EEEE 381 – Electronics I
Lab #1: Diode Characteristics and Rectifier Circuits
Overview
The objectives of this lab are: (1) to extract diode model parameters by measurement of the
diode current vs. voltage characteristics; (2) to simulate half-wave rectifier circuits; and (3) to
evaluate the performance of a half-wave rectifier.
Theory
Parameter Extraction
The current iD in a diode is related to the voltage vD across it by
i D  I S e qvD / nkT  1
eq. 1
where IS = reverse saturation current (that is, the current that flows through the diode when it is
reverse biased, but not in breakdown)
q = magnitude of the charge on an electron (= 1.6 x 10–19 Coulomb)
n = a non-ideality factor that ranges in value between 1 and 2; ideally, n = 1
k = Boltzmann's constant (= 1.38 x 10–23 J/K)
T = absolute temperature (K).
The strongly asymmetric nature of the diode’s behavior should be noted. When vD > 0 (i.e.,
under forward bias), the current rises exponentially with applied voltage and significant amounts
of current can flow. On the other hand, when vD < 0 (i.e., under reverse bias), current is limited
to the reverse saturation current IS, which is typically in the picoamp to nanoamp range. Is is a
strong function of temperature. (Under reverse bias the electric field in the space charge layer
can exceed breakdown, typically 3E5 V/cm for silicon, resulting in significant reverse current.
Some diodes, known as Zener diodes, are designed specifically to be used in breakdown mode.)
A useful approximation is that when vD > 0, the exponential term in the diode equation can be
considered to be significantly greater than 1, and the diode equation can be written as:
i D  I S e qvD / nkT
By obtaining an appropriate plot of iD as a function of vD from a circuit such as that shown in
Figure 1, it is possible to extract the parameter n and the reverse saturation current IS.
R = 330 
iD
vs
+
–
vD
+
–
Figure 1. Circuit for measurement of diode characteristics
Half-Wave Rectifier
If the diode in the rectifier circuit shown in Figure 2 is ideal, then it will act as a short circuit
when vs(t) > 0 and as an open circuit when vs(t) < 0. The output voltage will consist only of the
positive half cycles of the input. The expressions for the output are
v t  when v s t   0
vo t    s
when v s t   0
0
(Ideal)
vs(t)
RL
1 k
~
+
–
vo(t)
Figure 2. Half-wave rectifier circuit with ideal diode
If the diode in the circuit is not ideal, then it can be modeled by a series equivalent circuit shown
in Figure 3. The ideal diode component reflects the rectifying nature of the circuit and, as
before, has no voltage drop across it when it is on (forward-biased). The output is then given by
 RL
v s t   VD 0  when vs t   VD 0

vo t    RL  rD
 0
when v s t   VD 0

VD0 rD
–
(Ideal)
+
vs(t)
~
RL
1 k
+
–
vo(t)
Figure 3. Half-wave rectifier circuit with non-ideal diode behavior
Electronics II – EEEE 482 — Lab #1: Diode Characteristics and Rectifier Circuits — Rev5_1
Rochester Institute of Technology
Page 2 of 7
Dr. Lynn Fuller, et.al.
There will be a certain interval in each cycle when the output is zero. This corresponds to time
intervals when v s t   VD 0 .
Two measures can be used to characterize the rectifier’s performance — the conduction ratio and
the peak offset, defined as follows:
 Conduction time of the diodes 

Conduction ratio  
 Period of the input signal 
Peak offset  (Peak value of vs(t) – peak value of vo(t)).
where the conduction time is the time that the diode is on and conducting current during one
cycle of the input signal. For an ideal diode in the half-wave rectifier circuit, the conduction
ratio would be 0.5 and the peak offset would be 0.
The output voltage from the circuits of Figures 2 and 3 will be highly variable over time,
approximately duplicating the input voltage when it swings high, and remaining at zero when the
input swings low. Although this constitutes a DC voltage in the very limited sense of having a
non-zero average value, it is clearly not true DC, which is invariant over time.
