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Ujt uni junction transistor - basics
A unijunction transistor (UJT) is a three-terminal semiconductor device primarily used as an electrically controlled switch, notable for its role in triggering devices like SCRs and triacs, as well as in timing circuits and oscillators. It consists of a lightly doped n-type silicon bar and a heavily doped p-type material, with specific regions termed base 1, base 2, and emitter. The document outlines its construction, working principles, characteristics including cutoff and saturation regions, and various applications.
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Ujt uni junction transistor - basics
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- 2. TOPICSFOR DISCUSSION Presentation Outline What isUJT Symbol Construction Working Characteristics Applications 1. 2. 3. 4. 5. 6.
- 3. What is UJT? Aunijunction transistor is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch. BSI|2020BrandGuidelines
- 4. BasicsofElectronics The most common application of a unijunctiontransistor is as a triggering device for SCR's and Triacs but other UJT applications include sawtoothed generators, simple oscillators, phase control, and timing circuits. WHY UJT?
- 5. The symbol of UJT is designed in sucha way that arrow is bent and shown that it is in the direction towards the channel. Symbol of UJT
- 6. BSI|2020BrandGuidelines Construction of UJT InUnijunction Transistor, the PN Junction is formed by lightly doped N type silicon bar with heavily doped P type material on one side. The ohmic contact on either ends of the silicon bar is termed as Base 1 (B1) and Base 2 (B2) and P-type terminal is named as emitter.
- 7. WorkingofUJT The simplified equivalent circuit(at Figure) shows that N-type channel consists of two resistors RB2 and RB1 in series with an equivalent diode 'D' representing the PN junction. The emitter PN junction is fixed along the ohmic channel during its manufacturing process. 1. 2. 3.
- 8. WorkingofUJT 4. Thevariable resistance RB1 is provided between the terminals Emitter (E) and Base 1 (B1), the RB2 between the terminals Emitter (E) and Base 2 (B2). Since the PN junction is more close to B2, the value of RB2 will be less than the variable resistance RB1.
- 9. WorkingofUJT The voltage across resistanceRB1 of the voltage divider circuit is calculated by
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- 11. CUTOFF Cutoff region isthe area where the Unijunction Transistor (UJT) doesn’t get sufficient voltage to turn on. The applied voltage hasn’t reached the triggering voltage, thus making transistor to be in off state. NEGATIVE RESISTANCE REGION When the transistor reaches the triggering voltage, VTRIG, Unijunction Transistor (UJT) will turn on. After a certain time, if the applied voltage increases to the emitter lead, it will reach out at VPEAK. The voltage drops from VPEAK to Valley Point even though the current increases (negative resistance). SATURATION Saturation region is the area where the current and voltage raises, if the applied voltage to emitter terminal increases.
- 12. Applications of UJT Switching Device TriggeringDevice for Triacs and SCR’s Timing Circuits For phase control In saw tooth generators In simple relaxation oscillators 1. 2. 3. 4. 5. 6.
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