Operation - unijunction transistor, Electrical Engineering

Operation - unijunction transistor:

Operation : Imagine that the emitter supply voltage is turned biased and a small emitter reverse current flows. Then the intrinsic stand off voltage reverse biases the emitter diode, as mentioned above. If VB is the barrier voltage of the emitter diode, then the total reverse bias voltage is VA + VB = VBB + VB. For silicon VB = 0.7 V. Now let the emitter supply voltage VE be slowly increased. When VE becomes equal to n VBB, n will be reduced to zero. With equal voltage levels on each side of the diode, neither reverse nor forward current will flow. When emitter supply voltage is further increased, the diode becomes forward biased as soon as it exceeds the total reverse bias voltage. This value of emitter voltage VE is called the peak point voltage and is denoted by Vp. When VE = VP, emitter current IE starts to flow through RB to ground. This is the minimum current that is required to trigger the UJT. This is called the peak point emitter current and is denoted by Ip. Ip is inversely proportional to the inter base voltage, VBB. Now when the emitter diode starts conducting, charge carriers are injected into the RB region of the bar. Since the resistance of a semiconductor material depends upon doping, the resistance of region RB decreases rapidly due to additional charge carriers. With this decrease in resistance, the voltage drop across RB also decreases causing the emitter diode to be more heavily forward biased. This, in turn, results in larger forward current, and consequently more charge carriers are injected causing still further reduction in the resistance of the RB region. Thus the emitter current goes on increasing until it is limited by the emitter power supply. Since VA decreases with the increase in emitter current, the UJT is said to have negative resistance characteristic. It is seen that the base 2 (B2) is used only for applying external voltage VBB across it. Terminals E and B1 are the active terminals. UJT is usually triggered into conduction by applying a suitable positive pulse to the emitter. It can be turned off by applying a negative trigger pulse.

Posted Date: 2/8/2013 2:55:11 AM | Location : United States

Related Discussions:- Operation - unijunction transistor, Assignment Help, Ask Question on Operation - unijunction transistor, Get Answer, Expert's Help, Operation - unijunction transistor Discussions

Write discussion on Operation - unijunction transistor
Your posts are moderated
Related Questions
Describe the term (i) Automation (ii) Automated lines 04 List out the reasons for automation and discuss in detail the process of work part transport.

which ckt. Or components using for irregular ac sine wave change into pure sine wave.......

Consider the RL circuit of Figure with R = 2, L = 5H, and v(t) = V = 20 V (a dc voltage source). Find the expressions for the inductor current i L (t) and the inductor voltage v L

Decimal to Binary Coded Decimal Conversions Step1. Separate the digits in the decimal number Step2. Express each of the digits in their binary equivalent Step3. Combine all o

Discuss the need of PCI bus. Peripheral Component Interconnect (PCI): It was developed by Intel and introduced in 1993 year. This is geared particularly to fifth- and sixth-

Q. Using a minimum number of NAND gates, realize the following Boolean expression: F(A,B,C) = ∑ mi (0, 3, 4, 5, 7).

Determine the value of Resistance: Determine the value of R, so that the condition for resonance is fulfilled Figure Solution Admittance of first branch

Uses of Zener Diode Zener diodes are extensively used as voltage references and like shunt regulators to regulate the voltage across small circuits. While connected in parall

Q. Show the r’s Complement? Step1- get the (r-1)'s complement Step 2- add 1 to the result ex.            935 10                                     9 9 9

Figure shows the block diagram of an aircraft pitch stabilization system which uses position, velocity and acceleration feedback. i) Show that for a unit step input the steady s