Power Igbt 1i365l

IGBT: Insulated-Gate Bipolar Transistor • Combination BJT and MOSFET – High Input Impedance (MOSFET) – Low On-state Conduction Losses (BJT)

• High Voltage and Current Ratings • Symbol

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Cross-Sectional View of an IGBT Metal

Silicon Dioxide

Metal

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IGBT Equivalent Circuit for VGE
IEPNP

ICNPN IBNPN

INP

VCC

Leakage Current Both transistors are OFF

IENPN

IRBE

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IGBT Equivalent Circuit for VGE>VT + PNP transistor turns ON,

VCC

RMOD decreases due to carrier injection from the PNP Emitter.

MOS transistor conducts, drawing current from the Base of the PNP transistor.

NPN Transistor becomes forward biased at the BE, drawing current from the Base of the PNP transistor.

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Channel is Induced When VGE>VT

RMOD

PNP electrons

NPN

RBE Induced Channel

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IGBT Output Characteristics

Follows an SCR characteristic

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IGBT Transfer Characteristic

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IGBT Used as a Switch

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Fairchild FGA25N120AND IGBT

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Cut-off region Saturation region Active region

I) IGBT is a hybrid device which combines the advantages of MOSFET and BJT. ii) An IGBT is formed by adding a p+ collector layer on the drain drift layer of a Power MOSFET. (ii) Punch through IGBT has a thin n+ buffer layer between the p+ collector layer and n-drain drift layer. They have significantly lower conduction loss. (iii) The IGBT cell structure embeds a parasitic thyristor in it. Latching up of this thyristor is prevented by special structuring of the body region and increasing the effectiveness of the

body shorting. (iv) From the operational point of view an IGBT is a voltage controlled bipolar device.

Characteristics Features Modes of operation POWER IGBT

Advantages

(i) The IGBTs have a slightly positive temperature coefficient of the on-state voltage drop which makes paralleling of these devices simpler. (ii) An IGBT does not exhibit second break down phenomena as in the case of a BJT

Disadvantages

(i) The maximum allowable collector current in an IGBT is restricted by the static latch up consideration. (ii) The RBSOA of IGBT is rectangular for low values of dvcece/dt

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SUMMARY 1. IGBT is a hybrid device which combines the advantages of MOSFET and BJT. 2. An IGBT is formed by adding a p+ collector layer on the drain drift layer of a Power MOSFET. 3. Punch through IGBT has a thin n+ buffer layer between the p+ collector layer and ndrain drift layer. They have significantly lower conduction loss. 4. The IGBT cell structure embeds a parasitic thyristor in it. Latching up of this thyristor is prevented by special structuring of the body region and increasing the effectiveness of the body shorting. 5. From the operational point of view an IGBT is a voltage controlled bipolar device. 6. The operational equivalent circuit of an IGBT has an n channel MOSFET driving a p-n-p BJT. 7. Like other semiconductor devices on IGBT can also operate in the cut off active and saturation regions. 8. When the gate-emitter voltage of an IGBT is below threshold it operates in the cut off region. 9. For a given load resistance the operating point of an IGBT can be moved from cut off to saturation through the active region by increasing the gate-emitter voltage. 17