Download Electrical and Electronic Principles P3 Task 1 Electrical and

Electrical and Electronic Principles P3
Task 1 Electrical and Electronic Principles P3
You are required to use test equipment to measure the forward and reverse characteristics of two semi-conductor
diodes. In order to carry out this experiment you will need to read through the instructions in the electrical/electronic
course handbook.
Tasks
1.
2.
3.
4.
Draw and label a diagram of a general purpose diode connected in forward bias and reverse bias mode
Measure the forward and reverse characteristics of the 1N4001 diode, record your results in a suitable table
and use them to plot a graph.
Measure the forward and reverse characteristics of a zener diode of your choice, record your results in a
suitable table and use them to plot a graph
Compare the two graphs showing the conduction characteristics of both diodes, consult the data sheets and
evaluate your findings in terms of forward and reverse voltages, power dissipation and maximum operating
current
Diode circuit symbol
CAD picture of a
diode
Anode = + (positive)
Cathode = - (negative)
The terminal connected to the black body is
Positive. The silver band is negative.
Diodes are semiconducting devices. For a semiconductor to allow current to flow, certain conditions have to be met.
In the case of the diode connecting 0.6 volts between the positve and negative terminals will cause the diode to begin
conducting. This is called forward biasing the diode.
Connecting the voltage the other way around (technically called reversing the polarity) is called reverse biasing
when a diode is reverse biased no current will flow until a certain point known as the maximum DC reverse voltage
is reached. When this point is reached the diode will conduct large amounts of current in the reverse direction. Diodes
are normally operated in the forward biased mode.
The diode you will be testing is the 1N4001 GP (General purpose) diode. When you are using electronic components
for the first time (and sometimes many times afterwards) it is normal to look at something known as a datasheet.
The datasheet will give details about the technicial specification of the component. At this stage you won’t be
concerned with a lot of the details on the sheet but some are very important.
Datasheets can easily be found with an internet search. Here for example is the webaddress for the datasheet for the
1N4001 http://www.fairchildsemi.com/ds/1N%2F1N4001.pdf.
I have pasted the relevant section for the diode here and you can read the information @
http://www.allaboutcircuits.com/vol_3/chpt_3/3.html to give you an idea what the various ratings mean.
Here are a few questions you could answer about this data sheet
Can you find the maximum reverse voltage the 1N4001 should be able to handle?
Can you find the maximum current the 1N 4001 can conduct?
How much surge current can this component deal with?
What is the maximum power dissipation of the diode? And what would most likely happen if this figure was
exceeded?
Tabulating your results (Just means putting them in a table)
Now in the forward direction I would suggest a table like this.
1N4001 Diode Forward Conduction Characteristic
Forward Voltage in Volts Forward Current in Amps
0V
0.1V
0.2V
0.3V
0.4V
0.5V
0.6V
0.61V
0.62V
0.63V
0.64V
0.65V
0.66V
0.67V
0.68V
0.69V
0.7V
0.048
0.75V
0.8V
The reason is that a diodes conduction is not linear unlike that of a resistor. The interesting stuff (conduction) begins
at around 0.6 volts so it makes sense to focus on that area.
A diode has what is known as dynamic resistance (non linear). This basically means that as the applied voltage
changes the amount of current conducted by the diode is not directly proportional. Also because a diode is a
semiconductor, changes in temperature will affect the current conducted.
Remember as the temperature of a semiconductor increases it tends to conduct more current
Tabulate the Reverse Conduction Characteristic
If you read the data sheet you can find the reverse breakdown voltage for this diode (V RRM). Bearing in mind the
tabling technique I showed you above, once you know this value, you should be able to come up with a relevant table
which focuses on the part where the diode begins to breakdown and conduct.
In reverse bias mode a diode will always be conducting a very small amount of current, it is known as leakage
current. Below VRRM the leakage current is seen as negligible. Once VRRM is exceeded, this current becomes very
large indeed, it is known as the avalanche effect.
Once you have completed both tables, you need to plot the values on a graph. Once completed you are required to
choose a zener diode and do exactly the same tests as shown here, but using the physical diode and test equipment.
I will show you how to do that in the next demonstration.
Here is one way of plotting the values from Excel
Diode Conduction Characteristic
0.4
0.2
Applied Voltage in Hundreds
-0.60
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0
0.10
C
u
r
r
e
n
t
-0.2
i
n
-0.8
A
m
p
s
-1
-0.4
-0.6
-1.2
-1.4
Of course a major problem with the graph above is that it has to cover such a large data range that the area of
interest is not easy to read. You can solve this by selecting a specific range of data within your data set and then just
graphing that.
Diode Forward Conduction Characteristic
0.25
0.2
0.1
0.05
0.00
0.20
0.40
0.60
Voltage Applied
0.80
0
1.00
-0.05
Current in Amps
0.15
Series1
0.4
0.2
Applied Voltage
-0.60
-0.50
-0.40
-0.30
-0.20
-0.10
0
0.00
0.10
Hundreds
C
-0.2
u
r
-0.4
r
e
n
-0.6
t
i
n
A
m
p
s
-0.8
-1
-1.2
-1.4