# UNIVERSITY OF TEHRAN Electrical and Computer Engineering

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```					                    UNIVERSITY OF TEHRAN
Electrical and Computer Engineering Department
Electronic Circuits Lab I
Experiment 1
Characteristics of a P_N Junction Diode

1.0    Objectives
In this experiment, characteristics of the P_N junction diode will be introduced. You will
measure some of these characteristics you may have previously found in catalogs. That
will make you familiar with the real functionality of a diode.

2.0 Necessary Equipments

Diodes to be used are 1N4148, 1N4001, 1N4002 or 1N4004 as well as Zeners diode with
break voltage of 4 to 7 volts. Furthermore, you will need 1KΩ, 10KΩ, 100KΩ, 100Ω,
560Ω and 10Ω resistors. Other essential items include a DC power supply, an
oscilloscope, a function generator, a breadboard, an ohmmeter and wires.

3.0 Pre_lab
3.1 Consider the circuit below:

a) Draw the output characteristic diagram, Vo versus Vin.
b) Draw the approximate diode characteristics diagram Io versus Vin and calculate
the diagram slope in the work point, as you know we refer to this value as diode’s
dynamic resistance.
c) Now assume that sinusoid signal with amplitude of 6 Volts and frequency of
1KHz is applied to the circuit, draw Vo(t) diagram. Assume the threshold voltage
or Vγ for the diode is 0.6 Volts.
d) Now replace the diode D with a Zener diode with a reverse break voltage of 7
Volts and a forward turn-on voltage of 4 Volts, draw the zener characteristic
diagram, Io versus Vz. Also draw the circuit’s output characteristic diagram. Vo
versus Vin.
e) Once again, replace the input with a sinusoid signal ‘similar to the one in section
(c) and draw Vo(t) diagram.

3.2 As you may have already guessed the circuits described above can be used as voltage
rectifiers; however actual application for such circuits in their current is limited by to
Consider the circuit below; each diode has a Vγ of 0.6 Volts. Assume RL=1KΩ.

(a)Draw output characteristic diagram Vo versus Vin for this circuit.

(b)   Consider circuit3. Draw the Vout/Vin characteristic for this circuit, now add a
1KΩ resistor to the output and sketch the said diagram again. Compare the two
( c) Re-do segment (b) for a zener diode with Vγ=4 and Vbreak=7 volts.which of the
two circuits are more suitable? (Note that the maximum reverse current for a
zener diode is 50mA)

4.0 Procedure
4.1 Static Characteristic Diagram:
4.1.1 Assemble Circuit 1. Input must be sinusoid signal with amplitude of. 6Volts, at 1
KHz frequency. Hint: with your knowledge of electronics, you must be able to
detect the cathode and anode of a diode; nevertheless the line on the body of a
diode shows the Cathode.

Circuit 1: The circuit to show the characteristic diagram of a diode.

4.1.2 Connect the GND of the oscilloscope to point 2 and main probes of channel 1 and
2 points 1 and 3 in order to see diode’s characteristic diagram on screen. Set the
mode on X-Y and observe the characteristic diagram of the diode. Sketch
conclusion. Compare it with what you have drawn in Pre_lab. Measure the Vγ.
4.1.3 Repeat these steps with 1N4004 diode. try again with a 4 to 7 volt zener diode.
Find the reverse break point voltage in the related zener diagram. Using the
diagram, calculate the Vγ for all the diodes and VZ for the zener diode. (Vγ is the
forward turn_on voltage and VZ is the reverse break voltage) write down how you
have found these two parameters.
4.1.4 Change the sinusoid input to a square shaped. Explain what you see. Again, in the
sinusoid mode, increase the frequency continuously and follow the output. Find
the reason why you see difference when you increase the frequency. Hint: there
are junction capacitors in the diode, which collapse when frequency is increased.
4.1.5 Back to Circuit 1 with 1N4148 diode, 1K resistance and sinusoid 6 volt input;
connect the GND of the oscilloscope to point 3 and check points 1, 2 as input and
output. Set the input frequency at 100Hz.
Explain the difference between input and output positive amplitudes.
4.1.6 Increase the frequency once again and observe the output, as its shape gradually
becomes a complete sinusoid, change the sinusoid input to the square pulse and
sweep the frequency while watching the output. Measure the turn-on and turn-off
delay times. Then change the diode with a 4 to 7 volt zener, and at 100Hz see the
output.
Try to find an explanation for what you see at high frequency for the output.

