Project Sample: To Learn How a Diode Works

Experiment:
To
Learn
How
a
Diode
works
Monday 25 November 2013

• We
will
do
this
experiment
in
two
phases.
In
the
ﬁrst
phase,

we
will
learn
about
the
basic
func:oning
of
a
diode.
• In
the
second
phase,
we
will
vary
voltage
across
the
diode

and
observe
how
the
current
changes
through
it.
Then,
we

will
plot
a
graph,
current
(I)
vs
voltage
(V).
Points
to
Remember

Circuit
Diagram
PHASE-‐1

i. Breadboard
-‐
1
ii. Diode
4007
-‐
1
iii. LED
-‐
1
iv. Resistor:
1
kΩ
-‐
1

Colour
Code:
1
kΩ
-‐
Brown
Black
Red
Gold
v.

9
V
BaRery
-‐
1
vi.

Connec:ng
Wire
Pieces
Materials
Required
PHASE-‐1

Take
a
breadboard
and
connect
its
two
halves
as
shown
in
ﬁgure

below.
Step
No.
1
PHASE-‐1

Connect
a
9
V
baRery
on
the
breadboard.
Step
No.
2
PHASE-‐1

Connect
a
diode
on
the
breadboard.

Note:
The
black-‐side
of
the
diode
represents
its
p-‐side
and
its
silver

stripe
is
the
n-‐side.
Step
No.
3
PHASE-‐1

Connect
the
posi:ve
terminal
of
the
LED
to
the
n-‐side
of
the
diode

and
its
nega:ve
terminal
to
any
diﬀerent
column
of
the
breadboard.
Step
No.
4
PHASE-‐1

Connect
one
leg
of
a
1
kΩ
resistor
to
the
nega:ve
terminal
of
the

LED
and
its
other
leg
to
any
diﬀerent
column
of
the
breadboard.

Step
No.
5
PHASE-‐1

Connect
the
p-‐side
of
the
diode
to
Vcc
and
the
right
leg
of
the

resistor
to
ground.

Step
No.
6
PHASE-‐1

Reverse
the
connec:ons
of
the
diode.
On
reversing
the
connec:ons

of
the
diode,
the
LED
stops
glowing.
Step
No.
7
PHASE-‐1

Again,
reverse
the
connec:ons
of
the
diode.
Measure
the
voltage

across
the
diode
when
the
LED
is
glowing.
The
voltage
reading
across

the
diode
is
0.69
V.
Step
No.
8
PHASE-‐1

The
LED
glows
when
the
p-‐side
of
the
diode
is
connected
to

Vcc,
and
the
n-‐side
is
connected
to
ground
through
the
LED

and
the
resistor.

The
LED
does
not
glow
when
the
n-‐side
of
the
diode
is

connected
to
Vcc
and
the
p-‐side
is
connected
to
ground.
When
a
diode
is
conduc:ng,
a
voltage
drop
of
0.69
V
takes

place
across
its
terminals.
The
diode
needs
a
minimum

voltage
of
0.6
-‐
0.7
V
to
allow
current
to
pass
through
it.
ObservaGon
PHASE-‐1

Disconnect
all
components
from
the
breadboard.
We
have
learned
how

a
diode
works.
Now
its
:me
for
Phase-‐2.
Refer
the
circuit
diagram
and

follow
the
steps
given.
Next
Steps

Circuit
Diagram
PHASE-‐2

i. Breadboard
-‐
1
ii. Preset:
10
kΩ
-‐
1
iii. Diode
4007
-‐
1
iv. Resistor:
1
kΩ
-‐
1
Colour
Code:
1
kΩ
-‐
Brown
Black
Red
Gold
v. 9
V
BaRery
-‐
1
vi. Connec:ng
Wire
Pieces
Materials
Required
PHASE-‐2

Take
a
breadboard
and
connect
its
two
halves
as
shown
in
ﬁgure

below.
Step
No.
9
PHASE-‐2

Connect
a
9
V
baRery
on
the
breadboard.
Step
No.
10
PHASE-‐2

Step
No.
11

Insert
a
10
kΩ
preset
on
the
breadboard
such
that
its
middle

terminal
(2)
is
connected
on
the
upper
half,
and
side
terminals
(1

and
3)
are
connected
on
the
lower
half
of
the
breadboard.
PHASE-‐2

Step
No.
12

Connect
terminals
1
and
3,
of
the
preset
to
Vcc
and
ground,

respec:vely.
We
have
built
a
voltage
divider
circuit
using
the
preset.

