Unijunction Transistor Tutorials


Posted on Feb 5, 2014

The unijunction transistor (UJT) is made of a bar of N type material with a P type junction (the emitter) near the centre. Base 1 is connected to zero volts and base 2 to the positive supply. The resistance between the two bases (the INTERBASE RESISTANCE) is typically 10k. With the emitter unconnected, the bar acts as a potential divider, and abou


Unijunction Transistor Tutorials
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t 0. 5 volts appears at the emitter. If a voltage is connected to the emitter, as long as it is less than 0. 5 volts, nothing happens, as the P-N junction is reversed biased. (see the right hand diagram). When the emitter voltage exceeds 0. 5 volts, the junction is forward biased and emitter current will flow. This increase in current is equal to a reduction of resistance between base 1 and the emitter. In the circuit, C charges via R1. When the voltage across C exceeds 0. 6 volts, the b1/emitter junction goes low resistance and discharges C. The result is a sawtooth waveform across C. There is also a pulse of current through R3, giving a pulse of voltage across it. This circuit is called a relaxation oscillator. The voltage across C charges up slowly then suddenly relaxes.




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