DIODE CIRCUITS LABORATORY
A solid state diode consists of a junction of either dissimilar semiconductors (
or a metal and a semiconductor (Schottky barrier diode).
Regardless of the type, the circuit
symbol for a diode is as shown in Fig. 8.1a, and the corresponding device in Fig 8.1b
is positive, the diode is
Then, the diode can conduct a significant
is a small voltage of typically 0.7 V for the most common diode
is negative, the diode is
This negative current is so small
that it is often considered to be zero.
Thus, the usual function of a diode is to allow current to
flow in the direction of the arrow (the forward direction) for positive
s, but not allow any
current to flow in the reverse direction for negative
Only a small forward bias (positive
) is required to cause a diode to conduct a
, and the less this voltage, the better.
Ideally, this voltage would be zero
Also, ideally, a diode can conduct any value of current
in the forward direction, with this
value being determined not by the diode, but by other components in the circuit in which the
diode is connected.
Also, ideally, a diode conducts zero amperes for a negative
, regardless of
the voltage magnitude.
Put another way, an
for a voltage
that tends to be positive
(but it cannot be more than 0 V).
Also, an ideal diode is an
for a negative V.
an ideal diode acts like a switch that is closed for current flow in the direction of the arrow in the
diode circuit symbol, and open otherwise.
Essentially, it is an electronically operated switch.
This ideal approximation is satisfactory for analyzing many circuits that contain diodes, provided
that the voltage levels are much greater than 0.7 V.
Fig. 8.2 shows the
characteristic for an