V-I Characteristics of Diode

V-I Characteristics of Diode

In ideal conditions, diodes will block any current flowing the reverse direction It simply acts like a short-circuit if current flow is forward. But actual diode behavior isn’t ideal. Diodes consume some amount of power when conducting forward current, and they won’t block out all reverse current. Real-world diodes work differently from an ideal diode and are a bit more complicated.

The important diode characteristic is its current-voltage (i-v) relationship. This defines what the current running through a component is, given what voltage is measured across it.

The current-voltage relationship of a diode.

A Diode will operate in one of three regions, Depending on the voltage applied across it,

1. Forward bias: When the voltage across the diode is positive the diode is in “on” condition and start conducting and current can run through. The voltage should be greater than the forward voltage (V_F) depend upon material from which it is constructed in order for the current to be anything significant.
2. Reverse bias: This is the “off” mode of the diode, where the voltage is less than V_F but greater than -V_BR. In this mode, diode does not conduct because of opposite polarity applied current flow is (mostly) blocked, and the diode is off. A very small amount of current (in order of nA) which is reverse saturation current – is able to flow in reverse direction through the diode.
3. Breakdown: When the voltage applied across the diode is very large and negative, lots of current will be able to flow in the reverse direction, from cathode to anode. This is called breakdown condition and diode may damage.

Forward Voltage

In order to make diode “turn on” and conduct current in the forward direction, a diode requires a certain amount of positive voltage to be applied across it. This voltage required to turn the diode on is called the forward voltage (V_F). Or cut-in voltage or on-voltage.

We can conclude from i-v curve, the current through and a voltage across a diode are interdependent. More current means more voltage, less voltage means less current. Once the voltage gets to about the forward voltage rating, though, large increases in current should still only mean a very small increase in voltage. If a diode is fully conducting, it can usually be assumed that the voltage across it is the forward voltage rating. V_F depends on which semiconductor material it’s made out of. Generally, a silicon is used to make diode and silicon diode will have a V_F   around 0.6-1V. A germanium-based diode may be, around 0.3V...

Breakdown Voltage

If a very large negative voltage is applied to the diode, it starts conducting allow current to flow in the reverse direction also. This large negative voltage is called the breakdown voltage. Some diodes are actually designed to operate in the breakdown region, but for most normal diodes it’s risky for them to be subjected to large negative voltages. Value of breakdown voltage for normal diodes is around -50V to -100V.