Lab 7 - EE 420L: Engineering Electronics II
02/20/2017
This
lab will again utilize the ZVN3306A and ZVP3306A MOSFETs.
Design
an audio amplifier (frequency range from roughly 100 Hz to 20 kHz) assuming
that you can use as many resistors, ZVN3306A transistors, and ZVP3306A
transistors as you need along with only one 10 uF capacitor and one 100 uF
capacitor. Assume that the supply voltage is 10 V, the input is an audio signal
from an MP3 player (and so your amplifier should have at least a few kiloohms
input resistance), and the output of your design is connected to an 8-ohm
speaker (so, ideally, the output resistance of your amplifier is less than 1
ohm).
Your
lab report should detail your thoughts on the design of the amplifier including
hand-calculations. A good place to start is with the push-pull amplifier
characterized in lab 6. Simulate your design. Document the results in your lab
report.
Experiment:
The
first part of the experiment I started simulating the push pull amplifier to
determine the value of the resistors I needed to use with the push-pull
topology to meet the requirements of this lab. Below in figure 1 is the
basic push pull topology followed by the gain calculations.
Figure 1
As
can be seen the push-pull topolgy is very simple to implement and easy to
calculate gain. I will show below in figure 2 the topology I decided to
use in spice with simulations results.
Figure 2
Figure
2 demonstrates the amplifier meets all the requirements of the lab. The
amplifier operates over a large frequency range demonstrated here at 100Hz to
100kHz. The outputs at 100Hz and 20kHz are nice sine waves, no DC
signals. DC signals are very bad for speakers, A DC signal will
hold the speaker in a “in” or “out” position. This hold will damage the
speakers by over heating the voice coil and eventually burning the wire.
This is known as a blown speaker. The purpose of the capacitors in this
circuit are intended to remove all DC voltages before the signal is sent to the
speaker.
After
finding a suitable simulation I built the amplifier seen in figure 2 on a bread
board and the output at 100Hz and 20kHz can be seen below if figure 3.
Figure 3
The
results demonstrate that the amplifier works as intended. The output
resistance was calcuted as 6.49 Ohms and can be seen below in figure 4.
The input resistance is set by R2 from the schematic in figure 2. My
circuit used a 4k Ohm input resistance. Manipulating the input resistance
and R1(reference) the gain of the amplifier can be adjusted. My circuit used
2.3 watts across the frequency range.
Figure 4
Conclusion
Lab 7
introduced me to a real world application of an amplifier, below is a demonstration
of my design using the bread board and a speaker with my iPhone as the source.
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