Construction - unijunction transistor, Electrical Engineering

Construction - UniJunction Transistor:

Construction: The basic structure of uni junction transistor is shown in fig. (a). It essentially consists of a lightly doped N type silicon bar with a small piece of heavily doped P type material alloyed to its one side to produce single P N junction, the single P L junction accounts for the terminology uni junction. The silicon bar, at its ends, has two ohmic contacts designated as base 1 (B1) and base 2 (B2), as shown and the P V; region is termed the emitter (E). The emitter junction is usually located closer to base 2 (B2) than base 1 (B1) so that the device is not symmetrical, because symmetrical units does not provide optimum electrical characteristics for most of the applications. The symbol for uni junction transistor is shown in fig. (b). the emitter leg is drawn at an angle to the vertical line representing the n type material slab and the arrowhead points in the direction of conventional current when the device is forward biased, active or in the conduction state. The basic arrangement for the UJT is shown in fig. (c). The worth noting points about UJT are given below :

1.  The device has only one junction, so it is called the uni junction device.

2.  The device, because of one P N junction, is quite similar to a diode but it differs from an ordinary diode that it has three terminals.

3.  The structure of UJT is quite similar to that of an N channel JFET. The main difference is that P type material surrounds the N type material in case of JFET and the gate surface of the JFET is much larger than emitter junction of UJT.

4. In a uni junction transistor the emitter is heavily doped while the N region is lightly doped, so the resistance between the base terminals is relatively high typically 4 to 10 k when the emitter is open.

5. The N type silicon bar has a high resistance and the resistance between emitter and base 1 is larger than that between emitter and base 2. It is because emitter is closer to base 2 than base 1.

6. UJT is operated with emitter junction forward biased while the JFET is normally operated with the gate junction reverse biased.

7. UJT does not have ability to amplify but it has the ability to control a large ac power with a small signal.

8. It exhibits a negative resistance characteristic and so it can be employed as an oscillator.

Posted Date: 2/8/2013 2:53:52 AM | Location : United States

Related Discussions:- Construction - unijunction transistor, Assignment Help, Ask Question on Construction - unijunction transistor, Get Answer, Expert's Help, Construction - unijunction transistor Discussions

Write discussion on Construction - unijunction transistor
Your posts are moderated
Related Questions
What are the blocks of the microprocessor depends system? The blocks of the microprocessor depends system are: The Memory and I/O System The Data Operating System

Let me know if you can help during the test

Explain Acceptance cone? The fibre air - core interface is display below: In this figure Omax is the maximum angle, inside that the rays undergo total internal reflecti

Figure 1(a) shows a simple one-stage MOSFET amplifier. The input-output relationship is graphed in Figure 1(b), where the solid curve indicates operation in the saturated region an

Hexadecimal Number System Similar  to octal number hexadecimal number system is also used to represent long  binary  numbers in  smaller  form. In microprocessor  we use  hexad

Q. Show Capital asset pricing model? This model was developed by the William F Sharpe ( 1990 Nobel prize winner in the economy ) and john linter in 1960. The model attempt to c

Consider an S band (3 GHz) radar with a rotating aperture antenna with a width of 3 m.  Suppose the antenna rotates at a rate of one rotation every 10 seconds.  Assume the 3 dB bea

Series-Parallel Magnetic Circuit: Figure shows an electromagnet made of cast steel contain a coil of 500 turns wound on the central limb. The cross-sectional area of the outer

define the physical significance of damping coefficient

what is the future scope of matlab in india?