# In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

1. ## In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

Dear sir,
I have observed in some circuits of IGBT, there are using 4.7K across the Gate and Emitter terminals,
what is the purpose of using that resistor, how to calculate that one...

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2. ## Re: In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

You are perhaps referring to the pull-down resistor which is required due to the characteristic high impedance of the MOSFET input; it is intended just to assert that any spurious electrostatic charge will not put it in the conduction region in the absense of input.

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3. ## Re: In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

Hi,

It simply ensures default OFF state.

Klaus

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4. ## Re: In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

thank u sir for u reply..
if not connected 4.7k resistor b/w gate and emitter terminals what happened ...

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thank u sir

5. ## Re: In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

You are forgetting that a single potential is meaningless in an electronic circuit. You always need to refer to the potential difference. Yes, you need to apply a potential to the gate but this potential must have a reference point.

In a circuit with many alternative low resistance path, potentials settle down to their intended values very quickly. But this becomes a problem when the circuit has only high impedance path.

If you do not have the potential well defined, it will appear as a noise. Say you have applied 10V to the gate but this must internally be reflected as a voltage with respect to the emitter or collector or whatsoever.

Using one resistor between the gate and the emitter you ensure that the applied voltage is felt on the gate -emitter voltage internally.

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6. ## Re: In IGBT,why we are using resistor acorss the Gate and Emitter teriminal.

The gate-emitter resistor serves a purpose if the gate driver output can become high impedance under circumstances (e.g. driver supply failure) or a driver cable connection is broken (provided the resistor is located directly at the IGBT). If bus voltage is still present in this situations, the IGBT can inadvertently turn on by collector-gate leakage or capacitance without the resistor.

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