When
we
rotate
the
preset
from
its
one
extreme
end
to
the
other,

we
will
get
a
range
of
voltages
from
zero
to
a
maximum
value
at
its

middle
terminal
2.
PHASE-‐2

Insert
a
screwdriver
in
the
rotary
slot
of
the
preset.
Rotate
the

preset
and
stop
it
somewhere
in
the
middle
posi:on.
Now
we
will

measure
the
voltage
at
the
middle
terminal
(2)
of
the
preset
(w.r.t

ground)
at
the
corresponding
posi:on
of
the
preset.

Step
No.
13
PHASE-‐2

Rotate
the
mul:meter
dial
to
20
V
of
the
DC
Voltage
region
(V

).

Note:
To
measure
DC
voltages,
we
rotate
the
dial
to
V

region.
To
measure

AC
voltages,
we
rotate
the
dial
to
V
~
region.

Step
No.
14
PHASE-‐2

To
measure
the
voltage
at
terminal
2
of
the
preset,
connect
the
red

and
black
probes
of
the
mul:meter
to
terminals
2
and
3,
of
the
preset,

respec:vely.
Note:
Alternately,
we
can
connect
the
black
probe
to

ground
(zero
volt).
Voltage
at
Terminal
2
(middle
posiGon)
=
4.96
V
Step
No.
15
PHASE-‐2

Again,
insert
the
screwdriver
in
the
rotary
slot
of
the
preset
and

rotate
the
preset
to
its
extreme
le].
Measure
the
voltage
at
this

posi:on
using
a
mul:meter.
Step
No.
16
PHASE-‐2

To
measure
the
voltage
at
terminal
2,
connect
the
red
and
black

probes
of
the
mul:meter
to
terminals
2
and
3,
of
the
preset,

respec:vely.
Voltage
at
Terminal
2
(extreme
leP)
=
9.05
V
Step
No.
17
PHASE-‐2

Again,
insert
the
screwdriver
in
the
rotary
slot
of
the
preset
and

rotate
the
preset
to
its
extreme
right.
Measure
the
voltage
at

terminal
2
of
the
preset
at
this
posi:on.
Step
No.
18
PHASE-‐2

Step
No.
19
PHASE-‐2

To
measure
the
voltage
at
terminal
2,
connect
the
red
and
black

probes
of
the
mul:meter
to
terminals
2
and
3,
of
the
preset,

respec:vely.
Voltage
at
Terminal
2
(extreme
right)
=
0
V

We
have
learned
that
using
a
voltage
divider
circuit,
we
can

provide
variable
voltage
values
at
terminal
2
ranging
from
0

to
9
V
(assuming
that
we
have
a
connected
a
single
baRery,

providing
9
V).
Result

Take
a
diode.
Connect
its
P-‐side
(black-‐side)
to
terminal
2
of
the

preset
and
N-‐side
(silver
stripe)
to
any
diﬀerent
column
of
the

breadboard.

Step
No.
20
PHASE-‐2

Take
a
1
kΩ
resistor.
Connect
its
one
leg
to
the
N-‐side
of
the
diode

and
its
other
leg
to
any
diﬀerent
column
of
the
breadboard.

Step
No.
21
PHASE-‐2

Connect
the
other
leg
of
the
resistor
to
ground.

Step
No.
22
PHASE-‐2

Congratula:ons!
We
have
completed
our
circuit.
Its
:me
for
some

readings.

Now
we
will
set
various
voltage
values
at
terminal
2
of
the
preset.
At

each
value,
we
will
measure
voltage
across
the
diode
and
the
current
in

the
circuit.
Next
Steps

Insert
the
screwdriver
in
the
rotary
slot
of
the
preset.
Stop
the

preset
at
a
posi:on
which
lies
just
before
the
extreme
right
.
We
will

now
measure
the
voltage
that
we
have
set
using
a
mul:meter.
Step
No.
23
PHASE-‐2

Rotate
the
mul:meter
dial
to
20
V
of
the
DC
Voltage
region
(V

).

Note:
To
measure
DC
voltages,
we
rotate
the
dial
to
V

region.
To
measure

AC
voltages,
we
rotate
the
dial
to
V
~
region.

