Why is pulse train gating preferred over pulse gating? Explain with relevant circuit and waveforms, the pulse train gating of SCRs.

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Description : Draw a neat sketch of Gating system. State the functions of any four elements.  

Answer : Gating system:  1. Sprue: The circular cross section that minimizes heat loss and turbulence is sprue, and the area of it is quantified from the choke area as well as the gating ratio.  2. ... the molten metal flow from the ingate has to be proportional to the casting area's volume. 

Description : Explain the pulse width modulation technique for control of AC output voltage.

Description :  A pulse radar has a pulse repetition frequency (PRF) of 3 KHz. If the radar is emitting at 10 GHz, what is the maximum unambiguous range for this radar? A) 5 Km B) 5 m C) 50 Km D) 15 m 

Answer :  A pulse radar has a pulse repetition frequency (PRF) of 3 KHz. If the radar is emitting at 10 GHz, what is the maximum unambiguous range for this radar? A) 5 Km B) 5 m C) 50 Km D) 15 m 

Description : A pulse compression radar transmits an encoded pulse having a frequency chirp from 990 MHz to 1010 MHz centred around 1 GHz. The range resolution capability of this radar is A) 7.5 m B) 7.5 Km C) 75 m D) 750 m 

Answer : A pulse compression radar transmits an encoded pulse having a frequency chirp from 990 MHz to 1010 MHz centred around 1 GHz. The range resolution capability of this radar is 7.5 m

Description : The clock frequency of an 8085 microprocessor based system is 3 MHz. What should be the minimum pulse width of the INTR signal so that it is recognized successfully? A) 5.6 µs B) 5.7 µs C) 5.8 µs D) 5.9 µs

Answer : The clock frequency of an 8085 microprocessor based system is 3 MHz. What should be the minimum pulse width of the INTR signal so that it is recognized successfully? A) 5.6 µs B) 5.7 µs C) 5.8 µs D) 5.9 µs

Description : What is the Fourier transform of a Gaussian time pulse? A) Uniform B) Gaussian C) Impulses D) Pulse

Answer : What is the Fourier transform of a Gaussian time pulse? A) Uniform B) Gaussian C) Impulses D) Pulse

Description : A 1ms pulse can be stretched to 1 s pulse by using (A) an astable multivibrator (B) a monostable multivibrator (C) a bistable multivibrator (D) a Schmitt trigger circuit

Answer : A 1ms pulse can be stretched to 1 s pulse by using a monostable multivibrator

Description : Specific energy consumption of an electric train is the ratio between (A) Specific energy output at driving wheels and efficiency of the traction motor (B) Specific energy output at driving wheels ... (D) Specific energy output at driving wheels and efficiency of the (motor + transmission gear)

Answer : Specific energy consumption of an electric train is the ratio between Specific energy output at driving wheels and efficiency of the (motor + transmission gear)

Answer : Power for lighting in passanger coach, in a long distance electric train, is provided through individual generator of bogie and batteries.

Answer : The resistance encountered by a train in motion is on account of resistance offered by air, friction at the track, friction at various parts of the rolling stock.

Answer : The wheels of a train, engine as well as bogies, are slightly tapered to facilitate in taking turns.

Description : Is a train a locomotive?

Description : How GTO is advantages over SCR

Answer : i) It is turned-off by negative gate pulse. ii) No commutation circuit required, reducing the cost, size, weight and volume of the circuit. iii) As commutation choke is not used, the associated acoustic ... turn off time permits high switching frequency. v) It has higher di/dt rating at turn-off. 

Description : Why SCR is called as thyristor?

Description : After firing as SCR, the gating pulse is removed. The current in the SCR will  1. remain the same 2. immediately fall to zero 3. rise up 4. None 

Answer : After firing as SCR, the gating pulse is removed. The current in the SCR will remain the same

Description : Explain triggering of SCR using opto-coupler. State its advantages. 

Answer : Triggering of SCR using opto-coupler:  A simple opto-coupler based triggering circuit for SCR is shown in the figure. An optocoupler or opto-isolator is a combination of light source ... is small size and light weight device. iii)Interfacing with logic circuits is easily possible.

Description : Draw the circuit diagram of battery charger using SCR and explain it’s working.

Answer : Battery charger circuit using SCR: The figure shows the battery charger circuit using SCR. A 12V discharged battery is connected in the circuit and switch SW is closed. The singlephase 230V ... not fired. In this way, after full charging, further charging is automatically stopped.

Description : Explain the thermal triggering method of SCR. Enlist different triggering methods of SCR.

Answer : Types of Triggering: 1) Forward voltage triggering 2) Thermal triggering (Temperature triggering) 3) Radiation triggering (Light triggering) 4) dv/dt triggering 5) Gate triggering ... generated leakage current increases. This current gets multiplied internally and thyristor is turned on. 

Description : Explain working of AC circuit breaker using SCR with circuit diagram.

Answer : AC Circuit Breaker:  The circuit configuration of static AC circuit breaker using SCR is shown in the figure. When switch S' is closed, the SCRs T1 and T2 are fired in positive ... to non-availability of gate current. Thus the maximum time delay for breaking the circuit is one half-cycle.

Description : Temperature controller using SCR

Answer : Temperature controller using SCR The temperature control circuit is used to regulate the temperature. Figure shows the temperature control circuit using thermostat as temperature detector and SCR as ... half-cycle and heater gets connected to source to produce heat and raise the temperature.

Description : Compare SCR and TRIAC

Answer : SCR TRIAC It is an unidirectional device. It is a bidirectional device. It is turned-on by only positive gate current. It can be turned-on by either ... applications including lamp dimmer, heating control, zero voltage switched AC relay, small AC motor control etc.

