Government Girls’ Polytechnic, Bilaspur


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Government Girls’ Polytechnic, Bilaspur
Name of the Lab: Electronics Lab
Practical: Power Electronics Lab
Class : 4th Semester ( ET&T )
Teachers Assessment:10 End Semester Examination:50
EXPERIMENT No- 1
OBJECTIVE: - Performance of Thyristor.
EQUIPMENT REQUIRED: - Trainer kit, Patch cards, Multimeters.
THEORY: - In power electronics the thyristor is the most common and popular family of
switching devices. According to constructions, the numbers of semiconductor layer of thyristor family member are nearly similar but their position arrangements are different and also the terminals are connected in different positions. For this they have shown different characteristics. Some of the family members are bidirectional that is they conduct current in both terminals and have no polarity limitations and use to switch in the heavy ac load, otherwise unidirectional member conduct current in only one direction and use mostly in rectification of ac and also switch. Usually four layers and also five layers semiconductor devices are called the thyristor. According to their construction they have at least two terminals to maximum four terminals. Specifically the five layer members (TRIAC, DIAC) of thyristor family are used their four semiconductor layer in the state of conduction.

Construction

Symbol

CIRCUIT DIAGRAM:-

Power Electronics Lab Manual: 4th semester(ET&T)

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PROCEDURE:- Circuit diagram for V-I characteristics of thyristor.

Power Electronics Lab Manual: 4th semester(ET&T)

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OBSERVATION TABLE:-

Power Electronics Lab Manual: 4th semester(ET&T)

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RESULT:- Static characteristics of thyristor are determined.

PRECAUTIONS: - 1) All the connection should be tight.
2) Ammeter is always connected in series in the circuit while voltmeter is parallel to the conductor.
3) The electrical current should not flow the circuit for long time, Otherwise its temperature will increase and the result will be affected.
4) It should be care that the values of the components of the circuit is does not exceed to their ratings (maximum value).
5) Before the circuit connection it should be check out working condition of all the Component.

Power Electronics Lab Manual: 4th semester(ET&T)

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EXPERIMENT No- 2
OBJECTIVE: - Performance of DIAC.
EQUIPMENT REQUIRED: - Trainer kit, Patch cards, Multimeters.
THEORY:- The other bidirectional operated member of thyristor family is DIAC or diode for
alternating current or bilateral diode switch. The DIAC is a five layers and contains two terminal, anode A1 (or main terminal MT1) and anode A2 (or main terminal MT2) like a TRIAC just without a gate terminal. The DIAC construction is such that in conduction state it uses its two different four layers for each polarity changes of the terminal.

CIRCUIT DIAGRAM:-
Circuit diagram for V-I characteristics of DAIC.

Power Electronics Lab Manual: 4th semester(ET&T)

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PROCEDURE:OBSERVATION TABLE:RESULT:- Static characteristics of DIAC are determined.

Power Electronics Lab Manual: 4th semester(ET&T)

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PRECAUTIONS: - 1) All the connection should be tight.
2) Ammeter is always connected in series in the circuit while voltmeter is parallel to the conductor.
3) The electrical current should not flow the circuit for long time, Otherwise its temperature will increase and the result will be affected.
4) It should be care that the values of the components of the circuit is does not exceed to their ratings (maximum value).
5) Before the circuit connection it should be check out working condition of all the Component.

Power Electronics Lab Manual: 4th semester(ET&T)

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EXPERIMENT No- 3
OBJECTIVE: - Frequency calculation of pulse in UJT relaxation oscillator.
EQUIPMENT REQUIRED: - UJT, resistance box, decade condenser box, variable d.c. power
supply, C.R.O. and connecting terminals.
THEORY:- The UJT has negative resistance characteristic, because of this character the UJT provides
trigger pulse. Any one of the three terminals can be taken for triggering pulse. The UJT can be used as relaxation oscillator i.e. it produces non-sinusoidal waves.
First the capacitor „C‟ starts charging through the resistor R when VBB is switched on. During the charging of the capacitor, the voltage across it increases exponentially until it reaches to the peak point voltage VP. Up to now, the UJT is in off state, i.e. no conducting state at which RB1 value is high. When the voltage across the capacitor reaches to peak point voltage (VP) then, UJT comes into conducting state as the junction is forward biased and RB1 falls to low value (50_). Then the capacitor „C‟ quickly discharges through UJT that means the discharging time is very less as the capacitor discharges through the low resistance UJT. When the voltage across the capacitor decreases to valley point voltage (VV) then the UJT shifts to off state and once again the capacitor gets charged through the resistor R and this process is repeated. This generates saw-tooth wave form

Construction

Characteristics

Formula: - Frequency of oscillator

Symbol

Where R = Resistance of the resistor (Ω) C = Capacity of the condenser (F) η = Intrinsic stand off ratio = 0.6

CIRCUIT DIAGRAM:-

Power Electronics Lab Manual: 4th semester(ET&T)

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PROCEDURE: - 1) Connect the circuit as shown in Fig and apply a fixed voltage VBB (5V to 10V)
between the two bases B1 and B2. 2) As the Y – plates of CRO is connected across the condenser a saw tooth wave form is observed on its
screen when the power is switch on. 3) Adjust of voltage sensitivity band switch of Y-plates and time base band switch X-plates such that at
least one or two waves displayed in the screen. 4) Now note the horizontal length(l) between two successive peaks, in the table. When this horizontal
length (l) is multiplied by the time base(t) i.e. sec/div , we get the time-period(T). 5 ) The reciprocal of the time-period(1/T) gives the frequency(f). This is the experimental value. 6) Note the values of resistance R and capacitance C of those connected in the circuit and take the
intrinsic stand off ratio η as 0.6, substitute these values in the above formula and find the frequency. This is the theoretical value. Compare the theoretical and experimental frequencies. Repeat the experiment by changing the values of R or C or both.
OBSERVATION TABLE:-

Power Electronics Lab Manual: 4th semester(ET&T)

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RESULT: - Saw-tooth wave form across the capacitor which can be viewed on the CRO
Screen.
PRECAUTIONS: - 1) The continuity of the connecting terminals should be checked before going
to connect the circuit. 2) Identify the two bases and emitter of UJT and connect properly. 3) The power supply should be „on‟ only when the observations are taken. 4) Measure the horizontal length of the wave with out any error.

Power Electronics Lab Manual: 4th semester(ET&T)

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Government Girls’ Polytechnic, Bilaspur