It is the converter whose output frequency is less than the input frequency.
It is the converter whose output frequency is more than the input frequency.
Multimeter in AC mode shows RMS value of the voltage or current. Also when it is DC mode it will show
the RMS value only.
General purpose motors (Induction motors, synchronous motors) are neither precision speed nor
precision position motors. For many automated systems require high precise speed and high precise
positioning motors. In such cases special purpose motors like stepper motors, PMDC motors etc. are
used.
Q-15 What is delay angle or what is firing angle of phase controlled rectifier?
The delay angle is the angle at which thyristors are triggered after zero crossing.
After zero crossing of supply voltage, one pair of thyristors is forward biased. ie, After delay angle(α)
these SCRs are triggered.
Q-16 What is Universal Motor?
It is defined as a motor which can be operated either on DC or single-phase AC supply at approximately
the same speed and output.
The universal motor is built exactly like a series DC motor.
But a series DC motor cannot be run as a universal motor, even though both motors look the same
internally and externally.
We cannot use these motors in the industrial applications due to the low efficiency (25% -35%).
It has high starting torque and a variable speed characteristic. It runs at dangerously high-speed on no
load.
Q-17 Give some examples of power electronics applications in the day-to-day life?
We can list a huge number of power electronics applications. Few of the applications which we can see
in our daily life are
- UPS – Uninterruptible Power Supply
- SMPS – Switch Mode Power Supply
- Speed Control of Motors
- ICU
Q-18 What is meant by PMDC?
PMDC stands for Permanent Magnet DC Motor
A Permanent Magnet DC Motor is similar to an ordinary dc shunt motor except that its field is provided
by permanent magnets instead of salient-pole wound field structure.
There are three types of permanent magnets used for such motors namely;
- Alnico Magnets
- Ceramic magnets
- Rare-earth magnet
The major advantages are low noise, small size, high-efficiency, low manufacturing cost.
Q-19 What are the different turn on methods of SCR?
Forward voltage triggering
Gate Triggering
dv/dt triggering
Temperature triggering
Light triggering
Q-20 What is snubber circuit?
The snubber circuit is used for the dv/dt protection of the SCR. It is a series combination of a resistor and
a capacitor in parallel with the SCR.
Q-21 What is hard switching of the thyristor?
When gate current is several times higher than the required gate current, the SCR is said to be hard
fired. It reduces the turn ON time and enhances the di/dt capability.
Q-22 What is firing angle?
The angle between the zero crossing of the input voltage and the instant the SCR is fired is called as
delay angle or firing angle.
Q-23 What is meant by SOA?
SOA – Safe Operating Area determines the voltage and current boundary within which the Power Device
can be operated without destructive failure.
Q-24 What are the main components used for isolating the Power Circuits, Power Semiconductor from
the low-power circuit?
- Opto-Couplers,
- Transformers
Q-25 Name some of the current controlled (current driven) devices ?
- SCR,
- GTO,
- GTR
 |
| DTO |
 |
SCR
|
Q-26 Name some of the voltage driven ( Voltage controlled) devices ?
- IGBT,
- MCT,
- IGCT,
- SIT
Q-27 What is duty cycle?
It is the ratio of the ON time of the chopper to total time period of the chopper.
D = Ton / [Ton + Toff]
Q-28 Can fuses with an AC voltage rating be used in a DC applications?
Fuses must be rated for the voltage AC or DC in which they will be used.
Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating.
Q-29 What are the characteristics of ideal Opamp?
Infinite open loop voltage gain
Infinite input impedance
Zero output impedance
Infinite Bandwidth
Zero offset voltage
Q-30 For High voltage applications will you prefer MOSFET or IGBT?
For High voltage applications we have to use IGBT.
Because MOSFETs are low voltage devices. ie, Their voltage rating is lesser than IGBT.
General rule is MOSFETs are suitable for applications which has breakdown voltage less than 250V.
The IGBTs are suitable for applications which has breakdown voltage upto 1000V.
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