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

• 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.

1- Forward 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.

2- Reverse biasing

• 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

VI characteristic of PN junction Diode

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

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 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

of VV

of VV

of VV

• The voltage at which the potential barrier is over come by the forward voltage is called

( cut in or threshold voltage).

Forward characteristic

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