Figure 3-42. UJT Voltage Gradient
Figure 3-43. Forward Bias Point on UJT Voltage Gradient
3-70. If the voltage level on the emitter is less positive than the voltage gradient opposite
the emitter, the UJT is then reverse biased. No current will flow from base 1 to the emitter.
However, a small current, called reverse current, will flow from the emitter to base 2. The
reverse current is caused by the impurities used in the construction of the UJT and is in the
form of minority carriers.
3-71. More than forty distinct types of UJTs are presently in use. One of the most
common applications is in switching circuits. They are also used extensively in oscillators
and wave shaping circuits.
3-72. Although it has brought about a revolution in the design of electronic equipment,
the bipolar (PNP/NPN) transistor still has one very undesirable characteristic. The low
input impedance associated with its base-emitter junction causes problems in matching
3-73. For years, scientists searched for a solution that would combine the high input
impedance of the vacuum tube with the many other advantages of the transistor. The result
of this research is the FIELD-EFFECT TRANSISTOR. In contrast to the bipolar transistor,
which uses bias current between base and emitter to control conductivity, the FET uses
23 June 2005