_________________________________________________________________ Semiconductor Diodes
Table 1-1. Major Electrical Characteristics for Rectifier and Signal Diodes
(continued)
SIGNAL DIODES
PEAK REVERSE VOLTAGE [PRV] - the maximum reverse voltage that
ƒ
can be applied before reaching the breakdown point. PRV also applies to
the rectifier diode.
REVERSE CURRENT [IR] - the small value of DC that flows when a
ƒ
semiconductor diode has reverse bias.
MAXIMUM FORWARD VOLTAGE DROP AT INDICATED FORWARD
ƒ
at the indicated forward current.
REVERSE RECOVERY TIME (TRR) - the maximum time taken for the
ƒ
forward bias diode to recover its reverse bias.
1-94. The ratings of a diode (as stated earlier) are the limiting values of operating
conditions which if exceeded could cause damage to a diode by either voltage breakdown
or overheating. The PN junction diodes are generally rated for MAXIMUM AVERAGE
FORWARD CURRENT, PEAK RECURRENT FORWARD CURRENT, MAXIMUM
SURGE CURRENT, and PEAK REVERSE VOLTAGE.
Maximum average forward current is usually given at a specified temperature,
usually 25 C (77 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 which 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 non-recurring pulses. Current should not equal
this value for more than a few milliseconds.
Peak reverse voltage 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. For example, if
the operating temperature is above that stated for the ratings, then the ratings must be
decreased.
DIODE IDENTIFICATION
1-95. Many types of diodes vary in size. Diodes can be the size of a pinhead (used in
subminiature circuitry) to large 250-ampere diodes (used in high power circuits). Since
there are so many different types of diodes, then some system of ID is needed to
distinguish one diode from another. This is accomplished with the semiconductor
identification system (see Figure 1-25). This system is not only used for diodes but also for
transistors and many other special semiconductor devices. The identification system uses
numbers and letters to establish a code in order to identify different types of semiconductor
devices. The first number in the code indicates the number of junctions in the
semiconductor device and is a number, one less than the number of active elements.
23 June 2005
TC 9-62
1-29
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