Step
No.
24
PHASE-‐2

Step
No.
25
PHASE-‐2

To
measure
voltage
at
terminal
2,
connect
the
red
and
black
probes

of
the
mul:meter
to
terminals
2
and
3,
of
the
preset,
respec:vely.

Voltage
at
Terminal
2
=
0.5
V;
let
us
call
it
V01.

Let
us
measure
the
voltage
across
the
diode.
To
do
this,
connect
the

red
and
black
probes
of
the
mul:meter
to
the
P-‐side
and
the
N-‐side

of
the
diode,
respec:vely.
Let
us
call
this
voltage
V1.
So,
V1
=
0.45
V.
Step
No.
26
PHASE-‐2

Now
let
us
measure
the
current
in
the
circuit.
To
do
this,
we
will

insert
the
mul:meter
(in
ammeter
mode)
in
series
with
the
circuit.
Step
No.
27
PHASE-‐2

Rotate
the
mul:meter
dial
to
20m
of
the
DC
Ampere
region
(A

).

Step
No.
28
PHASE-‐2

To
measure
the
current,
connect
the
red
and
black
probes
to
the
N-‐
side
and
the
le]
leg
of
the
resistor,
respec:vely.
Since
the

mul:meter
dial
is
on
20m
posi:on,
the
current
in
the
circuit,

I1
=
0.04
mA
=
0.00004
A
≅
0
A.
Step
No.
29
PHASE-‐2

Reconnect
the
N-‐side
of
the
diode
to
the
le]
leg
of
the
resistor.

Step
No.
30
PHASE-‐2

Insert
the
screwdriver
in
the
rotary
slot
of
the
preset.
Rotate
the

preset
slowly
in
an
an:-‐clockwise
direc:on
(towards
le])
and
stop

rota:ng,
a]er
giving
it
a
slight
rota:on.
Measure
the
output
voltage

at
terminal
2
of
the
preset
using
a
mul:meter.
Step
No.
31
PHASE-‐2

Rotate
the
mul:meter
dial
to
20
V
of
the
DC
Voltage
region
(V

).

Note:
To
measure
DC
voltages,
we
rotate
the
dial
to
V

region.
To
measure

AC
voltages,
we
rotate
the
dial
to
V
~
region.

Step
No.
32
PHASE-‐2

Step
No.
33
PHASE-‐2

To
measure
voltage
at
terminal
2,
connect
the
red
and
black
probes

of
the
mul:meter
to
terminals
2
and
3,
of
the
preset,
respec:vely.

Voltage
at
Terminal
2
=
1.01
V;
let
us
call
it
V02.

Step
No.
34
PHASE-‐2

Let
us
measure
the
voltage
across
the
diode.
To
do
this,
rotate
the

mul:meter
dial
to
20
V
DC
and
connect
the
red
and
black
probes
of

the
mul:meter
to
the
P-‐side
and
the
N-‐side
of
the
diode,

respec:vely.
Let
us
call
this
voltage
V2.
So,
V2
=
0.55
V.

Now
we
will
measure
the
current
in
the
circuit.
To
do
this,
make
a

gap
between
the
diode
and
the
resistor
as
shown
below.

Step
No.
35
PHASE-‐2

Rotate
the
mul:meter
dial
to
20m
of
the
DC
Ampere
region
(A

).

Step
No.
36
PHASE-‐2

Step
No.
37
PHASE-‐2

To
measure
the
current,
connect
the
red
and
black
probes
to
the
N-‐
side
and
the
le]
leg
of
the
resistor,
respec:vely.
Since
the

mul:meter
dial
is
on
20m
posi:on,
the
current
in
the
circuit,

I2
=
0.46
mA.


Reconnect
the
N-‐side
of
the
diode
to
the
le]
leg
of
the
resistor.

Step
No.
38
PHASE-‐2

Step
No.
39
PHASE-‐2

Insert
the
screwdriver
in
the
rotary
slot
of
the
preset.
Rotate
the

preset
slowly
in
an
an:-‐clockwise
direc:on
(towards
le])
and
stop

rota:ng,
a]er
giving
it
a
slight
rota:on.
Measure
the
output
voltage

at
terminal
2
of
the
preset
using
a
mul:meter.

Rotate
the
mul:meter
dial
to
20
V
of
the
DC
Voltage
region
(V

).

To
measure
the
voltage
at
terminal
2
of
the
preset,
connect
the
red

and
black
probes
to
terminals
2
and
3,
of
the
preset,
respec:vely.