A first step toward producing true DC is shown in Figure 4, in which a capacitor is added in
parallel to the load RL. The resulting output signal will still vary somewhat with time, but
significantly less than the output from Figures 2 or 3 since the capacitor attempts to hold the
output voltage. During the half cycle when the diode is conducting, the capacitor charges; when
the diode is off, the capacitor discharges through RL. The difference between the maximum and
the minimum output voltages is known as the “ripple voltage.” Ideally, the ripple voltage, Vr,
would be 0. Practically, the larger the capacitor, the smaller the ripple voltage. Irrespective of
the specific amount of ripple voltage, however, the resulting output signal is significantly closer
to true DC than the output without the capacitor in place.
vs(t)
~
CL
RL
1 k 10 F
+
–
vo(t)
Figure 4. Half-wave rectifier circuit with capacitor to limit output voltage variation
Electronics II – EEEE 482 — Lab #1: Diode Characteristics and Rectifier Circuits — Rev5_1
Rochester Institute of Technology
Page 3 of 7
Dr. Lynn Fuller, et.al.
Pre-Lab
There are many different types of diodes including, large high current devices for power, small
size (small junction capacitance) diodes for rectification of high frequency AC signals, zener
diodes, photodiodes, light emitting diodes (LEDs) and pn junctions inside of MOSFETs and
BJTs. They all are similar and can be modeled with the ideal diode equation above, eq. 1.
The RIT labs have 1N4004, 1N4148 diodes in each lab supply cabinet, the Analog Discover kits
come with 1N4448 diodes. SPICE models for these diodes are in the PSPICE Library
Diode.OBL. For example the 1N4004 is model D1N4004, 1N4148 is model D1N4148 and
1N4448 is model D1N4448. If you wish to model other pn junctions you can load the Dbreak
component and change the SPICE model to represent the device you wish to model. You may
do this lab with any of these diodes.
(0) Look up the data sheet for the diode you will be using. Record reverse leakage, max current,
breakdown voltage, junction capacitance, etc.
(1) Given the ideal diode theory presented in lecture and above, explain how you will plot
measured diode iD – vD characteristics and how you will extract the non-ideality factor n and
the reverse saturation current IS from your data.
(2) Use PSPICE to simulate the iD – vD characteristics of a diode as shown in the circuit of
Figure 1. The SPICE model for the diode would be identified in parts libraries as
D1N4xxx. You may need to add the Diode.OBL library (use Add library in the Place
Part pull-down menu). Use the procedure outlined in step (1) above to extract the nonideality factor n and the reverse saturation current IS from your simulated data. This will
serve as a comparison to experimentally determined values.
(3) Use PSPICE to simulate the half-wave rectifier circuit of Figure 2. Use a sinusoidal signal
for vs(t) with peak-to-peak amplitude of 10 V and frequency of 60 Hz. Use the 1N4004
diode model for the diode so you have a legitimate comparison to experimental
measurements. Determine the conduction ratio and the peak offset. Also, based on the
theory presented above, extract values of rD and VD0.
(4) Use PSPICE to simulate the half-wave rectifier circuit of Figure 4. Use a sinusoidal signal
for vs(t) with peak-to-peak voltage of 10 V and frequency of 60 Hz. Determine the ripple
voltage, Vr.
Electronics II – EEEE 482 — Lab #1: Diode Characteristics and Rectifier Circuits — Rev5_1
Rochester Institute of Technology
Page 4 of 7
Dr. Lynn Fuller, et.al.
Lab Exercise
(1) Construct the circuit shown in Figure 1. Make sure that you measure and record the actual
resistance of your nominal 330  resistor. Using a 0 to 10 V ramp as the input source (vs),
measure the diode voltages and currents for one cycle. Transfer the data from the
oscilloscope to Excel. (Alternatively, you may set vs manually using a power supply and
measure the resulting vD and iD. This must be done for at least five (5) positive values of vs.)
Tabulate your data and draw the diode characteristic curve (iD vs. vD).
Note: Students who have the Analog discovery module from Digilent may set it up as a
curve tracer. Set the waveform generator for a -5 volt to +5 volt sawtooth. Use a 100
ohm series resistor. Use the oscilloscope to measure the voltage across the diode and the
voltage across the 100 ohm resistor. Select the math function to plot the current versus
voltage. (see: the reference document)
(2) Construct the half-wave rectifier circuit shown in Figure 2. Make sure that you measure and
record the actual resistance of your nominal 1 k resistor. Use a sinusoidal signal for vs(t)
with peak-to-peak voltage of 10 V and frequency of 60 Hz. Observe and plot the voltage
waveforms of the source voltage vs(t) and the output voltage vo(t). From the plots, measure
the peak value of vs(t), the peak value of vo(t) and the interval of time in each cycle when the
diode is conducting.
