Gate Current

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WalmirSantos
Level 2
Level 2
First like received 10 replies posted 5 questions asked

Hello Guys,

One question: The mosfet switching with gate voltage. We know internal capacitances of mosfet and the charge necessary for QG. In the case gate drive with reference IR2183S that has IO+ of 1,4A that in moment of switching is draining to HO with destiny gate mosfet, what is the function this current, there is view that put the mosfet from cut to driving, it depends exclusively  of gate voltage? It will be the current the factor that speed outs the charging of internal capacitances of mosfet, Qgs and Qgd?

Thanks if you can help me.

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1 Solution
Abhilash_P
Moderator
Moderator
Moderator
50 likes received 500 replies posted 250 solutions authored

Hi,

   Thank you for posting on the Infineon community.

    Power MOSFETs have a defined gate charge QG, which must be supplied with sufficient current to raise VGS from zero to the required gate drive voltage (typically 10 V for a standard-level device).
In order to achieve this, a current pulse is required:
𝑄𝐺 = ∫ 𝑖(𝑡). 𝑑𝑡 𝑡
    Gate drive circuits supply a voltage through a resistance consisting of an external gate resistor RGD in series with the internal gate resistance of the MOSFET RG added to the output impedance of the gate driver circuit. Consequently, the drive current is not constant and the peak gate drive source current occurs when the gate drive first transitions high when VGS is zero.
𝑖𝐺(𝑡) =𝑉𝐷𝑅𝐼𝑉𝐸−𝑉𝐺𝑆(𝑡) 𝑅𝐺𝐷+𝑅𝐺+𝑅𝑆𝑅𝐶 
    The gate of the MOSFET is considered to be a capacitance. The gate voltage of a MOSFET does not increase unless its gate input capacitance is charged, and the MOSFET does not turn on until its gate voltage reaches the gate threshold voltage Vth. In considering a drive circuit and a drive current, the gate charge Qg of a MOSFET is more important than its capacitances. During the turn-on of a MOSFET, a current flows to its gate, charging the gate-source and gate-drain capacitances. The gate starts to accumulate the charge when gate voltage is applied to it. When the gate capacitances are charged, the drain current starts to flow .
    Therefore, as VGS rises, IG falls to zero. The waveforms illustrated in the simulation below show 10 kHz gate drive waveforms . A 20 Ω gate resistor (RGD) has been used.

Abhilash_P_0-1683525333701.png

Basically  when the gate voltage crosses the gate threshold voltage, a gate current is used to charge the gate capacitances Ciss and Coss. Once the gate is completely charged, the drain current starts to flow. 

Abhilash_P_3-1683526341046.png

 


I hope the above explanation has helped you in understanding the gate driver voltage and drive current.

 

Regards,
Abhilash P

 

 

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3 Replies
Abhilash_P
Moderator
Moderator
Moderator
50 likes received 500 replies posted 250 solutions authored

Hi,

   Thank you for posting on the Infineon community.

    Power MOSFETs have a defined gate charge QG, which must be supplied with sufficient current to raise VGS from zero to the required gate drive voltage (typically 10 V for a standard-level device).
In order to achieve this, a current pulse is required:
𝑄𝐺 = ∫ 𝑖(𝑡). 𝑑𝑡 𝑡
    Gate drive circuits supply a voltage through a resistance consisting of an external gate resistor RGD in series with the internal gate resistance of the MOSFET RG added to the output impedance of the gate driver circuit. Consequently, the drive current is not constant and the peak gate drive source current occurs when the gate drive first transitions high when VGS is zero.
𝑖𝐺(𝑡) =𝑉𝐷𝑅𝐼𝑉𝐸−𝑉𝐺𝑆(𝑡) 𝑅𝐺𝐷+𝑅𝐺+𝑅𝑆𝑅𝐶 
    The gate of the MOSFET is considered to be a capacitance. The gate voltage of a MOSFET does not increase unless its gate input capacitance is charged, and the MOSFET does not turn on until its gate voltage reaches the gate threshold voltage Vth. In considering a drive circuit and a drive current, the gate charge Qg of a MOSFET is more important than its capacitances. During the turn-on of a MOSFET, a current flows to its gate, charging the gate-source and gate-drain capacitances. The gate starts to accumulate the charge when gate voltage is applied to it. When the gate capacitances are charged, the drain current starts to flow .
    Therefore, as VGS rises, IG falls to zero. The waveforms illustrated in the simulation below show 10 kHz gate drive waveforms . A 20 Ω gate resistor (RGD) has been used.

Abhilash_P_0-1683525333701.png

Basically  when the gate voltage crosses the gate threshold voltage, a gate current is used to charge the gate capacitances Ciss and Coss. Once the gate is completely charged, the drain current starts to flow. 

Abhilash_P_3-1683526341046.png

 


I hope the above explanation has helped you in understanding the gate driver voltage and drive current.

 

Regards,
Abhilash P

 

 

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Hello Abhilash,

Thank you very much for your answer.

Is it possible send me your file of simulation or the side down of the curves?

Thanks,

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Abhilash_P
Moderator
Moderator
Moderator
50 likes received 500 replies posted 250 solutions authored

Hi,

  Please refer the following application note for more details,

https://www.infineon.com/dgdl/Infineon-Gate_drive_for_power_MOSFETs_in_switchtin_applications-Applic...

Regards,
Abhilash P

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