Voltage
at
Terminal
2
=
3.01
V;
let
us
call
it
V03.
Step
No.
40
PHASE-‐2

Step
No.
41
PHASE-‐2

Let
us
measure
the
voltage
across
the
diode.
To
do
this,
rotate
the

mul:meter
dial
to
20
V
DC
and
connect
the
red
and
black
probes
of

the
mul:meter
to
the
P-‐side
and
the
N-‐side
of
the
diode,

respec:vely.
Let
us
call
this
voltage
V2.
So,
V3
=
0.63
V.

Step
No.
42
PHASE-‐2

Now
we
will
measure
the
current
in
the
circuit.
To
do
this,
make
a

gap
between
the
diode
and
the
resistor
as
shown
below.


Rotate
the
mul:meter
dial
to
20m
of
the
DC
Ampere
region
(A

).

Step
No.
43
PHASE-‐2

Step
No.
44
PHASE-‐2

To
measure
the
current,
connect
the
red
and
black
probes
to
the
N-‐
side
and
the
le]
leg
of
the
resistor,
respec:vely.
Since
the

mul:meter
dial
is
on
20m
posi:on,
the
current
in
the
circuit,

I3
=
2.4
mA.


Reconnect
the
N-‐side
of
the
diode
to
the
le]
leg
of
the
resistor.

Step
No.
45
PHASE-‐2

Step
No.
46
PHASE-‐2

Insert
the
screwdriver
in
the
rotary
slot
of
the
preset.
Rotate
the

preset
slowly
in
an
an:-‐clockwise
direc:on
(towards
le])
and
stop

rota:ng,
a]er
giving
it
a
slight
rota:on.
Measure
the
output
voltage

at
terminal
2
of
the
preset
using
a
mul:meter.

Step
No.
47
PHASE-‐2

Rotate
the
mul:meter
dial
to
20
V
of
the
DC
Voltage
region
(V

).

To
measure
the
voltage
at
terminal
2
of
the
preset,
connect
the
red

and
black
probes
to
terminals
2
and
3,
of
the
preset,
respec:vely.

Voltage
at
Terminal
2
=
6.04
V;
let
us
call
it
V04.

Step
No.
48
PHASE-‐2

Let
us
measure
the
voltage
across
the
diode.
To
do
this,
rotate
the

mul:meter
dial
to
20
V
DC
and
connect
the
red
and
black
probes
of

the
mul:meter
to
the
P-‐side
and
the
N-‐side
of
the
diode,

respec:vely.
Let
us
call
this
voltage
V2.
So,
V4
=
0.67
V.

Step
No.
49
PHASE-‐2

Now
we
will
measure
the
current
in
the
circuit.
To
do
this,
make
a

gap
between
the
diode
and
the
resistor
as
shown
below.


Rotate
the
mul:meter
dial
to
20m
of
the
DC
Ampere
region
(A

).

Step
No.
50
PHASE-‐2

Step
No.
51
PHASE-‐2

To
measure
the
current,
connect
the
red
and
black
probes
to
the
N-‐
side
and
the
le]
leg
of
the
resistor,
respec:vely.
Since
the

mul:meter
dial
is
on
20m
posi:on,
the
current
in
the
circuit,

I4
=
5.59
mA.


Reconnect
the
N-‐side
of
the
diode
to
the
le]
leg
of
the
resistor.

Step
No.
52
PHASE-‐2

Insert
the
screwdriver
in
the
rotary
slot
of
the
preset.
Rotate
the

preset
towards
the
extreme
le]
(in
an:clockwise
direc:on).
Step
No.
53
PHASE-‐2

Step
No.
54
PHASE-‐2

Rotate
the
mul:meter
dial
to
20
V
of
the
DC
Voltage
region
(V

).

To
measure
the
voltage
at
terminal
2
of
the
preset,
connect
the
red

and
black
probes
to
terminals
2
and
3,
of
the
preset,
respec:vely.

Voltage
at
Terminal
2
=
8.82
V;
let
us
call
it
V05.

Step
No.
55
PHASE-‐2

Let
us
measure
the
voltage
across
the
diode.
To
do
this,
rotate
the

mul:meter
dial
to
20
V
DC
and
connect
the
red
and
black
probes
of

the
mul:meter
to
the
P-‐side
and
the
N-‐side
of
the
diode,

respec:vely.
Let
us
call
this
voltage
V2.
So,
V5
=
0.69
V.

