77701. A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is
77702. For a 12 pulse operation, the two 6 pulse units are fed by
77703. In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is
77704. An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be
77705. The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes
77706. In a step down chopper using pulse width modulation, Ton = 3 x 10-3 and Toff = 1 x 10-3 s. The chopping frequency is
77707. Thyristors are suitable for dc circuit breakers but not for ac circuit breakers.
77708. Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off time.
77709. The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by
77710. A chopper
77711. Assertion (A): If the duty cycle of chopper is low the current would not become discontinuousReason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.
77712. In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally
77713. An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is
77714. A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is Is and rms value of load current in Irms. Then
77715. The terminals of a power BJT are called
77716. In single phase half wave regulator, the average current over one full cycle
77717. The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode)
77718. A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current
77719. Current derating may be necessary when thyristors are operating in
77720. If duty cycle is a and the load is a resistance R, the rms value of output voltage is
77721. For a BJT a = 0.98, then β =
77722. Assertion (A): Power transistor has lower switching time than SCR Reason (R): Power transistor has greater switching time than SCR
77723. A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is
77724. In a circuit using a full wave converter (M - 2 connection) the PIV of each thyristor is 400 V. For the same output voltage and fully controlled bridge converter, PIV will be
77725. A dc separately excited motor has constant field current. The armature is fed from a single phase supply through a full converter. When a = 0, speed is 500 rpm. If a = 45°, the speed is likely to be
77726. In a multiphase chopper, all choppers operate together.
77727. The terminals of a power MOSFET are called
77728. Assertion (A): The surge current which an SCR can withstand is much higher than rms on state current.Reason (R): The duration of surge current is very small.
77729. A single phase half wave controlled rectifier circuit has a free wheeling diode. The load is a combination of R and L. The firing angle is a . The period of conduction of SCR and free wheeling diode respectively are
77730. Assertion (A): A transistor requires a continuous base signal for conduction but a thyristor requires a gate pulse.Reason (R): Transistor find widespread application in power electronic circuits.
77731. In a thyristor the gate current is increased, then
77732. Thyristors are not suitable for logic circuits.
77733. A single phase half wave rectifier is feeding a resistive load. Input voltage v = Vm sin ωt. The output dc voltage is Vdc and output rms voltage is Vrms . If firing angle is 180°, Vdc and Vrms respectively are
77734. The number of leads in an SCR are :
77735. A thyristor has a turn on time of 6 μs. If the anode circuit is inductive, the turn on time will be
77736. The total number of leads in reverse conducting thyristor is
77737. Assertion (A): A TRIAC is a bidirectional SCR.Reason (R): A TRIAC is a four layers 3 terminal device and can conduct in both directions.
77738. If Vdc1 is the dc output voltage in half wave controlled rectifier circuit feeding resistive load and Vdc2 is the dc output voltage in full wave controlled rectifier circuit (M - 2 connection) feeding resistive load, then
77739. A semi converter operates in two quadrants.
77740. Figure shows a chopper feeding RLE load, The free wheeling diode conducts when
77741. Assertion (A): An ideal rectifier should have unity harmonic factorReason (R): An ideal rectifier should have unity displacement factor.
77742. A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30°, the dc output voltage will be about
77743. A dc circuit breaker must use
77744. In a single phase full wave regulator feeding R-L load, the minimum firing angle can be zero.
77745. An RC snubber circuit is used to protect a thyristor against :
77746. A DIAC has two terminals, anode and cathode.
77747. A single phase semiconverter has a freewheeling diode. If the firing angle is a and the load is purely resistive, the periods of conduction and freewheeling respectively are
77748. A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be
77749. A static induction thyristor
77750. A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to
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