PHYSICS 330 LAB – Load Lines
Objectives: We will investigate the characteristics of a forward-biased diode
using load lines.
Introduction: See text, pages 134 - 136.
Procedure:
I.
Basic Load Lines:
Construct the circuit shown below, using a variable power supply for VSS, a
fixed resistor for R and a variable resistor for RL.
Set VS = 5.0 Volts, and choose R to be about 250Ω (measure it with your
multimeter).
VS : _________ V
R: _________ Ω
Vary RL and measure the terminal voltage, VT. Use Ohmʼs Law to
calculate the current, I, going through RL. Fill out the data table and make
a plot of VT (x-axis) vs. I. Fit a straight line through your data.
What is the relationship between the slope of your line and values of
components in your circuit?
RL
VT
0
50
100
150
250
350
500
750
1000
2000
Physics 330 - Revised 10/19/10
I
Change R to about 500 Ω and repeat.
VS : _________ V
RL
R: _________ Ω
VT
I
0
50
100
150
250
350
500
750
1000
2000
How did your load line change? How is that related to the value of R?
II.
Diode Characteristic Curve
Construct the circuit shown below with a 1N4004 diode. In this circuit, the
diode is forward biased. Set Vss to +12 Volts
We will change R to change the operating point of the diode by moving the
load line. Be careful not to make R too small or the current will get large
enough to destroy the diode (and maybe R!).
Physics 330 - Revised 10/19/10
Vary R to change the operating point of the diode. Measure several
(about 10) values of VD and ID, (using the oscilloscope for VD and the
meter for ID) covering a range from 0 to about 25 mA and Plot an I-V curve
for the 1N4004 diode.
R
III.
VD
ID
Forward Biased p-n Junction: (diode)
Build the load line circuit shown below with Vss = 12 V and R = 240Ω .
Predict the operating point (VD and ID).
Predicted values:
VD : _________ mV
ID: _________ mA
Measure these quantities and compare to your predictions.
Actual values:
Physics 330 - Revised 10/19/10
VD : _________ mV
% Error ______
ID: _________ mA
% Error ______
Assuming that VT is 29.4 mV, and n = 1, calculate Is for your operating
point using the Shockley equation (3.15) and plot the theoretical curve for
the diode along with your data from part II.
How good is the fit?
IV.
Light Emitting Diode Characteristic Curve
Construct the circuit shown below with a yellow LED. In this circuit, the
diode is forward biased. Set Vss to +12 Volts
We will repeat the procedure of part II and change R to change the
operating point of the diode by moving the load line.
Vary R to change the operating point of the diode. Measure several
(about 10) values of VD and ID, (using the oscilloscope for VD and the
meter for ID) covering a range from 0 to about 20 mA and Plot an I-V curve
for the yellow light emitting diode.
R
VD
Physics 330 - Revised 10/19/10
ID
Physics 330 - Revised 10/19/10