1. Calculate the voltage across the freewheeling diode when the output voltage is 24 V.
A. -15 V
B. -24 V
C. 28 V
D. 39 V
Answer: B
The freewheeling diode is used to provide a freewheeling path. It is connected in the anti-parallel direction of the load. The voltage across the diode is -Vo=-24 V.
2. Calculate the value of the conduction angle for SCR for R-L load with a freewheeling diode if the value of β and α are 65° and 12°.
A. 168°
B. 170°
C. 130°
D. 180°
Answer: A
The conduction angle for SCR for R-L load with a freewheeling diode is
π-α=180°-12°=168°.
R-L load is a current stiff type of load. The current in the SCR only flows from α to π.
3. Calculate the value of the conduction angle for the diode for R-L load with a freewheeling diode if the value of α is 45°. (Continous conduction mode)
A. 220°
B. 225°
C. 230°
D. 280°
Answer: B
The conduction angle for the diode for R-L load with a freewheeling diode is
π+α=180°+45°=225°.
R-L load is a current stiff type of load.
4. Calculate the value of the conduction angle for the diode for R-L load with a freewheeling diode if the value of β is 226°. (Discontinuous conduction mode)
A. 40°
B. 45°
C. 50°
D. 46°
Answer: B
The conduction angle for the diode for R-L load with a freewheeling diode is
β-π=226°-180°=45°.
R-L load is a current stiff type of load.
5. Calculate the value of the conduction angle for R-L load if the value of β and α are 56° and 18°.
A. 48°
B. 38°
C. 57°
D. 15°
Answer: B
The conduction angle for R-L load is
β-α=56°-18°=38°.
R-L load is a current stiff type of load. The current in the circuit only flows from α to β.
6. Calculate the value of the fundamental displacement factor for 1-Φ Full wave bridge rectifier if the firing α=17°.
A. .98
B. .19
C. .56
D. .95
Answer: D
The fundamental displacement factor is the cosine of angle difference between the fundamental voltage and fundamental current.
D.F=cos(∝)=cos(17°)=0.95.
7. Calculate the value of the fundamental displacement factor for a 1-Φ Full-wave semi-converter if the firing angle value is 95o.
A. .60
B. .68
C. .62
D. .67
Answer: D
The fundamental displacement factor is the cosine of angle difference between the fundamental voltage and fundamental current. The fundamental displacement factor for 1-Φ Full-wave semi-converter is cos(∝÷2)=cos(47.5o)=.67.
8. Which one of the following loads is suitable for lagging power factor load in a Single-phase Half-bridge inverter?
A. C load
B. R-L-C overdamped
C. R-L-C underdamped
D. L-C load
Answer: B
R-L-C overdamped loads are generally lagging power factor loads. They require forced commutation. Anti-Parallel diodes do not help in the commutation process.
9. Which one of the following loads is suitable for the leading power factor load in a Single-phase Half-bridge inverter?
A. C load
B. R-L-C overdamped
C. R-L-C underdamped
D. L-C load
Answer: C
R-L-C underdamped are leading power factor loads. They do not require any forced commutation technique. Anti-Parallel diodes help in the commutation process.
10. A step-down chopper has an input voltage of .1 V and output voltage of .01 V. Calculate the value of the duty cycle.
A. 0.1
B. 0.2
C. 0.3
D. 0.5
Answer: A
The output voltage of the step-down chopper is Vo = Vin×(D. The value of the duty cycle is less than one which makes the Vo < Vin. The step-down chopper is used to step down the voltage. The value of the duty cycle is .01÷.1=.1.
