clipping and clamping circuits. Students will build and test diode clipper circuits that limit input signals to certain maximum and minimum voltages, accounting for diode cut-in voltages. They will also construct and analyze a diode clamper circuit that clamps the maximum of an input signal to a reference point, such as ground. The goals are to observe the output waveforms and understand how real diodes differ from ideal ones in these applications.

Uploaded by

abraham8085
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Lab 2

Diode Applications
Purpose
In this lab, several applications of the diode will be studied. These include
clipping and clamping.

Material and Equipment


NI ELVIS
1N5404 Diodes(4)
1N4148 Diode(1)
Assorted Resistors
Assorted Capacitors

Pre Lab
a) Review clipper and clamper circuits.
b) Design a clipper circuit which limits input signals to +1V and -1.5V.
c) Make sure you know the what to except at the output of the clipper. (Remember
you are using real diodes. There will be diode cut-in voltages.)

Theory
The diode has many applications. In this lab, a few of them will be investigated.
The first is the clipper circuit. This circuit limits an input voltage to certain minimum and
maximum values. In the circuit in Figure 2-1, one can see that as long as VI is less than
VB1, then the diode will be reverse biased(an open circuit). In this case, the output voltage
will track the input voltage. If VI exceeds VB1 then the diode turns on and then Vo will be
VB1 thus this circuit limits the output voltage to less than VB1. (We ignored diode cut-in
voltages, but in real circuits you need to consider). By rearranging the components,
variations on this circuit can be achieved.

Figure 2-1: Schematic of a clipper circuit.

The next circuit is the clamping current. This circuit works by allowing the
capacitor to charge up and act like a battery. This is the voltage across the capacitor
depends on the input waveform, the output maximum( or the minimum depending on the
orientation of the diode) will be clamped to a fixed reference point (in this case, ground
potential). The only design constraint is that 2πRC be five times larger than the period of
the input waveform.

6
.

Figure 2-2: Schematic of a clamper circuit.

Procedure

1) Diode Clipper Circuits

Diode clipper circuits can be used to limit a voltage to some maximum or


minimum value. This is useful for designing protection circuits.

Figure 2-3: Clipper Circuits

7
a) Connect the circuit in Figure 2-3a. Use R = 100 kohm and a 1N5404
diode. For the input signal vI, use 5Vp-p, 1kHz sine wave and use
variable power supply (VPS) to provide the battery voltage. Set VB=1 V.
Measure and sketch the input and output waveforms.

Warning: When you set the VPS source to 1V, make sure this is in fact at
1V by measuring it with Elvis Voltmeter. Some units may have calibration
issues. You may need to re-adjust until you see desired voltage on the
Voltmeter

b) Repeat the procedure for the remaining circuits. For Fig 2-3d, set
VB1=0.5 V, VB2=1 V. Again verify Variable Supply Source output
voltages using Voltmeter. Re-adjust if necessary.

2) Clamper Circuits

a) Design a clamper to clamp the upper limit of the input voltage to 0 V.


Assume that the input signal is 1 kHz and that the load is 5.1 k ohms.
Construct the design circuit and use a 1 kHz, 3Vp-p square wave input
signal. Use a 1N4148 diode. Measure and capture the input and output
waveforms. Note what happens when the input amplitude is varied.
b) Lower the load resistance to 100 Ohms, measure and roughly sketch the
output waveform.

Questions for the Lab Report

1) Discuss the output waveforms from the clipper circuits. How do these
waveforms differ from those expected if ideal diodes were used? Why?

2) Discuss how lowering of the load on the clamper circuit affects the output.

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