AReS

PART7Basic Circuit of Semiconductor

Experiment 10 :Chacracteristic of UJT

Theory

UJT transistor, as in fig.7-40, is composed of a stick semiconductor whose resitivity is high and a electrode attached to the semiconductor in order to inject the carrier in the middle, so one junction is generated. N type semiconductor becomes the base and three electrodes, that is, the first base B1, the second base B2, and the emitter E are included.

The single junction between B1 and B2 usually works as the resistance. This resistance is the base resistance R_BB and it has the resistance value of 9.1kΩ range.

fig7-40

Fig. 7-40UJT Equivalent Circuit

It is operated by changing the conductivity between B1 and B2 by the positive hole injected from the emitter and generating negative resistance, and is called double base diode. The reasons that it is used as the trigger generator are that its rated peak current is big, the trigger voltage is stable, the power consumption is small, its size is small and the operation is simple.

fig7-41

Fig. 7-41UJT Equivalent Circuit

Total resistance between base terminals r'_BB =r'_B1 +r'_B2

$V _{r 'B1} =[ {r' _{B1}} over {r' _{B2} } ]V _{BB}$

fig7-42

Fig. 7-42Characteristic Curve of UJT

Turn On and Turn Off Condition

Turn On Condition : V_BB-V_P>I_PR₁ , Turn Off Condition : V_BB-V_V>I_VR₁
Range of R₁ for Proper Turn On and Turn Off: :

${V _{BB} -V _{P}} over {I _{P}} >R _{1} > {V _{BB} -V _{V}} over {I _{V}}$

fig7-43

Fig. 7-43UJT Relaxation Oscillator and Waveform

The cycle of pulse changes in wide range according to the value of R1, C, and for a stable oscillation, the maximum and minimum value of R1 should be limited to certain value(2kΩ～3MΩ).

Experiment Process

fig7-44

Fig. 7-44UJT Characteristic Measurement Circuit

1. To experiment the characteristic of UJT, make a connection as in fig.7-44 using Block d of M07 and supply DC 10V power.

- VR4 is used to adjust the emitter voltage(VE) between E and B1. R11 is the emitter series resistance and R10 is current limiting resistance.

2. Measure the emitter voltage(V_E) by connecting the voltmeter between E and B1.

- Observe the change of emitter current(I_E) by emitter voltage(V_E) when turning VR4 to the right slowly as the voltage given in table 7-15 and record the result in the relevant column of the table.

- Measure and record the peak point voltage(V_P) when the emitter voltage(V_E) suddenly decreases.

- If you turn VR4 to the right slowly, the emitter voltage(V_E) passes the peak point voltage(V_P) and reaches the minimum value. The emitter voltage(V_E) here is the valley point voltage(V_V).

- Record the valley point voltage(V_V).

3. Calculate the intrinsic standoff ratio of UJT η by the following calculation

$eta `=` {V _{P`} -V _{E}} over {V _{BB}}$
(Here, V_E = 0.7V)

tab1

Experiment 7-10.1 UJT Characteristic Measurement (In Block d of M07, compose a circuit as infig.7-44.)

1.Connection(Block d of M07)

1.Circuit Connection

In Block d, connect between B1 polarity terminal of UJT and the earthing terminal with yellow line.

In Block d, connect between B2 polarity terminal of UJT and lower terminal of R10 with yellow line.

2.Power Connection

Connect between V1 terminal of Variable Power on the left of M07 board and V+ terminal of Block d with red line, and between COM terminal and the earthing terminal with black line.

3.Measuring Instrument Connection

Ammeter Connection

UJT emitter current(I_E) measurement : Measure by using the current measurement function of separate Digital Multimeter. Conenct the red lead wire of Digital Multimeter to center terminal of VR4 of Block d and the black lead wire to the terminal connected to the bottom of R11.

Voltmeter Connection

Measuring emitter voltage(voltage between R11’s both ends(V_E)): Connect between High terminal of Multimeter on the front panel and the terminal connected to SW5 of Block d with red line, and between Low terminal and the earthing terminal with black line.

2.Wiring Diagram

flash

3.Measurement

1Choose variable power at the left menu of Touch LCD panel and set up at 3 CH DC to make V1 as 10V with button_arrow.
Click on to supply DC 10V output to the circuit.
2Choose dmm at the left menu of Touch LCD panel, and click dcv.
3Turn on SW5.
4Observe the change of emitter current(I_E) by emitter voltage(VE) when turning VR4 to the right slowly as the voltage given in table 7-15 and record the result in the relevant column of the table.
Choose dmm at the left menu of Touch LCD panel and record the measured value of emitter voltage(V_E) in the relevant column.

Record the value of UJT emitter current(I_E) measured by separate digital multimeter in the relevant column. .
5After the measurement, choose variable power at the left menu of Touch LCD panel and click on red to cut off the power supply.

Experiment Result Report

result
Title	Chacracteristic of UJT	Date
Department		Id Number		Name

1. Experiment Result Table

Table 7-15

result_table
Emitter Voltage[V_E]	Emitter Current [I_E]	Peak-Point[V_P]	Valley-Point[V_V]	etc.
1.0V
1.5V
2.0V
2.5V
3.0V
3.5V
4.0V
4.5V
5.0V
5.5V
6.0V
6.5V
7.0V
7.5V
8.0V
8.5V
Maximum

2. Review and Explanation

1) In table 7-15 above, draw a characteristic curve between emitter voltage[V_E] and emitter current[I_E].

2) How much is the peak point voltage(V_P)?

3) How much is the valley point voltage(V_V)?

section paper

4) Calculate the intrinsic standoff ratioη by the following formula.