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• Unijunction_transistor abstract "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 an amplifier control. The UJT has three terminals: an emitter (E) and two bases (B1 and B2). If no potential difference exists between its emitter and either of its base leads, an extremely small current flows from B2 to B1. On the other hand, if an adequately large voltage - relative to its base leads-, known as the trigger voltage, is applied to its emitter, then a very large current will flow from its emitter and join the current flowing from B2 to B1, which would create a larger B1 output current.The base is formed by lightly doped n-type bar of silicon. Two ohmic contacts B1 and B2 are attached at its ends. The emitter is of p-type and it is heavily doped. The resistance between B1 and B2 when the emitter is open-circuit is called interbase resistance.There are three types of unijunction transistors: The original unijunction transistor, or UJT, is a simple device that is essentially a bar of N type semiconductor material into which P type material has been diffused somewhere along its length, defining the device parameter . The 2N2646 is the most commonly used version of the UJT. The complementary unijunction transistor, or CUJT, that is a bar of P type semiconductor material into which N type material has been diffused somewhere along its length, defining the device parameter . The 2N6114 is one version of the CUJT. The programmable unijunction transistor, or PUT, is a close cousin to the thyristor. Like the thyristor it consists of four P-N layers and has an anode and a cathode connected to the first and the last layer, and a gate connected to one of the inner layers. They are not directly interchangeable with conventional UJTs but perform a similar function. In a proper circuit configuration with two "programming" resistors for setting the parameter , they behave like a conventional UJT. The 2N6027 is an example of such a device.The UJT is biased with a positive voltage between the two bases. This causes a potential drop along the length of the device. When the emitter voltage is driven approximately one diode voltage above the voltage at the point where the P diffusion (emitter) is, current will begin to flow from the emitter into the base region. Because the base region is very lightly doped, the additional current (actually charges in the base region) causes conductivity modulation which reduces the resistance of the portion of the base between the emitter junction and the B2 terminal. This reduction in resistance means that the emitter junction is more forward biased, and so even more current is injected. Overall, the effect is a negative resistance at the emitter terminal. This is what makes the UJT useful, especially in simple oscillator circuits.Unijunction transistor circuits were popular in hobbyist electronics circuits in the 1960s and 1970s because they allowed simple oscillators to be built using just one active device. For example, they were used for relaxation oscillators in variable-rate strobe lights. Later, as integrated circuits became more popular, oscillators such as the 555 timer IC became more commonly used.In addition to its use as the active device in relaxation oscillators, one of the most important applications of UJTs or PUTs is to trigger thyristors (SCR, TRIAC, etc.). In fact, a DC voltage can be used to control a UJT or PUT circuit such that the "on-period" increases with an increase in the DC control voltage. This application is important for large AC current control.UJTs can also be used to measure magnetic flux. The hall effect modulates the voltage at the PN junction. This affects the frequency of UJT relaxation oscillators. This only works with UJTs. PUTs do not exhibit this phenomenon.".
• Unijunction_transistor thumbnail Unijunction_transistors.jpg?width=300.
• Unijunction_transistor wikiPageExternalLink unijunction.htm.
• Unijunction_transistor wikiPageID "108824".
• Unijunction_transistor wikiPageRevisionID "602667001".
• Unijunction_transistor hasPhotoCollection Unijunction_transistor.
• Unijunction_transistor subject Category:Transistor_types.
• Unijunction_transistor comment "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 an amplifier control. The UJT has three terminals: an emitter (E) and two bases (B1 and B2). If no potential difference exists between its emitter and either of its base leads, an extremely small current flows from B2 to B1.".
• Unijunction_transistor label "Transistor de unijunção".
• Unijunction_transistor label "Transistor unijonction".
• Unijunction_transistor label "Transistor uniunión".
• Unijunction_transistor label "Transistore unigiunzione".
• Unijunction_transistor label "Tranzystor jednozłączowy".
• Unijunction_transistor label "Unijunction transistor".
• Unijunction_transistor label "Unijunctiontransistor".
• Unijunction_transistor label "Unijunctiontransistor".
• Unijunction_transistor label "Однопереходный транзистор".
• Unijunction_transistor label "ユニジャンクショントランジスタ".
• Unijunction_transistor label "單接合面電晶體".
• Unijunction_transistor sameAs Unijunctiontransistor.
• Unijunction_transistor sameAs Transistor_uniunión.
• Unijunction_transistor sameAs Transistor_unijonction.
• Unijunction_transistor sameAs Transistor_sambungan_tunggal.
• Unijunction_transistor sameAs Transistore_unigiunzione.
• Unijunction_transistor sameAs ユニジャンクショントランジスタ.
• Unijunction_transistor sameAs Unijunctiontransistor.
• Unijunction_transistor sameAs Tranzystor_jednozłączowy.
• Unijunction_transistor sameAs Transistor_de_unijunção.
• Unijunction_transistor sameAs m.0rfq_.
• Unijunction_transistor sameAs Q1129455.
• Unijunction_transistor sameAs Q1129455.
• Unijunction_transistor wasDerivedFrom Unijunction_transistor?oldid=602667001.
• Unijunction_transistor depiction Unijunction_transistors.jpg.
• Unijunction_transistor isPrimaryTopicOf Unijunction_transistor.