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Unijunction Transistor

      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.

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     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.

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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:

PART NO.

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

h

Intrinsic Standoff Ratio @VBB=10V

Iv

Valley Current Min. (mA)

Ip

Peak Point Emitter Current     Max. (ľA)

VOB1

Base One Peak Pulse Voltage  Min. (V)

Package Style

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

T0-5

  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

TO-18

  2N2647   4.7 - 9.1   .68 - .82        8        2         6

Programmable Unijunction Transistors (PUT) supplied by American Microsemiconductor

  PART NO

Gate to Anode Reverse Voltage Max. (V)

DC Anode Current Max. (mA)

IGAO

Leakage Current @40V Max. (nA)

IV

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

Vo

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,

P. O. Box 104, 133 Kings Road, Madison, New Jersey 07940, Phone: (973) 377-9566, Fax: (973) 377-3078
Questions, Comments, Suggestions - Email To: info@americanmicrosemi.com