Editing Unijunction transistor (section)

==Types==
[[File:UJT caratteristica.png|thumb|Graph of UJT characteristic curve, emitter-base1 voltage as a function of emitter current, showing current-controlled negative resistance (downward-sloping region)]]
There are three types of unijunction transistor:
# The original unijunction transistor, or UJT, is a simple device that is essentially a bar of [[n-type semiconductor]] material into which p-type material has been diffused somewhere along its length, fixing the device parameter <math>\eta</math> (the "intrinsic stand-off ratio"). The 2N2646 model is the most commonly used version of the UJT.
# The complementary unijunction transistor, or CUJT, is a bar of [[p-type semiconductor]] material into which n-type material has been diffused somewhere along its length, defining the device parameter <math>\eta</math>. The 2N6114 model is one version of the CUJT.
# The programmable unijunction transistor, or PUT, is a multi-junction device that, with two external resistors, displays similar characteristics to the UJT. It is a close cousin to the [[thyristor]] and like the thyristor consists of four p-n layers. It has an [[anode]] and a [[cathode]] connected to the first and the last layer respectively, and a [[gate]] connected to one of the inner layers. PUTs are not directly interchangeable with conventional UJTs but perform a similar function. In a proper circuit configuration with two "programming" resistors for setting the parameter <math>\eta</math>, they behave like a conventional UJT. The 2N6027, 2N6028<ref>2N6027, 2N6028 data sheet by ON Semiconductor, at [http://www.farnell.com/datasheets/112532.pdf farnell.com]</ref> and BRY39 models are examples of such devices.