Exercise 1 Diode Characteristics

Electronics I Laboratory

(AEEE238)

Exercise 1:

V-I Characteristics of Si Diode

Name: / Stathis Efstathiou
Reg. No.: / 2222
Semester: / Fall 16
Date: / 04/11/2016
Instructor: / Dr. Michael Komodromos


Objective:

The objective of this experiment is to make measurements in order to determine the V-I characteristics of a silicon diode. Biasing voltage and dynamic resistance is extracted from the plot and their importance in design is demonstrated.

Equipment:

1.  1x 1N4001 Si Diode

2.  1x 0.5W 100Ω Resistor

3.  1x 0.5W 470Ω Resistor

4.  IDL-600 Trainer with DC PSU

5.  GW-394 DMM

6.  Wires

Theoretical Backround

A silicon PN junction (or diode) is a two-terminal device that “ideally” conducts only in one direction and has zero resistance to the flow of current, while it acts as open switch in the other. The diode examined in this experiment is a silicon diode, which practically conducts – or is forward biased- when the potential difference between anode and cathode is more then 0.7volts.

An Ideal Diode it conducts perfectly (no resistance) when is forward biased and the voltage drop between anode and cathode is 0v. A Practical Diode is the model used in design. Although it acts as a perfect conductor when forward biased, a constant voltage drop of 0.7 volts occurs at the terminals and when is reversed biased it acts as an insulator.

Figure 1.1.: Ideal and Practical Diode V-I Characteristics

In Real Diode on the other hand, there are more characteristics to consider. When Reversed biased, a leakage current is occurred because the semiconductor depletion region has very large resistance. The same happens for positive but not high enough biasing voltage, but when barring voltage is exceeded current gradually (and almost linearly) increases.

Figure 1.2.: V-I Characteristics of Ideal Diode

During this experiment the following circuit was built and measurements were made.

Figure 1.3.: Diode biasing circuit

Procedure

Part one

1.  On the breadboard, the 100 Ω resistor was connected in series with an 1N4001 diode. Then the circuit was supplied through an adjustable positive power supply.

2.  The source voltage was set to 0.2volts (0volts measurement was omitted).

3.  Using a DMM, VRs and VD was measured with the polarity shown in Figure 1.3. The results were recorded in Table 1.1 in Results section.

4.  By gradually increasing VS, step 3 measurements were repeated. Accuracy on the source adjustment was trivial, so Kirchhoff’s Voltage law might not but exactly true when comparing data.

5.  Current ID was calculated using Ohm’s Law i.e ID=VRs100

6.  A plot of VD versus ID was constructed to display the data as shown in Figure 1.4.

7.  Using the results in Table 1.1, barrier voltage, dynamic and static resistance was calculated.

Part two

1.  The resistor in the circuit was replaced with a 470 Ω while the voltage was adjusted to 12v.

2.  The current was measured using a DMM.

3.  By using Rd from Part one, the current on the resistor was calculated. (30.31mA)

Results & Calculations

Part One

7VS
(v) / VRs
(V) / VD
(V) / ID
(mA)
0.0 / 0 / 0 / 0
0.2 / 0 / 0.18 / 0
0.4 / 0.0002 / 0.478 / 0.002
0.6 / 0.0048 / 0.633 / 0.048
0.7 / 0.02 / 0.664 / 0.2
0.8 / 0.109 / 0.743 / 1.09
1.0 / 0.238 / 0.768 / 2.38
1.5 / 0.72 / 0.796 / 7.2
2.0 / 1.23 / 0.811 / 12.3
3.0 / 2.25 / 0.825 / 22.5
4.0 / 3.31 / 0.837 / 33.1
6.0 / 4.27 / 0.844 / 42.7
8.0 / 7.29 / 0.857 / 72.9
10.0 / 9.12 / 0.858 / 91.2
12.0 / 11.23 / 0.869 / 112.3

Table 1.1

Figure 1.4: V-I Characteristics of the 1N4001 diode

Dynamic Resistance:

Vb=0.796 v

Rd= ΔVΔI=0.869-0.796112.3-7.2=0.69 Ω

Part Two

Id= Vs-VbRs+Rd=12-0.796463+0.69=30.63mA

%d(Id)=30.31-30.6330.63100=1.04%

Conclusions

The measurements on the diode biasing circuit proved the forward biased operation of the junction. It can be seen that the actual biasing voltage of the diode differs slightly from 0.7v. The leakage current on small biasing voltages as well as the linear response near the operating point is also shown in the graph.

Page 5 of 6 Stathis Efstathiou