Electronic Devices & Semiconductors:

Diodes

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Semiconductor Devices: Diodes

Diodes

●A semiconductor device
●A single pn junction and metal connections
●Passes current in only one direction.
Energy

p n Conduction
band

Depletion Valence
region
band

0
p region n region
Depletion
region

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Diodes: Forward Bias

Semiconductor Devices: Diodes

Forward bias is the condition which allows current in

the diode. The bias voltage must be greater than the
barrier potential.
IF (mA)

VF
+ –
C
IF
–
R
+ VBIAS
+ – B Knee
A VF
0
0 0.7 V

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 Revise Bias
Semiconductor Devices: Diodes

Reverse bias is the condition in which current is

blocked.
VBR 0
VR 0
VBIAS Knee
– +

I=0A
R
VBIAS
– +
IR

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Approximating Diode Function

Semiconductor Devices: Diodes

Three diode approximations are:

IF IF IF

VR V F VR VF VR VF
0.7 V 0.7 V

IR IR IR

Ideal Practical Complete

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Approximating Diode Function

Semiconductor Devices: Diodes

Three diode approximations are:

IF IF IF

VR V F VR VF VR VF
0.7 V 0.7 V

IR IR IR

Ideal Practical Complete

In addition, the complete model includes the effect of a large

reverse resistance that accounts for a tiny current when reverse-
biased.
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 Example
Semiconductor Devices: Diodes

Use the practical model to determine the current in the

circuit:
R

+
3.3 k W
VBIAS 12 V
–

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Example
Semiconductor Devices: Diodes

Use the practical model to determine the current in the

circuit:
R

+
3.3 k W
VBIAS 12 V
–

VR VBIAS  0.7 V 12 V  0.7 V 11.3 V

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Example
Semiconductor Devices: Diodes

Use the practical model to determine the current in the

circuit:
R

+
3.3 k W
VBIAS 12 V
–

VR VBIAS  0.7 V 12 V  0.7 V 11.3 V

V 11.3 V
I R  
R 3.3 k

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 Example
Semiconductor Devices: Diodes

Use the practical model to determine the current in the

circuit:
R

+
3.3 k W
VBIAS 12 V
–

VR VBIAS  0.7 V 12 V  0.7 V 11.3 V

V 11.3 V
I R   3.4 mA
R 3.3 k

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Diode Packages
Semiconductor Devices: Diodes

Some common configurations are

K
K A K
A
A K
A K
A
K

K
A

K A
K K

A A
K
K
A

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Summary
Semiconductor Devices: Diodes

●
Semiconductors can be used to make
specific circuit functions;
●
Diodes are one of the simplest;
●
Consist of a single pn-junction;
●
Allow current to pass in one direction;
●
Small voltage drop across PN junction.

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