ECE 233
LAB 9
DIODE CIRCUITS
CH1
CH2
I1(t)
R1
D1
VDC1
D2
VDC2
R
I(t)
R2
I2(t)
VAC
+

V(t)
-
Figure 1: Diode circuit 1
Theoretical analisis for the circuit in Figure 1, (assuming that the diodes are ideal).
If V  VDC1 then I 1 
V  VDC1
V  VDC1
, I 2  0 and I  I 1  I 2 
Amper
R1  R
R1  R
If  VDC 2  V  VDC1 then I1  0 , I 2  0 and I  I1  I 2  0 Amper
If V  VDC 2 then I1  0 , I 2 

 VDC 2  V
V  VDC 2
and I  I1  I 2 
Amper
R2  R
R2  R
Theoretical analisis for the circuit in Figure 1, (assuming that the diodes are not ideal
and their threshold values are VT).
If V  VDC1  VT then I1 
V  VDC1  VT
V  VDC1  VT
, I 2  0 and I  I1  I 2 
Amper
R1  R
R1  R
If  VDC 2  VT  V  VDC1  VT then I1  0 , I 2  0 and I  I1  I 2  0 Amper
If V  VDC 2  VT then I1  0 , I 2 
 VDC 2  VT  V
V  VDC 2  VT
and I  I1  I 2 
Amper
R2  R
R2  R
1- Construct the circuit in Figure 1 on the breadboard. The circuit parameters are as follows:
VDC1=1.5 Volt, VDC2=1.5 Volt, R1=2.2 kΩ, R2=1 kΩ, R= 1 kΩ, VAC=8sin(2πft) Volt (For
VDC1 and VDC2 use the small batteries, for VAC use the function generator and take f=1000
Hz). If the channels of the oscilloscope are connected as in Figure 1, CH1 will show the total
voltage drow over the circuit whereas CH2 will show the total current over the circuit. Hence,
when we use x-y operation on the oscilloscope we will observe the V(t) versus I(t)
characteristic for the circuit. For both channels (CH1 and CH2) take Volt/Div= 2 Volt. Draw
what you have observed on the oscilloscope in x-y mode to Figure 2, indicate the important
points in your plot.
Figure 2: Oscilloscope view when Volt/Div=2 Volt for part 1.
CH1
CH2
I1(t)
R1
D1
VDC1
R
D2
R2
I(t)
VDC2
I2(t)
VAC
+
V(t)
-
Figure 3: Diode circuit 2

Theoretical analisis for the circuit in Figure 3, (assuming that the diodes are not ideal
and their threshold values are VT and VDC1+VT>VDC2-VT).
If V  VDC1  VT then I1 
V  VDC1  VT
V  VDC1  VT
, I 2  0 and I  I1  I 2 
Amper
R1  R
R1  R
If VDC 2  VT  V  VDC1  VT then I1  0 , I 2  0 and I  I1  I 2  0 Amper
VDC 2  VT  V
V  VDC 2  VT
and I  I1  I 2 
Amper
R2  R
R2  R
Theoretical analisis for the circuit in Figure 3, (assuming that the diodes are not ideal
and their threshold values are VT and VDC1+VT=VDC2-VT).
If V  VDC 2  VT then I1  0 , I 2 

If V  VDC1  VT  VDC 2  VT then I1 
I  I1  I 2 
V  VDC1  VT
, I 2  0 and
R1  R
V  VDC1  VT
Amper
R1  R
If V  VDC 2  VT  VDC1  VT then I1  0 , I 2 
V  VDC 2  VT
Amper
R2  R
Theoretical analisis for the circuit in Figure 3, (assuming that the diodes are not ideal
and their threshold values are VT and VDC1+VT<VDC2-VT).
I  I1  I 2 

VDC 2  VT  V
and
R2  R
V  VDC1  VT
V  VDC 2  VT
, I 2  0 and I  I1  I 2 
Amper
R1  R
R1  R
V  VDC1  VT
V
 VT  V
, I 2  DC 2
and
 VT then I1 
R1  R
R2  R
If V  VDC 2  VT then I1 
If VDC1  VT  V  VDC 2
 1
1  VDC1  VT VDC 2  VT
 
Amper
I  I 1  I 2  V 


R1  R
R2  R
 R1  R R2  R 
V
 VT  V
If V  VDC1  VT then I1  0 , I 2  DC 2
and
R2  R
V  VDC 2  VT
Amper
I  I1  I 2 
R2  R
2- a) Construct the circuit in Figure 3 on the breadboard. The circuit parameters are as
follows: VDC1=1.5 Volt, VDC2=0 Volt, R1=2.2 kΩ, R2=1 kΩ, R= 1 kΩ, VAC=8sin(2πft) Volt
(For VDC1 and VDC2 use the small batteries, for VAC use the function generator and take
f=1000 Hz). If the channels of oscilloscope are connected as in Figure 3, CH1 will show the
total voltage drow over the circuit whereas CH2 will show the total current over the circuit.
Hence, when we use x-y operation on the oscilloscope we will observe the V(t) versus I(t)
characteristic for the circuit. For both channels (CH1 and CH2) take Volt/Div= 2 Volt. Draw
what you have observed on the oscilloscope in x-y mode to Figure 4, indicate the important
points in your plot ( VT  0.7 Volt).
Figure 4: Oscilloscope view when Volt/Div=2 Volt for part 2-a.
b) Construct the circuit in Figure 3 on the breadboard. The circuit parameters are as follows:
VDC1=0 Volt, VDC2=1.5 Volt, R1=2.2 kΩ, R2=1 kΩ, R= 1 kΩ, VAC=8sin(2πft) Volt (For VDC1
and VDC2 use the small batteries, for VAC use the function generator and take f=1000 Hz). If
the channels of oscilloscope are connected as in Figure 3, CH1 will show the total voltage
drow over the circuit whereas CH2 will show the total current over the circuit. Hence, when
we use x-y operation on the oscilloscope we will observe the V(t) versus I(t) characteristic for
the circuit. For both channels (CH1 and CH2) take Volt/Div= 2 Volt. Draw what you have
observed on the oscilloscope in x-y mode to Figure 5, indicate the important points in your
plot. ( VT  0.7 Volt).
Figure 5: Oscilloscope view when Volt/Div=2 Volt for part 2-b.
c) Construct the circuit in Figure 3 on the breadboard. The circuit parameters are as follows:
VDC1=0 Volt, VDC2=3 Volt, R1=2.2 kΩ, R2=1 kΩ, R= 1 kΩ, VAC=8sin(2πft) Volt (For VDC1
and VDC2 use the small batteries, for VAC use the function generator and take f=1000 Hz). If
the channels of oscilloscope are connected as in Figure 3, CH1 will show the total voltage
drow over the circuit whereas CH2 will show the total current over the circuit. Hence, when
we use x-y operation on the oscilloscope we will observe the V(t) versus I(t) characteristic for
the circuit. For both channels (CH1 and CH2) take Volt/Div= 2 Volt. Draw what you have
observed on the oscilloscope in x-y mode to Figure 6, indicate the important points in your
plot. ( VT  0.7 Volt).
Figure 6: Oscilloscope view when Volt/Div=2 Volt for part 2-c.