What is UJT in SCR?

A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch.

How UJT firing circuit will generate pulse for an SCR?

Initially the capacitor charges through R whose voltage is applied to the emitter of UJT. When the capacitor voltage reaches peak point voltage of UJT. Now the capacitor discharges through the output resistance. Thus the pulse is generated in the circuit.

What is the function of UJT?

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.

Why UJT is used as relaxation oscillator?

UJT is an excellent switch with switching times in the order of nanoseconds. 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 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.

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.

When a UJT is used for triggering of an SCR the wave shape of the voltage is a wave?

saw-tooth wave
When a UJT is used for triggering an SCR, the wave shape of the voltage obtained from the UJT circuit is a saw-tooth wave.

How is UJT used as an oscillator?

But in this circuit, when the voltage across capacitor reaches a value, which enables the UJT to turn ON (the peak voltage) then the capacitor stops to charge and starts discharging through UJT. As the output is a non-sinusoidal waveform, this circuit is said to be working as a relaxation oscillator.

Why UJT is called transistor?

Why UJT is called Unijunction Transistor?

The UJT consists of an n-type silicon semiconductor bar with an electrical on each end. Since the device has three terminals and one pn-junction, for this region this is called as a Unijunction Transistor (UJT). The device has only pn-junction so it forms a diode.