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AMS Semiconductor Tutorials

Tutorials Graphic We provide tutorials to help our customers better understand semiconductors and other electronic devices. Whether you have a question regarding a particular component, or simply want to know more about semiconductors, browse through our tutorial section for help. If you are still stuck, give us a call at (973) 377-9566 and we'll be happy to recommend a device for your application.

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Unijunction Transistor Tutorial

      The unijunction transistor(UJT) is a three terminal device with characteristics very different from the conventional 2 junction, bipolar transistor. It is a pulse generator with the trigger or control signal applied at the emitter . This trigger voltage is a fraction (n) of interbase voltage, Vbb.The UJT circuit symbol, junction schematic, and characteristic curve are shown below.

10A.jpg (16028 bytes)

     The emitter terminal does not inject current into the base region until its voltage reaches Vp. Once Vp is reached the base circuit conducts and a postive pulse appears at the B1 terminal and a negative pulse at B2. The UJT incorporates a negative resistance region, a low emitter current, and a high output pulse current at terminals B1 and B2, making it an ideal pulse trigger. A simple RC timer circuit using a UJT is shown below.

10B.jpg (14636 bytes)

The very basic specifications of a UJT are:

(a) Vbb(max) - The maximum interbase voltage that can be applied to the UJT
(b) Rbb-the interbase resistance of the UJT
(c) n - The intrinsic standoff ratio which defines Vp.
(d) Ip - The peakpoint emitter current

Here are a few of our most requested UJT's:


RBBO Interbase Resistance @VBB=3V  IE=0(KOhms)


Intrinsic Standoff 




Peak Point Emitter Current     Max. (µA)


Base One Peak Pulse Voltage  Min. (V)

Case Style

  2N489   4.7 - 6.8   .51 - .62        8        12         --


  2N490   6.2 - 9.1   .51 - .62        8        12         --
  2N491   4.7 - 6.8   .56 - .68        8        12         --
  2N1671   4.7 - 9.1   .47 - .62        8        25         --
  2N2160   4.0 - 12.0   .47 - .80        8        25         3
  2N2646   4.7 - 9.1   .56 - .75        4        5         3


  2N2647   4.7 - 9.1   .68 - .82        8        2         6
Programmable Unijunction Transistors (PUT) supplied by American Microsemiconductor

Gate to Anode Reverse Voltage Max. (V)

DC Anode Current Max. (mA)


Leakage Current @40V Max. (nA)


Valley Current         Min. @RG =10k  (µA)


Output Voltage Min.   (V)

2N6027 40 150 10 70 6
2N6028 40 150 10 25 6

American Microsemiconductor produces a very broad line of standard unijunction  transistors.
Many of the basic applications include:

oscillators, timers, sawtooth generators, SCR triggers, frequency dividers, stable voltage sensing,

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