Step
No.
56
PHASE-‐2

Now
we
will
measure
the
current
in
the
circuit.
To
do
this,
make
a

gap
between
the
diode
and
the
resistor
as
shown
below.


Rotate
the
mul:meter
dial
to
20m
of
the
DC
Ampere
region
(A

).

Step
No.
57
PHASE-‐2

Step
No.
58
PHASE-‐2

To
measure
the
current,
connect
the
red
and
black
probes
to
the
N-‐
side
and
the
le]
leg
of
the
resistor,
respec:vely.
Since
the

mul:meter
dial
is
on
20m
posi:on,
the
current
in
the
circuit,

I5
=
8.14
mA.


Reconnect
the
N-‐side
of
the
diode
to
the
le]
leg
of
the
resistor.

Step
No.
59
PHASE-‐2

V1
=
0.45
V

I1
=
0.04
mA
V2
=
0.55
V

I2
=
0.46
mA
V3
=
0.63
V

I3
=
2.40
mA
V4
=
0.67
V

I4
=
5.59
mA
V5
=
0.69
V

I5
=
8.14
mA
Plot
these
readings
on
the
graph
paper.
Take
V
on
the
X-‐axis

and
I
on
the
Y-‐axis.
See
next
slide.
ObservaGon
PHASE-‐2

V-‐I

CharacterisGcs

of
a
Diode

We
can
represent
the
working
of
diodes
using
a
voltage-‐
current
characterisGc
curve.
The
curve
explains
how
a
diode

behaves
when
diﬀerent
voltages
are
applied
across
it.
We

know
that
an
ordinary
diode
is
a
p-‐n
junc:on,
which
when

forward
biased
allows
the
current
to
pass
through
it
and

when
reverse
biased
stops
the
ﬂow
of
current.

Result

Consider
the
posi:ve
voltage
region.
Let
us
analyse
the
curve

in
this
region:
a)
The
current
remains
zero
un:l
the
voltage
reaches
0.5
V

(reading
2).
We
know
that
a
diode
needs
a
minimum
voltage

to
get
forward-‐biased.
Un:l
then,
the
diode
resists
the
ﬂow

of
current.
Hence,
the
current
is
zero.
b)
The
diode
starts
conduc:ng
at
0.5
V.
It
gets
forward

biased
at
0.6-‐0.7
V,
and
then
the
voltage
across
its
terminals

becomes
constant
Analysis
from
the
Curve

c)
On
further
increase
in
voltage,
the
current
increases

exponen:ally
through
the
diode.
We
can
see
this
by

observing
the
‘exponenGal
behavior
of
the
curve’.
This
is
the

forward
current,
measured
in
milliampere
(mA).
The
current
through
the
diode
in
nega:ve
voltage
region
is

zero
because
the
diode
gets
reverse-‐biased
and
it
does
not

conduct.
We
have
seen
it
when
the
diode
was
connected
in

reverse
direc:on
in
phase-‐1
experiment.
Analysis
from
the
Curve

• Ensure
that
the
baRery
voltage
is
more
than
6
volt.
• Ensure
that
the
wires
of
the
baRery
connector
are

properly
inserted
into
the
breadboard.
The
red
wire

should
be
inserted
into
the
ﬁrst
row,
and
the
black
wire

into
the
second
row
of
the
breadboard.
• Ensure
that
the
pins
of
the
preset
are
properly
inserted

into
the
holes
of
the
breadboard,
and
are
not
popped
out

or
twisted.
• Press
the
preset
a]er
connec:ng
it
on
the
breadboard
so

that
its
pins
go
completely
inside
the
breadboard.
• Ensure
that
the
stripped
ends
of
the
connec:ng
wires

should
be
long
enough
to
ﬁt
inside
the
holes
of
the

breadboard
completely.
TroubleshooGng
Tips

TroubleshooGng
Tips
• Ensure
that
you
have
iden:ﬁed
P
and
N
side
of
the
diode

correctly.
• Ensure
that
the
there
are
no
loose
connec:ons.

Result
PrecauGon
Notes
Circuit
Measure
AcGvity
Advantages
ModiﬁcaGon
Do
you
know?

Project Sample: To Learn How a Diode Works

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Project Sample: To Learn How a Diode Works