Programmable unijunction transistor

A programmable unijunction transistor (PUT) is a three-lead electronic semiconductor device which is similar in its characteristics to a unijunction transistor (UJT), except that its behavior can be controlled using external components. In a UJT, the base region is divided into two parts by the emitter. The two parts of the base form a voltage divider, which sets the operating point of the UJT. That voltage divider can be programmed with two physical resistors connected to the gate terminal of the PUT. This allows the designer some control over the operating point of the PUT.