# UJT CHARACTERISTICS

AIM

To plot the characteristics of UJT (2N 2446) and to determine the intrinsic stand off ratio from the graph.

COMPONENTS AND EQUIPMENTS REQUIRED

1. UJT

2. Resistors

3. Voltmeter

4. Ammeter

5. Rheostat

6. Power supply

CIRCUIT DIAGRAM

EQUIVALENT CIRCUIT OF UJT

THEORY

UJT is the Uni Junction Transistor. It is a three terminal device. They are: a) emitter     b) base1  c)base2.The equalent circuit is shown with the circuit diagram. So there are two resistors. One is a variable resistor and other is a fixed resistor. The ratio of internal resistances is referred as intrinsic standoff ratio (η).It is defined as the ratio of the variable resistance to the total resistance. Due to the existing pn junction, there will be a voltage drop. If we apply a voltage to the emitter, the device will not turn on until the input voltage is less than the drop across the diode plus the drop at the variable resistance R1.When the device is turned on holes moves from emitter to base resulting in a current flow. Due to this sudden increase in charge concentration in base1 region   conductivity increases. This causes a drop at base1.This region in the graph is known as negative resistance region. If we further increase the emitter voltage the device undergoes saturation. So a UJT has 3 operating regions:

1. cut off region
2. negative resistance region
3. saturation region

PROCEDURE

1. Set up the circuit as shown in the circuit diagram

2. Give the power supply.

3. By varying the input voltage, take the values of voltage and current values

4. Plot the graph

5. Find the in intrinsic standoff ratio from graph.

OBSERVATIONS

For VBB=12 V                                                           For VBB=6 V

 VE IE VE IE

GRAPH

CALCULATIONS

VBB=12 V

VP= Vd + ηvbb

Find the value of Vp from graph.

η  = Vp – Vd/VBB

Similarly find the value of intrinsic stand off ratio for all values of VBB.

RESULT

Characteristics of UJT were plotted and intrinsic stand off ratio was found.

η = ………………..

SAMPLE VIVA QUESTIONS

1.      Name a UJT

2N 2446

2. Define intrinsic standoff ratio-See theory

3. Mention any application of UJT

In triggering circuits

##### We recommend:
• shankar
November 1, 2014

nice site

• October 30, 2011

could not to see any graph or circuit diagram

• karthik
October 26, 2011

cud nto see any graph or circuit diagram

• seetharaman
May 21, 2010

Hi friends it should be 2N2646, which is an UJT. 2N2446 is a germanium bipolar transistor which has become obsolete long back.
you can getthe application circuit and application data from the following site.
http://www.datasheetcatalog.org/datasheet/philips/2N2646.pdf

• subramanya
May 21, 2010

circuit diagram not diplayed.

• shakira
March 22, 2009

HI M SHAKIRA .. this web side is very useful

• jojo
January 14, 2009

Thanks Mohan raj!! Please do tell all your friends and warm welcome!

• Mohan Raj
October 30, 2008

I Am Doing B.E…. This website consists of very useful contents required for a B.E. student…. It’s Really an Excellent website… i am sure that i will inform about this website to all my friends… Thank You ! ! ! !