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Electrical Systems > Power Semiconductors > Flashcards

Power Semiconductors Flashcards

1
Q

What does IGBT stand for?

A

Insulated gate bipolar transistor

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2
Q

Draw the circit symbol for and IGBT, as well as its equivalent circuit.

A
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3
Q

What are the 3 key features of an IGBT?

A
  • No intrinsic anti-parallel diode
  • No change in conduction losses with temperature
  • Switching losses increases with temperature
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4
Q

What voltage and frequency ranges should an IGBT be used for?

A

Medium frequency (approx. 100kHz)

Medium voltage (0.1-10V)

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5
Q

What does BJT stand for?

A

Bipolar junction transistor

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6
Q

Draw an NPN BJT

A
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7
Q

Draw a PNP BJT

A
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8
Q

When does an NPN BJT conduct?

A

When current is flowing into its base terminal

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9
Q

In order for a BJT to conduct, what is required of the base terminal?

A

That it takes a continuous current

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10
Q

Draw a thyristor

A
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11
Q

Draw the equivalent circuit for a thyristor

A
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12
Q

List the key features of a thyristor

A
  • Slow switching speed
  • di/dt needs limiting to reduce instantaneous power dissipation and current crowding
  • dv/dt needs limiting to prevent injection of current from stray capacitance (causes false triggering)
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13
Q

What applications is a thyristor most suitable for?

A

High-voltage (+10V)

Low frequency (<100Hz)

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14
Q

What does MOSFET stand for?

A

Metal-Oxide-Semiconductor Field-Effect Transistor

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15
Q

What is the defining feature of a source terminal?

A

Primary charge carriers enter the semiconductor at it

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16
Q

What are the four types of MOSFET?

A
  • N-Channel Enhancement-mode
  • N-Channel Depletion-mode
  • P-Channel Enhancement-mode
  • P-Channel Depletion-mode
17
Q

What does “enhancement-mode” mean with regards to a MOSFET?

A

It means that no conducting channel is present across the source-drain terminals of the MOSFET until a voltage is applied across the gate-source junction

18
Q

What does “depletion-mode” mean with regards to a MOSFET?

A

A conducting channel exists in the MOSFETs default state: applying a gate-source voltage removes this channel

19
Q

What are the primary charge carriers in an N-channel MOSFET?

A

Electrons

20
Q

What are the primary charge carriers in P-channel MOSFETs?

A

Holes

21
Q

Why is it important to energise the control circuitry for D-mode MOSFETs before their attached power circuitry?

A

Because D-mode MOSFETs default to the ON-state - in order to have control of the power system as soon as it becomes live, it must be possible to drive the gate OFF before any voltage exists between the drain-source terminals.

22
Q

Draw and label the 4 types of MOSFET

A
23
Q

What applications are MOSFETs most suitable for?

A

High frequency ( > 100kHz)

Low voltage ( < 0.1V)

24
Q

List the key features of a MOSFET

A
  • Voltage-driven (draws no steady-state current and therefore does not incur gate conduction losses)
  • A transient capacitive current exists whilst it is switching
  • Source-drain resistance is temperature-dependent
  • Low switching losses
  • Source-drain resistance is proportional to the max. drain-source voltage to the power of 2.6
25
Q

What are the three possible sources of power loss in a diode?

A

Conduction losses

Leakage current losses

Switching losses

26
Q

What does “reverse-recovery behaviour” mean?

A

The amount of reverse current following switch off due to remnant charge carriers in P-N junction

27
Q

Draw a Schottky diode

A
28
Q

State five attributes of the Schottky diode

A
  • Low forward voltage drop
  • Limited voltage and current ratings
  • High reverse leakage current
  • Good reverse-recovery behaviour
  • Expensive
29
Q

In what situations is it economically viable to use a Schottky diode?

A

High frequency

Low voltage

30
Q

What is the relationship between source-drain voltage and drain-source current for an E-mode MOSFET?

A

Direct proportionality

31
Q

Why is an N-channel MOSFET preferred over its P-channel counterpart?

A
  • Higher charge carrier mobility
  • Lower on-state resistance
  • Lower conduction losses
32
Q
A

Electrical Systems (3 decks)

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