AMS Semiconductor Tutorials
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.
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.
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.
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 |
Iv Min. |
Ip Peak Point Emitter Current Max. (µA) |
VOB1 Base One Peak Pulse Voltage Min. (V) |
Case 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 |
| 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 (µA) |
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,