Description : Describe triggering of SCR using UJT relaxation oscillator. 

Answer : Triggering of SCR using UJT relaxation oscillator: 

Description : Draw a neat labelling V-I characteristics of SCR and explain the region

Answer : (i) Latching current: It is the minimum anode current required to maintain the SCR in the conduction state just after turn-on and the gate signal has been removed.  (ii) Holding current: It is the minimum anode current required to hold the conducting SCR in the ON state. 

Description : Draw construction of SCR using two transistor model. Explain its operation.

Answer : Two Transistor Model of SCR or Thyristor

Description : The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply frequency of A) 10 kHz B) 10 Hz C) 5 kHz D) 5 Hz 

Description : SCR is more utilized as compared to Triac because it is

Answer : SCR is more utilized as compared to Triac because it is available with higher ratings

Description : A 230 V, 50 Hz phase controlled single-phase full-controlled SCR bridge converter draws 15 A constant dc current. If the source inductance is 3 mH, the drop in dc output voltage is (A) 4.5 V (B) 6.75 V (C) 9 V (D) 13.5 V

Answer : A 230 V, 50 Hz phase controlled single-phase full-controlled SCR bridge converter draws 15 A constant dc current. If the source inductance is 3 mH, the drop in dc output voltage is 9 V

Description : In a 230 V, 50 Hz single-phase SCR bridge converter operating at a firing delay angle, α and with large R-L load, the input source current is (A) sinusoidal current (B) constant dc current (C) continuous rectangular pulses (D) alternating rectangular pulses

Answer : In a 230 V, 50 Hz single-phase SCR bridge converter operating at a firing delay angle, α and with large R-L load, the input source current is alternating rectangular pulses

Description : An SCR without any external connections is considered as (A) two diodes in series (B) three diodes in series (C) two n-p-n transistors in series (D) two p-n-p transistors in series

Answer : An SCR without any external connections is considered as three diodes in series

Description : Is a SCR a thyristor?

Answer : Yes, SCR is a thyristor. Thyristor is the family and SCR is the member of that family but SCR is universally known as thyristor.

Answer : Yes, SCR is a unidirectional switch.

Answer : SCR turned off when the anode current falls below holding current.

Description : What is holding current and latching current in SCR? Draw the gate characteristics of an SCR and explain the characteristics. What are the different signals which can be used for turning on SCR by gate control? compare them.

Answer : (i) Holding Current: Holding current is defined as the minimum anode current required to maintain conducting SCR in the on-state.  (ii) Latching Current: Latching current is defined as the ... the on-state immediately after the SCR has been turned on and the gate signal has been removed.

Description : What is the use of SCR?

Answer : SCR are use in lamp dimming, power regulators, motor control, rectifications of high power AC, control of welding machines and also use as switch these are some uses of silicon controlled rectifier.

Answer : Because it has a higher switching frequency and heat tolerance.

Description : A thyristor is triggered by a pulse train of 5 kHz. The duty ratio is 0.4. If the allowable average power is 100 W, the maximum allowable gate drive power will be 

Description : A FET is preferred over an ordinary transistor because it  1. Permits high degree of isolation between input & output circuits 2. Has low noise level 3. Has very high power gain 4. Has all the above properties 

Answer : A FET is preferred over an ordinary transistor because it Has all the above properties 

Description : Why thyristor are not preferred for inverter?

Description : drive the expression for the  (1)current that commutates the scr, (2)the peak current, (3) conduction time?  in class B,C,D and E.

Description : using the SRC gate current ,load current, ARC voltage and capacitor voltage , explain the working principle of class B commutation

Description : Purpose of Selective Catalytic Reduction (SCR)

Answer : Purpose of Selective Catalytic Reduction (SCR) : 1. It reduces Nox 75% to 90% 2. Converts it in to molecular nitrogen and water vapor 3. It reduces HC emission up to 80% 4. It reduces PM emission 20 to 25%.

Description : An inductor is connected in series with SCR to protect it from A) Excessive high voltage B) Excessive high dv/dt C) Excessive high di/dt D) Excessive large forward current 

Answer : An inductor is connected in series with SCR to protect it from Excessive high di/dt

Description : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ (A) directly proportional to α and Φ (B) ... proportional to α and inversely proportional to Φ (D) directly proportional to Φ and inversely proportional to α

Answer : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ directly proportional to α and inversely proportional to Φ

Description : In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in (A) voltage notching (B) harmonic distortion (C) voltage sag (D) voltage swell

Answer : In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in voltage notching

Description : How do you test an SCR?

Description : Why silicon is preferred over Ge?

Answer : 1) Silicon is plenty available compared to Ge. 2) Extraction process of Si is easy and less expensive. 3) Si has more thermal stability as compared to Ge. 4) Si has more breakdown voltage as compared to Ge.

Description : Synchronization is achieved by a timing device called a ................. which generates a periodic train of .................. (A) clock generator, clock pulse (B) master generator, clock pulse (C) generator, clock (D) master clock generator, clock pulse

Answer : Answer: A and D

Description : In single pulse modulation of PWM inverters, third harmonic can be eliminated if pulse width is equal to   (a) 30o (b) 60o (c) 120o (d) 150o

Answer : In single pulse modulation of PWM inverters, third harmonic can be eliminated if pulse width is equal to 120o

Description : A 3 -stage ripple counter has Flip Flop with propagation delay of 25 nsec and pulse width of strobe input 10 nsec. Then the maximum operating frequency at which counter operates reliably is

Answer : A 3 -stage ripple counter has Flip Flop with propagation delay of 25 nsec and pulse width of strobe input 10 nsec. Then the maximum operating frequency at which counter operates reliably is 12.67 MHz

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