Power Electronics

When the temperature increases, the inter-base resistance (RBB) of a UJT ___________.

Power electronics essentially deals with control of a.c. power at ___________.

A DIAC is ___________ switch.

A diac is simply ___________.

A triac has ___________ semiconductor layers.

A diac has ___________ semiconductor layers

When a UJT is turned ON, the resistance between emitter terminal and lower base terminal ___________

The triac is ___________.

A triac is equivalent to two SCRs ___________.

An SCR is a . . . . . . . . triggered device

An SCR has a turn on time of 4 µs. The gate pulse should be of duration about

Which of the following is false for a thyristor? 1. Thyristor is a majority-carrier device. 2. The forward-bias portion of thyristor's i-v characteristics has two stable operating regions. 3. The forward-bias portion of thyristor's i-v characteristics has one stable operating region. 4. The negative gate current turns off the thyristor.

The above graph depicts

Which of the following does not cause permanent damage of an SCR?

Which of the following is control element in Silicon Controlled Resistor (SCR)?

The effect of source inductance on the performance of a single-phase and three-phase full converter is to

An SCR has three terminals viz . . . . . . . .

Which statement is correct for a UJT?

In the NMOS inverter

The frequency of oscillation of an UJT relaxation oscillator is

Which of the following is correct for inverters?

Which one of the following statements regarding the two transistor model of the p-n-p-n four layer device is correct?

An SCR combines the features of . . . . . . . .

The duty cycle of a pulse of width 2 microsecond and repetition frequency 4 kHz is

Which semiconductor device behaves like two SCRs?

The number of terminals present in IGBT is

From circuit design simplicity and economy point of view, one of the following configurations for a converter is the best. Which is that?

Which of the following device used for high frequency applications?

An SCR can be switched from a non-conducting state to a conducting state by applying 1. A voltage with high $$frac{{{ ext{dv}}}}{{{ ext{dt}}}}$$ 2. Voltage greater than forward break over voltage 3. Negative gate current with positive anode voltage 4. Positive gate current with positive anode voltage Which of the following is correct?

A TRIAC is similar to

An UJT, the p-type emitter is . . . . . . . . doped

A single-phase full-wave AC phase controller feeds power to a resistive load of 100 Ω from a 220 V, 50 Hz supply. What will be the rms output voltage at delay angles $${alpha _1} = {alpha _2} = alpha = frac{pi }{2}$$ xa0 xa0of both transistors?

Consider the following statements: A four-layer PNPN device having two gate leads can turned on by applying a 1. positive current pulse to the cathode gate 2. positive current pulse to the anode gate 3. negative current pulse to the anode gate 4. negative current pulse to the cathode gate Which of these statements is/are correct?

A Silicon Controlled Resistor (SCR) is made up of silicon and not germanium because

An a.c. regulator can be designed with

The gate current required to turn on an SCR is

A freewheeling diode in a phase controlled rectifier

Consider the following statements: An SCR, from its OFF state, can be made ON by- 1. increasing its anode voltage 2. increasing its gate current 3. decreasing its gate voltage 4. decreasing its anode current Which one of the following statements is correct?

Power diode are used with

Match List-I with List-II and select the correct answer using the options given below: List-I (SCR Rating) List-II (Protective element) a. di/dt limit 1. Snubber circuit b. dv/dt limit 2. Heat sink c. i 2 t limit 3. Series reactor d. Junction temperature limit 4. Fuse

An SCR is turned off when its turn-off time is

Which one of the following statements is NOT true?

The average on state current for an SCR is 20 A for a conduction angle of 120°. The average on-state current for 60° conduction angle will be

Match List-I with List-II and select the correct answer. List-I (Device) List-II (Property/item associated with it) a. BJT 1. Pinch-off effect b. FET 2. Controlled rectification c. SCR 3. Negative resistance characteristics d. Tunnel diode 4. Punch-through effect

Which semiconductor power device out of the following is not a current triggered device?

The purpose of connecting a Zener diode in a UJT circuit, used for triggering thyristors, is to

When the pnpn diode is biased such that the p side is more positive than the n side, the junction J 1 and J 3 are:

A six pulse thyristor rectifier bridge is connected to a balanced 50 Hz, three phase AC source. Assuming that the DC output current of rectifier is constant, the lowest frequency harmonic component in the AC source line current is

The triac can be used only in

The turn-off time of thyristor is 30 µ sec at 50°C its turn-off time at 100°C will be

To turn on UJT, the forward bias on the emitter diode should be ___________ the peak point voltage.

A UJT is sometimes called ___________ diode.

A diac is turned on by ___________.

The device that exhibits negative resistance region is ___________.

When the emitter terminal of a UJT is open, the resistance between the base terminal is generally ___________.

When the temperature increases, the intrinsic stand off ratio ___________.

In a UJT, the p-type emitter is ___________ doped

The device that does not have the gate terminal is ___________.

The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of ___________ in its first quadrant

A Triac has three terminals viz ___________

A voltage source inverter is normally employed when

Identify the given symbol.

