A thyristor (SCR) turns off when the 

A) Gate pulse is removed B) Gate pulse is applied C) Thyristor current is below holding value D) Anode voltage is made negative

1 Answer

Answer :

A thyristor (SCR) turns off when the Thyristor current is below holding value

Related questions

Description : Turn-on of a thyristor (SCR) takes place when  A) Anode to cathode voltage is positive B) Anode to cathode voltage is negative C) Positive current is applied to gate D) Anode to cathode voltage is positive and positive current pulse is applied to gate

Last Answer : Turn-on of a thyristor (SCR) takes place when Anode to cathode voltage is positive and positive current pulse is applied to gate

Description : Is a SCR a thyristor?

Last 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.

Description : What is a thyristor? What is an SCR?

Last Answer : A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bi stable switches, conducting when their gate receives a current trigger, and continue ... ) is a four-layer solid state device that controls current. It is a type of thyristor.

Description : What is the difference between SCR and thyristor?

Last Answer : SCR is a type of thyristor. Like GTO, IGCT, MCT, TRIAC, DIAC etc. are the types of thyristor.

Description : Circuit turn-off time of an SCR is defined as the time  (A) taken by the SCR turn to be off (B) required for the SCR current to become zero (C) for which the SCR is reverse biased by the commutation circuit (D) for which the SCR is reverse biased to reduce its current below the holding current

Last Answer : Circuit turn-off time of an SCR is defined as the time for which the SCR is reverse biased by the commutation circuit 

Description : An SCR can only be turned off via it's   (A) cathode (B) anode (C) gates (D) none

Last Answer : An SCR can only be turned off via it's anode 

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

Description : Draw the structural diagram of GTO. Explain briefly the switching behavior of GTO with the help of appropriate voltage and current waveform.

Last Answer : Gate Turn Off Thyristor (GTO) Conventional Thyristor can be turned on with gate terminal but can not turn off from gate terminal. But in case of Gate Turn Off Thyristor (GTO), we can turn it on and off ... subdivided as storage period (Ts), fall period (Tp) and tail period (Tt).

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

Last 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.

Last 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.

Last 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.

Last 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

Last 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

Last 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. 

Last Answer : I need it's operation

Description : How GTO is advantages over SCR

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

Last 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.

Last Answer : Two Transistor Model of SCR or Thyristor

Description : Turn on time of an SCR can be reduced by using a:

Last Answer : Turn on time of an SCR can be reduced by using a: Rectangular pulse of high amplitude and narrow width

Description : During forward blocking state, the SCR has:

Last Answer : During forward blocking state, the SCR has: low voltage, large current

Description : An SCR starts conducting with appreciable current when

Last Answer : An SCR starts conducting with appreciable current when anode and gate both are positive

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 

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

Description : Surge current rating of an SCR specifies the maximum  (a) Repetitive current with sine wave (b) Non-repetitive current with sine wave (c) Non-repetitive current with rectangular wave (d) Repetitive current with rectangular wave  

Last Answer : Surge current rating of an SCR specifies the maximum Non-repetitive current with sine wave

Description : Turn-on time of an SCR in series with RL circuit can be reduced by   (a) Increasing circuit resistance R (b) Decreasing R (c) Increasing circuit inductance L (d) Decreasing L 

Last Answer : Turn-on time of an SCR in series with RL circuit can be reduced by Decreasing L 

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

Last 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

Last 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

Last 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

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

Last Answer : Yes, SCR is a unidirectional switch.

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.

Last 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?

Last 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.

Description : Is gate turn on mechanism of GTO is similar to conventional thyristor?

Last Answer : Yes gate turn on mechanism of GTO is similar to conventional thyristor.

Description : In a thyristor, the magnitude of anode current will:

Last Answer : In a thyristor, the magnitude of anode current will: Not change with any variation in gate current

Description : The number of p-n junctions in a thyristor are  A)1 B) 2 C) 3 D) 4

Last Answer : The number of p-n junctions in a thyristor are  3

Description : Anode current in an thyristor is made up of   (A) electrons only (B) electrons or holes (C) electrons and holes (D) holes only

Last Answer : Anode current in an thyristor is made up of electrons and holes 

Description : In a thyristor, holding current is   (a) More than latching current IL (b) Less than IL (c) Equal to IL (d) Very small

Last Answer : In a thyristor, holding current is Less than IL

Description : Thyristor can be protected from over voltages by using

Last Answer : Thyristor can be protected from over voltages by using Voltage clamping device

Description : Leakage current flows through the thyristor in

Last Answer : Leakage current flows through the thyristor in Forward blocking mode and Reverse blocking mode.

Description : What is meant by firing angle of thyristor?

Last Answer : The point at which SCR is triggered is known as firings angle of thyristor.

Description : How is a thyristor used to convert AC to DC?

Last Answer : thyristor

Last Answer : Yes ,it is one of the main advantage using thristors as a  switch in DC  circuit ,it has a high current gain

Description : Explain thyristor gate drive circuit.

Last Answer : Thyristor Gate Drive Circuit: The thyristor can be turned on by pulse voltage signal at gate terminal and it does not require continuous drive signal like the transistor. The gate ... circuit provide required minimum gate voltage and gate current then the thyristor conducts properly.

Description : In a thyristor D.C. chopper, which type of commutation results in best performance ?

Last Answer : voltage commutation

Description : parallel operation of MOSFET can be done more easily as compared to thyristor. why?

Last Answer : Parallel operation of MOSFET can be done more easily as compared to thyristor because the resistance of MOSFET is increases with increase in temperature. MOSFET have the positive temperature coefficient. In ... the parallel operation of MOSFET can be done more easily as compared to the thyristor.

Description : what are the disadvantages of thyristor?

Last Answer : Disadvantages of thyristor The silicon controlled rectifier (SCR) is unidirectional devices, so it can control power only in DC power during positive half cycle of AC supply. Thus only DC power is ... cycle. It cannot be used at higher frequencies. The gate current cannot be negative

Description : write short notes on thyristor CSI .

Last Answer : Current-source inverter (CSI) is an inverter with a DC current input. Current source inverters are most commonly used in very high power AC motor drives.

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

Last 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 :  To turn a conducting SCR to off state, it is necessary to make : -  a) anode current less than holding current b)gate current zero  c) anode voltage less than break over voltage  d) gate voltage zero

Last Answer :  To turn a conducting SCR to off state, it is necessary to make : - anode current less than holding current

Description : Why circuit turn off time should be greater than the thyristor turn-off time?

Last Answer : Circuit turn off time should be greater than the thyristor turn-off time for reliable turn-off, otherwise the device may turn-on at an undesired instant, a process called commutation failure.

Description : How can a thyristor turned off?

Last Answer : A thyristor can be turned off by making the current flowing through it to zero.