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ECE 202 – Experiment 8 – Lab Report
TRANSFORMERS AND MAXIMUM POWER TRANSFER
YOUR NAME______________________
GTA’S SIGNATURE_________________
LAB MEETING TIME______________
The laboratory transformer, shown below, has two primary windings (terminals 1-2 and 3-4) and a
single winding for the secondary (terminals 5-7) with a center tap (terminal 6). The taps allow the
user to operate the transformer with two different primary voltages.
The lower primary terminals 3 and 4 and the secondary center tap terminal 6 will not be used in this
experiment.
For the following experiments, use Agilent 33522A Function Generator set to a frequency of 5 kHz
and magnitude 5 V (rms).
Laboratory transformer Jameco, Part #104387
CHARACTERIZATION OF THE SOURCE AND THE TRANSFORMER
3. a) The output impedance of the function generator may affect the results of the measurements
made below. Measure the output resistance Rg of the 33522A. Show the circuit you used and
describe the method.
Rg = ________________
Note: For the remainder of this experiment, use terminals 1-2 as the primary and terminals 5-7
as the secondary. Leave terminals 3, 4 and 6 open.
b) Determine the dot convention of the transformer using the function generator and oscilloscope.
Show the circuit you used and describe the method. Draw the dot convention on a diagram of
the transformer. Call GTA to verify.
ECE 202 – Experiment 8 – Lab Report
c) Determine the transformer winding ratio, defined as n = N2/N1. Draw the circuit you used and
describe the method.
n = __________________
d) Calculate the turns ratio nspec from the transformer specifications and compare to the measured
value of n. Show your calculations.
nspec = __________________
e) Measure resistance of the primary winding Rp. Draw the circuit you used and describe the
method.
Rp = __________________
f) Measure resistance of the secondary winding Rs. Since Rs is expected to be less than 1 Ω, use
the 4-wire method to measure Rs with your ohmmeter. Your GTA will demonstrate the
procedure. Make your connections directly to the transformer terminals. Draw the circuit you
used and describe the method.
Rs = __________________
g) Explain whether the winding resistances Rp and Rs or the source resistance Rg have affected
your measurement of the winding ratio in Part 3.c.
ECE 202 – Experiment 8 – Lab Report
h) Use Cadence to find power delivered to the load for Vs,rms = 5 V at 5 kHz if RL = 50 Ω, and Ro
= 4.0 kΩ, when using a real transformer model with RP = 100 Ω, RS = 1 Ω and with values of
L1, L2, and coupling coefficient k provided. (See Cadence section on the last page of this Lab).
Use Cadence to generate a plot of power delivered to the load as a function of RL. Make sure
that the range of RL used is large enough to clearly observe the maximum in PL. Attach
printout of your work.
MAXIMUM POWER TRANSFER
4. For the remaining parts of the experiment, start from the circuit below:
- keep Vs constant during the measurements
- f = 5 kHz
- about 5 Vrms output at the function generator
- Ro = 4 kΩ.
a) Show here a complete schematic of the circuit you used for this part of the lab: including the
losses (i.e., Rp and Rs), function generator, multimeter and oscilloscope (if used).
b) Measure PL as a function of RL during the experiment. Use RL values in the range of
approximately RLOAD/2, RLOAD /1.5, RLOAD, 1.5 RLOAD, 2 RLOAD, 4 RLOAD, and 8 RLOAD, where
RLOAD = 50Ω. Make sure that the range of RL used is large enough to clearly observe the
maximum in PL. Write measurement results in the table below (use as many fields as needed,
given the number of measurements).
RL [
]
PL [
]
c) Find theoretical values of RLopt for maximum power transfer and value of PL, assuming
1) an ideal transformer, and
2) a non-ideal transformer with losses in the primary and in the secondary windings.
Attach paper with your work.
ECE 202 – Experiment 8 – Lab Report
d) Cadence Real Transformer Setup
For the real transformer, use the Cadence components “ind” and ”mind” from AnalogLib to
make real transformer. Enter the values of L1, L2 and k provided. Ground both sides. Add the
RP and RS resistors and the rest of your circuit.
Do an AC Sweep and use Probe with cursor to read the value of the AC rms voltage across RL
at the frequency of interest.
Nominal Values:
(Jameco 104387, f = 5 kHz)
L1 = 0.30 H
L2 = 0.0036 H
k = 0.85
e) Compare your results, plot PL versus RL in the same window using Matlab / Excel (RLOAD/2
to 8*RLOAD, where RLOAD = 50Ω; pick the proper interval to correctly capture the variation
and maximum point of PL) for four cases:
1) Theoretical calculation: ideal transformer,
2) Theoretical calculation: non-ideal transformer with losses in the primary and secondary
windings,
3) Cadence real transformer, and
4) Breadboard experiment,
Plot the data as a continuous curve for each of the cases. Comment on the results (i.e., do the
losses affect your results, which theory is the best fit to the measured data and why?).
Summarize results for maximum power transfer below:
Theory (ideal transformer, from 4.c.1):
RLopt = __________
PL = __________
Theory (lossy transformer, from 4.c.2):
RLopt = __________
PL = __________
Modeling (Cadence transformer):
RLopt = __________
PL = __________
Experiment (from 4.b):
RLopt = __________
PL = __________
Remember GTA’s signature!