Maximum average forward current is usually given at a special temperature, usually 25º C, (77º F)
and refers to the maximum amount of average current that can be permitted to flow in the forward
direction. If this rating is exceeded, structure breakdown can occur.
Peak recurrent forward current is the maximum peak current that can be permitted to flow in the
forward direction in the form of recurring pulses.
Maximum surge current is the maximum current permitted to flow in the forward direction in the
form of nonrecurring pulses. Current should not equal this value for more than a few milliseconds.
Peak reverse voltage (PRV) is one of the most important ratings. PRV indicates the maximum
reverse-bias voltage that may be applied to a diode without causing junction breakdown.
All of the above ratings are subject to change with temperature variations. If, for example, the
operating temperature is above that stated for the ratings, the ratings must be decreased.
Q31. What is used to show how diode parameters vary over a full operating range?
Q32. What is meant by diode ratings?
There are many types of diodes varying in size from the size of a pinhead (used in subminiature
circuitry) to large 250-ampere diodes (used in high-power circuits). Because there are so many different
types of diodes, some system of identification is needed to distinguish one diode from another. This is
accomplished with the semiconductor identification system shown in figure 1-25. This system is not only
used for diodes but transistors and many other special semiconductor devices as well. As illustrated in this
figure, the system uses numbers and letters to identify different types of semiconductor devices. The first
number in the system indicates the number of junctions in the semiconductor device and is a number, one
less than the number of active elements. Thus 1 designates a diode; 2 designates a transistor (which may
be considered as made up of two diodes); and 3 designates a tetrode (a four-element transistor). The letter
"N" following the first number indicates a semiconductor. The 2- or 3-digit number following the letter
"N" is a serialized identification number. If needed, this number may contain a suffix letter after the last
digit. For example, the suffix letter "M" may be used to describe matching pairs of separate
semiconductor devices or the letter "R" may be used to indicate reverse polarity. Other letters are used to
indicate modified versions of the device which can be substituted for the basic numbered unit. For
example, a semiconductor diode designated as type 1N345A signifies a two-element diode (1) of
semiconductor material (N) that is an improved version (A) of type 345.