What are unijunction transistors used for?
The UJT is not used as a linear amplifier. It is used in free-running oscillators, synchronized or triggered oscillators, and pulse generation circuits at low to moderate frequencies (hundreds of kilohertz). It is widely used in the triggering circuits for silicon controlled rectifiers.
What is meant by unijunction transistor?
The Unijunction Transistor or UJT for short, is another solid state three terminal device that can be used in gate pulse, timing circuits and trigger generator applications to switch and control either thyristors and triac’s for AC power control type applications.
How does a unijunction transistor work?
The Unijunction Transistor (UJT) will act as voltage breakdown device, when the input applied between emitter and base 1 reduces below breakdown value i.e., RB1 increases to a higher value. This shows that RB1 depends on the emitter current and it is variable.
What is UJT PPT?
Original Uni-junction transistor or UJT is a simple device in which a bar of N-type semiconductor material into which P-type material is diffused; somewhere along its length defining the device parameter as intrinsic standoff. The 2N2646 is the most commonly used version of UJT. Read more. Engineering.
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 characteristics of UJT?
The special features of a UJT are :
- A stable triggering voltage (VP)— a fixed fraction of applied inter base voltage VBB.
- A very low value of triggering current.
- A high pulse current capability.
- A negative resistance characteristic.
- Low cost.
What are the types of unijunction transistor?
Types of UJT’s The 2N2646 is the most commonly used version of the UJT. The complementary unijunction transistor (CUJT) consist of a bar of P type semiconductor material into which N type material has been diffused somewhere along its length, defining the device parameter ‘η’. The 2N6114 is one version of the CUJT.
What are characteristics of UJT?
Special Features of UJT. A stable triggering voltage (VP)— a fixed fraction of applied inter base voltage VBB. A very low value of triggering current. A high pulse current capability. A negative resistance characteristic.
What are the terminals of unijunction transistor?
Detailed Solution. The UJT is a three-terminal, semiconductor device which exhibits negative resistance and switching characteristics for use as a relaxation oscillator in phase control applications. We observe that the emitter terminal is p-type. The structure of a UJT is quite similar to that of an N-channel JFET.
Why is UJT known as a unijunction transistor?
Definition: Unijunction Transistor is a semiconductor switching device having 2 layers and 3 terminals and is abbreviated as UJT. It is called so because of the presence of only one junction. It has the ability to limit large power with a small input signal and is also known as a double base diode.
What is a unijunction transistor?
A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch. The UJT is not used as a linear amplifier.
What is the schematic symbol for unijunction emitter current vs voltage?
The schematic symbol is Figure (c) The Unijunction emitter current vs voltage characteristic curve (Figure (a) below ) shows that as V E increases, current I E increases up I P at the peak point. Beyond the peak point, current increases as voltage decreases in the negative resistance region.
How does The unijunction emitter work on a capacitor?
R E charges C E until the peak point. The unijunction emitter terminal has no effect on the capacitor until this point is reached. Once the capacitor voltage, V E, reaches the peak voltage point V P, the lower emitter-base1 E-B1 resistance quickly discharges the capacitor.
What is the typical unijunction emitter current at peak point?
It varies from 0.4 to 0.8 for different devices. The schematic symbol is Figure (c) The Unijunction emitter current vs voltage characteristic curve (Figure (a) below ) shows that as V E increases, current I E increases up I P at the peak point. Beyond the peak point, current increases as voltage decreases in the negative resistance region.