The PUT stand for Programmable Unijunction Transistor, it is actually a type of Thyristors and not like the UJT at all. The only similarity to a UJT is that the PUT can be used in the same oscillator to replace the UJT.
Construction of PUT
The construction of PUT (Programmable Uni Junction Transistor) is similar to that of SCR, it has four layer of semiconductor material PNPN or NPNP structure, with three junction J1 J2 and J3, terminal which is connected to the P-Type material is called anode and the terminal which is connected to N-Type material is called cathode. The gate terminal is connected to the N-Type material near to the anode terminal.
Operation / Working of PUT
When we bias the PUT properly, the current can not be flow because the gate terminal is positive w.r.t cathode, when the anode voltage is increase form the cut off, the PN junction is forward bias, the PUT turn ON. The PUT remains in ON state until the anode voltage decreases below the cut off level and at that time the PUT is turn off.
Biasing of PUT
The gate terminal of PUT can be biased through voltage divider network to active the desired voltage as shown in the given diagram.