Unijunction Transistor

June 16, 2024 Post a Comment

Unijunction transistor

The most common application of a unijunction transistor is as a triggering device for SCR's and Triacs but other UJT applications include sawtoothed generators, simple oscillators, phase control, and timing circuits. The simplest of all UJT circuits is the Relaxation Oscillator producing non-sinusoidal waveforms.

Why it is called unijunction transistor?

Near to base B2, a pn-junction is formed between a p-type emitter and the n-type silicon bar. The terminal of this junction is called emitter terminal (E). Since the device has three terminals and one pn-junction, for this region this is called as a Unijunction Transistor (UJT).

What are the types of unijunction transistor?

Commonly available unijunction transistors include the 2N1671, 2N2646, 2N2647, etc, with the 2N2646 being the most popular UJT for use in pulse and sawtooth generators and time delay circuits.

What are the elements of a unijunction transistor?

A unijunction transistor consists of two bases (B1, B2) attached to a resistive bar of silicon, and an emitter in the center. The E-B1 junction has negative resistance properties; it can switch between high and low resistance.

What are the advantages of UJT?

Advantages of Unijunction Transistor (UJT) low cost. negative resistance characteristics. Requires low value of triggering current. A stable triggering voltage.

What is UJT and its characteristics?

A Unijunction Transistor (UJT) is an electronic semiconductor device that has only one junction. It has three terminals an emitter (E) and two bases (B1 and B2). The base is formed by lightly doped n-type bar of silicon. Two ohmic contacts B1 and B2 are attached at its ends.

Is UJT unipolar or bipolar?

UJT is also called double-base diode, as it has two bases. BJT simply known as transistor. The conduction in UJT is based on the movement of majority charge carriers only. Thus, it is a unipolar device.

Why does UJT have 2 bases?

UJT consists of a lightly doped N-type silicon bar in which a P-type material is diffused thus producing PN junction. Due to the existence of a single PN junction, it is termed as a Unijunction device. It consists of two ohmic contacts at the end of the bar which is labelled as base 1 (B1) and base 2 (B2).

What is the measure of UJT?

UJT parameters The typical range of RBBO is from 4KΩ to 10KΩ. Intrinsic standoff ratio (η) : It is the ratio of RB1 to the sum of RB1 and RB2. It can be expressed as η = RB1/(RB1+RB2) or η = RB1/RBBO. The typical range of intrinsic standoff ratio is from 0.4 to 0.8.

What is difference between UJT and BJT?

UJT is only one junction is present in BJT, while in BJT consist of two junctions. It is two junction transistors. UJT is also known as double-base diode as contains two bases while in BJT contain three-terminal namely emitter, base, and collector.

What is peak voltage in UJT?

A UJT sweep operates with a valley voltage of 3 V and a peak voltage of 15 V. A sinusoidal synchronizing voltage peak of 6 V is applied as a sync signal.

Why UJT is called as relaxation oscillator?

It has a negative resistance region in the characteristics and can be easily employed in relaxation oscillators. The UJT relaxation oscillator is called so because the timing interval is set up by the charging of a capacitor and the timing interval is ceased by the rapid discharge of the same capacitor.

What is valley current in UJT?

Valley Point Current IV The valley point current is the emitter current at the valley point. It increases with the increase in inter-base voltage VBB. Special Features of UJT. The special features of a UJT are : A stable triggering voltage (VP)— a fixed fraction of applied inter base voltage VBB.

What is UJT firing circuit?

The UJT is atwo layer pn device with three terminals. The terminals are called emitter (E), base-1 (B1) and base-2 (B2). It consists of an n type silicon bar with ohmic contacts for the two base terminals. A single p type emitter junction is formed by alloying a p type material on the side of the silicon bar.

Is UJT a diode?

Uni Junction Transistor (UJT) is also known as double base diode . It acts as a switching transistor instead of amplifying the signals. In UJT the PN junction is formed by lightly doped N-type silicon with heavily doped P-type material on one side.

Is UJT a relaxation oscillator?

The following figure shows how to use a UJT as a relaxation oscillator. Initially, the voltage across the capacitor is zero. The UJT is in OFF condition. The resistor R provides a path for the capacitor C to charge through the voltage applied.

What is a UJT also known as?

Uni Junction Transistor (UJT): The uni-junction transistor is a solid-state three-terminal device that can be used in gate pulse, timing circuits, and trigger generator applications to switch and control both thyristors and triacs for AC power control type applications.

Is UJT used as an oscillator?

The UJT relaxation oscillator applications are These oscillators produce low-frequency signals. UJT Relaxation Oscillator is used in function generator to produce sweep signals, Electronic Beepers, SMPS, blinking lights, Voltage-controlled oscillators, inverters, etc..

How many layers are there in UJT?

Uni-junction transistor is also known as double-base diode because it is a 2-layered, 3-terminal solid-state switching device. It has only one junction so it is called as a uni-junction device.

Is UJT unidirectional?

A Unijunction Transistor is a 3 terminal device with a single PN junction and is basically used to trigger a SCR or a TRIAC. It is a unidirectional device.