# Power Electronics Two Marks Questions and Answers

### Power Electronics Two Marks Questions and Answers

[1] How choppers are classified based on commutation technique?
Chopper circuits are classified into two types based on the methods of turn off process (commutation).
They are
(1) Natural Commutated Choppers
(2) Forced Commutated Choppers
The forced commutation is further classified as
(1) Voltage commutated Chopper
(2) Current commutated chopper

[2] How choppers are classified based on quadrant of operation?

1. Class-A or Type-A (1st Quadrant)
2. Class-B or Type-B (2nd Quadrant)
3. Class-C or Type-C (1, 2 Quadrant)
4. Class-D or Type-D (1, 3 Quadrant)
5. Class-E or Type-E (All four Quadrants)

[3] What are the various types of forced commutation methods?
Voltage commutation (apply the stored charge from the capacitor to turn off the SCR)
Current commutation (apply the stored field from the Inductor (reactor) to turn off the SCR)

[4] Give the example for Voltage commutated Chopper?

Jones Chopper

[5] Give the example for Current commutated Chopper?

Morgan Chopper

[6] What is meant by s-factor or softness factor in power diode?
The ratio between t2 and t3 in the reverse recovery characteristics of the power diode is called as softness factor.

[7] How the power diode is classified based on reverse recovery characteristics?

1. Slow recovery diode
2. Fast recovery diode
3. Schottky diode

[8] What are the design parameters to be considered to select a power diode for the particular application?

• Reverse recovery time
• Reverse recovery charge
• Peak reverse current
• Rate of rise of current
• Forward current rating
• Forward voltage drop

[9] What is the difference between normal PN junction diode and Tunnel Diode?

• The tunnel diode is basically a PN junction diode with heavy doping of P & N type semiconductor materials.
• Usually tunnel diode is doped approximately 1000 times as heavy as a normal PN junction diode.
• Due to this, tunnel diode shows negative resistance in forward biased condition. Remember that PN junction diode shows positive resistance region.

[10] What is meant by negative resistance and positive resistance?

When the voltage applied across the device or circuit increases,

• If the current flowing through it increases, then it is called as positive resistance. (Example: PN Junction Diode)
• If the current flowing through it decreases, then it is called as negative resistance. (Example: Tunnel Diode)

[11] Name some of the special diodes?