(3) Construct the modified half-wave rectifier circuit shown in Figure 4, a 10 F capacitor. Use
a sinusoidal signal for vs(t) with peak-to-peak voltage of 10 V and frequency of 60 Hz.
Observe and plot the voltage waveforms of the source voltage vs(t) and the output voltage
vo(t).
Analysis of results
(1) Using the data collected from the circuit of Figure 1 in Part (1) of the Lab Exercise, and
following the methodology outlined in Part (1) of the Pre-Lab preparation, extract the diode
parameters n and IS.
Compare your experimental values to those obtained through
simulation in your pre-lab preparation.
(2) Using the data collected from the circuit of Figure 2 in Part (2) of the Lab Exercise, extract
the non-ideal diode parameters rD and VD0 (as shown conceptually in Figure 3). Also,
calculate the conduction ratio and the peak offset from your experimental measurements.
Compare your experimental values to those obtained through simulation in your pre-lab
preparation.
(3) Using the data collected from the circuit of Figure 4 in Part (3) of the Lab Exercise,
determine the ripple voltage, Vr. Compare your experimental value to that obtained through
simulation in your pre-lab preparation. Also, based on ripple theory from lecture and the
text, calculate the expected value of ripple voltage and compare it to your experimental and
simulated values.
Electronics II – EEEE 482 — Lab #1: Diode Characteristics and Rectifier Circuits — Rev5_1
Rochester Institute of Technology
Page 5 of 7
Dr. Lynn Fuller, et.al.
Check-Off Sheet
A. Pre-Lab
 Explanation of how to obtain n and IS.
 PSPICE simulation of the 1N4004 iD – vD characteristics and extraction of n and IS.
 PSPICE simulation of the half-wave rectifier circuit, and determination of the conduction
ratio, the peak offset, rD and VD0.
 PSPICE simulation of the modified half-wave rectifier circuit with capacitor, and
determination of the ripple voltage, Vr.
B. Experimental
 Obtain diode characteristic curve (iD vs. vD). Extract n and IS and compare to simulated
values.
 Measure the response of the half-wave rectifier circuit (Figures 2 and 3) and obtain
values for the peaks of the source voltage vs(t) and the output voltage vo(t), as well as the
conduction interval.
 Calculate the conduction ratio and the peak offset. Extract the non-ideal diode
parameters rD and VD0 from your experimental measurements and compare to values
obtained through simulation.
 Measure the response of the modified half-wave rectifier circuit with capacitor (Figure 4)
and obtain values for the maximum and minimum output voltages.
 Determine the ripple voltage, Vr. Compare your experimental value to those obtained
through simulation and theoretical calculation.
TA Signature: ____________________________ Date: ___________________________
Electronics II – EEEE 482 — Lab #1: Diode Characteristics and Rectifier Circuits — Rev5_1
Rochester Institute of Technology
Page 6 of 7
Dr. Lynn Fuller, et.al.
Appendix B:
Components Available in the Electrical Engineering Labs
(other values available on request)
100 Ω
330 Ω
470 Ω
820 Ω
1 kΩ
1.2 kΩ 3.9 kΩ
1.5 kΩ 4.7 kΩ
1.8 kΩ 5.6 kΩ
2.2 kΩ 6.8 kΩ
3.3 kΩ 10 kΩ
2N3904
2N4401
15 kΩ
1 MΩ
33 kΩ
1N914
47 kΩ
1N404
100 kΩ 1N4148
470 kΩ 1N4735
2N3906
2N4403
0.01 µF
0.1 µF
1 µF
10 µF
100 µF
Created:
Electronics II – EEEE 482 — Lab #1: Diode Characteristics and Rectifier Circuits — Rev5_1
Rochester Institute of Technology
8/11/2012
Page 7 of 7
Dr. Lynn Fuller, et.al.