Lab – 1
Objective
To apply the theoretical concepts studied about IV characteristics and different biasing conditions of diodes and
experimentally validate the theoretical framework. Data collected during this lab experiment will be compared to the
specifications available from the datasheet of the corresponding diode to build a strong sense of correlation between our
experimental and theoretical concepts.
Theoretical Framework
A diode is a two-terminal element, usually made by using a PN junction (the operation of which is explained in detail
in FE class). In this lab, we are concerned only with the external (voltage-current) characteristics of diodes.
The symbol for a diode is shown in Fig.1(a). Diode has two terminals. Usually, the terminal indicated by a horizontal
line in Fig. 1(a), called the cathode, is marked on a real diode; see, for example, Fig. 1(b). We define the voltage (VD) and
the current (ID) of a diode as shown in the figure. These two quantities are related, as shown in figure Fig. 1(c). When the
voltage VD is positive, the diode is said to be forward-biased; a large current can then flow, and the diode is said to conduct.
When the voltage VD is negative, the diode is said to be reverse-biased; the diode current is extremely small, and for our
purposes it is assumed to be zero; the diode is then said to be turned off. Thus, the diode effectively conducts current in
only one direction (downward in Fig. 1); its “refuses” to conduct current in the other direction.
Pre-Lab Section
Pre lab assignment for this lab is a hand out which discusses the semiconductor basics. Try to answer these questions 1How does the doping affect the conductivity of intrinsic semi-conductor?
In-Lab Section Experimental Setup
Required Equipment/Instrumentation
1.
2.
3.
4.
5.
6.
Variable Resistor: No
Fixed Resistor: 1k, 10k,10 Ω
Semiconductor: IN4007
Function Generator
CRO
Power Supply: Dual variable
Experiment Procedure
Low current switching diode characteristics Procedure
1. Construct the circuit as shown in the figure 1-1. Note the low current diode is connected to the terminal A and
B with forward biased polarity
2. Adjust the power supply voltage control for zero input
3. Switch on the power supply and carefully adjust the voltage to give the current levels listed of procedure on
the table-1. At each current level record the diode forward voltage.
4. Adjust power supply to return the diode voltage to zero. Switch off and then reconstruct the circuit as shown
in fig 1-2. Using the 20µA range ammeter. Note that the diode polarity is reversed the ammeter is connected
directly is series with diode and R1 is 10K ohms resistors
5. Switch on the power supply and adjust the device (reverse) voltage to 30V. Record the diode reverse current
on the table.
6. Plot resulting diode curve on the graph page graphically determine diode’s barrier potential (Vb) and forward
resistance Rf
Fig:1-1
Fig:1-2
Observations
Table-1
For Forward Bias
S.no
Vin (DC)
1.
OV
2.
0.2V
3.
0.4V
4.
0.6V
5.
0.8V
6.
1V
7.
2V
8.
5V
9.
10V
10.
15V
Voltage across
1KΩ Resistor
Diode Forward
Voltage
Diode Forward
Current
For Reversed Bias
S.no
Vin (DC)
1.
OV
2.
0.2V
3.
0.4V
4.
0.6V
5.
0.8V
6.
1V
7.
2V
8.
5V
9.
10V
10.
15V
Voltage across
1KΩ Resistor
Diode Reverse
Voltage
Diode Reverse
Current
Table-2
Biasing
Resistance
Forward
Reversed
Table-3
Parameters
Actual Value
Measured values
Diode barrier potential Vb
Diode forward Rf resistance
Questions
2- What happen if we increase the value of resistor in forward bias connection?
3- What is potential barrier?
GRAPH
Post-Lab Section
TASK-1:
Design a two input AND gate using diodes and resistors only, Simulate your designed circuit on MultiSim simulation tool.
Put your circuit on the bread board and prove the functionality of your design.
TASK-2:
Design a two input OR gate using diodes and resistors only, Simulate your designed circuit on Multisim simulation tool.
Put your circuit on the bread board and prove the functionality of your design.