UJT Transistors

UJT Transistors

UJT transistor or UJT is a three terminal solid state semiconductor with one junction that can be used in timing circuits, gate pulses and trigger generator applications to switch and control Thyristors and Triacs. UJT transistor works like a voltage control switch but does not amplify. The leads on the UJT are called the base1, base2 and the emitter.

UJT Construction

The UJT is constructed of a bar of lightly dope N type silicone with a small piece of heavily doped P type material attached to one side. Since the silicon bar is lightly dope it has very high resistance.

UJT Operation

When a positive bias voltage is applied to the emitter the P N junction becomes forward bias and current will flow through the PN junction, this causes the resistance of the N type bar material to decrease. With the decrease in resistance the voltage drop across the base 1 junction also decreases which in turn causes the PN junction to become more heavily biased.

As the PN junction is biased even further it cause a greater forward current flow which further reduces the resistance of the bar material, when the UJT is operating in this mode its operating in its negative resistance region the normal operating mode for the UJT.

UJT Characteristic Curve

The emitter section of the UJT has a resistance which rapidly decreases when the input voltage reaches a certain magnitude. This is referred as a negative resistance characteristic, it is this characteristic that makes a UJT useful in timing and oscillator circuits.

What is doping of semiconductors?

Doping is the inclusion of foreign atoms in the regular crystal lattice of silicon to produces changes in their electrical properties thus producing P type and N type semiconductors.

What is a UJT also known as?

Double base diode

What are the different types?

• Unijunction transistor

• Complementary unijunction transistor

• Programmable unijunction transistor

What is the basic structure?

UJT transistors basic structure consist of a base1, base2, P-N junction, silicon bar and emitter

Where would you find one?

UJT transistors are typically used in triggering circuits for silicon controlled rectifiers.

What is the main purpose?

UJT Transistors are primarily designed for use in pulse and timing circuits, thermistor trigger circuits and sensing circuits.

Applications Information

UJT Transistors are used in industrial applications such building oscillators, integrated circuits

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RS Stock No. 161-1533
Mfr. Part No.5.0SMDJ20A
BrandBourns
HK$13.156
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5000 (Minimum) W Surface Mount DO-214AB (SMC) 2 7.11 x 6.22 x 2.31mm 2.31mm 7.11mm +150 °C -55 °C 6.22mm
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BrandBourns
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