1
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How to reduce body
spreading resistance in the IGBT?
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The body spreading resistance in the
IGBT is reduced by making body region heavily doped.
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2
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How the latching problems
in the IGBT can be avoided?
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The latching problem in the IGBT is
avoided by modifying doping level and geometry of the body layer.
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3
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When the inversion layer
formed in the IGBT?
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When the gate – emitter voltage
exceeds threshold voltage, the inversion layer is formed in the p type body
region ( for n channel IGBT)
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4
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Why the doping level of
the drift region is kept low in the n – channel IGBT?
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Drift region
- The doping level and thickness of the
drift layer determines the current amplification factor of the PNP
transistor.
- The doping level and thickness of the drift layer is kept low
resulting most of the current flows through the MOSFET.
- Therefore the voltage drop across body
spreading resistance reduces and possibility of static latch up of the IGBT
is eliminated.
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5
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When the IGBT is operated
under cut off region?
OR
Explain the term : Cut
off region
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Cut off region
- When the gate – emitter voltage is
less than the threshold voltage, the collector – emitter voltage almost equal
to supply voltage and only leakage current flows through the device.
- This is
called as cut off region of the IGBT.
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6
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Why the maximum reverse
voltage in the non – punch through IGBT is very small?
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Due to heavily doped n+
drift layer
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7
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Explain the term : Active
region
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Active region
- When the gate – emitter voltage is
greater than the threshold voltage, the IGBT operated in the active region.
- The
collector current in the region depends upon transfer characteristic of the
IGBT.
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8
|
In which operating region
the voltage across IGBT remains constant?
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Saturation region
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9
|
Explain the term :
Forward breakdown voltage
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Forward
breakdown voltage
- It is collector to emitter voltage at
which avalanche breakdown occurs in the IGBT.
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10
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Why the IGBT is operated
below forward breakdown voltage?
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Importance
of the forward breakdown voltage
- The voltage across the IGBT and
current passes through IGBT is high at forward breakdown voltage.
- This will
result in high power loss in the device and it may cause damage it.
- Therefore
the IGBT is always operated below forward breakdown voltage.
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11
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How the dynamic latch up
of the parasitic thyristor in the IGBT avoided?
|
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The gate emitter voltage of the IGBT
is kept negative during its turn off period in order to avoid dynamic latch
up of the thyristor.
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12
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How the punch through
IGBT and non punch through IGBT affect the tail current?
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Tail current
- The punch through IGBT shortens the
duration of the tail current time.
- The n+ buffer layer acts as
sink for holes and it removes the holes from the drain drift layer therefore
the tail time is reduced.
- The tail current in the non punch through IGBT is
reduced by minimizes the magnitude of the current during failing interval.
- This is done by designing the MOSFET of the IGBT such that it carries as much
as of the total current.
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13
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Why IGBTs can be easily
connected in parallel without any compensating device?
|
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The IGBTs can be easily connected in
parallel without any compensating devices due to flat resistance temperature
coefficient.
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14
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Describe the advantages
of flat temperature coefficient of resistance in the IGBT.
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- Due to flat temperature coefficient of
resistance, the resistance of the IGBT remains constant under all
temperature conditions
- Secondary breakdown does not take
place
- The parallel operation of the IGBTs
can be possible without any compensating devices.
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15
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State the advantages of
the IGBT over the BJT.
|
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Advantages of the IGBT over the BJT
- The IGBT is voltage controlled device
so gate drive circuit is very simple.
- The IGBT can operate at higher
frequency.
- Secondary breakdown does not take
place
- Snubber circuit does not require
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16
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Describe the different
modes of latching in the IGBT.
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Latching modes in the IGBT
- Static latch
up
- Dynamic
latch up
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17
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Give reason : The
switching losses in the IGBT is determined only by turn off losses for pure
inductive load.
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Switching losses
- The turn on
losses in the IGBT is very small because the transistor is turned on at zero
current therefore the total switching losses consists of only turn off losses
particularly at pure inductive load.
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