The characteristic of UJT shown in Figure exhibits η = 0.5, V V = 1 V, I V = 10 mA, I P = 20 µA and V P = 14 V. The value of R 1 that will ensure proper turn on and turn off must be

In a GTO, anode current begins to fall when gate current

The output voltage waveform of a three phase square wave inverter contains

In an SCR circuit, the angle of conduction can be changed by . . . . . . . .

Which type of protection is provided for SCR by connecting the snubber circuit across it?

After firing an SCR, the gating pulse is removed. Then the current in the SCR will

In order to obtain static voltage equalization in series connected SCRs, connections are made of

When a thyristor and transistor as a switch are compared, true statement is

SMPS normally use Ferrite core transformers in place of Iron core because of

Which of the following devices does not have negative resistance characteristics

Inverters find applications in

A diac has . . . . . . . . terminals

In controlled rectifiers, the nature of load current is continuous or discontinuous

The operating state that distinguishes a silicon controlled rectifier (SCR) from a diode is

For a type A chopper, DC source voltage is 240 V. Calculate the average output voltage is the duty cycle is 0.4. Take a voltage drop of 4 V across the chopper when it is on.

If firing angle in an SCR circuit is increased, the output . . . . . . . .

In a thyristor, the minimum current required to maintain the device in the 'ON' state is called

For a single phase fully controlled converter bridge operating with continuous load current, the converter will operate in inverting mode for triggering angle, $$alpha $$, such that:

When UJT is used for triggering an SCR, the wave shape of the signal obtained from UJT circuit is

A 3-phase full convertor takes a voltage of 200 V. Calculate the supply power factor, if the charging current in the battery is 20 A. Given the power delivered to the load is $$3500sqrt 2 { ext{ W}}{ ext{.}}$$

When a UJT is turned ON, the resistance between emitter terminal and lower base terminal . . . . . . . .

What is the peak to average power ratio for the signal x(t) = Asin(ωt) with 50% duty cycle?

Consider the following statements: 1. In a silicon controlled rectifier (SCR), if the cathode gate is reverse-biased, then the SCR cannot fire at all. 2. The turn-on time of an SCR increases with temperature. 3. After an SCR is turned on, it can be made to turn off again by reverse biasing the gate. 4. Gate recovery time is the minimum time that the anode voltage must be maintained below holding voltage V H to turn off the SCR. Which of these statements are correct?

It is required to deliver an output DC power of 500 W to a resistive load. The transformer rating required in case of half-wave, conventional full-wave and bridge rectifiers, respectively, is

A single phase full wave mid-point thyristor uses a 220/200 V transformer with central tap on the secondary side. The PIV per thyristor will be:

In dc chopper if T on is the on-time and f is the chopping frequency, then output voltage in terms on input voltage, V s is given by

Which semiconductor device acts like a diode and two resistors?

A triac is a . . . . . . . . switch

Consider the following statements: 1. Speed of operation of MOSFET is more than the speed of operation of SCR. 2. SCRs have lower power loss than MOSFETs. 3. The current in conducting state can easily be controlled through the gate in SCR. 4. MOSFET is not a current-triggered device. The correct statements are:

Following are the applications of a Buck and Boost converters respectively 1. Regulated DC power supplies 2. Regenerative braking of DC motors 3. DC motor speed control

SCR can be used in

The primary function of a phase inverter is to change the phase of a signal by

Match List-I with List-II and select the correct answer using the options given below: List-I (Power Device) List-II (Maximum operation frequency) a. Bipolar transistors 1. 1 MHz b. Power MOSFET 2. 100 kHz c. Silicon controlled rectifier 3. 1 kHz d. Insulated gate bipolar transistor 4. 10 kHz

What are the different methods followed to take p-n-p-n device from its conducting state to the non-conducting state? 1. Reducing the anode current below the holding value. 2. Reducing the gate current to zero. 3. Reducing the gate voltage to zero. 4. Reducing anode voltage below the holding value. Select the correct answer using the options given below:

In an SCR circuit, the anode is grounded. The voltages at the gate and cathode at a particular working condition are measured to be -50 V and -55 V, respectively. Based on this observation, it could be inferred that

Which of the following statements is TRUE for DC switched mode power supply?

In order to make an SCR off, it is necessary to make

Which one of the following devices can be turned 'ON' or 'OFF' by applying gate signal?

The latching current of an SCR is 4 mA. Find the minimum width of gate pulse required to successfully turn on the SCR if source voltage is 100 V and inductance in the circuit is 0.1 Henry.

A 3-phase full wave bridge rectifier yields . . . . . . . . diodes.

How many diodes are present in a single phase, full-wave, mid-point convertor?

The turn-on time of an SCR is 5 µs. Its trigger pulse should have which one of the following?

Which of the following circuits can be used as a DC transformer

How is the GTO turned off?

A power diode has lightly doped n type substrate sandwiched between heavily doped p and n regions

An SCR has an anode supply of sine voltage 200 V r.m.s , 50 Hz applied through a 100 Ω resistor and fired at an angle of 60°. Assuming no voltage drop, the r.m.s. value of the output voltage is nearly

In the forward blocking region of a silicon controlled rectifier, the SCR is

An SCR is sometimes called . . . . . . . .

