Page 66 – 100 Very Tough MCQs (Part 1)
Level: GATE / PSU Advanced
🔹 Devices
Q1. IGBT is a combination of: A) BJT + MOSFET B) SCR + MOSFET C) MOSFET + Diode D) BJT + SCRAnswer: A
--- Q2. Latching current of SCR is: A) Minimum current to turn ON B) Minimum current to remain ON C) Maximum gate current D) Reverse currentAnswer: A
---🔹 Rectifiers
Q3. Single-phase full converter with RL load operates in inversion when: A) α < 90° B) α = 90° C) α > 90° D) α = 0°Answer: C
--- Q4. Ripple factor of full-wave rectifier is approximately: A) 0.21 B) 0.48 C) 1.21 D) 0Answer: B
---🔹 DC-DC Converters
Q5. Boost converter duty cycle for doubling voltage is: A) 0.25 B) 0.5 C) 0.75 D) 1Vo = Vin/(1−D) 2Vin = Vin/(1−D) D = 0.5 Answer: B
--- Q6. Buck-Boost converter polarity is: A) Same B) Opposite C) Zero D) ACAnswer: B
--- Q7. In DCM, gain depends on: A) Only D B) Only R C) D, R, L, fs D) Only LAnswer: C
---🔹 Inverters
Q8. Fundamental RMS of square inverter output: A) Vdc B) 0.9Vdc C) (4Vdc)/(Ï€√2) D) Vdc/2Answer: C
--- Q9. THD decreases when: A) Switching frequency increases B) Switching frequency decreases C) Load increases D) Voltage increasesAnswer: A
---🔹 PWM & Control
Q10. Modulation index m > 1 causes: A) Linear region B) Under modulation C) Over modulation D) No outputAnswer: C
---🔹 Numerical Tough
Q11. Buck converter: Vin=30V, D=0.6, R=10Ω Find Io.Vo = 18V Io = 18/10 = 1.8A Answer: 1.8A
--- Q12. Boost converter: Vin=24V, D=0.75 Vo = ?Vo = 24/(1−0.75) = 24/0.25 = 96V Answer: 96V
--- Q13. Natural frequency of Buck: L=100µH, C=50µFω₀ = 1/√(LC) = 1/√(100×10⁻⁶ × 50×10⁻⁶) = 1/√(5×10⁻⁹) ≈ 14142 rad/s Answer: 14.14 krad/s
---Page 66 Summary
✔ Devices fundamentals ✔ Rectifier inversion ✔ Boost & Buck calculations ✔ DCM vs CCM ✔ PWM modulation ✔ Stability basics
Power Electronics Very Tough MCQ Series – Shaktimatha Learning
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