A programmable unijunction transistor (PUT) is a three-lead electronic

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

device which is similar in its characteristics to a

unijunction transistor A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch. The UJT is not used as a linear amplifier. It is used in free-running oscillators, ...

, except that its behavior can be controlled using external components. In a

, the base region is divided into two parts by the emitter. The two parts of the base form a

voltage divider In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (''V''out) that is a fraction of its input voltage (''V''in). Voltage division is the result of distributing the i ...

, 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.

Construction

In construction, the programmable unijunction transistor is similar to the

silicon controlled rectifier A silicon controlled rectifier or semiconductor controlled rectifier is a four-layer solid-state current-controlling device. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor. The principle of fou ...

. It consists of four layers, two p-type layers and two n-type layers in equal proportion.

Applications

* It is used to trigger

thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current t ...

s. * It is also used as a

relaxation oscillator In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave. on Peter Millet'Tubebookswebsite The circuit consists of a feedba ...

. As of 2012

ON Semiconductor onsemi (stylized in lowercase; legally ON Semiconductor Corporation; formerly ON Semiconductor until August 5, 2021) is an American semiconductor supplier company, based in Phoenix, Arizona and ranked #483 on the 2022 ''Fortune'' 500 based on it ...

manufactured a part: 2N6027. 2N6028 was also made in the past.

References

Transistor types General Electric inventions {{Electronics-stub