A DC power supply was constructed by combining a power transformer, full-wave bridge rectifier, passive low-pass filter, and voltage regulator.

1. 1
EE 321 Lab 3
DC Power Supply with a
Full-Wave Bridge
Rectifier
Benedict Fawver, Kyla Marino, Andrew Rood
Abstract—A DC power supply was constructedby combining
a power transformer, full-wave bridge rectifier, passive low-
pass filter, and voltage regulator. The rectifier, low-pass filter,
and voltage regulator were connected on a proto board. The
transformer in lab was broken, so the input was connected to a
function generator providing a 14-V sine wave at 60-Hz. The
output for each stage was measured on an oscilloscope. The
measured rectifier output amplitude was much different from
the calculated value, but the measuredripple voltage was very
close to the calculated value.
I. INTRODUCTION
This report is to provide documentation of the steps taken
in the creation of a DC power supply.This supply consists of
a power transformer, a full-wave bridge rectifier, a passive
low-pass filter, and a voltage regulator. This power supply is
similar to those used to charge portable electronic devices,
such as cellular phones.
II. METHOD
The input voltage initially used was a wall socket voltage
through a 120:14 transformer. However, the transformer was
not producing a stable output through the negative terminal.
To continue the lab, a function generator producing 14-Volts
at 60-Hz was used instead. Initially, the full-wave rectifier
was constructed as shown in Fig. 1.
Figure 1: Full-wave bridge rectifier.
Then, the low-pass filter was constructed as shown in Fig.
2 and connected to the full-wave rectifier output.
Figure 2: Passive low-pass filter.
The voltage regulator was then constructed by attaching a
220Ω resistor and 5.6-Volt 1N752 Zener diode in parallel
with the load resistor from the low-pass filter to complete the
DC power supply.
III. PROCEDURE AND RESULTS
The voltage amplitude of the full-wave bridge rectifier
was then measured as 700-mV. The output waveform was
measured on an oscilloscope and is shown in Fig. 3.
Figure 3: Output waveform of full-wave bridge rectifier.
Once the low-pass filter was connected to the full-wave
rectifier, the ripple voltage was measured on an oscilloscope
as 420-mV. The complete waveform is shown in Fig. 4.

2. 2
Figure 4: Output waveform of passive low-pass filter connected to
full-wave rectifier.
Once the voltage regulator was attached, the DC output
of the power supply was measured on an oscilloscope as
6.08-V. The DC output waveform is shown in Fig. 5.
Figure 5: Output of completed power supply.
IV. ANALYSIS
The voltage amplitude of the full-wave rectifier, including
diode drops, was calculated as 5.6-V by subtracting the 1.4-
V drop for the diodes from the input amplitude of 7-V. The
ripple voltage delay was calculated as 0.467-V. This value
was calculated as seen in Eq.1.
𝑉 =
5.6
(2×120×(10×10−6)×5000)
= 0.467 𝑉 (Eq.1)
The current through the load was calculated as 27-mA as
seen in Eq. 2.
𝐼 𝐿 =
6.08 𝑉
220 Ω
= 27 𝑚𝐴 (Eq. 2)
The excess current through the Zener diode regulator, due
to voltages above the regulation voltage, was calculated as
875-mA as seen in Eq. 3.
𝐼 𝑒𝑥𝑐𝑒𝑠𝑠 = (27 𝑚𝐴)√(1 +
2𝜋 ×5.6
0.467
(Eq. 3)
V. CONCLUSION
A DC power supply was constructed using a full-wave
bridge rectifier, passive low-pass filter, and a Zener diode for
voltage regulation. Issues came about when one side of the
transformer used was faulty, resulting in improper
measurements. Once this problem was corrected by using a
function generatorinstead,the expected outputs were shown
through the oscilloscope.
However, the calculated voltage amplitude for the
regulator was much higher than the measured voltage. It is
possible that the measured value was taken with an
oscilloscope probe with settings off by a factor of ten.
Alternatively, it is possible that the measured value was
correct, and that the Zener diode regulator boosted the output
voltage up to the more reasonable 6-V measured at the
completed supply output. The measured ripple voltage for
the filter was very close to the calculated value.