Between the peak point and the valley point of UJT emitter characteristics we have . . . . . . . . region

The electronic circuit that converts AC to DC where the DC output peak value can be greater than the AC input peak value is-

A step down chopper is operated in the continuous conduction mode in steady state with constant duty ratio D. If V o is the magnitude of the DC output voltage and if V s is the magnitude of the DC input voltage, the ratio $$frac{{{{ ext{V}}_{ ext{o}}}}}{{{{ ext{V}}_{ ext{s}}}}}$$xa0is given by

In thyristor, holding current is

Which one of the following can be used in the lighting system for power interruptions?

A push pull inverter provides a

An inductor is connected in series with SCR to protect it from

The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply frequency of

An SCR triggered by a current pulse through its gate can be turned off by

A step-down chopper, fed from a 120 volt DC source, operates a DC motor whose armature e.m.f. and armature resistance are 100 volt and 0.5 Ω respectively. With the magnitude control ratio 0.6, the quadrant of operation DC motor is

Match List-I with List-II and select the correct answer using the options given below: List-I (Semiconductor Device) List-II (Application) a. Triac 1. Used in HVDC system b. IGBT 2. Used in pulse generation c. SCR 3. Used in motor control circuits d. UJT 4. Used in ac regulators

Which device is used in relaxation oscillator?

For a single phase half-wave controlled rectifier has 400sin314t as the input voltage and R as the load. For a firing angle of 60° for the SCR, the average output voltage is

What will be the one cycle surge current of a SCR if it has half cycle surge current rating of 5000 A for 50 Hz supply?

. . . . . . . . is the device which acts like an N-P-N and a P-N-P transistor connected base-tox02base and emitter-to-collector.

Consider the following statements: The turnoff time of an SCR can be reduced by 1. Quick withdrawal of the gate voltage. 2. Reducing lifetimes by doping with gold. 3. Applying a negative voltage pulse to the gate of these statements:

An SCR can be brought to forward conducting state with gate circuit open when the applied voltage exceeds

Which of the following statements about the working of SCR is INCORRECT?

Which of the following components convert fixed DC to variable DC?

In a DIAC the breakdown voltages are related with the following equation:

Which one of the following statements is correct about SCR?

Two Thyristors of same rating and same specification

Forward voltage drop during SCR turn-on is 1.5 V this drop remains

Identify A and B current limiting techniques in a.c. to d.c. power supplies respectively, in the graph below.

When a thyristor is negatively biased,

An SCR remains turned on if the anode current is more than the

Calculate the power factor of a single-phase thyristor-controlled bridge rectifier if the firing angle is 30°.

An incremental model of a solid state device is one which represents the

Which of the following thyristors can be used for high frequency of operation?

The ON voltage and forward break over voltage of an SCR depend on the

Once the SCR starts conducting a forward current, its gate loses control over

A High speed digital subsystem requires three voltages V 1 , V 2 and V 3 with 1 : 2 : 1 power ratings, respectively. The power supply is designed with the distribute power conversion scheme as shown in the following figure. What is the overall power conversion efficiency?

DC choppers belong to the category of,

A Triac has three terminals viz . . . . . . . .

How many SCR are to be connected in series with 800 V rating to be used for 3 kV circuit using derating factor of 15%?

A single phase voltage source square wave inverter feeds pure inductive load. The waveform of the load current will be

A circuit uses SCR of 800 V rating after which the derating is 25% then the SCR in series

In a thyristor DC chopper, which type of commutation results in best performance?

An ideal thyristor is driving an R-L load of impedance Z. Input AC voltage V s = V m sinωmt. If thyristor if fired at an input phase angle of 90°. What will be the output voltage and output current across R-L load as the instant of firing?

A thyristor equivalent of a thyratron tube is a

Buck-Boost converter is one of the,

A single phase one pulse controlled circuit has a resistance and counter emf load 200sin(512t) as the source voltage for a load counter emf of 100 V, the range of firing angle control will be:

In UJT, maximum value of charging resistance is associated with

Match List-I with List-II and select the correct answer using the options given below: List-I (Device) List-II (Associated Term) a. Diode 1. Pinch off voltage b. SCR 2. Holding current c. BJT 3. Forward resistance d. FET 4. Active region

The UJT may be used as ___________.

A diac has ___________ pn junctions

A diac has ___________ terminals.

A triac is a ___________ switch

The normal way to turn on a diac is by ___________.

Which of the following is not a characteristic of UJT?

A triac can pass a portion of ___________ half-cycle through the load.

Between the peak point and the valley point of UJT emitter characteristics we have ___________ region

After peak point, the UJT operates in the ___________ region.

For harmonic distortion reading of D 2 = 0.1, D 3 = 0.02 and D 4 = 0.01, with I 1 = 4 A and R C = 8 Ω, calculate the total harmonic distortion (THD) fundamental power component (P 1 ), and total power (P).

A UJT has ___________.