All Free Electrical Engineering MCQs with Answers

• A. 130 μs
• B. 135 μs
• C. 140 μs
• D. 145 μs

Explanation: Using the triangular reverse-recovery-current approximation, QRR = ½(di/dt)tRR² = ½(30)(3²) = 135 μC.

• A. delay time
• B. rise time
• C. spread time
• D. all

Explanation: During rise time, the SCR carries increasing current while still supporting substantial voltage, so their product produces the greatest…

• A. Turn on
• B. Not turn on
• C. Turn on if inductance is removed
• D. Turn on if pulse frequency us increased to two times

Explanation: At 2.5 kHz, the pulse period is 400 μs; with a 1:10 mark/space ratio, the mark duration is about 36.4 μs.

• A. Collector, emitter and gate
• B. Drain, source and gate
• C. Drain, source and base
• D. Collector, emitter and base

Explanation: A power MOSFET uses a drain and source for the main current path, with a gate controlling that path.

• A. gate current rises from 90 % to 100 % of it final value
• B. anode voltage drops from 90 % to 10 % of its initial value
• C. anode current rises 10 % to 90 % of its final value
• D. both B and C

Explanation: Rise time is measured while anode voltage falls from 90% to 10% and anode current rises from 10% to 90% of its final value.

• A. IGBT
• B. FCT
• C. MCT
• D. GTO

Explanation: An IGBT uses a MOSFET-like insulated gate for easy voltage control and a BJT-like conduction path for high current capability.

• A. BJT
• B. Power MOSFET
• C. Schottky diode
• D. Microwave transistor

Explanation: Power MOSFETs are majority-carrier devices, so they switch much faster than BJTs and are well suited to switching frequencies above 100…

• A. in series
• B. in parallel
• C. either series or parallel
• D. anti parallel

Explanation: An SCR snubber is normally an RC network connected in parallel with the SCR.

• A. Breakdown of junction
• B. Local hot spot
• C. Insulation failure
• D. None of these

Explanation: Excessive di/dt causes current to spread unevenly through the SCR, producing current crowding and localized hot spots.

• A. BJTs and SITs
• B. BJTs and MOSFETs
• C. SITs and MOSFETs
• D. None of these

Explanation: An IGBT combines the insulated-gate, voltage-controlled drive of a MOSFET with the low-conduction-loss and high-current characteristics of…

• A. Snubber circuit
• B. Fuse
• C. Equalizing circuit
• D. Circuit breaker

Explanation: An RC snubber connected across an SCR absorbs rapid voltage changes and limits dV/dt.

• A. 1 KVA
• B. 2 KVA
• C. 500 VA
• D. 100 KVA

Explanation: COOLMOS devices are high-voltage, low-loss power MOSFETs commonly used in switched-mode power supplies and converters in the…

• A. Fuse.
• B. Snubber circuit
• C. Inductor
• D. Voltage clamping device

Explanation: An inductor is connected in series with the thyristor to limit the rate of rise of current, since v = L(di/dt).

• A. TRIACs
• B. Semi conductor diodes
• C. MOSFETs
• D. Thyristor

Explanation: Thyristors have a low forward voltage drop in the on-state and can withstand much larger currents and voltages than ordinary transistors.

• A. high thermal conductivity
• B. large surface area
• C. high melting point
• D. All of these

Explanation: A practical heat sink needs good thermal conductivity and a large exposed area to transfer heat to the air; a high melting point also…

• A. Iron
• B. Aluminium
• C. Carbon
• D. Silver

Explanation: Aluminium is widely used for heat sinks because it combines good thermal conductivity, low weight, corrosion resistance and low cost.

• A. Use of snubber circuit.
• B. Using heat sink.
• C. Using CB and fuse.
• D. Using equalizing circuit

Explanation: Thermal protection is obtained by conducting heat away from the SCR, and a heat sink provides the required low-resistance path to the…

• A. Controlled transistor
• B. Controlled switch
• C. Amplifier with higher gain
• D. Amplifier with large current gain

Explanation: A thyristor has an essentially stable OFF state and, once triggered, changes to a conducting ON state that it latches into.

• A. lower power circuit.
• B. high power circuit.
• C. magnetic circuit.
• D. may be low power or high power circuit

Explanation: The gate only initiates conduction and requires a small triggering pulse compared with the main anode-cathode power circuit.

• A. 600 V/µs
• B. 800 V/µs
• C. 1200 V/µs
• D. 1000 V/µs

Explanation: The charging current is I = C(dv/dt), so dv/dt = 16 mA / 20 pF = 8 × 10^8 V/s = 800 V/µs. Therefore, option B is correct.