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Starting electronics
Reverse bias
From the curve you can see that there are two distinct parts
which occur when a diode is reverse biased. First, at quite
low reverse voltages, from about –0.V1 to the breakdown
voltage there is a more or less constant but small reverse
current. The actual value of this reverse current (known as
the saturation reverse current, or just the saturation current)
depends on the individual diode, but is generally in the order
of microamps.
The second distinct part of the reverse biased characteristic
occurs when the reverse voltage is above the breakdown
voltage. The reverse current increases sharply with only
comparatively small increases in reverse voltage. The reason
for this is because of electronics breakdown of the diode
when electrons gain so much energy due to the voltage that
they push into one another just like rocks and boulders rolling
down a steep mountainside push into other rocks and
boulders which, in turn, start to roll down the mountainside
pushing into more rocks and boulders, forming an avalanche.
This analogy turns out to be an apt one, and in fact the
electronic diode breakdown voltage is sometimes referred
to as avalanche breakdown and the breakdown voltage is
sometimes called the avalanche voltage. Similarly the sharp
knee in the curve at the breakdown voltage is often called
the avalanche point.
In most ordinary diodes the breakdown voltage is quite high
(in the 1N4001 it is well over –50 V), so this is one reason why
you couldn’t plot the whole characteristic curve, including
reverse biased conditions, in the same experiment — our
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