Programmable unijunction transistor (PUT) is a three-lead electronic semiconductor device with which is similar in characteristic to unijunction transistor except. This is simple circuit that illustrates the function of the programmable unijunction transistor. It may be quickly wired on a proto-board. PUT Flasher. Circuit Collection of the Programmable Unijunction Transistor (PUT).: A specific combination of 2 complementary transistors leads to an interesting self-latching.


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The main application of programmable UJT are relaxation oscillatorsthyristor firing, pulse circuits and timing circuits. The internal block diagram and circuit symbol of PUT are shown below. From the above figure, you can see that the Programmable ujt has a programmable ujt layered construction.

Topmost P-layer is called the anode A.

Programmable unijunction transistor

The N-layer next to the anode is called the gate G. The P-layer next to the gate is left alone. The bottom most N-layer is called cathode K. Ohmic contacts are made on the anode, cathode and gate layers for external connection.

The typical biasing programmable ujt and characteristics plot of a PUT is shown below. programmable ujt


The circuit above behaves like a thyristor. We can choose between inputs that function as gates: Q1 will not conduct, because it's base is pulled programmable ujt by R1. Q2 will not conduct, because it's base is floating and does not receive any current.

Because Q1 does not conduct, the OUTput will be high. By putting a small capacitance parallel to R1, the PUT can be programmable ujt into a non-conducting programmable ujt at power on.

The only way to reset the circuit back to the initial state, is to briefly disconnect it from the power supply. This is programmable ujt same self-latching behaviour as a thyristor.

2N6028: Programmable Unijunction Transistor

When Q2 conducts, the base of Q1 is pulled programmable ujt and Q1 will conduct. See Figure below a. The connections at the ends of the bar are known as bases B1 and B2; the P-type mid-point is the emitter. It varies from 0.

PUT (Programmable Unijunction Transistor) - roel arits electronics hobby shack

The schematic symbol is Programmable ujt below c Unijunction transistor: Beyond the peak point, current increases as voltage decreases in the negative resistance region. The voltage reaches a minimum at the valley point.

The resistance of RB1, the saturation resistance is lowest at the valley point. The relaxation oscillator in Figure below is an application of the unijunction programmable ujt.

2N Programmable Unijunction Transistor

programmable ujt RE charges CE until the peak point. The unijunction emitter terminal has programmable ujt effect on the capacitor until this point is reached.

Once the capacitor voltage, VE, reaches the peak voltage point VP, the lowered emitter-base1 E-B1 resistance quickly discharges the capacitor.