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Starting electronics
The exponential factor (e 40V ), of course confirms what we already
knew to be true — that the diode characteristic curve
is an exponential curve. From this characteristic equation
we may calculate the current flowing through a diode for any
given voltage across it, just as the formulae associated with
Ohm’s law do the same for resistors.
Hint:
But even with this simplified approximation of the characteristic
equation you can appreciate the value of having a characteristic curve
in front of you to look at. If I had the option between having to use
the equation or a diode characteristic curve to calculate the current
through a diode, I know which I’d choose!
Load lines
It’s important to remember that although a diode characteristic
curve is non-linear and non-ohmic, so that it doesn’t
abide by Ohm’s law throughout its entire length, it does follow
Ohm’s law at any particular point on the curve. So, say, if the
voltage across the diode whose characteristic curve is shown
in Figure 7.1 is 0V8, so the current through it is about 80 mA
(check it yourself) then the diode resistance is:
as defined by Ohm’s law. Any change in voltage and current,
however, results in a different resistance.
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