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The characteristics and applications of Unijunction Transistor

What is meant by ?

The semiconductor unijunction transistor, which may be used for switching or signal amplification, has just one junction. It comprises a high resistivity material, such as silicon, where a small, highly doped N-type area is produced.

The Characteristics (UJT):

Three factors may describe the features of unijunction transistors (UJT).

  • Cutoff:

 The cutoff zone is where the voltage applied to the Unijunction Transistor (UJT) is insufficient to cause it to switch on. The transistor is in an off state since the applied voltage hasn’t reached the triggering voltage.

  • Region of Negative Resistance:

When the transistor reaches the triggering voltage, VTRIG, the (UJT) will turn on. It will ultimately get VPEAK if the input power to the emitter lead grows over time. The voltage drops from VPEAK to Valley Point even though the current increases (negative resistance).

  • Saturation:

The current and voltage in the saturation zone will rise if a higher applied voltage is supplied to the emitter terminal.

What are the Advantages of using a unijunction transistor?

  • Reasonable price.
  • Exceptional qualities.
  • When working normally, a low power absorption device.
  • Features of negative resistance.
  • Low-value triggering current is necessary.
  • A consistent trigger voltage.
  • Low-powered absorption apparatus.

The Construction of unijunction transistor:

  • The UJT is an n-type silicon semiconductor strip with an electronic at either end. Base terminals are the connections’ terminals (B1 and B2). This junction’s terminal is known as the emitter terminal (E).
  • The component is referred to as a Unijunction Transistor for this area since it has three terminals and one pN-junction (UJT). The feature only has a PN-junction, which results in a diode. The gadget is also known as a double-based diode since the two base leads are extracted from a single part of the diode.
  • While the n-region is just mildly doped, the emitter is substantially doped. As a result, when the emitter terminal is open, there is a very high resistance between the base terminals.

Applications of Unijunction Transistor Oscillators:

The Transistors are useful in a wide range of applications, including:

  • Circuits for Triggers.
  • Generator of saw teeth.
  • Dual-stable networks.
  • Circuits for measuring voltage and pulses.
  • Oscillators for UJT relaxation.
  • Detectors for excess voltage.
  • Timing Circuit.
  • Switching Device.
  • Timing Circuit Switching Device. 
  • For the controlling phase.
  • Shaft-driven generators.

How does a unijunction transistor work?

  • The device is switched off until the applied voltage exceeds the triggering voltage when there is no voltage applied at the emitter due to the high channel resistance.
  • Positive voltage is provided to the emitter terminal to make Base 2 and Base 1 positive when the PN Junction is forward-biased. Since Base2 is positive, the majority carrier, the holes in the P-type, is rejected and drawn to the Base1 terminal as it enters the N channel. As a result, the resistance drops. The Emitter current grows, peaks, and then begins to decline.
  • It resumes rising after it reaches the valley point once more. The emitter current is shut off, and the PN Junction becomes reverse biased.
  • The magnitude of the applied voltage influences the fundamental operation of the UJT. If the applied voltage between the emitter and base1 terminals is intended to be zero, this UJT does not conduct. Therefore, it is more likely that the N-Type material will act as a resistor. As the practical voltage at the emitter terminal continues to increase and the device starts to conduct, the resistance value tends to grow. Conduction during the entire process relies entirely on the bulk of charge carriers. This is the fundamental idea of the unijunction transistor (UJT).

Why are you choosing the unijunction transistor?

The transistors were chosen due to their tiny size and reasonable price. The power requirements required a low-cost solution, and the Unijunction was the ideal choice. It is compact and runs on a minimal amount of electricity. It was the perfect option for an amazing application because of this. It is more effective than a Junction Transistor because it has a lower voltage drop and a greater gain. Because of their great current carrying capability and common power usage.

Circuit for unijunction transistor Speed Control:

The circuit is frequently used to produce a sequence of pulses that fire and regulate a thyristor. We may change the speed of a universal AC or DC motor by utilizing the UJT as a phase control triggering circuit in combination with an SCR or Triode. By adjusting the current flowing through the SCR, we may use the circuit above to regulate the speed of a universal series motor (or any other form of load, such as heaters, lights, etc.). Simply changing the potentiometer’s value will alter the saw tooth pulse’s frequency, which will change the motor’s speed.


A three-terminal semiconductor device known as a unijunction transistor (UJT) can function as a linear amplifier or electronic switch. A semiconductor bar with two P-N junctions makes up the device. The emitter is located in the center of the bar, and the base terminals are at the two ends. Our goal is to build a better world by providing sustainable transistors to everyone. Our primary goal is to help our clients locate the best transistor. Therefore, we frequently help people in this way. Because of constant innovation processes, advancements in design and expertise, and ongoing learning in the service delivery fields, we continue to endeavour to generate value and offer clients services that better value. You will be pleased and content with this approach. BOMZON is committed to providing our customers with top-notch customer service. You will never have to worry about being stranded againWe hope you enjoy our product range. Please do not hesitate to contact us if there is anything else we can do for you. For more information, please visit our website. Purchase and order right now. Get your today!

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