MTRX N410 – I-V Curves for PN Junctions. Richard Summerfield Programme Chair – Engineering Ras Al Khaimah Men’s College. MTRX N410 – I-V Curves for PN Junctions. A diode is an electronic device made from p and n type semiconductor material.
Programme Chair – Engineering
Ras Al Khaimah Men’s College
A diode is an electronic device made from p and n type semiconductor material.
The anode is connected to the p type and the cathode to the n type.
The Diode only allows a current to flow through it one direction:
- From Anode to Cathode
This is known as Forward Bias
When a diode is Forward biased, it’s anode is connected to a more positive voltage than the cathode.
When a diode is reverse biased, its cathode is connected to a more positive voltage and it will not conduct.
An Ideal Diode
An ideal diode would act like a conductor when it is forward biased and an insulator when reverse biased.
A typical diode has a different I-V curve.
It does not conduct until a ‘threshold’ junction voltage is released.
A small current will ‘leak’ through in reverse bias.
If the reverse voltage is large enough, it will break down.
The diode will not conduct until the pn junction depletion layer has been overcome.
0.7 volts for Silicon
0.3 volts for Germanium
A small current will leak in reverse bias as some electrons will manage to cross the depletion layer due to the effects of thermal energy.
If a sufficiently large reverse voltage is applied the diode will breakdown.
The breakdown voltage will depend on the diode type.
Typical I-V Curve for a Diode
Note how the scales on the Forward and Reverse Bias areas of the graph are different.
The scales used ‘exaggerate’ the curve to show the differences from an ideal diode.