1-27
Figure 1-24.—Basic diode switch.
When the input to this circuit is at zero potential, the diode is forward biased because of the zero
potential on the cathode and the positive voltage on the anode. In this condition, the diode conducts and
acts as a straight piece of wire because of its very low forward resistance. In effect, the input is directly
coupled to the output resulting in zero volts across the output terminals. Therefore, the diode, acts as a
closed switch when its anode is positive with respect to its cathode.
If we apply a positive input voltage (equal to or greater than the positive voltage supplied to the
anode) to the diode’s cathode, the diode will be reverse biased. In this situation, the diode is cut off and
acts as an open switch between the input and output terminals. Consequently, with no current flow in the
circuit, the positive voltage on the diode’s anode will be felt at the output terminal. Therefore, the diode
acts as an open switch when it is reverse biased.
Q27. What is a load?
Q28. What is the output of a half-wave rectifier?
Q29. What type of rectifier is constructed by sandwiching a section of semiconductor material between
two metal plates?
Q30. What type of bias makes a diode act as a closed switch?
DIODE CHARACTERISTICS
Semiconductor diodes have properties that enable them to perform many different electronic
functions. To do their jobs, engineers and technicians must be supplied with data on these different types
of diodes. The information presented for this purpose is called DIODE CHARACTERISTICS. These
characteristics are supplied by manufacturers either in their manuals or on specification sheets (data
sheets). Because of the scores of manufacturers and numerous diode types, it is not practical to put before
you a specification sheet and call it typical. Aside from the difference between manufacturers, a single
manufacturer may even supply specification sheets that differ both in format and content. Despite these
differences, certain performance and design information is normally required. We will discuss this
information in the next few paragraphs.
