Download Project One – AC to DC Converter

Project One – AC to DC Converter
EENG 3510 – Electronics 1
Spring 2012
Joshua Jenkins
Joshua Jenkins
February 26, 2012
Project One – AC to DC Converter
Joshua Jenkins
Abstract
Project one was to design and simulate an AC to DC converter that shapes a basic
sinusoidal voltage signal into a small ripple DC voltage.
Introduction
Our task for this project was to construct a basic AC to DC converter and simulate it in
PSpice. Most devices that we use in our everyday life require a DC signal to function,
yet voltage sources out of a wall outlet are 120V AC. That signal needs to be converted
to a signal that a particular device can use. For our AC to DC converter, our source
voltage would only be 8V at 60Hz. It would then be shaped into a small ripple voltage
with an average above 5V.
Problem and Constrains
Your task for this project is to design an AC-DC converter using a bridge rectifier. Refer
to Figure 3.24 for the block diagram. To simplify the design we will not have the power
transformer or voltage regulator. Therefore your job is to design the rectifier and filter.
Here are the specifications:
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Input: AC voltage source of 8V peak at 60 Hz. Use "Vin ? ? sin(0 8 60 0 0)"
Output: 5V DC
Load: 100 ohm resistor
Report
An AC to DC converter has four main sections.
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Power transformer. This section is first in any power source. A transformer
drops or raises voltage to a level that the device requires.
Bridge rectifier. There are several different types of rectifiers, but the bridge
rectifier is the most commonly used. It uses four diodes that reflect the negative
portions of a sinusoidal signal over the x-axis, so that the entire signal is positive.
Filter. The filter uses a capacitor to store a charge that is slowly released when
the signal dips down to zero. This creates a small ripple wave that is close to a
flat line DC voltage.
Voltage regulator. Finally, the small ripple is passed through a voltage regulator
that releases a constant DC voltage close to the average of the ripple.
Joshua Jenkins
February 26, 2012
For this project, only the bridge rectifier and filter were designed. An 8V sinusoidal
signal at 60Hz was given, so a power transformer was not needed to step the voltage
down. Also, the voltage regulator utilized components that have not been covered, so it
was skipped over for the first project. Because the voltage regulator was not used, the
output of the AC to DC converter was a small ripple voltage that wasn’t true DC.
The circuit was first drawn out by hand. In this diagram, each node and component was
labeled. This diagram would then be used to construct the text file in PSpice that would
be simulated. Knowing the connections between nodes was very important to ensure
that a proper simulation was run. Values for the diodes and load resister were fixed.
However, once the circuit was entered into PSpice, values could be altered for the
capacitor and other resistors to ensure the best result for the output.
Performance Analysis
Two designs were tested during this project. The first design used a fifth diode in the
filter, which proved to drop too much voltage, thereby creating too low of an average
output ripple.
While the ripple of the output was less than 200mV, it averaged only about 4.5 volts,
which was under the specification. One way to increase the average of the output
voltage would be to add a DC voltage source into the circuit, but this was not specified
as an option. Placing resistors in different configurations changed the output, but did
not increase the average voltage from the original design. Also, no alterations to the
capacitor value or placement increased the output voltage either. Finally, experimenting
with an inductor rather than a capacitor did not seem to work either.
For the second design, the fifth diode was removed. This allowed for a higher output
voltage. However, when connected to the filter, the bridge rectifier produced a
significantly different output than that of the first design. The second design was also
much simpler in that it used no added resistors, only the load resistor. Despite these
differences however, the design was still used because of its higher average output
voltage while maintaining a ripple under 200mV.
The capacitor value used was 2000μF, which was less than the maximum value specified
as 1000μF.
Conclusion
In conclusion, it was found that the simpler the design of the filter, the higher and more
predictable the value of the output was. The fewer diodes used, the less voltage was
taken away from the output.
Joshua Jenkins
February 26, 2012
The bridge rectifier uses a configuration of four diodes to reflect the negative portions
of the sinusoidal waveform across the x-axis, thereby creating a signal that is always
positive.
Keeping the filter simple proved better. A capacitor was the best option because it
stores a charge that can be released when the signal dips down, which creates a flatter
voltage across the peaks of the waveform, creating a small ripple.
(Capacitor eqns, how to choose value)