4.2 Forward Drop and Output Loads
4.2.1   In Circuit 1, replace the function generator with a DC voltage source as shown in
Circuit 2. (Point3 is the oscilloscope ground.)
Note: when measuring the Vd voltage, the ground probe must be attached to point
2 to minimize error.

Circuit 2: A DC voltage source is used to determine the DC parameters.
4.2.2 By changing the input voltage, set the current at about 5mA and measure the two
near working points (VD, ID).remember the two working points must be very close.
4.2.3 Following the next equation, determine Rd: Rd=(VD2 -VD1) / (ID2 -ID1)
4.2.4 Compare the two conclusions. Which result is more accurate?
4.2.5 Now around ID1, again calculate Rd using this formula: (assume η=1 and
VT=26mA) Rd=η*VT/ID (Rd: Dynamic Resistance)
4.2.6 Use again those two work point measurements to derive IS and η from yhe next
formula: ID=IS * exp (VD/ η* VT)
4.2.7 Build Circuit 3. using 1N4004 and a 100Ω resistor.

Circuit 3: by using diodes, we try to achieve to a constant voltage.

4.2.8   You may expect the output voltage to be fixed at 2.1V, so change the input
according to the next table and write output.

Vi         1.5 volt   2 volt      2.5 volt    3 volt     3.5 volt    4 volt       4.5 volt
Vo

Sketch the diagram of the Vo according to Vi.
Determine the diode line regulation (ΔVout/ΔVin) at several work
points.(change in output voltage / change in input voltage[mV/V].)
Now add the load resistors to the circuit. Connect a resistance in parallel with 3
diodes (between Vo and GND) and change it according to this table. Then
calculate Vo and Io. For each load calculate the voltage regulation percentage i.e.

R(Ω)         100K          10K          1K           560           100          10
Vo
Io
Vin

4.2.9  Now replace the diode in Circuit 2 with a 4 to 7 zener diode, first place the zener
diode in forward and find two working points (VZ1,ID1 and VZ2,ID2 ), using the
equation given in section 4.2.6 measure the η and IS for the zener diode and
compare them with that 1N4148 diode then, change the input voltage to set the
current at 5mA, again using the method described in section 4.2.4 ,calculate the
Dynamic Resistance of the zener diode and compare it to that of 1N4148.
4.2.10 Now place the zener diode in backward position and change the input voltage to
set the current at 5mA, measure Vd1 by changing the input voltage. Set the
current at 5.1mA and measure Vd2. now calculate the reverse rd using
rd = (Vd2-Vd1)/ (Id2-Id1) and compare it to the forward dynamic resistance.
How can you justify your findings with the zener’s characteristic diagram? Can
we calculate zener’s backward dynamic resistance using the rd=ηVT/IDG
formula? Why?
4.2.11 Now return to Circuit 3 and replace the 3 diodes with a zener diode and add and
the load resistors according to the table in section4.2.8 measure the Vo and Io
accordingly and calculate Sload for each step. Also note that maximum reverse
current, which the zener can handle, is about 50mA, what is the maximum input
voltage you can apply to this circuit? Is this circuit better than the one built with
3 diodes? Why?
5.1 Problem
What is the proper range for RL in this circuit?
Vz = 7 volts   Iz(min)=0.6mA
Vγ = 4 volts   Iz (max)=50mA

Pre_lab1.4 Consider circuit3. Draw the Vout/Vin characteristic for this circuit, now
add a 1KΩ resistor to the output and sketch the said diagram again. Compare the
two diagrams. Is this circuit suitable when loaded with large loads? Why?
Pre_lab1.5 Re-do the 1.4 segment for a zener diode with Vγ=4 and Vbreak=7
volts.which of the two circuits are more suitable? (Note that the maximum
reverse current for a zener diode is 50mA)

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