Download Diode characteristics

Diode characteristics
PN Junction Diode
• The resulting device which get after
junction formation is called a Diode.
The symbolic representation
Anode
Cathode
• The region connected to the P-region of the
diode is called “Anode”.
• The region connected to the N-region is
called “Cathode”.
• The diode can conduct current only in one
direction.
• The diode can be biased in two ways:1- Forward Biasing
2- Reverse Biasing
1- Forward biasing
• The positive terminal of battery is connected
to the anode and the negative terminal of
battery is connected to the cathode.
• The applied external voltage cancel the
potential barrier, permitting current flow
through the junction.
• This current is called forward current, it is in
the range of milli amperes.
2- Reverse biasing
• When the positive terminal of the battery is
connected to the cathode and the negative
terminal to the anode, the resulting bias is
known as the reverse bias.
• The applied voltage increases the potential
barrier, preventing the flow of charge carriers
across the junction.
• Small current flows due to the movement of
minority carriers. This is known as reverse
current. It is in the range of micro amperes.
VI characteristic of PN junction Diode
• The VI characteristic of PN junction Diode is
the curve drown between voltage across the
junction in the x-axis and the diode current in
the y-axis.
• The characteristic is obtained under two
conditions:1- forward bias condition
2- Reverse bias condition
1- Forward bias condition
In this case the diode is connected in forward bias. The
ammeter is connected in series to measure the current and
the voltmeter is Connected in parallel to the diode to
measure the voltage across the diode
- If the forward bias is increased from zero V f  Vo
V f  Vo
the forward current If is zero until
because the potential barrier prevents the
holes and electrons to flow across the
depletion region in the opposite direction.
- For V f  Vo the potential barrier at the
junction completely disappear, the holes cross
the junction from P- type to N-type and the
electrons cross the junction in the opposite
direction
Forward characteristic
• The voltage at which the potential barrier is
over come by the forward voltage is called
( cut in or threshold voltage).
2- Reverse bias condition
In this case the diode is connected in reverse bias. The
ammeter is connected in series and the voltmeter is
Connected in parallel
• As the reverse voltage is increased above zero
in suitable steps, the depletion region gets
enlarged due to reverse bias condition.
• The is very small due to minority carriers. It
is in the range of micro amperes.
• As the reverse bias further increase, break
down of covalent bonds occur due to the
phenomenon of a avalanche break down and
the current increase rapidly.
Reverse characteristic