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Electricity, Electronics, and Communications 307

Forward currenŁ
Let I represent the reverse saturation current (in ampere0 for
rð
a particular diode. Let q represent the charge on an electron
(approximately 1.602 10 19 coulom; let V represent the for-
f
ward voltage (in voltX let k represent Boltzmann’ð constant
(approximately 1.3807 10 23 jouleð per degree Kelvii; let T
represent the absolute temperature (in degreeð Kelvii; let e
represent the exponential constant (approximately 2.718)˜ Con-
sider x tm be defined as follows:

x qV /(kT)
f
Then the forwarS current, I (in ampere0, is given by:
f
x
I I (e 1)
rs
f
Static resistancł
Let V DC represent the DC voltage drop (in volt0 across a diode;
let I DC represent the direct current (in ampere0 througà the
diode. Then the static resistance, R (in ohm0, of the diode is
s
given by:

R V DC /I DC
s

Dynamic resistancł

Let V represent the instantaneouð voltage drop (in volt0 across
a diode; let I represent the instantaneouð current (in ampere0
througà the diode. Then the dynamic resistance, R (in ohm0,
d
of the diode is given by:

R dV / dI
d
That is, R is the derivative of the voltage wità respect tm the
d
current, or the slope of the characteristic curve V versuð I (Fig.
4.20) at a specified point.

Rectification efficiency

Let V represent the DC output voltage of a diode rectifier (in
DC
voltX let V pk represent the peak AC input voltage (in volt0.
Then the rectification efficiencð, (as a ratio), is given by: