EE
2212
EXPERIMENT
4
14
October 2021
Diode
Parameter Extraction and the Half Wave Rectifier
PURPOSE
Ø
Use
laboratory measurements to extract key diode model parameters including IS,
n (also called η or in SPICE, N) from the ID-VD
measurements of the 1N4002. Don’t
confuse “n”=N = η
ideality factor with n as an electron concentration. Apparently not enough letters in the
alphabet!
Ø
Implement
designs of the half wave rectifier circuit and measure time domain
characteristics and the transfer characteristic, vo(t)
vs. vs(t).
Ø
Measure
and compute ripple voltage as a percentage and as an rms
value. You can use both the soft-keys on
the oscilloscope or the multimeter. I will demonstrate this.
Ø
Compare
individual diode results and circuit results using SPICE simulations.
COMPONENTS
Ø
1N4002
Diodes (Use the 1N4002 diode model in the SPICE library)
Ø
100
Ω and 1 kΩ resistors
Ø
0.1
μF, 1μF, and 10μF capacitors Actual values not critical since you
are just showing the “filtering/smoothing” effect to minimize ripple
voltage.
PROCEDURE
ID-VD
Characteristics and Diode Model Parameter Extraction
Ø Using SPICE, simulate the circuit shown in Figure 1.
Obtain the ID-VD characteristic curve for the
1N4002 in SPICE over
a range at least of 0 to 0.8 volts for VD and find the diode current value for the diode when VD = 0.7 volts. For this, it might be useful to use a DC
voltage sweep in conjunction with a VDC source. In addition, you will need to
change the x-axis value to be the voltage across the diode (v+) – (v-) under Plot_Axis Settings…_Axis Variable…-
Ø Examine the model characteristics for the 1N4002
PSPICE, which can be
found
by selecting the device and then Edit_Model…_Edit
Instance Model (Text)… You will use this
information for comparing to your measurements.
Ø Construct the Figure 1 circuit. Use the multimeter to
measure ID and the multimeter also
to measure VD. Note the ID is measured by measuring the voltage across the
series resistor and dividing by R, that is apply Ohm’s Law. Pay
attention to the diode orientation. The banded side is the cathode end. Change the supply voltage VS to
adjust ID to the desired current setting, then measure VD.
Take enough readings to accurately define the diode characteristic. You should measure out to ID values of a few mA. Record your results in a data table in both
your laboratory notebook and in your laboratory report. Use EXCEL for calculations and graphing. For
example your data columns might look like:
VD |
VR |
ID=VR/R |
LOG(ID) |
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Number of data
points is at your discretion. You can
then graph ID vs. VD and LOG (ID) vs VD for parameter extraction. It is then straight forward to get intercept
and slope using a linear regression.
Do not use of the multimeter for measuring
current directly because very often the internal fuse in the mutimeter is “blown”, that is open-circuited, given the high laboratory equipment
usage factor and it is a stinker to replace since we have to open the case-poor
instrumentation design in my opinion! Use
Ohms law to obtain current by measuring the voltage across the series
resistor. The power supply ammeter is
not as accurate for this current measurement.
Ø Consider
the equation which approximates to when the diode is
forward biased. To facilitate graphing
over a number of orders of magnitude we obtain and graph,
Note
that log(base 10) e = 0.434
Ø From this equation, determine and fit a straight
line (linear regression) to your plotted log(ID)-VD
semi-log graph. Your equation will be in the form y = mx + b.
Ø Use these data to find Is and n. Compare to the SPICE model parameters.
Figure
1
Half-Wave
Rectifier
Ø Refer to Figure 2. Change your signal source to a 10 volt zero-to-peak 100 Hz sinusoid. Perform a SPICE transient analysis simulation
and observe the half-wave
rectified output like we did in a class demonstration. Refer to class notes. Also note the effect of the diode offset
voltage when you compare the input and output waveforms. Observe and plot Vout(t)
and the transfer characteristic, Vo vs Vinput.
Ø Experimentally observe the operation on the
oscilloscope in both the time domain and as a transfer function.
Ø Now we want to “smooth out” the pulsating DC by
using capacitors. Place a C across the
1 kΩ resistor.
Now use all three values of C to illustrate the change in the ripple voltage by
measuring Vout(t).
Use the the oscilloscope to measure the rms
voltage of the output using dc and ac coupling.
Explain the differences in these measurements and explain what these
measurements are illustrating. Use your
diode model and check your lab measurements using SPICE. Observe that ripple voltage is defined as
either the (DV/Vpeak) x 100% or
as (Vrms or as
Vrms of the
output-voltage/Vpeak)x 100% )x 100%. Watch your polarity on the electrolytic
capacitors or else Also, since
electrolytic capacitors have a broad
tolerance, their values must be checked on the capacitance meter to obtain accurate results.
Figure
2
(An added historical note: The background screen is a photo of a “cat
whisker” diode used as an AM radio detector in the 1905-1915 era of early radio
before the widespread use of vacuum tubes.
You can purchase these setups on the WEB. A sharp “springy” wire (“cat
whisker”)-phosphor bronze formed a pressure (point contact) junction with a
galena crystal. Galena is PbS (lead sulfide) and has a bandgap of about 0.4 eV. Historically, of course, the underlying
physics was unknown at the time. The
physics to explain this phenomena was several decades in the future. Primitive, but it did work-sort of.
Sometimes SiC (carborundum)
with a 3 eV band gap was used
A
reincarnation of this was used by soldiers in World War II in what was called a “foxhole
radio”. The junction for detection of
strong AM radio signals was a sharp, springy wire or even a pencil lead
(carbon) contacting a
“blue edge” or oxidized razor blade to form a crude junction.
The metallurgical “bluing”
process to harden the steel cutting edge on the single edge razor blade of the
time creates a difference in the work functions between the wire and the metal razor which results in
a rectifying junction
This is the
historically classic data sheet for a Write Only Memory
produced by Signetics
Engineers with too much time on their hands
and probably written over a long liquid lunch.
This data sheet
actually slipped by the Signetics
Quality Control managers and was
published in a data book before the “joke” was discovered. It has become a classic in the semiconductor
industry. I was never able to find out
if there was a subsequent employment issue with the engineers involved but
things were different in the industrial world in those days. Read it carefully including the footnotes
for this “Write Only Memory”.
enjoy!